Thermocaps
 

I had the radiator removed/re-cored and had the fan and fan clutch replaced on my XJ-S when I bought it 13 months and 5k miles ago. At the time, I had the electric fan switch replaced with a unit that comes on 10 degrees cooler than the OEM switch and when I got it back, the car ran at the bottom of the N most of the time, wandering into the middle of the N only after a hard run on a hot day or after climbing a long, slow hill and then it would cool itself back down. Lovely!

Lately, it's been wandering into the upper region of the N, usually after I've spent some time stuck in traffic. And it has been a hot summer and warm autumn so far. This makes me think the fan clutch I had installed last year is going bad on me. My mechanic thinks the coolant gauge is off so I'm trying to collect some data.

Which brings me to: Does anyone have experience with Thermo(radiator)caps such as these:

Mr. Gasket® 2476BK - Jaguar XJ-Type 1988 Thermocap™ Radiator Cap

Thanks,
Rhett

Sounds good!





Which might not necessarily be anything to be alarmed about





Ummm....how hot? And how long in traffic? A couple minutes? Half an hour?




Plausible. Next time it gets to the top of the "N" shut the engine off and give the fan a spin with your hand. If it spins less than a full revolution it's OK. If it spins 3 or 4 times it's clearly fault. Anything in between is iffy.





Also plausible. The XJS gauges are notoriously flakey






No experience with that. Most use one of those hand held infra-red thermometers to get a rough idea of engine/coolant temp

Cheers
DD

I've one. I still want more data.

Still, at what should I point my IR thermometer?

Thanks for your input.

@Rhett

I think the IR thermometer is the best idea, although those caps with the thermometers on them look cool :-)

When I went through my cooling debacle 2 years ago, I picked 4 arbitrary places on the engine..... 2 on each side....... one near the front of the block and one near the back of the block.

Always using the same IR thermometer, I would record the IR temps and correlate them to what my temperature gauge was showing.

This way I knew what actual temps on the engine translated to on my gauge. If you point your IR gauge on the casting just beside where your temperature sensor is, what reading are you getting when you gauge is at its highest ?

If I point it at the outside of the 82 degree (C) fan switch and it comes on at 72 degrees regardless of what the needle reads.. which brings me to: where is the sensor that drives the gauge? Embarrassed I don't know...

The gauge sensor is on top of the RH thermostat base, with a single greenish wire attached.

I reckon you have lazy thermostats, AND/OR the wrong length stats in there in the first place. I have written this up many times. I have it in "word" format if you or anyone wants it. It is toooooo large to upload here, so a PM will have it at your inbox real quick, even for an Aussie.

ALSO, check the pressure cap on the LH header tank. Just because its new, does NOT mean it is OK. I had this fiasco with one of mine 10 years ago, and replaced some really silly stuff trying to sort this "hotter than expected" gauge readings. Teenage daughter with a little knowledge (scary item that) suggested the cap might be faulty, HAHAHA. She was right. The 15psi spec cap was actually blowing off at 7psi. A new cap, check for blow off spec first, fixed the beast. Could have saved $$$$$$ if I listened to her earlier.

I have one of the Mr Gasket caps on my XJS. I use it as a reference only because it's not all that accurate.

I ordered two when I bought it, one for the Jag and one for my dd. I tested them both for accuracy against a kitchen thermometer in a pan of water before I installed them. They were not very accurate according to the kitchen thermometer for what thats worth, and, they weren't both reading the same. I believe one was about 10* higher than my thermometer and the other cap was 25* higher than the first. I returned them and got replacements and they still read different than my thermometer and each other.

I have them both installed and as I said use them as a reference point.

They look kinda cool and like any chrome accessory, they improved top end performance, upped my fuel mileage, lowered emissions and chicks dig 'em.

Did they also make you taller?

Thanks for the input, everyone. I'm going to pass.