Worried - Engine hot

Thanks everybody,
I am certainly happier about this than I was before and as the proud owner of an Infra Red Thermometer and a new Thermocap (it is on the way) I feel that I have been pro-active on the subject. I am also having the cooling system checked from start to finish so things should be ok. This message was just to prove that all of your input has not been ignored and that we new guys do listen occaissionaly.
Cheers and thanks again,
Don

Infra-red thermometers are an invaluable tool, for sure. But as with anything else, you have to know their limitations. I use one daily, use it to find or verify everything from failed thermostats, to misfiring cylinders to failing hub bearings. Even can head off relay failures, high resistance relay contacts get much warmer than normal, that can be detected with the IR.

Every material has it's own quality called emissivity. That is in relation to how reflective it is in infra-red. This has to be taken into account if the reading is to be trusted as accurate. Below is a link to a good document that explains the concept. Aluminum in particular has a low emissivity factor, and reads much lower than steel at the same temp, unless it is adjusted for emissivity.

Lots of folks that use these devices regularly aren't aware of this.

Hope this helps!

Cheers,

You might consider getting a THERMOCAP from Summit raceing, get a 16 psi and you will have a direct reading of coolent temp to check. my temp peaks at about 215 after shutdown as the engine heat soaks everything under the hood.

Dan
94 XJS 6.0L

Edited on 2012-07-17 9:18:20

Shoot, that sounds good.

IMHO if you keep a Jag V12 running at 199??F or less in 90??F ambient conditions, that's pretty good :-). That's usually the point where the system would begin struggling to control coolant temp, in my experience.

Cheers
DD

Hi Doug,
Thanks for getting back to me.
I tried to make it as bad as I could with the weather we were having. I drove reasonably hard for 20 minutes in 90 degree quite humid conditions. I then let the engine run for 10 more minutes with the car parked and with the sun directly on the hood.
Linda and I had to get into the shade.
I look forward to your comments once more.
Thank you very much,
Don

Assuming you have typical 88??C (190??F) thermostats you can expect reading of at least that much ...so I'd say you in good shape as far as outright coolant temp goes.

Still, though, I wouldn't get lulled into ignoring the many well documented issues that can be expected with XJS V12 cooling systems.

What were the ambient conditions at the time? Just wondering.

Cheers
DD

Thanks everybody,
We got hold of an infra red / laser thermometer and, after a 30 minute run and 10 minutes standing still in the sun with the engine running, took readings everywhere we could reach. We concentrated on the areas around the radiator and the thermostats before going deep ito the compartment and got readings between 180 and 199.
I believe that these readings are to be expected but would ask you all to comment on what you think about them.
I am a little relieved and look forward to what you have to say.
Thanks again,
Don

Agreed in the laser/infra red hand held thermometer. Take readings at each water rail at the thermostats....to see if it's really as cool as the (notoriously flaky) temp gauge suggests.

High underhood heat is normal and typical....to at least some "degree" (tee hee). After all, you have five pounds of s**t in a three poung bag :-)

Engine damage (typically a dropped valve seat) generally occurs in two ways. First is outright over-heating. Seconfd and jess obvious, is lack of coolant flow ...creating hot spots/steam pockets in the cylinder heads even when the coolant temp itself isn't particularly high.

I hate to sound alarmist but I wouldn't say "don't worry" until you've verified the cooling system is 100% up-to-snuff. Clean radiator (internally and externally), correct thermostats, good fan clutch, operational elect fan, and properly bled.

Don't rely on the temp gauge reading alone.

Cheers
DD

The engine will get hot! but, your gauge shows normal so presumably the fans are operating. One of the problems with the V12 is that the engine has virtually two cooling systems. Having a thermostat on each bank! The temperature sender is on the right bank and so will only indicate the conditions there. If the left side system has a problem such as a bad thermostat, you will not know until it is too late. Also the engine driven fan cools mainly the right side,if the electric fan does not operate (with AC or high temperatures) that bank wll once again overheat!