"Heat Retention"

XJ-S
1

I noticed something the other day during our recent cold snap here in the the north Texas area. I can’t recall whether I had this same situation with Superblue’s predecessor, Supercat, my '95 4.0 coupe,

It seems like it takes quite awhile for the engine temp to fully heat up and then, whenever I shut her down and go into a store for say less than an hour, I come back out and, according to the water temp gauge, she is completely cold again (i.e. gauge needle is all the way to the left). :angry: This basically means I’m in the cold inside the car again until I’ve driven for at least another 10 minutes before things have heated up once more to where the heater blows hot (well, warm). :confounded: I do know with Harlem, my 2000 XJ8, she stays just below fully-warmed up when I come out of a store, even more than an hour later. :+1:

I guess it’s possible I have a faulty temp gauge, but the heater air really doesn’t get warm until the time period I mentioned above has passed. It’s also possible that my thermostat is stuck open or was removed by the PO, but then I would think the engine would never get fully warmed-up (i.e. with the needle just to the left of the “N” on the temp. gauge) but she does so quite well. Also, in the hot summers she gets right on the “N”. :pensive:

It seems some time back I remember something in the Jag literature about switching between a “summer” thermostat and a “winter” one whenever the seasons change, but, IIRC, that was back when I had my XJ40s.

2

Maybe the thermostat is only partly stuck. Did you check for coolant level?

3

Thermostat is probably stuck open (be glad it’s not stuck closed!). Engines still warm up w/o thermostat, it will just take a good 20 mins of city driving. Why it cools so fast after sitting? I would guess engine really never got up to operating temp. I would replace thermostat right away. It’s not just comfort, you want your engine running full operating temp to burn off condensation so you don’t get oil sludge. Do an oil change too, just to help.

1 Like
4

Yes, full as always. :crossed_fingers: I wish there was some way to check the thermo operation w/o having to pull the cover … Does the old “feel the hose and see if it’s hot” trick work on our cats? I also do have one of those laser remote temp readers that I can shoot onto the radiator hose and get temp readings. If it’s stuck open, I’m a bit leery to remedy the situation. Probably no problemo in winter, but I know last summer whenever the temps got into the 90s she would run a needle’s width shy of the red zone sometimes (b/c the auxiliary cooling fan is bust). In fact, if the thermo is missing, that might be why (per the PO). :angry:

5

It… should. If it runs hot while driving it has to be the thermostat because the fans don’t contribute much anymore. Even more so if it runs cold in winter, yes, change it. It shouldn’t be too difficult, I hope, and is cheap so one of the easier things to try anyways! Cheap trick is to go old school and put cardboard in front of the radiator, go for a drive and see if it warms up better then. With no thermostat the water could also do the Ford T routine and circulate thus cooling the engine.
Check for the thermostat.