erratic engine temps

[SHO_ME96]

I performed a search in the forum and found some info on engine cooling issues but nothing like what I am experiencing.

I have a 96 GEN III. I have done nothing exciting to the engine except for a K&N Filter. Transmission was rebuilt at 98K miles. I currently have 113K on it. I’ve owned the cars since it was new. My wife drives it most of the time. Besides the tranny and chewing up brakes like no ones business the car has been great!

THE PROBLEM: I took it for a spin about a month ago and decided to turn off the A/C and enjoy the cool night air. As I was sitting in traffic I noticed the temp of the engine climbing. I pulled off opened the hood to check the coolant level (no idiot lights were/came on). Everything looked fine. Coolant level was fine no leaks were noticed. The weird thing is that when the A/C is on the engine operates at normal temps and with the A/C off it runs hot? Except if I’m on the highway then the temp will climb even with the A/C on. This is the craziest thing I have ever experienced!!

I recently took it in and had both cooling fans, t-stat, and water pump replaced (don’t ask the price it will just make me cry again). The worse thing about this is that it still does it. The engine temp is all over the gauge. It can fluctuate from ¼ to ¾ of the gauge. It never gets out of the normal range but it’s just un-nerving to see the temp climb and fall like it is.

Historically I recall it would normally hang out around ¼ of the gauge. Of course I am looking at the stock gauge so no numbers. Any ideas would be helpful.

 

[SHO#7]

Do the fans turn on? The fans will be called to turn on with the A/C at any time. And will automatically turn on when reaching a predetermined temp with the A/C off.

To me, with your symptoms. That is where I would start.

 

[SHO_ME96]

I will double check that myself but since I had the fans replaced I just figured they were operating.

 

[Mr Anonymous]

Sounds like you could have a bad ECT (engine coolant temp.) sensor. I find most V8 SHO's usually have a temp reading which is pointing at about 24MPH on the speedo. If you're still running a steady temp with the A/C on (which as Mike said turns the fans on constant), try letting it run without the A/C and see if the fans ever kick on, and if they do at what point on the gauge.

 

[Shoman594]

I have the same problem

Fans kick on at a little over half way and then kick into high gear at just before 3/4 up the gauge. Its fine in highway driving but at idle or traffic it climbs all the time and the fans keep having to come on. Paul Nimz suggested that the radiator may be clogged. or could it be a tstat ? If it is the ECT sensor failing how is it malfunctioning? Is it sending the wrong temp to the computer ?

 

[Mr Anonymous]

Yours sounds more like a cooling problem than an ECT problem. Your fan behavior is consistent with a good ECT. When an ECT fails, it will often not provide the full range of output to the PCM to accurately reflect the temp. If the ECT is telling the PCM that the coolant is plenty cool, it won't ever turn the fans on, or only will when it gets way too hot.

 

[Off Road SHO]

First thing I would do is get an infrared thermometer. That way you could verify if the high reading on the guage is related to high temperature coolant/air pocket or a faulty signal from the guage's sending unit.

If it is hot coolant, check the system and the cap for a tight pressure seal. Also check to make sure the coolant recovery system; bottle and hose, are in good condition. A small hole in the hose will allow coolant to travel only in one direction; out of the radiator. When the engine and radiator cool down, air is sucked into the system instead of the coolant from the recovery tank.

Good luck and let us know what you find.

Tom

 

[SHO_ME96]

I have ruled out a clogged radiator because if my A/C is running then normally my temp will stay below 1/2 and more often will stay at about 1/3 on the gauge (pointing at 24mph). The only time it reaches 1/2 with the A/C is if it is very hot outside and I'm at highway speeds. If the A/C is off then regardless of the temp outside my engine temp will climb to about 2/3 of the gauge then will cool itself back down to halfway mark.

My problem I bet is what Chris said and that the ECT is not working properly. I will check the cap and lines to be sure there are no leaks. I'm running out of options because as I said eariler I have already replaced both fans, t-stat and water pump.

I will check tonight to see if/when fans are engaging with A/C off.

Thanks
Tim

 

[Shoman594]

Thanks for the info guys. Can i check to make sure that system does not have have a hole in it by using a coolant pressure tester? If i pressurize the system and it has a leak some where the pressure should go down right ?

But the gen 3 cap is different so im not sure if i can even do that

 

[SHOWHAT9]

SW9'S MISFORTUNE IN THE DESERT

Scroll down to the post morteum section. If all else checks out, I also had a cracked ect sensor, then you better drop the radiator and inspect it. Pull the tranny stick after driving while still hot. Look for any sign of water. It's a long shot I grant you, but if it happened to me it can happen to anybody. Also pull both ECT sensors and inspect the porclean carefully. Good Luck

 

[shoteen95]

my mothers car recently had a strange flirtation with overheating on her. Gauge would soar right up the red zone. Had the coolant flushed, but it still overheated. A local ford dealership told us that the impellers in the water pump are plastic, and if the engine gets to hot they'll melt...sounds kinda stupid, but ya never know.

Anywho, after a brief inspection of the radiator from under the car, appearantly my mother went offroading, cause there was mad sandwhiched between the radiator and condensor up the height of the radiator..a few minutes with the garden hose and i coated the driveway with mud/bugs/tar..

it helped out a good bit

not that this is probably the cause of this erratic engine temp..but

uhm...

moral is, dont go mud slinging in your SHO!

 

[SHOWHAT9]

Moral is really do what you did - inspect the radiator closely! Good Form sir - Bravo.

 

[SHO_ME96]

OK, I started the car cold in the driveway. The temp continued to climb to about 2/3 of the temp gauge. At which point the second fan kicked in cooling the engine down to 1/2. This is with the A/C off.

With the A/C on it maintains temp at about 1/3 of gauge (pointing at 24 mph) and did not move.

Maybe it is a clogged radiator?! With both fans going it maintains temp? The only thing left is radiator or ect sensor. I've replaced everything else. Is the ect sensor difficult to replace?

 

[SHOZ123]

Both fans should be running whenever they are told to run. There is a high and low speed fan circuit.

With the A/C on and the car idling the low speed fans should be on no matter what the engine temp. As the engine gets over 225F then the fans should go to high speed.

 

[Shoman594]

Ok next question is how do you pressure test this system, with that new ford cap ? I also checked the coolant with my coolant tester and it was fine. I would like to pressure test before i go replacing things. On thing i did notice though is after the car has been hot for a while i took off the cap with a big rag over it and barely heard any noise like there was no pressure built up in the system

 

[SHOWHAT9]

Ok next question is how do you pressure test this system, with that new ford cap ? I also checked the coolant with my coolant tester and it was fine. I would like to pressure test before i go replacing things. On thing i did notice though is after the car has been hot for a while i took off the cap with a big rag over it and barely heard any noise like there was no pressure built up in the system

We have a closed system, Ryan. Did you " burp" the coolant to get air bubbles out?? Another long shot but this will cause your temp gauage to do the hully gully until all air is expelled. (ok your'e way too young to remember the hully gully) :****:

 

[SHOZ123]

My experience with the V8 is to fill the degasser tank all the way when refilling and it will soon settle out. No burping required. That's for them infant SHOs......

 

[projectSHO89]

These sounds like perfectly operating cooling systems. Only an accurate temperature reading will tell for certain.

Steve

 

[padukes]

We have a 96 SHO and the engine seems to be running hot with the AC on. In traffic or even at highway speeds the temp gauge keeps rising past the middle and up just below the overheat bar, then the fans come on and it cools down a bit, but it keeps repeating that. I thought the fans would come on a lot sooner than that. We flushed the radiator, changed the thermostat and the temp sensor, but the problem is still happening. Someone said at one point that the CCM(?) could be the problem with why the fans are coming on so late. Anyone have any ideas?