I have been driving my Jag very little over the last few months (Due to the Coronavirus lockdown). Today I took it out for a short run and got a warning that the engine was overheating. It was about 95F in Phoenix today. I let it cool then took it the short distance home. The fans were going full blast and coolant was dripping out.
I topped up the coolant and let it cool down completely (several hours).

Tonight, I let it idle in the drive for about 20 minutes. It was about 78F at the time. The engine seemed hot, but I got no warnings. I took it on the road, and the moment I pulled away from the house, the overheating warning flashed on, then went back off. I drove it in stop and go fashion for about 20 more minutes, but it never came back on.
When I got back home, the fans weren't even running and the engine seemed no hotter than usual.

Sticky Thermostat? Or?

 

You said coolant dripped out, did you see where from? Could be the thermostat as you said.

 

Investigate the loss of coolant.

The plastic thermostat housing is a known weak spot on your car. Let us know what you find.

 

I had a similar issue a few months ago, and it was a mystery because I could never see where the coolant was leaking. There was a crack in the coolant expansion tank where the hose connects. Car ran absolutely fine until the engine got hot and it pressurized, then a very very fine mist of coolant would spray out of the small crack. Check that out as well. I had to refill the coolant reservoir three or four times before I found the leak, but, hey, I checked "change coolant" off my to do list at the same time.

Replacing the coolant reservoir is really easy if that turns out to be the problem.

 

Overheating on these engines is a serious issue, something that can easily cost you your engine. Please don't drive it or idle it until you figure out coolant loss. If you have to take it to the mechanic, get it towed.

 

I'd worry if it keeps alerting you of overheating. If coolant is low, it is going somewhere. There is a bleed screw on reservoir that will help get air out of the system when filling. Not sure if that would account for low level, but I had to top off mine this year from sitting and after a heat warning. It has not reappeared. Look for any evidence of fluid loss, white smoke from exhaust, etc. There are dye kits that use UV light to find leaks. If the thermostat is older, change anyway, it is fairly easy to change. It was the 1st thing I did outside of more regular maintenance.

Had an issue with other car where small crack in reservoir just below fill marks. When under pressure, fluid leaked out. Never saw it when sitting, but always low. Car would run hot. After constant top offs and worry about a bigger problem, I removed and inspected tank. Filled with water and found the weep. So make no assumptions. Vehicle common issues and detective work seem like the best avenues.

We get close to 75 degrees here in New England today so I am going to take it for a ride today to get the top down.

 

I had same problem it was the thermostat housing was cracked and then at 150 mph a big peace broke off ended in the water pump Mack shurr

you have all peace’s you won’t find this part any where take your vin number to dealers parts department when you buy it’s about $187.00

 

At first I thought that I was going to get all the problems every one was having with this car they had to jump start the car that day drove it for a week no problems then sometimes it didn’t want to start so I looked at the most important things to this car and that’s the key change the battery $6 at auto zone have no problems I take 400 trips miles from Dallas to Laredo 800 miles round trip no problems I love my car this car is not for everyone It’s made to go fast I do 150
I had same problem it was the thermostat housing was cracked and then at 150 mph a big peace broke off ended in the water pump Mack shurr

you have all peace’s you won’t find this part any where take your vin number to dealers parts department when you buy it’s about $187.00

 

Looking for a good place here in New England to stretch the legs out a bit with +150 being my goal. I do not want to hijack this thread, but since you mentioned TexasDang, any specific precautions taken for the speeds you are hitting? Do you wear any protective gear or do any specific maintenance in prep for this speed. If this sounds like a loaded question it is not. Just want to learn anything I can. What is your top speed? These are limited at 186. Time for a fastest speed in your XK thread..if it doesnt already exist.

Oh, and to keep on topic, I have the Android Torque app and OBDII dongle. I believe it has temps the computer is seeing for intake, coolant, etc. Pretty cheap diagnostic tool and may shed light on where /if temp issue exists. Also has GPS speed logging for the speed tests.

 

A 4.2 with a limit of 186 mph. I thought that was only the XKR-S that had this?

A bog standard 4.2 XKR with the factory limiter is 155, my 5.0 Dynamic is supposedly 174

 

this is my daily driver so I’m always looking for anything out there that looks out of order look at your tiers make sure you have fresh change of oil check your brakes look under your car for any kind of leaks and if you’re planning on going fast make shurr your clear to run with no one else around you use caution at all times and don’t go stomping on your gas pedal take it ez and pay attention to your cat should be smoot I’m old so I’m always driving safe at any speed I get to go fast when I’m going out of town in the open road know the road I have traveled it since I was 16 so I know where the bear’s hang out be safe.

 

Yes, do replace the thermostat housing with the metal one.
As for wanting to see your real acceleration and top speed, please be responsible unto others and try that at a race track or airport runway. I've done both. What fun!
Little obvious things like SUSPENSION! (especially condition of bushings) BRAKES! (pads and fluid) TIRES! Oil change before and after, and a coolant flush before. And I went further and changed the fluids in the transmission and differential before and after as well. Yes, some tracks insist you to wear a helmet.

 

Most tracks I've looked into for membership or track day for Jag clubs require helmet (which is no problem) but will not allow convertibles. I was not planning anything over 90 on the street or hwy. Seeing that when I'm cruising in the center lane going 75-80 small econoboxes are whizzing by like I am standing still. Info and reminder on coolant, oil change is helpful. Thx.

 

This is the only time I have noted the coolant as low - and that was after I got the heat warning. My thought was that sitting over the summer in the Phoenix heat may have caused some to evaporate and caused it to run too warm today. I'm going to have it looked at...maybe tomorrow.

 

Considering that you did a combustion byproducts test on the coolant that came out negative, I would still be suspicious that the oil in the coolant could be transmission. Before pulling the heads and ordering gaskets, I would do the leak-down test. As mentioned earlier, having the coolant analyzed can tell you if it's tranny fluid or motor oil in there. And maybe check the tranny fluid to see what's in it.

 

Probably need a coolant change, malfunctioning radiator fan,faulty thermostat,bad water pump,or leaking coolant.Could be any 1 of these and if it's the right one you fix,then it's problem solved

 

J4GU4R who is the OP has not been back to this thread since April 2020.....yet the thread has come back to life! FYI.....Coolant never evaporates in our pressurized systems. Our cars can and do have issues where the coolant loss is either not obvious or can not be found. If it's a negligible amount (few ounces every few months) no big deal other than topping up. If any of our cars ever have the low coolant or overheat message on the screen it is advisable to NEVER ATTEMPT TO DRIVE EVEN A FEW FEET TO GET HOME. It's best to shut the car off and get towed to your destination. Our engines are easily turned into toast at the earliest signs of low coolant.

 

Heat warning means you need to add coolant to the engine while the engine run and don't let it get too hot when adding more coolant cause you've ran completely out of coolant that's inside the engine enough for your engine to blow a head gasket.So fill up the reservoir tank and then turn the car on cause the engine gone keep sucking it all up until it's none left,so you gotta keep adding more and more coolant to the reservoir while the engine running until you see it's no longer deplenishing any more coolant and that might take more than 4 or 5 jugs depending on how bad it is.That's the way you're going to have to do it unless you feel you're going to need a professional mechanic to do it where they can put coolant in right where the radiator is attached at and it's really better to not take a risk and do it that way if you don't know how to detach the radiator to do it yourself