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Car Forum / Jaguar Cars / January 20062000 S Type Cooling system
Hey all - I hope that life is good in Jaguar land. My mother's Jaguar has me a little bit flummoxed, and I was hoping that you guys might be able to help. She has a little problem with exploding thermostats. The first three lasted about 18 months each. The first went with a seized AC compressor that caused the engine to overheat, and the car was towed to the dealer. The dealer replaced the compressor, thermostat under warranty and returned the car. 18 months later on a very hot day again, the thermostat snapped closed causing an extreme overheating condition and the car was then towed to the independent garage who replaced the dealership when they were unable to service the car competently. Again the thermostat was replaced. 18 months later that thermostat went on a very hot day, and again the thermostat was replaced. That thermostat lasted about 1 month leading to an overcooling condition and inoperable heat. My mechanic showed me the remains of the thermostat, which was mostly lieing in the lower radiator hose when the clips to the housing blew apart. I had him replace the water pump along with the thermostat since I felt that there must be something else wrong with the car. It currently operates perfectly, but I have inspected the old pump, heated it and tried to get the impellar to spin on its shaft, and I can't really find a problem with the thing. Any theories as to whether the pump was bad or if there is something that I am overlooking? I have had the fans and fan switches checked and they are working at specification. I don't get it, and we are looking at selling the car if my mother can't rely on it to run. Anything that you guys can tell me about Jaguar cooling systems could help. Help! I am at a total loss. > Hey all - > [quoted text clipped - 29 lines] > Anything that you guys can tell me about Jaguar cooling systems could > help. Help! I am at a total loss. The S-Type uses a pretty standard thermostat. I've had thermostats "stick" on me in either the open or the closed position but I've never had one "explode" and I'm not sure how an engine could possible cause a thermostat to explode. I would suggest making sure that you use a good quality thermostat but if the work was done at the dealership then this should already have been the case. Even if the engine were overheating and the coolant pressure getting too high I can't see how this would case the thermostat to explode. One reason is that the hoses and radiator are much weaker than the thermostat and they would go first. The other reason is that the built-up pressure would be the same on both sides of the thermostat so the pressure differential would be pretty negligible. One thing to possible check would be the makeup of the coolant... make sure the concentration/mixture is correct. If it isn't correct I could see other longer-term problems but it's a bit of a stretch to see a scenario where this would cause thermostats to explode. Good luck. My guess as to how the engine could cause the thermostat to catastrophically fail, or explode, is from working too hard. If the temperature of the coolant exiting the engine is constantly hotter than it should be the thermostat tries to open further than it is capable and the wax in the pressure cylinder either blows out of the cylinder shutting the thermostat catastrophically, or in the last case, it caused the thermostat to just blow apart from its housing. The thing is though that now four thermostats in five and a half years is insane. There has to be some reason for this. All thermostats for the S Type come through the dealer. If I could find an after market manufacturer, I would have bought one two thermostats ago. > My guess as to how the engine could cause the thermostat to > catastrophically fail, or explode, is from working too hard. If the [quoted text clipped - 3 lines] > shutting the thermostat catastrophically, or in the last case, it > caused the thermostat to just blow apart from its housing. This sounds reasonable except for one thing. I don't have an S-type (it's a 2005 X-type 3.0 Sport) but on ours there's a temperature gauge just to the left of the tachometer. Seems that if the coolant temperature were getting so hot that it was causing the thermostat to explode the temp gauge would show the engine running hot. It would be so hot that the over-temp indicator/buzzer would go off and the gauge would be all the way in the red. > The thing is though that now four thermostats in five and a half years > is insane. There has to be some reason for this. Hopefully we'll figure out what it is. > All thermostats for the S Type come through the dealer. If I could find > an after market manufacturer, I would have bought one two thermostats > ago. - LQ The S Type also has a temperature gauge. The thing is that generally, and I have not checked this in the Jag, the sender for the temp gauge is usually somewhere up stream of the exhaust valves or nearer to the coolant inlet. In other words, the radiator is between it and the outlet flow from the engine so the temperature gauge will not tell you what temperatures the thermostat is experiencing. I mean think about this. The outlet temperature of the coolant changes dramatically with driving conditions eg: load, acceleration, gearing, blah blah blah. If the temp sender were where the thermostat is then it would read all over the place all the time. It would not go up to the middle and sit there like a rock. Actually, the gauge in our jag just demonstrated this rather well, since the last thermostat blew to pieces, the system was running full open. The gauge constantly wandered up and down and down again, which is what happens when you don't have a thermostat. Anyhoo, what I am saying here is that the Temp gauge won't show you what the thermostat is actually experiencing from the outlet flow. It could also be that the car just runs hot from some internal problem, but the car runs so bloody well, and I've had it compression tested so it rules out alot of internal problems. I'm just flummoxed. > The S Type also has a temperature gauge. The thing is that generally, > and I have not checked this in the Jag, the sender for the temp gauge [quoted text clipped - 15 lines] > but the car runs so bloody well, and I've had it compression tested so > it rules out alot of internal problems. I'm just flummoxed. Hmmmmm. I'm not familiar with where the actual sensor is located on the Jags but last year I had a stuck thermostat (stuck closed) on my 5-series. What was happening there is a little similar to what you're seeing so I'll go ahead and post it in case it somehow helps. I was driving my car down Route 128 (I live just outside of Boston) and everything was fine. I took the exit for Route 2 to get home and when I reached the traffic light I noticed that my over-temperature light was on. This was strange because the temperature gauge was reading perfectly normal. Eventually what I found out was this. The "over temp sensor" is on a different circuit than the temperature gauge. The temp gauge is closer to the inlet of the coolant flow while the over-temp switch is located somewhere closer to where the coolant exits the engine block. Since the thermostat was stuck closed the temp-gauge appeared normal because the very hot coolant wasn't flowing all the way to the sensor. But the block itself was getting extremely hot and the over-temp sensor was picking this up and indicating a problem. I don't know how much this helps the issue you're seeing but there does appear to be a possible connection. One thing that you might possibly consider would be to have the cooling system flushed and make sure that the coolant can freely flow through the block. Perhaps there's some obstruction somewhere that's causing the block temperature to get hotter than it should be. - Larry Thanks for the posts. I don't think that flushing will do it. The coolant has been changed each time the thermostat has been and the car isn't that old, although an obstruction is one thing that could be causing this so it is a point well taken. However, I think that the culprit was the water pump. I think that the impellar might have been slipping under extreme temperature and load. It's just such a screwy theory. On the other hand, I have a real suspicion of the plastic impellar. I don't know. There just isn't anything else in the cooling system that it could be as far as I know. If it happens again, I think that it will be a new car for my mom, which is sad because she loves this thing. She loves it better than any other car that she has owned, and no matter how many times I tell her that it's just her car and not endemic to the type, I think that she will get another car. I don't know what it will be but something else. I remember the first time I took the S type out for a run while my parents were away on vacation. I got behind a new mercedes E that was racing along this little road, and I thought oh what the hell. I passed him. I got in front of him and just walked away from the guy. I looked in the rearview and around turns that the Jag took flat, his car was heeling over on its suspension and sliding a little sideways. It's just such a good car. Anyway, here's to hoping that it was the water pump and thanks again! - H |
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