So I've been methodically working through the issues with my new 95 XJ6 and have knocked out most of them. One peculiarity is that my engine seems to run very cool (an unusual complaint for Jags I know )

I have installed a new 88c (190F) thermostat and it is working correctly but my engine coolant temp never gets above 192F. Most of the time it is operating at 186-188F and the stat is definitely closed (as it should be). Once the temp gets up to 192 the stat starts opening (can feel the top hose getting hotter) and then temp goes right back down to 188F within 30 secs and of course the stat is once again closed. All temps are those recorded by the ECM via my scan tool and I have confirmed the readings by measuring the temps at the thermostat housing using an IR thermometer. Is this normal behaviour for X300s?

My car appears to have the cooling fan modification done so that the fans are always on but I'm wondering if they are operating only at high speed and that is causing the cool temps?. I plan on checking the fan switch today but I'm actually thinking about going back to the original design with a minor modification to prevent the fuses blowing. Has anyone else gone that route?

My AJ6 powered XJS generally runs between 195 and 200F which is the accepted norm for petrol engines for efficient combustion. My auxiliary fan almost never comes on and the car operates perfectly.

 

I don't see a problem.

The coolant temp seems to be hovering right around the 190ºF point with the thermostat opening and closing as needed. That's how things are supposed to work....the thermostat actually *controlling* coolant temp by continually opening and closing.

We're not accustomed to that, especially not with Jags. With many cars the cooling system isn't capable of this. The coolant temp typically exceeds thermostat control range, and the thermostat just stays open all the time. In theory, that's NOT how things are supposed to work but in reality that's often the case.

If you want to *ensure* that your coolant stays at 195º-200ºF then install a thermostat rated that high, if you can find one.

Bear in mind that thermostats are cheap mass produced things, not precsion designed, so it isn't unusual to get some variance in opening/closing temps and opening/closing rates.

Cheers
DD

 

Mine runs pretty close to yours. Ultragauge shows 186- 194. Once during the summer it got to 204 briefly in heave traffic on a hot day.

 

Interestingly, 204ºF is the warmest I've ever known mine to run as well.

Normally I see 188º to 195º or so

Cheers
DD

 

Doug,

Yes no overheating problem which is oft the complaint with Jags

But I do see it as a bit of a problem, for a couple of reasons.

With the thermostat rarely opening, the heater is less effective (I will be checking the heater core, pump and valve too)

Also engines that run cooler tend to consume more petrol and produce higher emissions.

My (probably old school) way of thinking about thermostats is that they are designed to control temps in their operating range (192-205F in this case), not to barely open every now and then.

I agree I could change to a higher temp stat but I'm more interested in whether the system is working as designed or not. Just my curious nature

 

I wonder what the running temps are for engines that do not have the fan mod done?

 

The 186-188º temps you're getting are MORE than hot enough for the heater to be effective





Yeah, when they're running wayyy too cool....which is not the case with your car.





The intent of a 190º thermostat is to keep the temp at about 190º. It gradually opens and closes to do so. The operating range of thermostats varies a bit, as I mentioned, simply due to manufacturing differences.


I'd say "yes, it is"

I have a 190 thermo and feel pretty good that actual running temps hover between 188 and 195 . To me, the thermo is doing exactly what it should do.

Cheers
DD