Engine coolant low ??

[fenlander]

Hi, I have a 98 XJR 4 ltr s/ch., which recently has been losing water. I can see no obvious leaks to pipework/rad etc. There is no sludge in
oil filler cap/ header tank cap - so one assumes the h/gaskets are ok.
The overflow tank ? under the n/s wing has quite a lot of water in it - is this usual ??
Just need to get some ideas before taking it to Main dealer, as the last time I had it serviced (80k) it came to about the same value as the
car.

Any thoughts please.

Cheers
Keith

[groomi]

I've had this in the past. It must be a very fine leak somewhere, but my specialist could never find it.

I would suggest just topping it up and keep an eye on the level (not just relying on the light) and then point it out when you next have the car serviced (at a specialist, not a dealer).

[fenlander]

Thanks for advise.
Problem is the "engine coolant low" sign comes up after about 15 miles !!
Its as though there is too much water pressure and its forcing the water back to the overflow tank

Anybody got any ideas
????

[Tame Technician]

Try this first, but you will probably be looking for a leak later. I am assuming the level is low and you dont have a nakered sensor of course.

When engine is cold, or at least not red hot, take the cap off the coolant reservior, have an assistant hold the engine rev up as high as you can, 3500 ish on S/C i think. The water level in the tank should drop, now fill it up and put the cap back on while the revs still held up. Works 90% of the time. I used to do so many, did it with watering can in one hand and throttle body in the other, hard on S/C as wont rev over half way. 4.0 XK8's we did at 5000-6000rpm, get about an extra pint in them.