From what I can tell, the housing breaks down after repeated thermal cycles work harden the nylon and make it brittle. I'm not sure which section comes apart, but I had a somewhat similar overheating issue on my car when I bought it, and replacing the thermostat housing assembly cured the issue. The car did not overheat until the outside temps went over 60 deg F, so for the first two months of ownership everything was fine (winter in the Pacific Northwest). The only thing I noticed was the fan ran at full speed if I got into traffic. Once outside temps got over 60, then it would start climbing the temp gauge at idle. Bringing the engine up to around 1500 RPM would bring the temp back down.

Note here I am not saying the housing SHOULD break down over time, just that it does. There are several threads here documenting similar issues, which is how I was able to solve my issue so quickly. The same thing appears to still be happening on GM radiator tanks more than others. I had to replace a cracked upper (inlet) tank on my GTO at 100,000 miles, while the radiator on our Jeep is still fine after 177,000 miles.

Dave

 

One question - the photo isn't really clear - is the coolant in the engine green or orange?

 

It's green

 

So today I had a little time to look at it. And I realized while the engine was running the upper and lower radiator hoses + the radiator where getting hot almost too hot to hold your hand on there ( I still have the thermostat out ).
The intercooler, supercharger hoses where way cooler than the main radiator hoses.
I checked the heater core lines and they weren't building heat at all.
So I checked the intercooler coolant pump down on the bottom left side of the radiator/intercooler radiator. I squeezed the bottem hose and I can feel fluid movement. Went to the upper hose on that pump and felt movement also.
I went to squeeze both heater core hoses and didn't feel any fluid movement in either side.

I found this diagram of the coolant system which helped me somewhat understand it. And I seen it has three coolant pumps, one main block pump the runs off the belt and two electric pumps.
The intercooler pump and the heater core pump (I think it's called auxiliary water pump).



I think maybe this auxiliary pump could be bad.
Or Is there any fuse or relay that runs this pump that would cause it to not turn on?
Does anyone know if this would cause blockage in the coolant system to make it overheat? Or maybe make and air pocket in it?

I know that's probably why my heater in the cabin doesn't work.

 

The aux pump or any kind of blockage in the heater core will not cause the engine to overheat. But, no flow in the engine cooling system will cause it to overheat. When I replaced the thermostat and belts (maintenance) on my former XJR , I also flushed the coolant (engine, radiator and heater core) and decided to install a new water pump (didn't want to deal with working on that area again). I think I installed new hoses too because I'm now remembering that one of the clamps was a nightmare to put on.

 

A full flush is in order then, once you get the flow situation sorted out. The coolant in these engines is supposed to be the GM Dex-Cool equivalent, Ford spec WSS M97B44-D.



.

 

+1 on the coolant flush. Green coolant is wrong and will hose your aluminum system up. If the prior owner just added green with Dec-cool (orange/pink) it can gell and clog the system. Check the flow thru the radiator for clogs from gelling up. As stated above, work on getting engine temps right before fixing the cabin heat. Your engine won't blow from no cabin heat, but head gaskets will from engine overheating. Don't play with a loaded gun. Have you tested the thermostat out of the car yet?

 

How is green coolant going to make it over heat. I understand about mixing.
But Honda uses green and everything is aluminum in them and nothing goes bad for them.
Maybe I don't understand but help me understand.

 

When the green stuff is mixed with the orange stuff it forms gloop.
I think what is being suggested is that perhaps the po refilled with the older green type when the correct type is the OAT orange stuff.
The orange left in the engine and the new green coolant when mixed form a gloop/sludge which can cause circulation problems.

 

I see so it's something to try.
What would you recommend to do for a flush on this engine?

 

EGR-M14P7-A Jaguar Premium Cooling System Flush.
Listed in the cooling system specs.
Sure another can be found.

 

Your car (our Jaguars) utilize OATS Coolant. The most common is GM's Dexcool. OATS comes in many colors now including green (dark green). OATS will gel all by itself. Mixing it with Ethylene Glycol (the light green stuff) will accelerate the process of clogging the cooling system but it will gel on it's own. See the class action law suits against GM if you want more detail.

Since you don't know what you have, a flush is definitely in order. Never mix coolant types. I've read others who have completely 100% replaced their OATS with Ethylene Glycol and claim it's fine. I don't know enough to doubt them.

Get yourself an infrared thermometer. They can be had for $20 and easy to read temps on either side of a stat, pump, heater hose, etc...

 

Would a water less coolant be better????

Several advantages, after the initial expense, and rather tedious process of eliminating all the water in your system.

Curious concept, boils at some very high temp.

So no pressure build up in the cooling system, runs cooler.