XK8 / XKR ( X100 ) 1996 - 2006

Coolant Dump After Driving

Old 06-04-2019, 10:06 AM
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Default Coolant Dump After Driving

Cooling issue with my 98’ XK8 which is a bit of a problem when one lives in the Las Vegas desert. The car is working great at the moment with one exception; after running the car with the AC on for more than a couple of miles, then parking I find all of the coolant from the overflow bottle has been expelled and resides on the ground. Of course after this the red light and warning “Engine Coolant Low” greets me. I fill the bottle up and the Jag is good for another trip. Some facts –

· Right now the air temperature is hitting the triple digits to the AC is a must
· The engine temperature from the gauge remains constant around ˝ the way up the dial
· This did not happen until the ambient air temperature hits about 90-95 degrees (F)
· When driving it appears to function properly, only when I stop and turn the engine off does it flush out the overflow bottle
· When I turn the engine off the cooling fans continue to run for only about 5 seconds
· A mechanic put the system under pressure for a weekend and the system maintained the pressure
· A new hose set was put in place about 8 months ago

I wonder if the fans (thermostatically controlled I assume going back to the ECM) or sensors/ECM may be faulty and not cooling the hot engine sufficiently after it is turned off while there is no coolant circulation.

Anyone have any ideas on what might be going on? In reading some of the strings it sound like a common advice is let the coolant find its own level. This would be fine except for the low coolant light and a nasty concern about overheating here when I am stuck in traffic and it hits 112 in about 2 weeks. I've read a number of the posts, though not all 499, on Jaguar coolant/cooling - do Jaguar's have a cooling problems?


Old 06-04-2019, 10:08 AM
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What shape is your radiator in?
Old 06-04-2019, 10:14 AM
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Can you tell exactly where the coolant is escaping from? How old is your coolant reservoir? And how old is your coolant reservoir cap? Both are common failure items in these vehicles....
Old 06-04-2019, 10:52 AM
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Start by checking the (plastic) piping to the overflow tank in the wheel well (driver side). You will have to take the wheel off, and the plastic liner off. The coolant cap is supposed to release extra pressure/fluid to the overflow tank, and then suck it back in when things cool off. That overflow tank should be somewhere near half full. Maybe the pipe to that overflow tank is cracked and the fluid can only escape on the ground, and air sucked back in. Likely a $0 fix, too.

Separately, would not hurt to get a cheap ELM327 to be able to read the actual coolant temp, as the gauge is not linear (stays flat for a range of temps).

Best of luck, keep us posted.
Old 06-04-2019, 11:32 AM
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I too have a 1998. Dont forget the factory mounted coolant pump is potentially defective. The blades can fragment , mine did. This was b4 I had a RealGuage. All was ok at cruise speeds, but as I slowed down temp hovered around overheating. How did I know? AC turns off when temp gets high.

Brought it to mechanic. Idling in parking lot while he walked over. As I waited I watched temp rise. Raised rpms - could watch temp drop! He saw this and pegged it: bad pump.

Let us know how you do.

Old 06-04-2019, 12:48 PM
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i had an intermittent cooling issue, with similar symptoms, turned out it was water pump, leaked under pressure only , so have system pressure tested?
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Old 06-04-2019, 01:25 PM
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Lets see if I can answer all -
Tank is original, hoses are new
Cap looks original, I've not replaced it (only owned the car about 6 months)
Radiator seems to be in good shape, I've not taken it down to explore further
I will take and track where the coolant is coming from exactly, good place to start
Will go to the scanner and see what it says about temperature

I needed something to do this weekend.

Thank you
Old 06-05-2019, 07:14 AM
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Mechanic pressure tested the system but did he pressure test the cap? Should be a 15 pound cap I think. Pressure raises the boilover point and a bad cap may be blowing off with heat soak once stopped.
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Johnken (06-05-2019)
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