I see a few of the folks I often get good answers from are lurking on here tonight so let me ask some borderline rookie questions.

This 2002 XJR is my fourth Jaguar, and my third X308.... so I have a little historical comparison on some issues. My XJ8 ran between 185 F and 199 F and only in extreme circumstances would go above 200 F (all coolant temperatures of course). My 03 XJR ran a little hotter between 92 F and 203 F with a rare burst up to 205 F or even 207 F.

Enter my new 2002 XJR. It runs between 203 F and 208 F most of the time with the occasional run up to 212 F (and hot weather isn't even here yet). Now I know these temperatures are not dangerous. The coolant is nowhere near boiling etc... I suspect the previous owner has put a 195 F thermostat in when the water pump was replaced. From my reading the car came with a 183 F thermostat when new.

I have a nice Motorad (made in Germany) 183 F thermostat on my shelf I picked up for the other XJR but never installed. I was thinking of popping it in and see if I get the temperatures I'm used to.

The youtube video on replacing the thermostat looks SO simple. Just open it up, replace, start the engine and add coolant to the reservoir until full. Is it really that simple? The air will bleed itself out? This is at the very top of the system so I guess it's believable but I don't want to end up with air in the system.

Thanks,

 

Well, for an XJR, the cooler the better to a degree (no pun intended). But, the fan will only come on at the temp. sensors set degree. The aspect is to cool the whole system at the same time, regulating an ambient temp. the engine is designed to be efficient at. So if you put in too high a temp one, the radiator fluid will be cool longer before the block fluid is released, not good for air/fuel regulation. Too cold a one and you'll struggle getting up to operating temp longer, same air/fuel issue. Both will cause excessive fuel usage and possible premature part wear and/or failure. Too hot oil is not good, especially on OHC's.

As for replacement, ....pretty much as you describe. But before I started mine, I pulled the coolant plug on the SC inlet and reservoir cap and topped off. Then started the car, gave it time to come to temp (therm opening), then shut it down, let it cool, then checked and topped off as needed.

 

Would this be the supercharger inlet?

 

Yes. You need a 19mm hex socket for that. Since they're not real easy to find cheap, I grabbed the closest 19mm box end wrench I had, stuck a long 19mm lugnut and used that as the "driver." My fill port was a bit gummed up, just since the coolant doesn't flow in that short section between the hose and port, and who knows how much the PO bothered...

Also for the XJR's you can add coolant to the s/c port, snug the cap down, turn the key to ON but don't start the engine, wait 30 secs and turn car off, then repeat. This will turn on the s/c coolant pump and bleed the s/c "loop." For this you want your other coolant port to be filled as well. If I remember the factory procedure right, you do that bleed a couple times, then do the regular system bleed for the engine coolant "loop." Loop in quotes since they're not entirely isolated, but nearly.

 

Thanks. I topped off the reservoir and started the engine. After it got up to temp and the "low coolant" light was not on, I went for a drive. Wow that car is fun to drive. Anyway, the Temps ran about 3 to 5 degrees cooler than before. In the morning when it's cool I will check the level and maybe try out the supercharger port fill. I drove it pretty hard and the supercharger was cool to the touch afterwards.

The thermostat that came out was a Waxstat 84 C. So, it did have the correct temperature thermostat but I think maybe it wasn't opening properly. It was stuck in there pretty good and looked old; I think it was the original.

 

The PCM wants to run the engine coolant hot but the SC coolant cooler. That's why there are separate pumps etc. If you want more power you want especially to concentrate on the SC part (as avos did). So, more cooling for it, change to KB, etc.

 

Thermostats vary. They may begin to open at 183 F but some do not fully open until 204 F or higher while others open too soon. I have three waxstats and only one of them allows the engine to run at 197 to 201 F.

 

With the car cool this morning I checked the reservoir and it was full; no additional coolant needed. I also took the coolant port cap off of the supercharger. There was coolant standing pretty much up to where the bottom of the cap was. I poured a little more in there to see what would happen but the level didn't rise; stayed the same.

Am I to safely think that the system is properly filled?

 

Yep, you may just want to give it a peak in about a week to be sure and that's it.

 

One of the easiest thermostat changes I've ever done on any of my vehicles, hands down. Glad to hear the report back on the temps too. Nice to know I'm right where you're experiences have shown as well.

 

The old thermostat was definitely going bad. I drove a 10 mile stretch of country road today where the temps were usually between 201 and 203 with an occasional dip to 199, 205 to 208 when stopped. Today it was steady at 194 most of the way, 196 when slowing and 198 to 201 when stopped.