Need Help to Diagnose Overheating Car

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Robert Crain

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2003 V8, 166,000 Every component of the cooling system has been replaced in the last 2-3k miles except the electric fans. First of all, thank you Joegr for your input on the chat line. The car has been running normal as it should. Last week. I was driving on the Interstate for a long period of time with no issues. At some point during this drive, I noticed the temp gauge jumped up to 3/4 hot then settled back down to 1/2 (normal). When I got off the Interstate onto a two lane road, the temp gauge pegged hot and the dash lit up like a Christmas tree. The coolant was boiling in the D-gas bottle. Every part of the cooling system is new-the radiator, DCCV, aux water pump, main water pump, thermostat, hoses, etc. Even that darn D-gas bottle is new. The system has not been leaking and there is no evidence now that something is leaking. My mechanic has flushed the system and says it might be a faulty heater control valve, DCCV or clogged heater core. I think his diagnosis is pure rubbish and he's only making guesses. I'm thinking I should start by removing the thermostat and assess that there is good coolant flow throughout the system. If there is, then maybe the thermostat is faulty?? Could use your input on a diagnosis strategy. The mechanic says he could get the electric fans to work as I initially thought that might be the problem. Just wanted to add that replacing that plastic elbow pipe located underneath the air intake was one of the worst automotive experiences of my life. So what do you think is going on here? Help! Thank you.
 
There is only one fan. Please have a look at the back of the radiator to see this.
One thing I didn't ask, are all these replacements Motorcraft or aftermarket. Your symptoms do match perfectly with those who have used the aftermarket crossover and thermostat assembly. It does not allow quite enough coolant circulation.
 
I had a thermostat housing fail on me after a couple years. It was Motorcraft. One of the shoulders inside broke off and the thermostat was sideways. Not saying that is your problem but it wouldn't hurt to look at it. You could verify with the cap removed I think?
 
any time you go into the red you’re risking blowing the head gasket or dropping multiple valve seats. get that fan running ASAP

in addition to the above make sure your system is bled. check for combustion in coolant
 
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ajv8 said:
...get that fan running ASAP
...
Click to expand...

I think that when he said he thought that the fan wasn't running, the engine was off. Of course, the fan does not run with the engine off.
The overheat started while he was in cruise, so the fan wouldn't be a factor there (it is turned off if the car is going fast enough to get good airflow without it.)
 
Did you use motorcraft parts when you replaced it initially? Because I didn't and mine was overheating right from the start but you wouldn't know it by looking at the gauge cuz the gauge doesn't move till you hit 230 degrees and mine was up around 210-220, you'd have to watch it on a monitor system like forscan on a Bluetooth adapter to even notice though cause the factory Temp guage is basically just an idiot light, there is no temp range, it's either cold, "normal" or too hot with no distinctions in-between
 
Thanks all for your input. Joegr, my thought process with the fan was that the car didn't seem to overheat until I got off the highway and onto a slower moving back road. Going at the slower speed would mean less air moving across the radiator. I could be wrong, but I thought the fan operated until it brought the coolant temps down to a certain temp even when the car wasn't running. No matter, the mechanic said the fan was working. Everything except the radiator, hoses and clamps are Motorcraft. I know that for certain because I purchased and replaced them all myself. The radiator I got from Summit Racing. So I'm thinking now, since everything is new, I'd start at the beginning with the thermostat. Question: Why would removing the thermostat divert coolant away from the radiator? I never knew of a car that did that but you all know the LS is a different beast. Would like to first assess if I'm getting any coolant flow. The car is still at the shop that did the towing. Rob
 
How about the radiator itself?

The way this sometimes goes... is once every other cooling system part has been replaced... the radiator usually fails at the passenger side top hose, (backside of radiator facing bumper).
 
Robert Crain said:
.... I could be wrong, but I thought the fan operated until it brought the coolant temps down to a certain temp even when the car wasn't running. ... Why would removing the thermostat divert coolant away from the radiator? I never knew of a car that did that but you all know the LS is a different beast. ...
Click to expand...
No, the fan will not operate with the engine off. Partly that is a safety feature, but more so it is because it would drain the battery very quickly. There is no provision for any fan control without the PCM operating. There is provision to operate the aux pump after shutdown if the engine temp is too high. You couldn't hear it running without putting your ear up to it.
As an aside, my Wife's Cadenza will run the fan for a little while after shutdown sometimes. However, it is a much lower powered fan, with a simpler control system.

No, removing the thermostat does not cause coolant to bypass the radiator. The LS is not different than other cars in this. Like other cars, removing the thermostat can cause the coolant to flow through the radiator so quickly that it does not have enough time to lose much heat there, so sometimes having no thermostat can be as bad as having one that is stuck mostly closed. If I was going to go through the trouble of removing the thermostat and then refilling and bleeding the cooling system, I would either replace it with an even newer one, or test it. Testing the LS (gen II V8) thermostat is more difficult than most, since you at least need the front housing with it.
 
joegr said:
No, the fan will not operate with the engine off. Partly that is a safety feature, but more so it is because it would drain the battery very quickly. There is no provision for any fan control without the PCM operating. There is provision to operate the aux pump after shutdown if the engine temp is too high. You couldn't hear it running without putting your ear up to it.
As an aside, my Wife's Cadenza will run the fan for a little while after shutdown sometimes. However, it is a much lower powered fan, with a simpler control system.

No, removing the thermostat does not cause coolant to bypass the radiator. The LS is not different than other cars in this. Like other cars, removing the thermostat can cause the coolant to flow through the radiator so quickly that it does not have enough time to lose much heat there, so sometimes having no thermostat can be as bad as having one that is stuck mostly closed. If I was going to go through the trouble of removing the thermostat and then refilling and bleeding the cooling system, I would either replace it with an even newer one, or test it. Testing the LS (gen II V8) thermostat is more difficult than most, since you at least need the front housing with it.
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from what i can see the thermostat housing is basically a glorified T fitting. the big disc on the thermostat is what blocks the radiator return hose until the stat opens and then blocks the direct to WP bypass.

no thermostat means the straight to WP bypass is always open
 
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Technically, the return hose (cool coolant returns from the radiator) is the hose at the bottom of the radiator that goes to basically to the inlet of the water pump. The thermostat blocks hot coolant from going to the radiator via the top hose.

From the service manual:
The fan motor:

  • operates only when the engine is running.
The engine coolant flows:

  • from the lower radiator hose to the coolant pump.
  • from the coolant pump to the engine block and the cylinder heads.
A closed thermostat returns the engine coolant to the coolant pump. An open thermostat allows the engine coolant to flow to the radiator.
 
Its better to drill a hole in the thermostat than to completely remove it if you're trying that method.
 
The local Lincoln dealership has a new thermostat on the shelf for me. I'll pick that up tomorrow and start there. It's not the radiator. A radiator fails by springing a leak or becoming clogged. Neither of which is happening here. What is the diagnostic test other than a voltage measurement for the aux coolant pump and DCCV? Again, I'm thinking flow. As always, thank you for your input. If it was easy, anybody could do it. Rob
 
Robert Crain said:
The local Lincoln dealership has a new thermostat on the shelf for me. I'll pick that up tomorrow and start there. It's not the radiator. A radiator fails by springing a leak or becoming clogged. Neither of which is happening here. What is the diagnostic test other than a voltage measurement for the aux coolant pump and DCCV? Again, I'm thinking flow. As always, thank you for your input. If it was easy, anybody could do it. Rob
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Mine was blowing the fuse, which is in the upper left corner of the fuse box under the hood, red, 10 amp I think. Runs ac compressor, dccv and aux pump if I remember correctly.
 
Robert Crain said:
The local Lincoln dealership has a new thermostat on the shelf for me. I'll pick that up tomorrow and start there. It's not the radiator. A radiator fails by springing a leak or becoming clogged. Neither of which is happening here. What is the diagnostic test other than a voltage measurement for the aux coolant pump and DCCV? Again, I'm thinking flow. As always, thank you for your input. If it was easy, anybody could do it. Rob
Click to expand...
A failed aux pump won't cause overheating, unless it is leaking. The same applies to the DCCV.
 
Robert Crain said:
At some point during this drive, I noticed the temp gauge jumped up to 3/4 hot then settled back down to 1/2 (normal). When I got off the Interstate onto a two lane road, the temp gauge pegged hot and the dash lit up like a Christmas tree. The coolant was boiling in the D-gas bottle.
Click to expand...
This almost sounds like you had an air pocket in the system. If the symptoms have gone away and the car is cooling normally now... it may have "burped" the air out of the system.

You also mentioned what a PITA changing out the o-rings at the gooseneck under the intake was.

You may want to check and make sure you don't still have a leak at that spot. If so... the coolant will run along the top of the block... and down onto the transmission and exhaust... and will "burn off" leaving a white stain on the trans or exhaust.
 
My vote is also for the thermostat and housing. Mine broke at under 90k and caused the thermostat to sit crooked, and caused some cooling issues.
 
No visible leaks or an odor of an unseen leak. I bought another Motorcraft thermostat and will start there. Thanks all. Rob
 
check for more leaks around the radiator hose connections, they crack. Have someone else start the engine while you look for leaks. i found two leaks that way.
 
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