Just got my car back from the dealer for that issue with it not warming up in cold weather.

They replaced the aux coolant pump (no idea why...) and told me the thermostat was just replaced in December for the last owner. Said everything was working fine now. I drove it back to work from the dealer, about 15 miles, it seemed to come up to temp pretty normally, but it's only 55F outside today.

When I got to work, I shut the car off and the radiator fan was running at full blast. I opened the hood, the radiator hoses were warm but not excessively hot. Certainly not overheating. The fan ran for almost 5 minutes after shutting down.

I called the service manager back and informed him of this new issue. I say that thermostat is stuck in one position and not allowing the car to warm up quickly or cool itself enough after a long drive.

That radiator fan should not run like that unless the PCM thinks it's overheating, should it?

 

Well, that dealership service department is incompetent.

I'm back to where I started in my post last week--in cold weather the engine doesn't come up to temperature. Now in warmer weather the PCM thinks it's overheating and the cooling fans run after shutting down the engine. I will bet anything the thermostat is stuck partially open, not allowing proper warmup and not letting the coolant flow at higher temperatures. Have ordered the parts and will do it myself. After I had my entire morning wasted trekking back and forth to get my car, it's not worth my time for them to try again and make another misdiagnosis. I should have done it myself the first time.

Also seeing some greenish stuff in my coolant reservoir. I think it's way overdue for a coolant flush. Just hoping this is the last of the "teething problems" with this new car.

 

The fan running after shutdown is not normal in this car. The usual cause for this is a sticking thermostat. Changing the aux coolant pump would be to solve a no/low heat problem. You didn't mention that the heater wasn't working right. The coolant temp sensor may be bad, sending an erronious signal to the ECM that the car is hotter than it is. You obviously need a good diagnosis. Your symptoms are conflicting, one indicates a sticking closed thermostat and the other indicates a sticking open one! This tells me that something else is amiss, probably the temp sensor.

 

I meant to mention that the green in the coolant is bad, it should be orange. Mixing antifreeze in this car is a bad practice. Someone probably didn't have any Dexcool and threw in some old green 2 year antifreeze. When this happens, all the anitfreeze becomes 2 year...so get it flushed and the right stuff put in.

 

I have ordered new parts, hopefully will get it apart and diagnosis it myself this weekend. The heat was never an issue--I told the dealer this. I said that the engine was not getting past the cold mark on a 6 mile drive, so of course I had low heat output. That should have been the red flag that the tstat was stuck open.

I feel like it may be a partially stuck now. So it's open slightly and the car won't warm up quickly in cold weather, but then when it's warm outside it starts to overheat slightly causing the fans to run (the gauge never went over the middle tick mark, but I have read that this is a very damped gauge?).

The temp sensor may have issues. But I know it's not warming up fast enough. After about 6 miles the heat finally starts putting out nice hot air. Is the only ECT the one in the tstat housing? Or is there another on the block somewhere?

Also will check on that purge line. The Northstars had issues with their purge line getting plugged and causing lots of air bubbles to become trapped/odd cooling issues.

I will definitely do a change. I had looked in the reservoir and only saw orange, but yesterday I cracked the bleeder and green came out Is the G05 coolant appropriate for this car?

Thank you very much for the reply! I appreciate the help!

 

On the anitfreeze colors, Dexcool is red, but there are green antifreezes that offer the same performance, without the Dexcool color. Prestone makes an all makes all models 150,000 mile 5 year antifreeze. If you are doing any major work, its always best to drain out whatever anitfreeze you have and start out with fresh.

 

I had a similar issue with the radiator fan running full blast for 3 - 5 minutes after shutdown - I changed my water pump and thermostat & coolant flush w/ new Dexcool and cooling system good as new.

Has the dealership ruled out your water pump?

 

I'm betting on the thermostat because the car won't get up to normal temperature when it's cold outside. I'll replace and check the tstat first. If the old one works, I'd have to think the main water pump may be at fault. Were the pumps in these series engine prone to failure? I ran across something a while back about plastic impellers? No idea if that applies to this engine.

Thanks ryejag. I had time yesterday and went through dozens of posts on coolant type. Seems to be that Prestone Dexcool meets the Jag spec for orange long-life coolant, I'll probably just go with that since I have the same stuff for my GM cars.

 

When the fans are running check both of the radiator hoses
If you have a hot hose the fan is working as it should

If the hoses are cold you may have a faulty sensor for the fan
IE its turning on to low

With a hot hose and fans on the cause will be the heat buildup in the radiator turning the fan on. This is what its meant to do

Now you need to find out why coolant is not flowing at the correct speed
As the engine is not getting hot you don’t have a blockage ie no flow
Its just the fans are cooling it enough for you to not overheat the engine

The most likely cause is a bad thermostat followed by the water pump and then a partial blockage

Remember the thermostats job is create a blockage. Even when fully closed you still have some flow.

You can do a test for the thermostat using the heater
If you have a FBH disconnect the fuse so it wont run
Run the car till the fans come on
Check the heater.
If you have hot air its the thermostat

In other cars this test will also let you know if the water pump status. But our heaters have an electric pump and don’t rely on the water pump. So the test is only vaild for the thermostat. The reason being is the heater is in paralell with the engine but does not use the thermostat


Cheers
34by151

 

Who in the world designed this coolant crossover? Of all the ridiculous, poorly designed pieces I've ever seen in my life.

Finally got my new thermostat, went to replace it and found the old tstat in pieces, and the inside of the crossover broken apart.

Certainly explains why it didn't get up to temp in cold weather, and overheated in warm weather. I took the tstat and the bigger pieces I could get out. This is going right back to the dealer tomorrow. Hopefully there will not be an issue with the warranty because I diagnosed it myself.

 

Welcome to the world of Jaguar plastics! - Not sure, but maybe they have an aluminum t-stat housing for your year - I upgraded my T-stat housing to aluminum (2000 MY)

 

There's no aluminum housing for this style (MY 2006+). I'm hoping maybe the aftermarket will come up with one, but by the time this one fails again I will probably have moved on. I think I want my Cadillac back

I have to say, as an engineer, that design is just a failure waiting to happen. Someone went wild with the "oh look what crazy design we can FDM now!" and came up with that nonsense. Hot water on the inner tube and cold water on the outer so that the thermostat can control cold water flow through the engine? Foolish.

 

I had the same exact problem with my '98 XK8. Never found the cause, along with other issues. Eventually I sold it. Problem solved

My current XJ8L, on the other hand, has been the most reliable daily driver I've ever owned, still going strong at 105k mi. On the 200-mi round trip to Palm Desert last weekend, it averaged 29mpg!

Cheers,
Wolfy

 

Ok I have a question about this: So I had a similar set of symptoms. Drive fine for 100 miles then overheat when you stop. I pulled out the thermostat and wala it fell apart in my hand. The two plastic pieces that are supposed to hold it in fell into my hand (thank heavens they didn't fall into the tubes). Anyway. So I took the thermostat out completely put everything back together figured that it wouldn't be a problem just would run too cool.... So I drove around for about an hour. Got gas... drove back and it overheated in my driveway just when I got home. Now I'm confused. surely with no restrictions it shouldn't overheat? any ideas? help? I have the entire assembly of spider octopus crossover assembly on order but do I need a waterpump? is that my problem?

 

Thermostat controls the engine temperature.

 

If I pull the thermostat on any other car I've ever owned it just runs cooler in general..... This had zero impact. it still overheats when stopping after a long drive. I'm confused.

 

I think the thermostat controls the temp up to the point it's fully open and the radiator controls it from there on.

The PCM (aka ECM) controls the radiator fan(s) and monitors the engine temp (ECT) to decide what to do.

It assumes the flow is not impeded and that the fan(s) do as commanded.

I think it will run the fans with the engine off if it sees the engine is hotter than it really ought to be in typical use.

 

yea.... ok.... but that still doesn't explain why if I remove the thermostat so that it is effectively running full open that it overheats only after stopping in my driveway. The fans are running the fluid is up no leaks and the radiator pipe going to the radiator is hot. So water must be getting to the radiator.... have I lost my water pump somehow? I still don't understand why removing the thermostat would not cool the engine.... is there some kind of secondary valve buried inside that mess of plastic that changes the water direction? but that still doesn't explain why the radiator and hoses are infact hot. (as they should be). Just to be clear no water in oil, no oil in water, no overpressure in the water. No rough running so I have no indication of a bad head gasket. Not to mention I drove at highway speeds in 60deg weather for over an hour and it didn't overheat till I got home and started idling.

 

You've got a lack of flow by the sounds of it. Poor/broken water pump or some such.

 

Not sure if this is of help, but our thermostats are dual purpose? They act like a sort of double valve? They oscillate between allowing water into the radiator for re-cooling and allowing it around the engine jacket for engine cooling? You cannot run the engine without a thermostat; it will overheat!

IMHO you need to replace the thermostat. I had exactly the same problem, put my thermostat in a saucepan and brought it to the boil...Nothing happened; replaced it, problem went away!