Hello all!
Paul from AB Canada here. I am an ex Brit Just bought a lightly used XJ8 Vanden Plas (108k) 1 owner from new.
Driving it home from the pick up point last night I had an issue with temperature.
After about 20 minutes of driving with the temp in the car set to 19c the temp ssensor went tup and the red light came on, I was in the middle of a 3 lane highway so no where to pull over so I pulled my old Austin mini trick and cranked all the heat and blower to full this got the temp down to normal (mid range) within a minute or two...after sweating 10 lbs off in my mobile sauna I reduced the temp to 20 and lowered the fan speed...20 minutes later the same thing happened again. So I made the mobile sweatbox and again it dropped quickly.
Eventually when I got home the fan ran for what seemed at least 5 minutes.
I dont think its a thermostat sticking (closed) issue as the heater ran hot the whole time... Any thoughts or suggestions please.

 

Hello Paul, welcome to the family!

So, this was your first time driving the car right? This the previous owners/seller told you about that issue? Maybe they can point you in the right direction if they recently replace or tried to fix something related to tha problem.

How was the level of the coolant after that issue?

J.A.G.

 

Hello J.A.G. Thanks for the reply!
The owner died sadly I bought the vehicle from his 79 yr old widow...It had been sat for two years prior to me taking it home last night. I have about 4 inches of service records, it has been serviced to an extreme level from new.
I had to replace the battery to get her moving, everything sounded great, there was an engine light on after the battery failure it has stayed on I will do an OBD2 code test to see what it reads.
The surging heat is what I'm questioning, if it just stayed hot I would be worried but it drops to normal temps when i crank the heater.
Its a little cold out right now when it warms up later today I will inspect fluid levels.

 

So I just went out and checked the coolant level while the car is cold.
The expansion tank level is at the minimum mark. Would that cause this I wonder?? Also checked the oil and there is no white residue or milkiness

 

Oh, that might be the reason, try to fill up to the corresponding mark and then take her to a ride to see if the same thing will happen. But keep monitoring the coolant, because even after being parked for two years, the coolant shouldn't be low or evaporated. But certainly a low level could cause some overheat.

Scan for the codes and probably that would lead you to something else. But at this point I think it should be good when you fill up the coolant.

J.A.G.

 

Hey JAG so I did the OBD2 scan and as I suspected the only code was the battery low voltage which I had to change to get it home.
It's cleared now. I'm going to take it to my local oil change and have them top up the coolant at the same time.

Will let you know how I get on.

Paul

 

All right.

Good luck and yes, let us know how it is.

J.A.G.

 

Hi @Sterling Silver ,
Congrats on the new car! When I first evaluated my car, before purchasing it, it overheated while sat in the driveway. I was unable to drive it as the suspension was completely flat and the entrance to the driveway was way too steep to drive out. I assumed/hoped thermostat.

I sent the car to the independent mechanic who serviced it regularly to have the air springs warrantied and decided to just have them also replace the thermostat/housing and water pump, and have not had a problem since. Mine too sat for a very long time due to the suspension issue and the owner not being able to drive it out of his driveway. I can only guess the the thermostat had seized closed, but mechanic never told me.

You can check the bottom and top hoses on the radiator when at operating temperature. If one or both remain cool enough to hold, the thermostat is likely closed. Another possibility is a clogged radiator. The heater trick is your best friend right now, good job employing it on your drive home! Good luck!

-j

 

Hello Jacuar,

I have a question, I have been dealing with some issues related the cooling system. So you said, check both hoses (Top and Bottom) but, even if the Thermostat stuck closed, the Top hose wouldn't be cold either way because that's the coolant coming from the engine?

All theses days I have been trying to figured out a few things, for example, both hoses (Top/Bottom) are really hard and certainly very hot when the engine reach operative temperature. I was thinking that could be a clogged radiator, but if that would be the case, just the Top hose would be hard and the lower should be soft and cold.

Unfortunately, I never monitored the temperature before I replaced the Thermostat, Water Pump and fresh coolant so I could be able to compare the temperature then and now. The engine is now running between 199F and 208F but most steadily on the 203/206F. The new thermostat is supposed to open at 197F

Thanks.

J.A.G.

 

Hi @J.A.G. ,

Good questions. I had suggested both hoses to be safe, but really only the hose from the thermostat housing will stay cool until the thermostat opens. While the thermostat is closed, the coolant bypasses the thermostat and, therefore, the inlet hose to the radiator (the right hose as you view the engine from the front). There is a small diameter bypass hose that goes from the thermostat housing to the radiator outlet hose (the hose on the left). This allows the coolant to circulate throughout the engine, but not the radiator, keeping the water pump from building up pressure while the thermostat is closed, and also to facilitate quicker heating of the engine coolant, as the engine is most efficient at operating temperature. The coolant in return hose from the radiator is not isolated from the engine, which allows the coolant to mix with the coolant in the engine thereby raising its temperature. You should feel it warm as the engine warms.

You rightly suggest that if the radiator is clogged the radiator inlet hose should be hot when the thermostat opens, but because the outlet hose is not isolated from the coolant in the engine, it will become hot as well. You are right, the inlet hose from the thermostat (top hose) will get hard when the engine is hot because the it is receiving pressurized coolant from the water pump. However, if you feel that you cannot squeeze that hose, it could be a sign of a clogged radiator. I would use an infrared temperature sensor to check for cold spots in the radiator if you suspect that it is clogged. The factory thermostat opens between 190 - 198 F and is fully opened at 216 F. When I have checked, mine is usually around 190 194 when driving around town, but I rarely check. I am not alarmed by 203 -206 F, but I would keep an eye on it. Does your fan cycle on and off or is it running continuously? Have you checked for debris on your a/c condenser? If the car is running overly hot, I would first verify that the cooling fan is operating.

I will follow up after I watch my running temperatures for the next couple of days and let you know what I see.

-j

 

Hi all, @Jacuar @J.A.G. thanks for the suggestions.
So today I did a full engine coolant flush, took it for a run seemed good for a while then I had to stop at a train line. Sat idling for 10 minutes and it red lined again.
Did the heater trick again and it pulled the heat away to normal levels.
So here is my question please if you can help, my biggest question is why the heater trick is working? If it's a sticky thermostat wouldnt the heat not come through the heater? If it's stuck the other way i dont thionk it would red line?...I'm no mechanic though.

I looked online for the thermostat thinking it would be a simple replcement but it seems like the whole housing needs to be replaced?

Any more thoughts.
Thanks!

 

No worries, happy to help!

The heater system works on the engine side of the thermostat, meaning that regardless of the status of the thermostat, engine-heated coolant will circulate through the heater core if you have the heater running. This serves two purposes, it allows for the heater to begin transferring heat to the cabin long before the thermostat opens, and, as you adeptly exploited, provides an emergency heat exchanger if the thermostat is stuck in the closed position :-)

-j

 

Old trick, turning the heater on.
Another, smaller, radiator, & fan, to help cycle the coolant

 

Ai 108k miles I would recommend that you replace the whole 'tree' except maybe the part attached to the engine (with 4 bolts)

which means that you do not need to remove the TB.

You can change the t"stat only but ensure that you photograph the one you remove

since it is not obvious how the parts go together.

My tree was cracked on one of the flanges and some of them fall to bits on the inside.

 

Thanks a lot, your explanation put me into a much clear understanding of the system.

Yes the cooling fan usually starts to work after the temperature reach the +195F.

I'm always monitoring the temperature at the stereo screen with the Torque lite app and after normal operative temperature has been steady around 199 and 206, depending on the speed. When idle it's between 206F and 208F.

I have cold air conditioner on both sides (driver/passenger), but the heat is kind of weak and is working just on passenger side, the driver side is blowing almost normal outside temperature, not even warm.

I have another question regarding what you said about the thermostat opening. There is a way that you for sure could find out if the thermostat is already open or not?

Thanks
J.A.G.

 

Your best option would be replacing yh whole thing, I mean the whole thermostat assembly because at some point you will need to do one of the other if you just replace the thermostat. Also is a headache trying to put the thermostat into the housing if you just get the thermostat. And something else, between the Just thermostat and the whole assembly, THE PRICE is Almost the same. So as a recommendation you better buy the whole assembly.

J.A.G

 

Do replace both pieces of the plastic housing.
It seems that, some have thought the lower plastic part looked ok.
Rear torx fasteners can be a problem.
Replaced mine with regular headed bolts

 

If the heat output from the vents is poor then you probably have a blocked heater matrix. Only way to fix it is to change it. I cut my old one open and it was very blocked, I was surprised it did anything it was that bad. I replaced most of my hoses not long ago I just did a search on ebay and got some at a very good discount compared to the *******s but one I couldn't get and the others were from the classic jag website.
The overheating would pont to restricted flow at some point. I wonder if a hose has collapsed internally?

 

Congrats on the purchase I am from Calgary myself. Where you located in Alberta?
I use XJ Auto in Calgary, also heard Sovereign Auto in Edmonton is good.

 

Thanks for your reply.

As you mentioned, the air flow through the air vents is very limited and a weak heat on the passenger side but not heat at all on the driver side with an even more limited air flow than the passenger side.

THERE IS something that always make me curious since the time that I bought the car. Most of the time wether the air conditioner is on or off, there is a weird noise coming from the vents, it's sounds like an offline/bad signal radio station.

Regarding the hoses, yes I noticed that the upper and lower radiator hoses collapse every time I turn off the car, but not immediately, but gradually when the coolant is getting colder. When I remove the reservoir tank cap they kind of get back to their normal shape. I already replaced the cap with 3 others caps but still keep happening.

I'm aware that I need to replace those hoses, they are not internally good, you can see they're deteriorating. I'll do that to see if that helps with the collapsing situation.

Thanks.
J.A.G.