Water temperature problem only when track driving!

[abk6]

Hello,

I have been enjoying my standard 98 XKR 4.0 (70k miles) since buying it in January. Its had the metal waterpump and timing chain replacements at some point. On purchase I had a thorough checkover done by a jag specialist, new coolant hoses put on plus a couple of other things fixed and it was declared in nice condition.

Done about 750 miles mostly motorway but including several long traffic jams and a few 0-60 tests and temperate gauge never even threatened to move above half way.

I entered the Pomeroy Trophy this weekend to give it a bit more of a shakedown as it includes 40 minutes round the Silverstone national. On about lap 3 the temperature gauge had risen which I noticed as the warning light had come on. I was about to call it an early night when I noticed as I backed off it dropped again, so I went round at 75% for the remaining 35 mins and was able to keep the temperature below the red zone, albeit above the magic half way point. Basically it would creep up whenever I pushed the engine much above 3000 rpm and creep down again if below that.

As soon as I came to rest afterwards, temperature dropped very quickly back down to normal, and there was seemingly no coolant loss or any other obvious signs of trouble. 150 miles and 2 normal drives later (including one traffic jam) and again its not even threatening to go above normal temperature.

I would love to know if anyone has seen this behaviour and if it points to any specific problem before I have the whole engine taken to bits at great expense!

many thanks

Jonathan

[J44EAG]

This thread may be relevant to your problem.

http://www.jec.org.uk/forums/viewtopic.php?f=201&t=6228

Mike K

[mike020150]

Naturally, Mike K's solution (above) would be the best outcome. However, if that proves not to be the case, don't assume that the water pump is innocent or that the radiator, if original, on a 15 year old car isn't in need of back-flushing or more likely, replacement. Mike.

[abk6]

Many thanks Mike and Mike.
- Any advice on how I can try to recreate the problem without another track day? It seems there is a rev limiter kicking in at about 2500/3000 rpm when I try to rev the engine in neutral/park.
- Other than that they seem to be tempremental, is there any logic as to why the temp sensor could be playing up only at higher revs?

[mike020150]

At rest, these engines have a rev limiter fitted to avoid damage being caused to the transmission which doesn't like being revved in park/neutral.

The temperature gauge sensors are not designed to work like they used to in the good old days. Jaguar designed it to work rather more like an on/off switch only registering hot on the gauge when the engine temperature rises very significantly. Hence, if the sensor is OK, it will only ever indicate the most serious increases in water temperature, something which will definitely occur when you give the car some 'stick' on a circuit. I can't find a specification (resistance vs temperature) for the sensor but if you know anyone with a spare sensor or if you buy a new one, you could compare your existing sensor's performance with a new one by heating both in a pan of water with a thermometer. The sensors are not expensive and a comparison of readings would tell you if the old one is faulty. Oh and a box of chocs for your better half might be a good idea as compensation for using the kitchen stove! Mike.

[abk6]

Thanks Mike. So actually, you're not that surprised my temp light went on when pushing the car hard? It would be normal for that to happen but actually the cooling system is working just fine?

I have ordered the replacement sensor and will try your side by side test in any case and will report back.

Now I know why we bought one of these :

[mike020150]

To respond directly to your question, no, I wouldn't expect a track day to result in your car's overheating symptoms but on an older car with only slight cooling issues (like a slightly silted radiator), it could happen with little detriment during normal road use. No older car is perfect and in everyday life, many of us live with car problems which we will only correct when convenient to do so. The gist of the comment being that the possible overheating problem isn't necessarily a crisis issue. As you are doing, the important thing is to narrow down the list of causes. Then, you can decide whether to panic your bank manager or to leave things alone until it's convenient to sort them. After all, judging by the pic, you've already spent a lot of money on the test equipment. Mike.

[abk6]

Long delayed update, I took the car out again at Oulton Park last week having changed the temperature sensor only, but also having checked that (i) I had the modern design of water pump and (ii) radiator was externally clean.

The car did start overheating again, this time after about 15 mins on track. However it was the first time I had been on the circuit so I wasn't really pushing it at first. Also of note is my dad (who has never raced cars) has a couple of 15-20 min sessions in the car without it overheating.

Temperature was definitely up this time as the fans were blaring when I came into pits. Again no loss of coolant or other issues and the temperature rapidly returned to normal with then fan on.

So my suspicions are now along Mike021050s lines that there's some crap in my cooling system that is not enough to cause an issue until the engine is stressed, and failing that, maybe the standard cooling system on these cars just aren't up to the job of proper track driving.

I'm also more relaxed about fixing the problem as I had my MX5 up there and frankly, that was much more fun on track! You can feel the missing 600kg, the steering is so much more alert and responsive, and you don't have the constant battle of tricking the auto box into the right gear. You can also thrash the crap out of it knowing tyres are £50/corner and it doesn't eat brake pads... I guess top speed isn't everything.

[mike020150]

The XKR in standard trim is far too comfortable and heavy to excel as a track machine. It's a bit like complaining an XKR can't carry as many people as a people carrier! The XKR is an intercontinental mile muncher designed to cruise rapidly over long distances with sufficient handling ability to add some spice to daily motoring. Light weight and stiff suspension will always win the day purely in the fun stakes around a circuit. It's simply 'horses for courses'.

Back to the overheating issue, has the car been on a Jaguar or Autologic (equipped with the Jaguar modules) diagnostics machine recently? If not, it might be helpful to confirm that nothing else is causing the overheating, eg like a fault affecting ignition timing or similar. Failing that, the radiator does still sound like the prime suspect. Mike.

[abk6]

Thanks Mike. Quite agree, have found no better way of transporting 2 people down the M1! It's also pretty useful at the half mile (see this quarters Vscc bulletin...)

I havent had the computer diagnostics, will ask about that at my next Service.