2005 LS V6, Overheating but not really

[StephenGlenn]

Had an overheating problem. Water pump bad, replaced. Month later car overheats again. Took it to water pump repair shop. "the car's not really overheating it just thinks it is". Sensors replaced. 2 weeks later, happened again, cooling fan starts, gauge pegs, warning light, warning bell, limp mode. Car not overheated. Waited 2 hrs, car starts up and drives fine. Coolant sensor replaced again. Went to 2nd shop, both reputable, 4 hours of analysis. "We can't find the problem, you need to go to the dealer, possible pcm". Heating and cooling function just fine. Car thinks it's overheating, moves to protect engine, shuts it down, waits for engine to "cool down" and then works fine for about another 30 min or 20 miles. PCM? If so, obsolete at dealer. Suggestions? Including son's 05 V8, this is my 4th LS, 2000 V8, 2002 V6, 2005 V6 and son's 2005 V8. Love them but baffled at this one.

 

[joegr]

Okay, I started, but I'm not going to bite on this one. Someone else should be along soon to explain it.

 

[StephenGlenn]

Oh, checked codes, are for coolant sensor. When sensor fails it fails to the overheating mode, ie pegged gauge. OBD II thinks it's a sensor failure too, but it's not. Thanks

 

[joegr]

If you want to know if it is really overheating (it is), you need to monitor the temperature in real time with an OBDII scan tool. You can't go by the gauge, it works more like a light than a gauge. Practically overheating is at the 1/2 way mark. Just a few degrees more pegs the gauge.
Why would it overheat and then be okay and then overheat? Air in the system blocking coolant flow. Why is there air? Micro-cracks in the plastic cooling system parts.

 

[milehighmikey]

I did not see where the cooling system has been purged of air. What happens when you do a bleed using the hose by the brake booster? If it bleeds and purges air, how long does it run before it gets that hi-temp condition?

 

[milehighmikey]

I have a personal attachment to this condition, as my water pump impeller detached from the shaft and caused an overheat that led to something allowing combustion gases into the cooling system. It would rapidly push the coolant out of the bottle. It doesn't sound like that happened in this case, so bleeding and taking note of whether it happens again quickly is important in diagnosing this condition. If it comes right back, you probably lost watertite integrity in the cooling system in the head gasket/head cooling passages, or cylinder wall cracking. Mine went from saveable to needing a new engine in 3 or 4 diagnostic startup tests. Keep in mind that my water pump was not functioning for about 3 miles of driving and then a few startups in the parking lot. Once it got cracked open (wherever it did) the water would rise up rapidly in the degas bottle and overflow. It wasn't long after that the water had a black tinge to it, from the combustion process. Hopefully, you didn't get it that far along.

 

[SultanGris]

Yea the gauge is worthless, i monitor my temps with forscan and at 225 degrees the gauge is still in the middle and sometime after 232 or so it pegs and turns on the overheat light, not sure why they even wasted their time putting a gauge on this car, lol

 

[joegr]

Yea the gauge is worthless, i monitor my temps with forscan and at 225 degrees the gauge is still in the middle and sometime after 232 or so it pegs and turns on the overheat light, not sure why they even wasted their time putting a gauge on this car, lol

I looked at some Jaguar XFs (sort of the sequel to the LS), and they didn't have temperature gauges.

 

[ajv8]

swinging coolant gauge = scary. results in service advisors being asked stupid questions. functional oil pressure gauges are even worse

idiot lights are much better for most people

 

[AmsterDutch]

I personally love my working oil and coolant gauges in my 1998 Z71 Silverado ...I'm like Sultan when it comes to my LSE ...Forscan lite is locked in on my so called Smartphone ( rolling eyes ) just like to monitor this computer as much as I can due to being g a giant computer