Bad Thermostat?

[maximos]

I thought I had put my cooling system issues behind me but there appears to be something wrong still. Just to give you guys a timeline:

August: Replaced radiator, cooling fan, and thermostat
December: No heat coming from vents, fan stopped working causing overheating - had a complete coolant flush and discovered a bad ground wire from fan
February: Heats works for the most part, occasional periods where only cold air comes through the vents despite the car being above normal operating temp. Sometimes when I turn the heat on it will cause the temp to rise from the "O" in NORMAL to the "L" then all of a sudden it will go back down to the "O" after about a minute. This appears to be completely random so I don't know what the cause is. I should also mention that this sudden rise in temperature has happened without the heat turning on, but I figured the connection was worth mentioning since I have noticed the sudden rise immediately after I turn the heat on.

Any thoughts?

 

[HISSIN50]

I'd replace the t-stat with a decent one just to rule that out.

Do you have a real temp gauge that you can watch?

Give more info about when it runs at what temp. I.e., while on the highway, you should be at around the t-stat rating in terms of operating temps. Once stationary, the fan dictates operating temps.

In case it helps, here's a little cooling system tech note

 

[maximos]

I'd replace the t-stat with a decent one just to rule that out.

Do you have a real temp gauge that you can watch?

What type of thermostat would you recommend? The only temp gauge I have is in the stock instrument panel.

 

[HISSIN50]

I've had good luck with Mr Gasket t-stats. That said, mine are older and some guys have complained that their newer ones were not working right.

Any balanced t-stat should be fine. I'd test it on the stove before installing it, just to be sure that it atleast works at 1 ATM.

15 bucks for a cheap mechanical guage could be helpful. It's a bit of work to install one, but if you've ever wanted some gauges for the car, now is the time to install some. Knowing actual temps is important IMHO.

 

[Chythar]

I'd check the ECT sensor as well, if the computer isn't reading the right temperature it might keep the engine in "warm-up" mode which will heat the engine up a lot. Does the cooling fan come on at all? If not, that's another sign of a bad ECT.

 

[maximos]

The cooling fan does come on. I was actually going to ask how I can wire it so it stays on all the time. Any negative side-effects to doing this?

Where is the ECT located? I wouldn't mind swapping that out at the same time as the thermostat.

 

[ProKiller]

i'd rather see you put in a manual fan switch rather than running it all the time. do a search for manual fan switch install and i'm sure you'll find what your looking for.

 

[k00ksta]

Its not that hard to wire the fan up to a switch, you will need a Relay, Some Automotive Wire and a decent switch. I can look tonight on which relay and switch I am using as well as write up a little description on how to do it if you can not find anything someone already did up.

 

[revhead347]

The cooling fan does come on. I was actually going to ask how I can wire it so it stays on all the time. Any negative side-effects to doing this?

Where is the ECT located? I wouldn't mind swapping that out at the same time as the thermostat.

Running the fan all the time will just lead it to wear out faster. If the car is below the normal running temperature of "O" then there is no need for the fan to be on. It's much better to program the chip to turn the fan on at a lower temperature. Of course this requires you to get a chip. Aside from that, I wouldn't bother with having it run all the time. If the car is overheating, than it's going to be on anyway.

On the topic of thermostats. When a thermostat fails, it usually just gives up the ghost, and stops working all together. A thermostat has an expansion fluid in it that expands when it gets hot, pushing the thermostat open. A failure means a leak of the fluid chamber. If it has a leak, then it's not going to open at all. I have a Mr Gasket high flow in my car. I'll tell you one thing, for sure. The thermostat flows so much water to the radiator, that nothing ever gets up to the heater core. If you run a high flow thermostat, you are basically going to be giving up your heat for it. If you replace the thermostat, go to Ford and get the original. Stant has a monopoly on aftermarket thermostats, and their quality control sucks. I can't tell you how many problems I've had with Stant thermostats.

If you have irradic temperature changes, it's either a bad sensor (or bad wiring associated with the sensor), or it's a blown head gasket. Unfortunately, usually it's a blown head gasket.

Kurt

 

[maximos]

If you have irradic temperature changes, it's either a bad sensor (or bad wiring associated with the sensor), or it's a blown head gasket. Unfortunately, usually it's a blown head gasket.

Kurt

What else should I look for as telltale signs of a blown head gasket? The low coolant light comes on every few weeks and I've had a feeling a blown gasket is the culprit.

 

[revhead347]

Ok, what happens is that the gasket blows from the combustion chamber to the water jacket. Exhaust gas gets into the cooling system and blows some of the coolant out. That exhaust gases also form bubbles inside the cooling system, that flow past your temperature sensor. That's what causes the gauge to move around and spike and stuff. There is a test kit you can buy that tests for exhaust gasses in the coolant. I think they sell it at NAPA. If there are gasses in your coolant system, then you definately have a blown head gasket.

Kurt

 

[Labora]

Ford Tstat or bust IMO. All the other brands seem to not be worth the trouble.

 

[revhead347]

Ford Tstat or bust IMO. All the other brands seem to not be worth the trouble.

Totally agree. It's not a whole lot of money anyway.

Kurt

 

[alecracing]

I'm new here so i don't wanna be a dick, BUT, I've been a Ford tech for 20 years and it sounds like you have air in your cooling system.

Whenever you fill up your cooling system, it is a good idea to take out the ECT sensor on the front of the manifold while pooring the coolant in the radiator. When the coolant starts coming out the ECT hole than engine is full and hopefully heater hoses also.

air in the cooling system is logical thing when you turn your heat on and cool air comes out sometimes and your guage is erratic. If "burping" your cooling system doesn't work, then get the cooling system tester for combustion chamber gases.

It consists of a turkey baster type of thing with a tip that goes on the radiator cap opening and has blue fluid in it. put it on radiator with vehicle running and squeeze rubber ball to suck vapors from cooling system, if blue fluid turns yellow, then you have combustion chamber gases in the cooling system. This could be caused by a few different things: blown head gasket (most common), cracked cylinder head, or a cracked block.

MAKE SURE YOU DO NOT SUCK UP ANY COOLANT INTO THE TESTER!!! this will cause a false reading.

 

[revhead347]

I've never had trouble with burping the cooling system on a Mustang. It always seems to take care of itself.

Kurt

 

[maximos]

air in the cooling system is logical thing when you turn your heat on and cool air comes out sometimes and your guage is erratic. If "burping" your cooling system doesn't work, then get the cooling system tester for combustion chamber gases.

I had the cooling system completely flushed and filled at a Valvoline center. They checked for air in the system and didn't find any. This problem I've been having started happening before I had the system flushed.

 

[maximos]

*UPDATE*

I believe my radiator is cracked. I got underneath the car and there was coolant covering the underside all the way back past the steering rack. Mishimoto is sending me a new one, but is there any way to prep the radiator prior to installation that will prevent future leaks, etc?

I figured out that the jumping temp needle was due to the fact that I had an extremely low amount of coolant in the system. I mistakenly trusted the "low coolant" light and relied on that to tell me when to put coolant in. I've been monitoring the coolant level more closely and I haven't had any problems other than the leaking.

 

[Chythar]

The low coolant sensor is in the overflow tank, it's attached to the cap. The "low coolant" system presumes your coolant system is intact and not leaking anywhere else. You now know how it can fail.

Our Mustangs have a lot of body flex right around the radiator support on the right side. Your radiator is likely cracked there. One theory to prevent the cracking is to cut the rubber radiator supports enough so the radiator isn't squeezed into place. If you have to yank back on the radiator to bolt the top brackets, it's in too tight.

Another theory is to install sub-frame connectors to reduce the body flex. Unfortunately, no one has been able to say 100% that these ideas will work.

 

[maximos]

Our Mustangs have a lot of body flex right around the radiator support on the right side. Your radiator is likely cracked there.

That's exactly where I suspect the leak to be - lower passenger side of the radiator.

I assumed the radiator cracked when the car overheated (badly) a couple months ago when the ground wire to the fan went bad.