Bizarre Overheating Issue Help

Thomas4406

Member
Nov 16, 2015
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Hello everyone, new to the forums, but a long time owner of an 04 Mustang GT. Car has done great since i bought it with 50k miles on it. I just recently popped over 100k miles on her, and seems to be running into issue after issue. First I will say that after a little bit of investigation it appears that the previous owner had wrecked the front end and did not have it reported any where. I am not sure of the extent of the damage, but i'm currently having some cooling problems.

It started about 5 months ago, the car just randomly over heated. I caught it quickly by noticing a loss in the AC quality, but the car still managed to spew most of the coolant through the cap. I replaced the thermostat and the coolant reservoir cap. It went probably 3 more weeks and then in stop and go traffic overheated on me again. I took it to a local shop where the mechanic diagnosed the problem to a failing radiator fan. He replaced the fan. About 2 weeks later same scenario; lost AC and overheated. Looked under the hood and apparently the fan was cutting off/on randomly and not cooling properly. The fan was replaced under warranty. I thought i was out of the wood works until 4 weeks ago it over heated on me again. I drove the car all day with no problems. Then, after having it all cooled down, I ran to the gas station about 10 miles and it overheated AGAIN! Took it to the mechanic and he did a coolant pressure check, as well as a block test with the blue liquid. He told me that the results were inconclusive but noticed that there was a crack in the stock intake manifold. The mechanic put in a brand new intake and intake gasket. The car was doing great up until last week. I started the car up and immediately noticed it was running louder than normal. I drove it home and it over heated on me as I was pulling in the drive way. Completely frustrated and not sure what the problem is. I did a block test on my own and the liquid remained a constant blue after several minutes of pumping.

A little bit of background on the car; I drive it every day and it normally runs fine. The overheating is not a result that I can easily replicate. It really seems to only happen randomly. I have never been hard on the car. The check engine light comes on occasionally with a Catalyst efficiency below threshold on bank 2, but appears to go off on its own and doesn't effect the running of the engine. I had hi-flow cats put in awhile back. The battery light comes on every now and again, but I suspect it is from the HID head/fog lights I put in as it has a brand new battery and never has trouble starting. I know it is extremely hard to diagnose problems over the internet like this, but is there any advice on where I can start? Is there a purge/bleeder valve to remove any air in the cooling system? I intend to do the work myself if I can, as the mechanic is becoming pricey. It seems weird that the block test and pressure test could come back with no results and the car be over heating. Thanks for your time, and I appreciate any help.
 
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Have you changed the fan temperature sensor ? For air bubbles sometimes it helps to add coolant with the front of the car up on ramps. A bad fan relay can cause symptoms that you're describing.
 
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Have you changed the fan temperature sensor ? For air bubbles sometimes it helps to add coolant with the front of the car up on ramps. A bad fan relay can cause symptoms that you're describing.

Okay thanks 90sickfox ill look into those areas. Much appreciated. I have searched through a few forums regarding the fan relay; I assume you are referring to the CCRM (Constant Control Relay Module)? Seeing as the issue is nothing that I can recreate and make happen, do you suggest just buying a new one, or is there a way to test the functions? Same question with the fan temp sensor. Thank you
 
Yes you can test both. The CCRM is a known problem with overheating issues. You've been through everything else...so it seems. A lot of shops don't know how to diagnose a CCRM issue. I don't know either off hand. If you could find out which wire is the power out to the fan you could tap the wire for a small 12 volt led or 194 bulb and socket...one wire to the output and the other wire screwed to a good ground. When the fan is activated the bulb will light up... If the light is lit and the fan isn't spinning then the problem is between CCRM and fan. If the light and the fan go out when it should be on ( about to overheat or above 3/4 ) then the problem is in the CCRM.
 
Yes you can test both. The CCRM is a known problem with overheating issues. You've been through everything else...so it seems. A lot of shops don't know how to diagnose a CCRM issue. I don't know either off hand. If you could find out which wire is the power out to the fan you could tap the wire for a small 12 volt led or 194 bulb and socket...one wire to the output and the other wire screwed to a good ground. When the fan is activated the bulb will light up... If the light is lit and the fan isn't spinning then the problem is between CCRM and fan. If the light and the fan go out when it should be on ( about to overheat or above 3/4 ) then the problem is in the CCRM.

Okay thanks ill try it out. I am still a bit confused as to how this would work on an intermittent issue, but perhaps I will find something. Thanks again
 
That way when it happens you'll notice the bulb either on - fan running or not...or off fan not running with temp at a level where it should be on. I'd replace it personally. An intermittent problem is super hard to diag. You've got to catch it screwing up. If it was me I'd replace the CCRM and take a chance.
 
The CCRM is rarely the culprit. If the fan is coming on then you should be able to rule it out. The temperature sensor is another spot to check because of an inaccurate reading it may cause the overheat. Burp the system as well as there may be air in there.

Get a Chilton's or Hanyes nanuel. Priceless when doing troubleshoots.
 
The CCRM is rarely the culprit. If the fan is coming on then you should be able to rule it out. The temperature sensor is another spot to check because of an inaccurate reading it may cause the overheat. Burp the system as well as there may be air in there.

Get a Chilton's or Hanyes nanuel. Priceless when doing troubleshoots.

Thanks for the reply. Honestly it is a bit hard to rule anything out when its impossible to recreate the situation in which the car over heats, but looking at all the options. I ordered a repair manual, but is the cooling fan temp sensor different than the coolant temp sensor? I mean you're not referring to the one that displays the temp. on the gauge in the car right? Where is the fan temp sensor located? Also, how do you recommend "burping" the system without a bleed valve. Much appreciated -T
 
Burping isn't an exact science. In the past I removed the top hose and filled from there. Started the car and let it heat up then shut it down, cool and filled again. The temperature sensor is mounted on the intake manifold forward. A bronze looking thing with a sensor wire plugged into the top.

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Burping isn't an exact science. In the past I removed the top hose and filled from there. Started the car and let it heat up then shut it down, cool and filled again. The temperature sensor is mounted on the intake manifold forward. A bronze looking thing with a sensor wire plugged into the top.

0996b43f802051fb.gif

Thanks buddy. Very helpful
 
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