Help on overheating 2001 Cobra

MacDaddy07 · Jan 19, 2009

I'm trying to help my son who bought an '01 Cobra a couple of months ago. It ran fine the first month, but then about a month ago started running hot. It goes well over 210, and he shuts it off to let it cool. It takes it a few (about 20) minutes in idle to reach the hot temps, but just keeps climbing.

No mods were performed since he bought it.

Runs hot at idle, or in traffic (highway and city).

The fan runs.

When it gets really hot, the coolant is running out of the cap on the plastic tank (forget the term) on the top corner of the radiator.

We've replace the thermostat, after checking it opens in boiling water, and I'm pretty sure it is the right direction. We have the spring pointing up towards the top of the engine.

Have "burped" it several times using the bleeder bolt. And burped it with the heater turned on.

He is using the 50-50 blend of anti-freeze.

When looking through the hole where the bleeder bolt is, you can see coolant flowing.

No coolant in the oil, and I don't believe there is any coolant leaking into the exhaust - no sweet smell.

He's very frustrated, and I'm pretty much out of ideas. Only ideas I can come up with are bad heads/gaskets, or a clogged radiator. The car doesn't have high miles on it, only about 60K. One thing I did notice is that the o-ring gasket on the bleeder bolt deteriorated and fell apart in pieces on the ground. But, he tightens it up pretty snug using a socket when he is finished burping it. And the belt orientation isn't the same as on the diagram in the service manual (forget the name, it isn't a Ford book).

Any suggestions? He's about to the point of getting rid of it and letting it be someone else's problem!

Thanks!

btmhwb · Jan 19, 2009

i was gonna suggest the radiator as well. I would think with a head gasket you would experience oil antifreeze mixing, which you said it wasn't. Maybe the radiator is fouled up to where it cannot adequately transfer heat!? Have you tried to fjush the radiator out or anything?

MacDaddy07 · Jan 19, 2009

Haven't tried flushing the radiator out ... yet.

He's already spent a small fortune on anti-freeze the last few weeks!

Since it takes about the same amount of time to heat up, either idling or on the highway, I wasn't too concerned about the radiator. My thinking was, the extra air flow on the highway would work more efficiently at cooling things off.

MacDaddy07 · Jan 20, 2009

Further update to the overheating problem....

A buddy of his decided to hardwire his fan so it would always stay on. The car ran fine last night and this morning, no overheating! I've asked him to check with his friend on exactly what he wired up - as I believe the stock fan is two speed and I know it isn't good to keep it wired on!

If this provides any additional insight for anyone, your feedback would be greatly appreciated!

timeless2 · Jan 20, 2009

Does it overheat when cruising or driving down the highway? You mentioned the serpentine routing looked different than what the manual specified, so I wonder if this issue could be partly attributed to or aggravated by underdrive pulleys or perhaps incorrect pulleys. Just a thought...

MacDaddy07 · Jan 20, 2009

Tim,

Yes, it would overheat at idle, as well as highway and city driving. The diagram comes from a non-Ford service manual, so I'm not sure of it's accuracy. And the label that is normally found under the hood is not there. I've searched, and could not find the belt routing on-line.

Gearbanger 101 · Jan 20, 2009

First things first....I'd take care of the inexpensive stuff right away and install a new thermostat. Its possible the stock 192* unit has gone belly up and needs to be changed. Replace it with a 180* unit and see how that works for ya.

The fan running all the time is just a temporary band aid. It still doesn't solve the problem at hand and is going to get him into real trouble if it ever quits on him during a hot day in stop and go traffic.

There is also a cooling modification that can be performed to the back of the drivers side head, but that's normally done just to remove hot spots from the rear bank of cylinders, not cool the entire engine down. Do a search on "Cobra head cooling mod" or some variation of that and something should come up for you.

MacDaddy07 · Jan 20, 2009

Brian,

Thanks for your suggestions! The thermostat is new, in fact it is the second new one. And we verified it works in a pot of boiling water.

I don't think he's quite ready for the head cooling mod you mentioned ....

Gearbanger 101 · Jan 20, 2009

MacDaddy07 said:
Brian,

Thanks for your suggestions! The thermostat is new, in fact it is the second new one. And we verified it works in a pot of boiling water.

I don't think he's quite ready for the head cooling mod you mentioned ....

What temperature thermostat did you instal? Its a pretty common cooling modification to swap out the stocker with a 180* unit. I wouldn't go any colder than that though, as you'll have drivability issues.

As far as the head cooling mod.....It wouldn't hurt to do, but it still doesn't sound like this is the basis of your problem. If it happened out of the blue all of the sudden, I would still lean towards some sort of obstruction in the cooling system.

It could very well be a slowly going head gasket....even if there isn't the presence of coolant in the oil. A pressure test will really be the only way to know for certain.

Before doing that though, try elevating the front end by either parkign up hill, driving up onto a curb or just jacking it off the ground and letting it come up to operating tempeature. A lot of the time this helps the coolant circulate to the rear of the engine and remove any remanents of air in the system. 4V's can be a bitch to burp and coolant sometimes has a tough time making it to the back of the heads, which is why I suggested the rear head modifications, but you might be able to accomplish this by just elevating the front end and letting gravity to the rest.

MacDaddy07 · Jan 20, 2009

Brian,

If I remember correctly, it was a 195 degree thermostat. We were in a hurry to replace it, and just took what the local AutoZone had. I'd agree with you on putting a cooler one in, but he's already burned through some $$ in anti-freeze (due to trying 2 new ones and double checking the last one). He'd probably flip out if I suggested replacing it one more time!

He has burped it quite a few times, using the bleeder bolt, and had the front end elevated a good bit on jack stands. He has a friend that will do a pressure check, but won't be able to until next week.

At this point I'm wondering more about the fan or it's associated relays.

Gearbanger 101 · Jan 20, 2009

MacDaddy07 said:
At this point I'm wondering more about the fan or it's associated relays.

Does the fan come on, on its own? The fan will only generally come on low unless the car is hot, or the defrost/AC is on....at which point you should hear the high speed fan Otherwise, it shouldn't run at all. Hard wiring it the way his buddy did will help for now, but having the fan run all the time will insure that it'll need replacing some time in the near future as well.

MacDaddy07 · Jan 20, 2009

Brian,

Yes, the fan was coming on before it was hardwired. What I'm not sure of, was if the speed was high or low - to be honest I'm not sure how to tell!!! Plus, I'm not sure which speed his friend hardwired to always be on.

Gearbanger 101 · Jan 20, 2009

Like I said.....its suposed to come on high for defrost/AC so if it speeds up when you turn to either one of those settings, you'll know its working right. Although now you'll have to undo what his friend did in order ot notice it.

MacDaddy07 · Jan 20, 2009

Thanks, will see what we can come up with!

COBRA90GT · Jan 21, 2009

For the OP:

Was his cobra moderately or severely modded prior to your son purchasing it? If so, can you list the modifications (particularly engine/cooling related).

Just to double check...when your son is refilling the cooling system with coolant, is he adding the fresh coolant in at the coolant crossover tube location (where the 1/4" plug is located, in front of the alternator)?

This is the location where new coolant should be poured in at. And, as you know it is the location where "burping" is performed.

I think it is likely one of the following: air bubble still in the cooling system, clogged radiator, or a bad thermostat.

I would tell him to stick with the factory thermostat for now (lower temp t stat won't help much for a stock car unless the fans/car computer is programmed to kick the fans on at a lower water temperature). He can verify that the thermostat is working properly by placing it in a pot of near boiling water on the stove...

Also, have him drain the existing coolant and start the refilling process over again (perhaps after the cooling system pressure test). The pressure test should let him know if he has a bad head gasket, but bad head gaskets are kind of rare on these particular engines...

Oh, and it's probably a good idea to avoid the passenger cylinder head cooling mod in the meantime until he resolves this current situation. Doing the above mod is fairly labor intensive anyways, but if he ever pulls the trans/engine out, it's much easier to do and should be done at that time IMHO.

G'luck troubleshooting...

MacDaddy07 · Jan 21, 2009

Cobra90, thanks for your feedback!

At this point he has a new thermostat in, it is the standard replacement available from AutoZone. We did verify it opens using the boiling water in the pot routine.

He is adding coolant mix using the plug located in the crossover, which is also where he has been burping the system.

As for prior mods, I'd have to get with him.

Appreciate everyone's continued help!

MacDaddy07 · Feb 1, 2009

Further update:

Just got a chance to take a look at how the friend set the fan up to always run. Turns out he bypassed what appears to be a temperature switch mounted to the radiator. I removed the bypass, and reconnected the switch, to do the following troubleshooting.

First, the fan was initially off. It turns on when the temperature reaches about 190-200 on the dash gauge. So far, so good.

Next, I turned on the A/C to see if the high speed fan would turn on. No such luck, the fan stayed at the same speed.

Next, I disconnected the cable to the fan to check the wiring. First with the A/C off. Of the three wires, one had power, the others did not. Turned on the A/C, and found the same thing.

At this point it appears that the high speed fan is not getting the power. The engine was not overly warm at this point (with A/C on), somewhere around 190.

First, from doing a bit of research, it appears this can be caused by either a faulty PCM and/or CCRM? If so, any help on troubleshooting (and a source to purchase) would be appreaciated!

Second, could this be the reason why his car overheats under any condition - idle, highway, local roads?

Thank you again for any and all help!

COBRA90GT · Feb 1, 2009

Well, it sure sounds like the new coolant was being poured in at the proper location - along with burping the cooling system for air pockets.

Just out of curiosity, did you check the fan wiring harness with a test light as well? I'm not saying your buddy did a hack job when he hooked up your cooling fan to run all the time in the past, but I would double and triple check all of your fan wiring just to be on the safe side and thoroughly rule that out as a possibility - no offense to your buddy's work.

Also, yes you are correct - the CCRM (located under passenger side plastic fenderwell - it looks like a small black box) can cause cooling problems. I'm not sure about what specific cooling problems a faulty CCRM induces, you would have to consult a manual (ie - Helm manual/Ford shop manual perhaps?).

You can find replacement CCRMs at dealerships. IIRC, a faulty CCRM is not "serviceable." The book calls for having to replace this module. I know Steve at Tousley Ford (in Minnesota) has stocked CCRMs in the past - Google for that dealership and confirm...

Lastly, has a check engine light of any kind lit up on your dashboard just prior to, or during, this cooling problem you are experiencing? If so, get your PCM scanned for trouble codes...

MacDaddy07 · Mar 2, 2009

Still hoping I can gain some further suggestions?

Latest updates.

We have now replaced the radiator, in addition to the water pump and thermostat (twice). Quadruple checked the thermostat to make sure it is facing the right way and it works. Re-filled the system, burped, etc. Temperature while parked with the heat on reaches 210, and hovers there.

Take it our for a drive, turn on the defogger (which runs the A/C) and it overheats and coolant spits out the degas bottle cap. Confirmed the fan is running when the overheating occurs. He turned on the heat (no A/C) while he was driving it, temperature dropped to 180 and stayed there.

Today he is driving on the highway, no heat and no defrost. Temp climbs up, hits "H" on the stock gauge. He pulls off an exit, temp starts coming down. Opens the hood, fan is running, but the outgas (overflow) cap has spewed fluid all over.

Very confusing! Also, he's spent a small fortune in anti-freeze from having to drain the system so many times.

Any help would be greatly appreciated!!!

hotcobra03 · Mar 4, 2009

overheating

2003 Mustang Workshop Manual
DIAGNOSIS AND TESTING Procedure revision date: 11/12/2002

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Engine Cooling Printable View (58 KB)

Special Tool(s) Pressure Tester
014-R1072 or equivalent
73III Automotive Meter
105-R0057 or equivalent
Worldwide Diagnostic System (WDS)
418-F224,

New Generation STAR (NGS) Tester
418-F052, or equivalent scan tool
Battery/Anti-Freeze Tester
014-R1060 or equivalent

Inspection and Verification

WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine or personal injury. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine is cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, turn and remove the pressure relief cap (still with a cloth).

CAUTION: Check the coolant level, engine oil and transmission fluid, top off the coolant if needed. If there is engine coolant in the engine oil or transmission fluid, the cause must be corrected and oil/fluid changed or major component damage may occur.

Verify the customer's concern by operating the engine to duplicate the condition.
Inspect to determine if any of the following mechanical or electrical concerns apply.

Visual Inspection Chart Mechanical
Leaks
Hoses
Hose clamps
Water gasket
Head gaskets
Intake manifold gasket
Coolant pump
Radiator
Degas bottle/coolant expansion tank
Heater core
Fan/fan clutch
Engine coolant temperature sensor (4.6L)
Cylinder head temperature sensor (3.8L)
Circuitry

If the inspection reveals an obvious concern that can be readily identified, repair as necessary.
CAUTION: Some vehicle cooling systems are filled with Motorcraft Premium Gold Engine Coolant VC-7-A (in Oregon VC-7-B) or equivalent meeting Ford specification WSS-M97B51-A1 (yellow color). Always fill the cooling system with the same coolant that is present in the system. Do not mix coolant types.

NOTE: The addition of Motorcraft Cooling System Stop Leak Pellets, VC-6, darkens Motorcraft Premium Gold Engine Coolant from yellow to golden tan.

Inspect the coolant condition.
Inspect the coolant color.
If Motorcraft Premium Gold Engine Coolant (yellow color) VC-7-A (in Oregon VC-7-B) or equivalent meeting Ford specification WSS-M97B51-A1 has a clear or pale yellow color, this indicates higher water content than required.
Dark brown can indicate unauthorized stop leak may have been used. Use Motorcraft Cooling System Stop Leak Pellets VC-6 or equivalent meeting Ford specification ESE-M99B37-5 except as noted in ES-F6SE-19A511-AA only.
A light or reddish brown color indicates that rust may be present in the cooling system. Flush the system and refill with the correct mixture of water and engine coolant.
An iridescent sheen on top of the coolant can indicate a trace of oil is entering the system. For additional information on engine diagnosis, refer to Section 303-00 .
A milky brown color may indicate that either engine oil or transmission fluid is entering the cooling system. If transmission fluid is suspected, the cause may be a leaky radiator. Pressure test the cooling system. For additional information, refer to component tests in this section. If engine oil is suspected the cause of the leak may be internal to the engine. For additional information, refer to Section 303-00 .
If the engine coolant appearance is acceptable, test the engine coolant freezing point range with the battery and anti-freeze tester. The freezing point should be in the range -40°C to -20°C (-50°F to -10°F). If the vehicle is driven in cold climates less than -32°C (-34°F), it may be necessary to increase the coolant concentration to get adequate freeze protection.
Maximum coolant concentration is 60% coolant/40% water.
Minimum coolant concentration is 40% coolant/60% water.
Adjust coolant range and level, if necessary:
If coolant is low, add specified coolant mixture only.
If the engine coolant tests too weak, add straight engine coolant until the readings are within acceptable levels.
If the engine coolant tests strong, remove some of the engine coolant and add water until the readings are within acceptable levels.
If the concern remains after the inspection, determine the symptom(s) and GO to Symptom Chart

Symptom Chart

Symptom Chart Condition Possible Sources Action
Loss of coolant
Radiator.
Coolant pump seal.
Radiator hoses.
Heater hoses.
Heater core.
Engine gaskets.
Degas bottle or coolant expansion tank.
Go To Pinpoint Test A .

The engine overheats
Thermostat.
Coolant pump.
Internal engine coolant leak.
Radiator.
Cooling fan.
Pressure relief cap or radiator cap.
Go To Pinpoint Test B .

The engine does not reach normal operating temperature
Thermostat.
Go To Pinpoint Test C .

Pinpoint Tests

PINPOINT TEST A: LOSS OF COOLANT
Test Step Result / Action to Take
A1 CHECK THE ENGINE COOLANT LEVEL
WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine or personal injury. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine is cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, turn and remove the pressure relief cap (still with a cloth). NOTE: Allow the engine to cool before checking the engine coolant level.
Key in OFF position.
Visually check the engine coolant level at the degas bottle or coolant expansion tank.
Is the engine coolant level within specification?
Yes
GO to A2 .

No
REFILL the engine coolant as necessary. GO to A2 .
A2 CHECK THE PRESSURE RELIEF CAP
Carry out the Cap—3.8L or Cap—4.6L test. Go to Component Tests in this section.
Is pressure relief cap/radiator cap OK?
Yes
GO to A3 .

No
INSTALL a new pressure relief cap/radiator cap. TEST the system for normal operation.
A3 CHECK THE ENGINE COOLANT FOR INTERNAL LEAK
Key in OFF position.
Inspect the engine coolant in degas bottle/coolant expansion tank for signs of transmission fluid or engine oil.
Is oil or transmission fluid evident in the coolant?
Yes
If engine oil is evident, REFER to Section 303-00 . If transmission fluid is evident, REPAIR or INSTALL a new radiator as necessary.

No
GO to A4 .
A4 CHECK THE ENGINE AND THE TRANSMISSION FOR COOLANT
Remove the oil level dipstick from the engine and the transmission.
Is coolant evident in the oil or transmission fluid?
Yes
If coolant is in engine, REFER to Section 303-00 . If coolant is in transmission, REPAIR or INSTALL a new radiator as necessary. To repair the automatic transmission, REFER to Section 307-01 .

No
GO to A5 .
A5 PRESSURE TEST THE ENGINE COOLING SYSTEM
Pressure test the engine cooling system. Go to Component Tests in this section.
Does the engine cooling system leak?
Yes
REPAIR or install new components. TEST the system for normal operation.

No
The cooling system is operational. GO to Symptom Chart .

PINPOINT TEST B: THE ENGINE OVERHEATS
Test Step Result / Action to Take
B1 CHECK THE ENGINE COOLANT LEVEL
WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine or personal injury. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine is cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, turn and remove the pressure relief cap (still with a cloth). NOTE: If the engine is hot, allow the engine to cool before proceeding.
Key in OFF position.
Check the engine coolant level at the degas bottle/coolant expansion tank.
Is the engine coolant OK?
Yes
GO to B2 .

No
REFILL the engine coolant at the degas bottle/coolant expansion tank. Go To Pinpoint Test A .
B2 CHECK THE COOLANT CONDITION
Check the coolant for dirt, rust or contamination.
Is the coolant condition OK?
Yes
GO to B3 .

No
FLUSH the engine cooling system. REFER to Engine and Radiator Flushing in this section. TEST the system for normal operation.
B3 CHECK FOR AN AIRFLOW OBSTRUCTION
Inspect the A/C condenser core and radiator for obstructions such as leaves or dirt.
Is there an obstruction?
Yes
REMOVE the obstruction. CLEAN the A/C condenser core and radiator. TEST the system for normal operation.

No
GO to B4 .
B4 CHECK THE WATER THERMOSTAT OPERATION
Start the engine and allow the engine to run for ten minutes.
Feel the inlet and outlet heater water hoses and the underside of the upper radiator hose.
Are the upper radiator hose and the heater water hoses cold?
Yes
INSTALL a new water thermostat. REFER to Thermostat — 3.8L , Thermostat — 4.6L(2V) or Thermostat — 4.6L(4V) in this section. TEST the system for normal operation.

No
GO to B5 .
B5 CHECK THE COOLING FAN OPERATION
Carry out the cooling fan component tests. Go to Component Tests.
Is the cooling fan operation OK?
Yes
For diagnosis and testing of the engine, REFER to Section 303-00 .

No
INSTALL a new fan component as necessary. TEST the system for normal operation.

PINPOINT TEST C: THE ENGINE DOES NOT REACH NORMAL OPERATING TEMPERATURE
Test Step Result / Action to Take
C1 CHECK THE ENGINE TEMPERATURE
Start the engine and allow the engine to idle for ten minutes.
Feel the inlet and heater water hoses and the underside of the upper radiator hose.
Are the upper radiator hose and the heater water hoses cold?
Yes
INSTALL a new water thermostat. REFER to Thermostat — 3.8L , Thermostat — 4.6L(2V) or Thermostat — 4.6L(4V) in this section. TEST the system for normal operation.

No
For diagnosis and testing of the engine coolant temperature gauge, REFER to Section 413-01 .

Component Tests

Pressure Test — 3.8L

WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine or personal injury. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine is cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, turn and remove the pressure relief cap (still with a cloth).

Remove the radiator cap. Fill the radiator as needed. Fit the pressure tester to the radiator neck, using an aftermarket adapter.
CAUTION: Do not pressurize the cooling system beyond 110 kPa (16 psi).

Pump the cooling system to a maximum of 102 kPa (14.9 psi) and hold for 2 minutes. If the pressure drops within this time, inspect for leaks and repair as necessary.

Pressure Test — 4.6L

Turn the engine OFF.
WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine or personal injury. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine is cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, turn and remove the pressure relief cap (still with a cloth).

Check the engine coolant level; refer to Cooling System Draining, Filling and Bleeding in this section.
Connect Radiator Heater Core Pressure Tester to the degas bottle nipple and vent hose. Install a pressure test pump to the quick-connect fitting of the test adapter.
CAUTION: Do not pressurize the cooling system beyond 152 kPa (22 psi).

NOTE: If the plunger of the pump is depressed too quickly, an erroneous pressure reading will result.

Slowly depress the plunger of the pressure test pump until the pressure gauge reading stops increasing and note the highest pressure reading obtained.
If the pressure relief cap does not hold pressure, remove and wash the pressure relief cap in clean water to dislodge all foreign particles from the gaskets. Check the sealing surface in the filler neck.
If 110 kPa (16 psi) cannot be reached, install a new pressure relief cap. If more than 124 kPa (18 psi) shows on gauge, install a new pressure relief cap.
CAUTION: If the pressure drops, check for leaks at the engine-to-heater core hoses, engine-to-radiator hoses, water valve hose (if applicable), oil cooler return tube gasket (6N789), radiator and heater core or other system components and connections. Any leaks which are found must be corrected and the system rechecked.

Pressurize the engine cooling system as described in Step 4 (using a pressure relief cap that operates within the specified upper and lower pressure limits). Observe the gauge reading for approximately two minutes; refer to General Specifications. Pressure should not drop during this time.
Release the system pressure by loosening the pressure relief cap. Check the engine coolant level and replenish, if necessary, with the correct engine coolant mixture; refer to Cooling System Draining, Filling and Bleeding in this section.
Cap — 3.8L

Inspect the radiator cap and seals for damage or deterioration. Install a new radiator cap if necessary.
Fit the radiator cap to Radiator/Heater Core Pressure Tester Kit, using the aftermarket adapter.
NOTE: If the plunger of the pressure tester is depressed too fast, an incorrect pressure reading will result.

Slowly pump the pressure tester until the pressure gauge stops increasing and note the highest pressure reading. Release pressure and repeat the test. Install a new radiator cap if the pressure is not 99.3-121.4 kPa (14.4-17.6 psi).

Cap — 4.6L

WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine or personal injury. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine is cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, turn and remove the pressure relief cap (still with a cloth).

Remove the pressure relief cap from the degas bottle.
Follow the instructions from the pressure tester.
NOTE: If the plunger of the pump is depressed too quickly, an erroneous pressure reading will result.

Slowly depress the plunger of the pressure test pump until the pressure gauge reading stops increasing and note the highest pressure reading obtained.
If the pressure test gauge readings are not within specifications, install a new pressure relief cap. If the pressure test gauge readings are within specifications, carry out the cooling system Pressure Test.

Thermostat — Water

A new water thermostat should be installed only after the following electrical and mechanical tests have been carried out.

Thermostat — Electrical Test

CAUTION: Always vent the exhaust to the outside when carrying out this test.

NOTE: The electrical thermostat test is most accurate if carried out at less than 37.8°C (100°F) ambient air. This test may be carried out with or without the hood open and with the engine warm or cold.

Check the engine coolant level. Fill as needed.
With the ignition OFF, remove the engine coolant temperature (ECT) (4.6L) or cylinder head temperature (CHT) (3.8L) sensor harness connector and attach ECT (4.6L) or CHT (3.8L) Sensor "T" Cable as a jumper between the powertrain control module (PCM) (12A650) and the ECT (4.6L) or CHT (3.8L) sensor. Attach the 73III Automotive Meter to the ECT (4.6L) or CHT (3.8L) Sensor "T" Cable. Voltage values (0-5 V) may now be monitored while the sensor retains its connection to the wiring harness.
An appropriate diagnostic tool may be used to monitor the ECT on vehicles equipped with data link connector (DLC).
NOTE: Running this test with the vehicle in gear or with the A/C compressor clutch engaged (running) will cause incorrect diagnosis.

Place the transmission in PARK (P) or NEUTRAL (N).
Start the engine and allow the engine to idle throughout this test. Allow the engine to run for 2 minutes, then record the ECT (4.6L) or CHT (3.8L) voltage. Record the ECT (4.6L) or CHT (3.8L) voltage every 60 seconds. When the ECT (4.6L) or CHT (3.8L) voltage trend changes direction or only changes slightly (0.03 volts or less) from the previous reading, record this as the thermostat opening voltage. Use the voltage and corresponding coolant temperature chart listed below for 4.6L engines only.

Coolant Temperature °C (°F) ECT (Volts)
22 (71) 3.00
43 (109) 2.01
71 (159) 1.01
82 (180) 0.75
91 (195) 0.059
97 (206) 0.050
105 (221) 0.040

If the thermostat opening voltage is greater than 0.75 volts and less than 82°C (180°F), install a new water thermostat.
If the thermostat opening voltage is less than 0.75 volts and greater than 82°C (180°F), the water thermostat is good and a new water thermostat should not be installed. GO to Symptom Chart for further instructions.

Thermostat — Mechanical Test

Remove the water thermostat.
Check the water thermostat for seating. Hold the water thermostat up to a lighted background. Leakage of light around the thermostat valve at room temperature indicates that a new water thermostat should be installed. Some water thermostats have a small leakage notch at one location on the perimeter of the thermostat valve, which is considered normal.
Immerse the water thermostat in a boiling coolant and water mixture.
See the General Specifications chart for water thermostat opening temperatures.

Radiator Leak Test, Removed From the Vehicle

CAUTION: Never leak test an aluminum radiator in the same water that copper/brass radiators are tested in. Flux and caustic cleaners may be present in the cleaning tank and they will damage aluminum radiators.

NOTE: Always install plugs in the oil cooler fittings before leak-testing or cleaning any radiator.

NOTE: Clean the radiator before leak-testing to avoid contamination of tank.

Leak-test the radiator in clean water with 138 kPa (20 psi) air pressure.

Fan — Electric Test

Refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.

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