Ok, here's the situation: My '97 XK8 has 30K miles. I just replaced the original (plastic) thermostat housing with an aluminum version (OE housing was leaking at the seal with the engine block), and re-filled the cooling system with the orange coolant. I elected to NOTchange the water pump or thermostat because of the low mileage. Now, after driving less than 80 miles since these changes, I'm having an engine temperature problem. From a cold start, the engine seems to warm-up in the usual manner with the temp gauge reaching its normal, fully warmed-up position (exactly mid-point on the temp guage) after just 1.5 miles or so. Then everything seems to behave normally for the next 6 miles or so, at which point the temperature reading will then slowly start to climb. The further I drive, the higher the temp goes. In each instance, the outside temp has been in the mid to upper 80s, and I have never driven the car to the point where the temp guage has gotten into the upper red zone.

So, I'm wondering: are these the signs of a failing water pump or thermostat? I'm leaning more towards water pump, but I've never experienced symptoms like these on any vehicle I've owned before, so your opinion & experiences would be greatly appreciated!

John

 

John, We have very similar circumstances. My '97 XK8 has 35,000 miles and just recently began running warmer than usual. After driving a few miles the high speed cooling fans would kick in as well. I took the car in to my independent jaguar mechanic and he suspected the thermostat. He changed out the thermostat and replaced the plastic OEM housing with the new aluminum housing. In my case, he also replaced the Coolant Temp switch which he identified as faulty.

The result? Now she warm-ups quicker, the fans no longer kick in and the temperature holds steady after driving. I suspect my thermostat was stuck in a somewhat middle position. This caused warm up to delay and when running, did not allow enough coolant to flow, causing slight overheating. If your temperature is rising, your thermostat could be stuck in a slightly more closed position than mine was. Restricted coolant flow causes overheating. Hope this helps.

 

That's funny... I read your description and I thought the exact opposite of what Jim thought. It sounds to me more like a water pump that isn't pumping correctly. Of course, I've never experienced those symptoms and Jim has, so what do I know? I think the thermostat is the cheaper/easier fix, though, so I'd start there.

 

The water pump and thermostat are about the cheapest parts on these cars. Since the early cars have a known problem with plastic pump impellers why not change out the pump AND the thermostat. These parts are now 14 years old.

 

+1 on the t-stat and pump, for piece of mind. The coolant temp sensor also while you're doing it. Don't chance it.

I assume you did 'flush' the system after dumping all the original greens stuff? Putting several gallons of distilled water thru the radiator and hoses, then filling it with the orange? If there is any green left in the system, it has a tendency to reacts with the orange and thicken. If you didn't, suck up the cost of the coolant and properly flush the system. With the radiator openings for coolant heat transfer being so small, you can't afford to restrict movement thru it.

 

Thank you for your replies. But now I'm confused. I thought the original coolant in my car was orange. Is this incorrect? I'm frustrated because neither the owner's manual, the JTIS (at least anywhere I have found), nor the Forum FAQ have a listing of all the factory-specified fluids vs. model year, other than engine oil. It would be nice to know what fluids the factory recommends for each model year (or VIN range) for the cooling system, automatic transmission, rear-end differential, power steering, convertible top hydraulics, brake fluid, etc. Where is this info published by Jaguar? How do the Jag mechanics and our own Forum Techs (no offense intended) know what is spec'd by Jaguar?

In the mean time, I think I will drain the cooling system, flush, then fill with plain water to determine if I have a coolant mix issue (as described by H2OBoy). I'm trying to understand what went wrong. It seems unlikely for the water pump or t-stat to fail at the same time as me having changed the t-stat housing when all was okay before the change (other than the coolant leak). At least with plain water in the cooling system I will be better able to rule-out the coolant issue, then move-on to the pump and/or t-stat if need be.

John

 

The early cars came with the green coolant which was changed to orange in the '99 time frame.

Check the FAQ Sticky above for a lot of information plus some of the techs, Motorcarman specifically, have copies of Technical Bulletins and other documents that they post in reply to questions. I try to capture such posts and get many linked in the FAQ Sticky.

Bet Motorcarman can post the specific bulletin discussing the coolant change.

 

Change the water pump, it's easy as pie, and the coolant temp sensor. Additionally check your fluid for any signs of breakdown a small amount of whitish paste in the coolant.

 

Thanks to all for the information! I'll report back with what I find as soon as I get the chance to work on it.

 

If your engine is original with a MY (97) and not replaced with an AJ27, I would get the orange coolant out of there PRONTO. and get back to the original green formula (or the Prestone mixes all formula).

Follow H2O's advice with water flushes, then recharge with the correct coolant as none of the coolant components or seals/gaskets were designed with an OAT formula in mind, and if they are, it's an accident.

That was the BIG "mistake", BTW, with GM and its fiasco with certain MY GM cars that had engine failures attributed to OAT coolant. They used a neoprene seal in the engine that wasn't compatible with OAT and the coolant attacked and SEMI-melted the seal...Semi, because chunks of it would dislodge, take on the consistency of bubble gum, then end up blocking water passages in the head and heater cores. This stuff was impossible to remove once into the bowels of the cooling system, thus the lawsuits

 

An easy way to tell what coolant you need is to look at the maintenance sheets in JTIS. If it says change at 60K you need green. If it says 150K you need orange. It specifies by VIN.

 

That is a roundabout way, with a slight flaw. The transition year was 1999 with a VIN crossover reference, and, staggered by engine type (NA vs SC). A better, more direct way, is to just use the Vehicle Spceifications document 07/2004 (pg 47) stickyed on this site. It will give you the crossover from the Dow D 542 green variant to the M97B44-D OAT variant by VIN on the crossover.

And, another more direct way, with one small caveat, that is, if all the equipment in the car is original, is to look at the sticker on the header tank. If you need the orange it specifies that along with an obligatory "only" admonition.

 

Thanks again for the info!

BTW, Steve11, the engine in my car is the original (only 30K miles). The Prestone Dexcool bottle says it's for use in "vehicles with aluminum radiators", and there is no coolant spec info on the pressure cap of the header tank (all original), so I thought the orange stuff was ok. I will be draining and flushing the orange coolant this evening!

John

 

Turn your heater on with engine running and see if any coolant can be added.
You may have air in the system and it can be a bitch at times to clear it all out.
On the new Chrysler hemi engines you have to remove a side plug and with engine off,fill it to the top of the hole.Then start engine and make sure the reservoir is kept full.
But air pockets can be tricky to get out if you never dealt with them before.
Sounds simple and stupid.
On the new hemi stuff you think that the system is full and then when I was told to remove the side plug.I had found out that it was bone dry inside.Had to let it run with the fill plug out.Burp it.
Just a thought...goodluck

 

Yes, sound advice. In fact, on all cars, when flushing/refilling, leave the heater or cabin thermostat set on HIGH, fans on HIGH. Keep it this way until the last part of the refill/system bleed is done.....hopefully it is not July in Yuma, Arizona when you're doing it...LOL.

 

Probably dumb question...can the T-stat be installed backwards?
Mike

 

Yes, and ask me how I know and what the result will be!

 

OK, here's an UPDATE of what I've done during the past week:
- Drained all the orange coolant, flushed the system, filled with plain water. Oh, and, yes, I checked and verified the t-stat was installed in the correct direction (thanks mike66).
- Drove the car around to get it up to full operating temp with the heater on full blast (thanks, Hemitwist, for that suggestion); all normal.
- Drianed, flushed and filled again with plain water, drove around again with the heater on, all normal.
- Drained, flushed and filled again as above. Drove the car on several occassions to some near-by errands, the furthest being about 15 miles, including highway speeds, ambient temp about 80; all normal.

Today, I drained all the water and filled it with a 50/50 mix of the green coolant. Took it for a test drive, including sustained speeds of 55+, top up and A/C on; all seemed ok. Then suddenly, after about 10 miles, the temp started to climb above normal again, very quickly! I immediately turned around for home and also switched-on the heater to MAX. The engine temp immediately dropped back to the normal point! The ambient temp at the time was about 82. As I continued home, I switched back to A/C, and it didn't take long for the temp to begin to rise again. As long as I have the heater on, the engine temp seems to be in control.

So now, I'm thinking t-stat, or possibly a restricted radiator (but I cannot fathom that given that the car only has 30K miles). If the pump were bad, I don't think the heater trick would have such an immediate cooling reaction.

What do you guys think?

 

Still think t-stat, and also checking to make sure your fans run (both) when the A/C is turned on. I've read on the XJs that all is well with the coolant temp until the A/C is switched on...then it spikes. There was a relay for the fans that wasn't working and fixed the problem.

A t-stat can stick partially open, or open much later than designed. The system can adequately cool when there's not a load on it such as the A/C. I would check both if it were me.

good luck, and report back.

 

Yes, the cooling fans have been operating normally all along. I'm thinking t-stat, too; it's just that in all my years of wrenching on cars I've never seen one fail like this. I'll pick up a new one tomorrow, change it out some time this week, and report back then.

John