Hi Guys,
I need a little help with my 1998 XK8 engine cooling system. The car is a new acquisition, which has covered around the 100k, but is immaculate and seems very well cared for. I have driven it for several months, around town and on the highway, all without incident and with temps in the normal position. All this was during the height of summer, with OAT's of 38+ degrees c.

Anyhow, returning home last weekend from a morning drive of around two hours on the highway, I noticed the engine temperature gauge sitting north from centre, one division. After closely watching this, it appeared to steady and not rise further, but it did concern me, due to the fact it normally sits in the centre (normal) position. I also heard the radiator cooling fans were now operating on high, which was of great concern. I slowed from 100kms to around 80kms, as the temp gauge began to increase to the next division on the gauge, which was one from the red band, however, this seemed to return back to the previous division within a minute or so.
Having previously read about the operation of the gauge and the critical nature of the cooling system, I stopped the car for serveral minutes, then decided to began the short drive home, during which the temp indicated one division above normal all the way. All this time the cooling fans stayed on high and never cycled to low at all.

I've since carried out some basic checks, coolant level, radiator for blockage, coolant temp sensor resistance checks, coolant returning to the expansion tank when running, and cap, all without any obvious faults. I am almost certain the water pump is of the one piece type, but despite the milage and lack of 100% history I have decide to change this anyhow.

I have since only drove the car locally to help diagnose and run it for the Eng Coolant Temp Sensor ECTS checks. I notice the fans seems to start off normal, i.e. off till half warm, then they start up in low (series) and then when fully warm after about 5kms, increase to high, but remain on until I shut down, irrespective of road speed.

During warm up, the temp gauge has always behaved normal and still does, increasing slowly and then sits in the normal position (needle horizontal). The fans begin normal too, i.e. initially off, then low, then into high, but when they switch onto high, the temp gauge still indicates normal position.

Just to be sure, I replaced the ECTS with a new one, but that made no difference when test driven tonight. The warm up was identical, normal gauge and fans as above, remaining on high again when I returned from a short, 6km drive.

I have ordered a new main water pump, modified aluminium T/Sta tower, new T/Stat and coolant too and planning to fit these as soon as they arrive. I was also going to perform a flush too, as I'm paranoid and will not drive out of town till I have this problem beat.

I would welcome any suggestions, or theories as to why my fans are going into high mode, as am working on the theory they are sensing a high temp, hence the reason for the parts I've ordered.

I have read several articles on the operation of temp gauge and can't believe that Jaguar would create such a monster and feel this could be masking a hot engine, hence the fans quickly kicking into high mode, due to a real fault, which is not been shown on the gauge.

Look forward to any replies.

Joe

 

The3 water pump and thermostat are both problem areas. The XK8 TS apparently has a habit of sticking closed or not opening enough when it fails, so replacement of those parts is likely to solve the problem.

It would be wise to replace the crossover pipe also, as they plastic cracks with age. A new pipe includes a new sensor. The short connecting hose and both radiator hoses should be considered at this time also.