With today's warm weather, I went for a ride with the top down in my 1997 XK8. But, I noticed some odd temperature behavior. On the freeway, at about 70-75 mph, the temperature would drift above the half way mark. It seems like it is always glued to the half way point. It drifts above then returns to halfway.

When I exited the freeway, the temperature would spike upward and set off the warning light before oscillating back down.

Thoughts on the culprit? I'm betting water pump.

 

It's possible that the electric fan is not activating if the car heats when you slow down.

 

Sounds more like a sensor failure, the gauge is not more than a switch rather than a gauge and only goes critical after the fact you have boiled your engine, check the connections on your main water pipe at the front where the sensor is and see what happens

 

I wouldn't place any bets as far as the cooling system of a V8 is concerned. The odds on serious damage if it overheats are stacked against you.

The standard Jaguar gauge is notoriously useless and sits in the middle unless dangerous overheating occurs.

It could well be a faulty sensor. Next in line as a forum favourite is Thermostat followed by Water Pump.

Graham

 

It's hard to believe you could still have the original water pump in a 97, but if so, that could easily be the problem. The early pumps lose their vanes, and as Graham says, the result would be catastrophic.

 

The fans seem to be working.

I am the third owner, so I'm not sure about the water pump. It's only got 66k on it. Do the pump vanes degrade regardless of usage? Seems like they would.

The more i think about it. I think it may be linked to going uphill, not necessarily lower speeds.

I'll give the sensor a look.

 

Chances are the sensor is fine...they do not fail often. Concentrate on the thermostat and water pump.

To better understand the operation of the temperature gauge see:
https://www.jaguarforums.com/forum/x...e-gauge-62813/

Consider usng an OBDII code reader to check your actual temperature or upgrade to ReagGauge: RealGauge - TheJagWrangler

 

You might as well replace the thermostat at the same time.
I don't know if you can tell a plastic vane pump from the outside - I'm sure someone can tell you that.
If you go into User CP>Edit signature and put your vehicle details in there it helps us all - saves scrolling about to find your car + MY.

 

Since the engine was warm last night, I didn't check the coolant level.

I just checked it this morning. It was remarkably low. But my low coolant sensor hasn't been activated. I topped it off but don't have time for a test drive til Friday.

 

Please be careful if you drive it. It is unlikely that the original water pump is still there, but if so, it needs to be changed as they were subject to failure. You are very likely dealing with a dangerous situation and delay in checking the pump and thermostat could easily cost you an engine. It would be wise to replace the thermostat housing with an after market aluminum one at the same time.

 

Make sure you repair your coolant low sensor also. If you were to lose a large amount of coolant, the temperature sensor will not register (it would not be immersed in coolant) and the coolant low sensor would be your only indication of a problem that could destroy your engine.

 

To expand on my comment in post #4 about the Temperature Gauge being notoriously useless - the Coolant Level Sensor is another one that has caused many reported problems. It can stick and either not report low level at all or permanently have the warning light illuminated regardless of the level in the tank.

You shouldn't be loosing coolant. The excess from the Expansion Tank flows into the Atmospheric Recovery Bottle in the wing as the engine heats up and is drawn back as the engine cools down. Level in the Expansion Tank with a cold engine should always be at the base of the filler neck. The loss needs to be investigated.

Graham

 

Your thermostat is giving you a heads up that it is going to fail closed. Replace it sooner than later, its 25-35 USD for a good cause and the lessor price of a water pump. While you change the tstat pull the water pump and inspect the vanes they are easily visible on the rear side of the pump.


D. Meyer

 

Just to close this topic out...

It was the water pump. Upgraded to a metal impeller, upgraded the thermostat housing to aluminum, too. (Wait is it aluminium since it's a British car?)

Thanks to all for the input.

On to the next challenge...

 

Good to hear you avoided catastrophe, not everyone is that alert.

 

Hi all, need help please...
I have a 2000 Jaguar S type V8 that a few weeks ago had the high engine temp light come on. It would come on for 45-60 seconds and then go back out.
Took it into the dealer - he replaced the expansion tank (after putting a new one on the car 2 years ago). Still had the same problem. They then decided it was the thermostat and replaced it. Upon driving the care to test it apparently two hoses blew so they had to replace those. At this point I am out $1100.

After replacing the hoses, still had the problem. Dealer now says head gaskets are bad, and on the age of this car with 185K miles, it is best to replace the engine.

I decided to get a second opinion and took it to a european car repair shop.

They test drove and when the light came on stopped the car and ran some tests. Engine was not heating up so they diagnosed the temp sensor was bad.

Had the temp sensor replaced. After several hours of driving once I got the car back the high engine temp light is back on. Repair shop now seems to think it may be electrical.

Any thoughts out there, as I am now out of $1500????

Any ideas would be welcomed. Thanks!

 

If the temp drops with RPM, think water pump (I speculate that the impeller just cant move enough water at lower RPMs). Just happened to me, and the poster who started this string. Compared to what you have been through the water pump replacement was cheap, about $235. Hope it helps.
John

 

When I said with RPM, I meant high rpms move more water = lower temperature.

 

Does the coolant need topped off regularly, or does it stay at the same level?

In either of those investigations, did they do a pressure test? That will tell you if there are leaks and / or a head gasket problem?

 

Water pump or radiator. I had a hose swell up huge because my radiator wasn't circulating water after I replaced the water pump. New rad and everything was good. Also make sure the fans are operating properly. A compression test may or may not reveal a leak depending on what's bad. Always go the cheapest route and work your way up.