About a week ago I noticed my dual fans were on constantly and it hasn't been that hot here. Usually the duals only come on during idling when it's in the upper 80's or more. Thought maybe a bad temp sensor since the first time it happened was just after starting the car and not even to temp, but then shut off again. Checked coolant level and that was fine so didn't worry about it too much as they weren't on when I would leave for work but were on when I got there, a 6 mile drive.

Was out running errands for a few hours the other day and on the way back to my shop I look down and temp gauge started rising fast. Looked for a spot to pull over as fast as possible. I'm sure I looked like a drunk driver or at least someone on thier cell phone.

Popped the hood and everything looked in order so I let it sit for half an hour which really isn't very long and figured I give it a shot and at least try to get back to the shop if at all possible. Drove away and temp stayed good for a few miles then started to climb again. Noticed it was fluctuating and not going into the red so I did the old trick of cranking the heat up and it worked, temp dropped to the normal center position and made it back my shop. Think I just about wet myself the first time it climbed.

Had a thermostat at the shop that I have been wanting to put in as it's been about 4yrs and just haven't gotten around to. I'm sure you can guess I made the time and did a flush and fill of the radiator to boot. Since then the duals haven't come on and all seems to be well. Whew!!

Guess the moral of the story is change your themostat at the 2 year intervals max 3 if you don't want to drive with your heat on max in August.

 

Changed my thermostat a couple of months ago as a preventative measure - I paid an extra $10 for one that fails in the open position.(Advance Auto)

 

See whiteXKR's real gauge mod, well worth the small expense and no guess work.

https://www.jaguarforums.com/forum/x...unction-74704/

 

Was trying to picture how a thermostat could be made to fail in an open position. Did a little digging and found this on Stant's website:

"All thermostats will fail in either a closed or open position; there is no such thing as a thermostat that will fail in a “safe” position. Although some brands may claim a thermostat fails in a safe position, it simply locks itself open while it is in a full stroke open position. It will not spring open if it fails in a closed position."

My purpose for posting isn't to be argumentative but rather informative. I'd hate to see someone rely on some misinformation and get burnt.

 

I'll sleep better tonight knowing I won't have to figure that one out.
It just didn't make sense.
RJ______________
97 XK8 85K mi

 

There are thermostats that will open some holes when a certain over-temp is reached. Rolls Royce Silver Shadows had a few holes around the periphery filled with a eutectic material that melted and fell out to let the coolant flow. I remember changing them back when I worked on them in the 80s.

I guess the 'lead-type' filler just flowed to the bottom of the radiator and stayed??

bob gauff

 

I saw the coolant mod White has but not quite ready for that yet.

Ran it through the paces today and it does seem to be fine. Had to pick up all the parts I dropped off Monday. So two hours of driving and never budged. Was alot hotter today here as it hit 90 so I was real glad to not have to put the heat on. Fan came on a few times but it also shut back off.

My only concern now is whether or not to replace the two hoses that run below the intake manifold since it did get pretty hot. Two weeks after I originally bought the car the pump had failed along with one of those hoses. That was a tow to the house and replaced all the coolant components. I did just replace the pump again about 2 months ago, the one I put in 5 or 6 yrs ago was starting to fail, and it was the later generation pump. It did last around 85K though.

I think a good detection system for the thermostat might be if yours duals start coming on constantly, especially at cooler outside temps, change it.

 

Google MotorRad Failsafe Thermostat - I also am not trying to be argumentative,If it's another thing that helps stack things in the car owner's favour I'm all for it.As we know,these engines are very intolerant of overheating so watch for the fans staying on(mine were), fit the real gauge option, fit the (possibly) failsafe thermostat- I subscribe to the aviation mantra of system redundancy

 

Yes, This is the CLASSIC Sign of a bad Thermostat.

 

If it happens to fail closed, it's still closed.

 

No it's not!!! do the search and read.

I thought like you until, I read the explanation.

 

T'stats function by way of a wax pellet in the capsule. As it heats and expands it pushes the valve open against spring pressure. If you have an overheating condition caused by something other than the t'stat and the pellet in the MotorRad becomes hyper-extended the valve will open far enough to become trapped open by a couple spring-locks. HOWEVER, what happens if the t'stat itself is the cause of the overheating? Typically t'stats fail because the wax has slipped past its seal (or the valve hangs) and becomes unable to push the valve open. In that case the MotorRad can't possibly hyper-extend and engage the spring-locks. If an engine overheats, is full of coolant and the t'stat isn't the cause any t'stat will already be wide open...

Granted, it is a little something extra but my WAG is it will benefit very few. Again, not being argumentative, just informative.

 

While (or is that whilst?) driving my XK8 and watching the as-of-recently functional temp gauge (compliments of JagWrangler / WhiteXKR) in action, I've been surprised how often it hovers in the center position (around 185) in a variety of stop/start and slow/fast driving conditions on a hot summer day. The A/C of course changes everything and when in operation it quickly pushes engine temps up to 205 or 210 territory particularly when idling at a stoplight.

It is very nice to have a functional temp gauge.

 

Thanks Randy. I am glad your cooling system is working well and now you know it for sure.

I just want to remind everyone that the temperature gauge upgrade is available now for immediate shipment to anyone reading this for only $99.95 from my website www.thejagwrangler.com with a discount code.

Installation on the temperature gauge upgrade alone is not difficult. Everyone who has tried has been successful. The instructions are several pages only beause they are detailed and do not leave anything to chance.

Email me at whitexkr@comcast.net or send me a PM for the discount code to get the $99.95 pricing.

I will not be offering these for this low a price for much longer.

 

Hi no record of my thermostat being changed in the last 7 years, overheated big time last week not sure why will find out tomorrow, I have all parts to upgrade to metal components, car still starts on first turn, sounds perfect apart from click from tensioners when revved.
Fingers crossed.

 

You may want to look at a few other things besides the thermostat Bones. If you're not sure about the water pump you may want to change that too.

The earlier water pumps on our years had a black plastic impeller that were know to fail after the car would overheat causing the fins to break off.

That's what happened to me after I first got mine way back when. Pump failed an took out one of the two hoses that run under the intake manifold. Or the hoses were old and one failed but the I had to fish the fins from the impeller out the engine so the pump started it.

If your a DIY the parts are fairly cheap, I think I did everything for less than $300.00

Good Luck

 

And beyond reading the manufacturer hype, there is also reading other sources and logic.

First, in the flesh, they look flimsily made. Second, it will lock open needlessly on a minor temperature surge. Third, if the mechanism fails, it no longer works as intended. For example, if as often happens, the bridge separates from the disc, it is impossible for the failsafe mode to kick in when needed.

Therefore, it is not truly "failsafe".

Better quality of materials and manufacture will trump marketing gimmicks every time.

 

Hi I managed to get the water pump off, just wanted to see if this had caused the overheating as I expected it had, none of the plastic blades were left.

 

Tony,

You've found the overheating culprit but any sign of the broken bits of impeller?

Graham

 

Never seen an actual device. So thanks for your information. Will steer clear!
As so often happens, what could be a good idea is ruined by cost cutting/economics.

I have an Ultragauge with the temperature alarm set to 215°, as my car normally stays below 210°, as an extra line of protection.