Weird Cooling Issue - anyone seen anything like this?

[Chythar]

A bit of background: I've got a bit of an overheating issue on my GT. I haven't put any serious effort into it yet because the fan keeps the heat manageable. The engine heats up faster then it should, and will retain the heat even on the FREEWAY. But not all the time - sometimes the temp stays down at the thermostat, sometimes not. It doesn't bounce up and down, which would indicate a bad thermostat. The engine just stays warm until I turn the engine off. Next time I drive the GT, it might run cool ,maybe not. I have a mechanical temperature sensor & gauge I'll install when I'm ready to work on it, but I pick at the problem now & then.

I noticed a coolant hose that was kinda kinked. Drained the coolant, cut a bit of hose off the ends and no more kink. Since then, the engine temps have been a bit strange. I gave it a couple of days to work all the air out of the system, and the engine does run a bit cooler, it doesn't heat up as fast and the fan doesn't kick on quite as often. But here comes the weird issue:

Temp gauge is at halfway or a bit over. From a stop, if I floor it up to about 35-40, the temp gauge will quickly DROP to somewhere around the "O". This is somewhat repeatable, depending on how long I'm at WOT. The temp stays down for about a minute, then slowly climbs back up.

Anyone seen anything like this? I have a WAG (wild-@$$ guess), but I'm gonna wait until I hear your ideas.

 

[BlownFiveLiter]

To me, that sounds like an air pocket. It gets hot, the coolant expands, the temp spikes temporarily as the sensor gets an actual reading from the gauge, not an air temp reding, then it cools once the coolant circulates. Rinse and repeat, as it keeps happening. Sometimes it'll eventually get the air pocket to the radiator and the level drops, but usually you have to pop the front end on some jackstands and let it come up to operating temperature with the radiator cap off. Then you get to "burp" the system and get the air to come out the radiator. It should be good to go after that.

 

[j_lutter31]

Yea, the temp gauge wont read air temps just fluid temps. When adding water/coolant to the engine after its been drained, its a good idea to turn the heater on. Doing so will get the coolant flowing through the system getting rid of all the air bubbles.

 

[desertcox05]

mine is doing similar things but i'm thinking i have crud on the sensor idk

 

[urban96]

any loss in coolant?

 

[Chythar]

any loss in coolant?

Some, but I would expect that since I partially drained the system enough to remove the kinked hose. My exhaust doesn't smell sweet so I shouldn't be burning coolant.

 

[Chythar]

Yea, the temp gauge wont read air temps just fluid temps. When adding water/coolant to the engine after its been drained, its a good idea to turn the heater on. Doing so will get the coolant flowing through the system getting rid of all the air bubbles.

What good does turning the heater on do? The coolant flows through the heater core no matter what, right? All turning the heat on would do is run air over the heater core.

 

[Zero_chance]

Exactly right Cythar. Coolant will be flowing regardless of heater position. I often have it on heat when I do coolant flushes though so I can tell if theres air or not. With air in the system youll notice the air goes cool then hot, cool then hot, etc. Whats the condition of your water pump? Original?

 

[Chythar]

Zero Chance. nice idea on turning on the heat. It's worth a check.

My water pump is about a year old, it's a Stewart Stage 1 pump. I also have on a 93 Cobra (I think) wp pulley, it's smaller than stock 94-95 so it spins the pump faster.

Is it possible to push the water through the engine too fast? I know there's theories on this, but I don't think it's possible.

 

[WHITE94COBRA]

What Temp thermostat do you have? If it's colder than stock did you tune the high speed fan to come on earlier (Ex: 180* therm high speed fan should be comming on at 192* the stock fan setting is 215* for the highspeed fan) ?

Putting a colder stat in without tuning the fan operation will do just the opposit of what you are trying to do, which is keep it cooler. I did that on my old 95 way back when and it was doing similar to what you are describing.

On a side note have you checked the actual temp? I have one of the laser temp readers and even when my temp guage shows at the A in normal, its actually only 209* I had this verified with a mechanical guage as well. I now have a autometer temp guage and it rarely gets past 210* with the air on and 100+ outside.

As for pushing the water through to quickly; if you have a thermostat inline, it should not flow past it too fast. If your running therm less, that very well could be your problem as well. Do you have all the rest of the cooling in place? The radiator cover actually helps ALOT, I had mine off and the air was going around and above the radiator, also the lower air diffuser, (the plastic black piece under the front bumper) if it's missing your losing alot of air through the radiator there too.

Off topic, did you get that pipe put on? I'm kinda anxious to hear it.

 

[Zero_chance]

I dont really think you can push the water through too fast. Mentioning a different size pulley, have you checked to make sure theres no slippage or anything? Youd likely hear it though so Im assuming thats all good. Have you checked actual temps at different spots with a laser temp reader. Thats the best way to know whats going on. My stock gauge used to be all over the place, I installed Autometer Cobalt gauges and my car is almost always at 195 or so unless I use the AC. Have you used any products like water wetter or anything like that? Theyve been know to cause gelly deposits with certain amounts of glycol concentrations. Has your water temp sender ever been replaced? Theyre cheap enough and can sometimes give the false impression that the cars heating system is on the fritz when it really isnt. Just some random thoughts.

 

[Chythar]

We're getting a bit more involved on troubleshooting the coolant system than I have time for - I'm still trying to find time for, much less finish my Cobra conversion. To answer the questions recently posted:

I have a Mr. Gasket 180* thermostat, about a year old. The EEC is stock, so the fan is still at the stock settings. I have a Black Magic fan which does do an effective job of cooling the engine when it turns on. However, it doesn't cover the entire radiator. I do not have the plastic radiator cover, though I have one from my other Stang - worth a try to install. I have the two lower air duffusers ( the plastic one before the radiator and the rubber one after). However, the radiator support I have is a junkyard one (installed before I bought the GT) and the bottom is kinda mangled up. So I'm not sure if the rubber air diffuser is aligned right.

The radiator cover is the easiest thing to try, I'll install that and give it a try.

The water temp sender is also about a year old, and was new. This engine is a used 91 Thunderbird engine (stock 5.0 but has the 93-95 Cobra cam), and I installed it - can you guess? About a year ago. The ECT is also the same age. The temp senders are worth checking into, they're something I will look at when I really did into this problem.

I haven't used Watter Wetter on this engine, but since it's a used engine I don't know what's been done to it in the past. I did have a coolant flush on this engine done about 8 months ago.

 

[stackz]

whats your battery terminals look like?? if they're nasty, I'd go ahead and put new terminal ends on with some terminal grease on them as well as the cable ends after they are cleaned as well.

bad battery connections can make your gas and cooling gauges develop weird habits...ask me how I know haha.

also, even though the t-stat is only a year old, sounds like it may be starting to stick a bit.

I'd just replace the t-stat with a cheap stocker and see what happens and then get a good thermometer and toss your 180* one in a pot of water and see what temp it opens up at on the stove...

while you're in there changing the t-stat, might want to look at the bleed hole on the water pump even though it's only a year old as well. If your engine really is getting that hot that often, the extra cooling system pressure could have already blown out the seal on the pump somewhat and that could be where you're losing some water at.

 

[STM1965]

interresting thread

My 95 has been a PITA for quite some time doing whats sounds to be the same thing. I bought the air damn for the bottom finder last summer, didn't make a whole lot of difference, replaced the sending unit for the EEC few weeks back, no noticable difference, water pump is brand new, rad is new, I even went so far as to wire in a toggle switch so I can if need be over ride the computer and bring the fan on manually. Actually tomorrow morning we going to finish up connecting the gauge pod we put in (autometers)(oil pressure & water temp) both mechanical...needed to buy a different adaptor for the temp guage (came with a 1/2 inch needed 3/8th) and running a copper tube to the psi guage instead of the nylon type the kit came with (frigging line runs so close to the headers it might have melted) hopefully that's it for me!

 

[Chythar]

A bit of an update. I put the top radiator cover on my GT, and drove the Stang around all weekend. In our lovely 100+* heat wave, and my A/C don't work. Anyway. The radiator cover seemed to do make the issue consistent - now the engine is ALWAYS hot. I can understand the engine running warmer than usual because of the heat, but at 65+mph it should NOT be running over half way. I did pull over once to verify the fan was turning on - it was.

Now that it's running consistently warm, it is now reminding me of a problem I had with my V6 Stang (which uses the same temp senders). I was having the same problem, the engine was running WAY warm. My local mechanic told me that the gauge was reading wrong, the engine was running at the correct temperature. He told me to drive the car and ignore the temp gauge for now, until I could bring the car back for a more in-depth diagnostic.

One day on the way back from work, the temp got up WAY high, approaching "L" on the gauge. I felt the engine lose power, kinda like I lifted my foot up off the gas. It was then I realized the engine WAS overheating. I bought a code reader (the V6 is an OBDII car, so the plug under the dash works) and checked the temp the computer saw. The value was boucing from cold to the actual temp and all over. So the ECT sensor was bad. Once I replace the sensor, the car's temp went back to normal.

My GT wasn't acting the same as the V6 was, so I didn't think the ECT sensor might be the issue. Now it's acting the same, so I'm gonna throw a Motorcraft ECT sensor at it and see how it goes.

Question - when the engine starts up, does the computer adjust the fuel mixture to make the engine warm up faster? Then once it reaches operating temperature, readjust the fuel mixture to optimal levels? I'm not saying this is what the computer does, I'm asking if anyone knows IF the computer does anything like this.

 

[STM1965]

well heres my update now that I have an autometer gauge installed! city driving the car will run 200 to 210, highway 180, run the A/C in city 180 to 200. On a side note my autometer oil pressure guage is all over the place! when it was tired into the factory dash gauge it was constant and never bounced about, now it'll show 40psi under normal driving conditions however pull up to light and it'll drop to 20psi and sometimes as low as 15psi depending on how long I've been driving...whats normal?

 

[Chythar]

well heres my update now that I have an autometer gauge installed! city driving the car will run 200 to 210, highway 180, run the A/C in city 180 to 200. On a side note my autometer oil pressure guage is all over the place! when it was tired into the factory dash gauge it was constant and never bounced about, now it'll show 40psi under normal driving conditions however pull up to light and it'll drop to 20psi and sometimes as low as 15psi depending on how long I've been driving...whats normal?

In general I'd say that's normal. The idiot gauge in our cars is just that - an idiot. Oil pressure does go up and down based on RPM - as long as it doesn't fall below a certain number you're fine. I believe it's 10-15 PSI - anyone know the specific number?

The idiot gauge on the dash has a resistor on the back, it's intended to keep the gauge steady at one specific value so the average consumer doesn't freak watching the oil gauge bounce around.

 

[stackz]

In general I'd say that's normal. The idiot gauge in our cars is just that - an idiot. Oil pressure does go up and down based on RPM - as long as it doesn't fall below a certain number you're fine. I believe it's 10-15 PSI - anyone know the specific number?

The idiot gauge on the dash has a resistor on the back, it's intended to keep the gauge steady at one specific value so the average consumer doesn't freak watching the oil gauge bounce around.

nail on the head. remember the oil pump is a pump and it is operated by a shaft from the distributor. obviously it will produce more pressure as the engine rpm increases...if it doesnt, that's when you worry haha.

the idiot light is there to make people feel better and not have to actually LEARN about their cars

it normally only moves during startup/shutoff or if the oil pressure sensor gets nothing...where the oil pump is pretty much dead at that point.

 

[Zero_chance]

The stock gauge indicates pressure with anything over 6 psi. After the initial reading, gauge position is irrelevant according to the Ford workshop manual for my car which is a 95. Just confirms how useless the stock gauges really are.

 

[HISSIN50]

Question - when the engine starts up, does the computer adjust the fuel mixture to make the engine warm up faster? Then once it reaches operating temperature, readjust the fuel mixture to optimal levels? I'm not saying this is what the computer does, I'm asking if anyone knows IF the computer does anything like this.

Most definitely.