96 cobra, overheating, no cooling fan

[ryanmancl]

Alright, I need some help. I have a 96 cobra. when I got the car it didnt have a thermostat in it and it would overheat when it idled for a long period of time. So I put a thermostat in it and tested the cooling fan, it works when direct power is put to it but wouldnt turn on when the engine warmed up.
I got a new coolant temp sensor and it does the same thing. runs cold for a long time even with a new thermostat and slowly raises well past normal operating temps. Still no fan turning on, when i unhook the sensor the fan kicks on, but the car turns over a long time before it will start.
On top of that, when the sensor is plugged in and the car warms up the idle bounces from 200 to 1500 rpm then dies, and does the same when I unhook the sensor and the fan runs.
I did refill the coolant from the proper place and have bled it numerous times, no air bubbles at all coming out now when i check. Any ideas? Any tests I can run? Thanks in advance for the help.

 

[wmburns]

My gut tells me that air is still trapped in the cross over. The DOHC 4V engines are difficult to bleed and WILL overheat if the bleed procedure is not followed EXACTLY.

Any sensor in contact with air instead of coolant will read LOW. The trap air is delaying the T-stat opening and is also blocking the flow of coolant. Because the sensor is also reporting a false low temperature the PCM is not calling for fan as it should.

If asked to handicap this thread, I suspect there is more going on. Consider why did the prior owner remove the T-stat? Perhaps because no matter how many times the system was bleed, it wouldn't work. What would cause this? A leak somewhere in the system. For example a head gasket leak allowing combustion gases to enter the cooling jacket.

The gases will collect around the T-stat, and bam! Overheating is the result. Removing the T-stat may have been done to get it to run well enough to sell.

What to do. A coolant pressure test for starters. There is also a dip test kit that can detect combustion byproducts in the coolant. This will let you know if the head gasket is leaking. The test kit is available from most local autoparts stores.

Another possibility is a leak in the intake manifold. The bouncing idle is a prime symptom of an intake leak. So if the coolant jacket were leaking into the air intake, that would explain the bouncing idle and the inability to get the cooling system purged. Pulling the spark plugs would give evidence of contamination.

I can not stress this strongly enough. It is madness to continue to diagnose this issue until the coolant system is completely air free and remains free of trapped air. The DOHC is difficult to bleed and there is more than one person that gave up and had a dealer vacuum fill it. It would be a waste of $$ to have it vacuum filled if there is a leak.

Good luck.

 

[darkhorse96]

There is a computer relay module in the passenger side fender that controls the cooling fan, fuel pump and a couple of other things. That may be the problem. its called a ccrm.

 

[ryanmancl]

So i went through and re-bled the system, so i am sure there is no air in it. still can't get the fan to turn on, so i know there is coolant in the upper tubes and it is hot at the coolant temp sensor. So it has to be something other than the bleed. I also found a small air leak in the upper intake gasket and have a new one coming from the dealership. so that probably accounts for the bouncing idle issue. still overheating at a very constant rate. from cold to too hot. as far as the ccrm goes, if the car runs and works fine except for the cooling fan could that still be the issue? and what is the testing procedure? probably replace with known good part knowing ford... it does have a custom tune, could that affect anything? thanks for the help so far guys. its appreciated.

 

[wmburns]

I got a new coolant temp sensor and it does the same thing. runs cold for a long time even with a new thermostat and slowly raises well past normal operating temps. Still no fan turning on, when i unhook the sensor the fan kicks on

The fact that the fan kicks on when the temperature sensor is disconnected says that the CCRM is at least working at some level.

Does the cooling fan run if the AC is turned on?

Has the fan been confirmed working for BOTH high speed and low speed? Power the fan directly from a 12 volt source. There should be an obvious speed difference between low speed and high speed.

Possibility: the PCM is not calling for fan because the PCM doesn't think the fan is needed. This could be from an error in the tune. For example, the set point is 300 degress or the units (F or C) have been entered incorrectly

Would be real handy to know what the PCM THINKS the temperature is. For this an ODB2 scanner capable of reading operational data is needed. There are also PID's that would tell us if the PCM is calling for fan. This is important information.

EDIT: I recall reading a post that stated there is a difference in the temperature sensor between the 96-98 MY's and the 99+ MY's. Might be worth checking that the correct temperature sensor was used for the application. Again knowing what the PCM thinks the temperature is would help.

 

[ryanmancl]

I have the intake taken off for the new gasket that is coming in on tuesday. so I wont be able to check anything til after that. as soon as it is running again ill throw a scanner on it and see what the engine thinks the temp is. The fan did have a high and a low when i tested from a direct 12v source. as far as the ac goes, I have an issue with my ac switch, so I couldn't accurately tell you if it turns on with the a/c just because I dont thing it is working properly at the moment.
Also what I did with the temp sensor is bought one that is supposed to be correct then i later bought one for the GT, the GT one runs the fan as soon as the engine starts but never turns it off, and it also cranks for a long time before starting, so it runs as if it is completely disconnected, which i think is the failure mode. and the 'correct' one starts the car perfectly, but never turns the fan on, so its either always reading cold, or the tune is incorrect... but as soon as i get a computer on it I will get back on here and update. thanks again.

 

[LaserSVT]

Its been a long time since I messed with a 96-98 Cobra but I mess with 93-98 Mark VIIIs all the time. Your cooling fan controller is more like the 97-98 Marks so if it goes on then its fine and not the issue. Thing is earlier Marks have three spots for coolant temp reading and use the one on the crossover tube AND one more sensor on the heater tube on the back of the passenger head to turn the cooling fan on.
Not saying thats the issue but maybe something to look at. Unfortunatly its a royal PITA to get to.

If the car has a tune then thats where my money is assuming the car is properly burped. I have had 4 Cobras (96,97 & 2-03s) and work on Marks for a living.
How I bleed them is get the nose up, fill the res tank, put its cap back on, remove crossover cap and top off then start the car with that cap off till it hits temp then put the cap on and let the car sit 10 minutes then slowly remove the surge tank cap. Sometimes I will have to add a couple cups more water and sometimes none at all.

If you want I can send you a known working sensor for the crossover tube.


Do you have a tune though? If so go through the file and see what the target temp is.

Another thing I have learned over the years is only use OEM thermostats on these cars that has the bypass hole. The 4V doesnt like any other kind EXCEPT the 160* Stant thats for V-6 Mustangs I think. I can go look up the part number.


As for the idle jump, I realize you found an intake vac leak but the IAC on these cars is very prone to failure and need to be replaced every 30K or so. Dont get an Autozone one, order from Rock Auto.

Hope it helps some.

The Teksid B head engines are my favorite motors and I have lots of experience with them. Wish you were closer so I could tell ya bring it by. I have the Matco scanner and SCT pro software as well as all the special 4v crap so working on them is fun for me.

 

[ryanmancl]

Its been a long time since I messed with a 96-98 Cobra but I mess with 93-98 Mark VIIIs all the time. Your cooling fan controller is more like the 97-98 Marks so if it goes on then its fine and not the issue. Thing is earlier Marks have three spots for coolant temp reading and use the one on the crossover tube AND one more sensor on the heater tube on the back of the passenger head to turn the cooling fan on.
Not saying thats the issue but maybe something to look at. Unfortunatly its a royal PITA to get to.

If the car has a tune then thats where my money is assuming the car is properly burped. I have had 4 Cobras (96,97 & 2-03s) and work on Marks for a living.
How I bleed them is get the nose up, fill the res tank, put its cap back on, remove crossover cap and top off then start the car with that cap off till it hits temp then put the cap on and let the car sit 10 minutes then slowly remove the surge tank cap. Sometimes I will have to add a couple cups more water and sometimes none at all.

If you want I can send you a known working sensor for the crossover tube.


Do you have a tune though? If so go through the file and see what the target temp is.

Another thing I have learned over the years is only use OEM thermostats on these cars that has the bypass hole. The 4V doesnt like any other kind EXCEPT the 160* Stant thats for V-6 Mustangs I think. I can go look up the part number.


As for the idle jump, I realize you found an intake vac leak but the IAC on these cars is very prone to failure and need to be replaced every 30K or so. Dont get an Autozone one, order from Rock Auto.

Hope it helps some.

The Teksid B head engines are my favorite motors and I have lots of experience with them. Wish you were closer so I could tell ya bring it by. I have the Matco scanner and SCT pro software as well as all the special 4v crap so working on them is fun for me.

I would love to just swing by, this is my first non 5.0 Mustang and first 4.6 of any kind. Thought I had a pretty good grasp on things, but this is getting the better of me.
So I just replaced the thermostat, with a stant, and it was the one for the cobra, don't know if its a different part that the v6 one you were talking about. If it is I will use your advice and get another to throw in.
As for the coolant, the reservoir is full and I have run it through a couple cooling and heating cycles, and keep checking the crossover and it is topped all the way up without even a small air bubble, so I am pretty confident that that is not the issue, fingers crossed...and the temp raises very gradually and evenly, so i dont believe its a mechanical cooling system problem.
The "correct" coolant temp sensor that i just got runs the car exactly as the original one i took out, and the wrong one i bought on purpose, runs the car like its hot all the time with the fan coming on and staying on no matter what. so I dont believe its the sensor now, just by trial and error.
I will probably just pick up a IAC as it seems everyone has issues with them and i think the previous owner was an idiot.
I am not sure if it has a tune, it almost has to, just because of the supercharger being added. unless someone really messed it up, i am also getting like 7mpg right now, maybe cause the car always believes it is cold.. Not sure, could also be a tune problem. so i am going to do the intake, and get a computer on it to see what everything is reading.
I appreciate all the help and will make sure to post what the issue was when and if i ever get it fixed.

 

[ryanmancl]

So I took my car in to a shop to have them run a scan on it. I explained everything that I have done and let them have it. Got a call later in the day saying it was done and working, and they replaced the cooland temp sender that runs the guage in the instrument cluster and said that fixed it. Said it was reading incorrectly. and thats what caused the fan to not come on, imagine my surprise when on my way home, it started to overheat, and i checked the fan, and yup, no cooling fan running. I didn't think the gauge sending unit had anything to do with the cooling fan. Am I wrong? I would hate to argue with the shop and be incorrect. Let me know what you think. I am bringing it back in tomorrow anyway and I hope to at least get some free labor time out of them.

 

[patman0911]

Yep, the sending unit for the gauge doesn't do anything other than drive the gauge. The PCM gets its info from the other sensor.

Looks like the shop doesn't know 96-98 Mustangs very well, or how to look it up in a book. And if they just let it idle for a while to if it would overheat then they may have thought they fixed it 'cause it might never get past normal temps just sitting there on a cool day.