S-Type 3.0 Petrol 2006 120,000 FJSH Overheating

[FirstAde]

Hi Guys and Girls in the JEC .

This is my first Jaguar. I went with a low cost S-type with a full history and plenty of signs of good ownership.

The first 1500 miles were fine, then the coolant system problems started. All so far covered under warranty- Phew!

The question is "what an earth is still causing the overheating given all the work below?"

1) Thermostat EML - Not warming up quickly enough. Replaced thermostat

2) 1000 miles later Coolant loss - a few small leaks from the water pump leading to "coolant low" message. Replaced coolant pump, checked all hoses and connections for leaks, replaced expansion tank cap, due to small leak around the cap. Sniffer test for leaking head gasket. OK. Oil check for coolant, OK.

3) 200 miles later. Coolant low after sitting in traffic jam. Temp got high. Kept it under control by opening all the windows and blasting the heater on full fan with HI temp on the climate control.

Diagnosis by garage: likely blocked radiator. Replaced. Repeat Sniffer test for leaking head gasket. OK. Oil check for coolant, OK. Double check temp of engine, it was high, gauges are all correctly reading and the radiator cooling fans are running properly.

4) Drove to Cambridge and back 240 miles. Joy! no problems. Then.,... 100 miles later. Coolant low and temp high at tick over (near red sector, but not in it)

Lifting the revs to 1200 rpm, gives a return of the temp gauge to normal position, so there is insufficient coolant flow to control the temperature at tick over.

All this despite new Radiator, coolant flushed out and renewed, new thermostat, new coolant pump, head gasket tests ok,

5) Garage and warranty company given up and referred to local Jaguar specialist who will be able to look at it in about 10 days time as he's very busy

Any suggestions gratefully received.

Thanks, Adrian

[J44EAG]

Cylinder head temp sensors can cause spoof overheat signals to the power train ecu and to the temperature guage on the dash. I know! I`ve replaced two on two different cars, each at 80k miles.

Reading your thread, I would have thought the CHT sensor is a likely candidate for immediate replacement. These sensors have a finite life as I have learned from my own experiences. Only buy genuine Jaguar OE replacements. Aftermarket units are often way off the mark as regards tolerances. An OE sensor comes at around £26.

Try that and see how the car then performs. Let us know how you get on.

Mike K

[FirstAde]

Many thanks for the tip Mike K, I will pass this on to the garage and let you know.
The garage say its defo getting too hot, thats why I'm losing coolant. It escapes the expansion cap at the specified pressure.

I've also had a pointer from another forum about "a Aux pump on the radiator that circulates water around the radiator" never heard of this.
Are they an after market item, or standard on s-type petrols?
Many thanks, Adrian

[J44EAG]

I am pretty certain that the auxilliary electric water pump only appears on V8 models. It works to help assist coolant provide cabin heat for a while even when the engine has been switched off. That would be a Hella produced unit which Jaguar fitted.

You need to find out whether the CHT sensor you have on the car is genuine Jaguar OE. Someone may have fitted an after-market unit which may be an unhappy mix when combined with other OE parts.

The thermostat fitted should also be OE grade. It should be checked to ensure it is of the correct temperature rating. A thermostat that may have been overheated may have become sluggish or have become completely closed. The water pump should also be checked to ensure it has not got a damaged impellor or that the impeller is not spinning on the drive shaft. The engine should be checked to ensure all water hoses have a full flow capacity.

Overheating may occur if the coolant system has not been completely purged of air to erradicate air locks. If cylinder heads have been taken off, were water channels within the head or block checked to ensure passages were not blocked with corrosive deposits. It is also possible that an incorrect head gasket set may not have the correct water jacket punchings in it and an obstruction may have covered vital transfer channels. It is possible that a head gasket may have failed between the cylinder liner and a water channel. That would pressurise the coolant system.

The radiator fans should only be operating if the engine is becoming overly hot or the CHT sensor is giving an incorrect signal to the ecu.

It is possible that a crack in the engine block has developed which opens up when the engine is hot and allows pressurisation of the cooling system. I`ve seen that twice on engines over the years.

You might try a coolant system flush additive. Most car part outlets should stock the product. The new radiator might perhaps have become blocked by internal engine corrosion by-product.

I would be looking to change the thermostat once again and to pressure flush the entire coolant system. My gut feeling having read your description several times, is a continued issue with the thermostat and the sensor. Special attention should be given to burping air from the system and attempting to keep a sufficient amount of coolant in the system at all times. Obviously the car should not be used if its temperature begins to rise uncontrolably. Your garage seem to have been diligent with their diagnostic approach and may now be as baffled as I now am.

Mike

[FirstAde]

Hi Mike K, thank you very much. That is gold dust, years of hard acquired knowledge there.
I will pass on to the garage, and let you know the outcome.
Likely to be around 28th July

Thanks again
Adrian

[oldtimer]

Hi Adrian,
I also have a 3litre V6 petrol S type so am very interested in your regrettable overheat problem.

It's past my bedtime so I shall keep my reply short.

I've been chewing this problem over all day and believe your garage have taken a sensible course of action but despite this it has all been a waste of time because the problem is still there. Having said that , it has eliminated certain possibilities

The KEY to this issue is the repeated loss of coolant !

You mention almost as a side issue that the radiator cap was replaced because it was seeping / leaking. I'm inclined to believe there was nothing wrong with the Rad cap ,it was doing what it is supposed to do and that is to relieve excess pressure.

I'm sorry to tell you but I have come to the conclusion that I believe you have a head gasket leak. This gas leak is over pressurizing the cooling system and in the process forcing water out of the system via the filler cap.

I was at the Jaguar Gaydon Breakfast Club on the 1st July and spoke to a fellow enthusiast from Cornwall with an S type who had suffered exactly the same problem you describe. He had both heads off because it was not possible to detect which one was leaking.

I shall be very interested in the outcome - I'm sure you will keep us updated with your progress

Oldtimer

[J44EAG]

As per my previous post and Oldtimer (Phil`s) observations, I also feel sure this engine must be suffering a failed head gasket. Removal of the spark plugs might show one or more of them to be overly clean. This would imply there has been coolant in the cylinders and the ony place that could come from is via a shot head gasket. You might try a compression test as part of a diagnostic session.

The only cure if gasket failure is suspected is head removal. A second hand short warranted engine from a good breaker such as Eurojag would probably cost less than reworking an engine suffering gasket failure. The fact that this car has had a new radiator implies it has at some point suffered an overheat. It is not unusual to find that later head gasket failure occurs at some point in the future.

You might try as a last ditch attempt as a temporary fix, administering a can of K-Seal into the cooling system. It may or may not help the situation on a short term basis. In all likelihood though, I would not expect too much joy from any product of this type. For minor issues, K-Seal is very useful but for more major issues, don`t expect it to be able to perform a miracle cure.

Chat to us a again if needed.

Mike