XK8 low coolant warning
Discussion
I appreciate that this has been discussed before but I cannot find here or on any other website a solution to my problem. My garage cannot solve it either.
I have a late 1998 XK8 convertible and for the past few months the low coolant light has come on after a few miles of driving. If I wait until the car has cooled sufficiently to open the header tank, the coolant level is normal. If I try to open it hot and release a little pressure the low coolant light goes out and stays out for 20 or so miles when it comes back on again. If I wait until it cools down the coolant level is okay however, if I release the pressure again and the light goes out when I next check the cold coolant level, it is low.
I had a new radiator a couple of years ago and I have replaced the water pump, the thermostat, all the hoses and the header tank but it makes no difference, the problem arises every time I drive the car. The garage has done a pressure test and say there is not a head gasket problem.
They have suggested a 'hot spot' within the cooling system. I have completely flushed out the cooling system and refilled it. Run the car until warm and left it to cool and checked the coolant level which is fine.
Does anyone have any ideas? Comments much appreciated.
I have a late 1998 XK8 convertible and for the past few months the low coolant light has come on after a few miles of driving. If I wait until the car has cooled sufficiently to open the header tank, the coolant level is normal. If I try to open it hot and release a little pressure the low coolant light goes out and stays out for 20 or so miles when it comes back on again. If I wait until it cools down the coolant level is okay however, if I release the pressure again and the light goes out when I next check the cold coolant level, it is low.
I had a new radiator a couple of years ago and I have replaced the water pump, the thermostat, all the hoses and the header tank but it makes no difference, the problem arises every time I drive the car. The garage has done a pressure test and say there is not a head gasket problem.
They have suggested a 'hot spot' within the cooling system. I have completely flushed out the cooling system and refilled it. Run the car until warm and left it to cool and checked the coolant level which is fine.
Does anyone have any ideas? Comments much appreciated.
Top the tank up right to the top, when cold.
There is another expansion tank in the osf wing.
Pop out the side repeater.
Make sure the tank is about half full.
The under bonnet tank has a foam float that turns the light on and off. The floats can lose buoyancy, this could be bring the light on.
Bridge the 2 pin level sensor plug, go for a drive see if the light still comes on. If it does then you need a new tank + sensor. Float is in the tank, tank comes with new sensor.
There is another expansion tank in the osf wing.
Pop out the side repeater.
Make sure the tank is about half full.
The under bonnet tank has a foam float that turns the light on and off. The floats can lose buoyancy, this could be bring the light on.
Bridge the 2 pin level sensor plug, go for a drive see if the light still comes on. If it does then you need a new tank + sensor. Float is in the tank, tank comes with new sensor.
Edited by melhookv12 on Tuesday 14th April 16:50
Two things to look at then.
With the engine absolutely stone cold remove the filler cap and start the engine. Hold it at around 1500 RPM and look inside the header tank. You should see a steady, bubble free stream of coolant from the thin black hose from the radiator feeding into the tank. Rev the engine up and down and carefully watch the tank level to see if it changes with engine RPM. Do so fairly quickly before the coolant temperature rises.
If you have bubbles in the return stream or the coolant level changes with RPM you may have an air lock somewhere which has the potential to cause hot coolant level to fluctuate. The system ought to self bleed but check to see if the interior heater gets hot and the giggle pin in the thermostat is fitted correctly in the 12 o Clock (top) position.
If the level doesn't change with RPM and the stream is bubble free then the header tank filler cap may be faulty allowing pressurized coolant to blow past when hot and into the expansion vessel. This lost coolant won't draw back into the engine when it contracts and cools - hence the lower level. I don't know where the expansion vessel is on an XK - on a contemporary XJ it's under the n/s front wing.
Oh... And what Melhook just said ^ too.
With the engine absolutely stone cold remove the filler cap and start the engine. Hold it at around 1500 RPM and look inside the header tank. You should see a steady, bubble free stream of coolant from the thin black hose from the radiator feeding into the tank. Rev the engine up and down and carefully watch the tank level to see if it changes with engine RPM. Do so fairly quickly before the coolant temperature rises.
If you have bubbles in the return stream or the coolant level changes with RPM you may have an air lock somewhere which has the potential to cause hot coolant level to fluctuate. The system ought to self bleed but check to see if the interior heater gets hot and the giggle pin in the thermostat is fitted correctly in the 12 o Clock (top) position.
If the level doesn't change with RPM and the stream is bubble free then the header tank filler cap may be faulty allowing pressurized coolant to blow past when hot and into the expansion vessel. This lost coolant won't draw back into the engine when it contracts and cools - hence the lower level. I don't know where the expansion vessel is on an XK - on a contemporary XJ it's under the n/s front wing.
Oh... And what Melhook just said ^ too.
Edited by Jaguar steve on Tuesday 14th April 17:04
Thanks for the replies. I had a new header tank but the problem persisted so I replaced it a second time with no change. I replaced the overflow tank in the right wing at the same time.
I connected the old tank to the wiring and lifted the float. The light went out, dropped it and it came back on. It's not the header tank nor the header tank connection.
I have flushed the whole system twice to clear any air locks. All new hoses, water pump, thermostat and it does not lose water when it's standing in the garage.
It's been pressure tested and there is no indication of water in the oil or oil in the water. When the engine is run with the header tank cap off there are no bubbles but, regardless of everything, after 5 or so miles, the light comes on, I release the pressure and it goes off. I then can drive for 20 plus miles with no problem. Today is was over 30 miles mostly in stop start town traffic.
I am stumped.
I connected the old tank to the wiring and lifted the float. The light went out, dropped it and it came back on. It's not the header tank nor the header tank connection.
I have flushed the whole system twice to clear any air locks. All new hoses, water pump, thermostat and it does not lose water when it's standing in the garage.
It's been pressure tested and there is no indication of water in the oil or oil in the water. When the engine is run with the header tank cap off there are no bubbles but, regardless of everything, after 5 or so miles, the light comes on, I release the pressure and it goes off. I then can drive for 20 plus miles with no problem. Today is was over 30 miles mostly in stop start town traffic.
I am stumped.
Thanks. Unfortunately, the last thing I want to do is take the heads off but it may come to that.
When I ordered a new header tank, I ordered two caps. I put the second new cap on less than a week ago.
The hose from the header tank to the overflow tank is new but one thing I haven't checked are the hot and cold levels in the overflow tank. The only thing that makes me think it's not that is the fact that if I open the header tank when the engine is cold, the header tank is usually full.
When I ordered a new header tank, I ordered two caps. I put the second new cap on less than a week ago.
The hose from the header tank to the overflow tank is new but one thing I haven't checked are the hot and cold levels in the overflow tank. The only thing that makes me think it's not that is the fact that if I open the header tank when the engine is cold, the header tank is usually full.
I had a 1998 XJR a good few years back. It had some funnies with coolant level which I eventually tracked down to being due to the pipe between the header tank and the overflow /reserve tank in the wing not being airtight, it had a small crack in it.
This meant water would expand and flow into the overflow bottle in the wing , but would not be drawn back up in to the header tank as it cooled again because the leak in the pipe meant it would suck in air though the crack rather than the water from the overflow bottle.
So I'd get a low coolant warning, I'd top the header tank up, then within a few days I'd get another warning. It's only when I spotted the puddle beside the front wing one day that I twigged what was happening.
Might not be exactly what yours is doing but worth thinking if it could fit.
This meant water would expand and flow into the overflow bottle in the wing , but would not be drawn back up in to the header tank as it cooled again because the leak in the pipe meant it would suck in air though the crack rather than the water from the overflow bottle.
So I'd get a low coolant warning, I'd top the header tank up, then within a few days I'd get another warning. It's only when I spotted the puddle beside the front wing one day that I twigged what was happening.
Might not be exactly what yours is doing but worth thinking if it could fit.
Thanks but I don't think it is the pipe to the overflow tank partly because it is new and partly because when the engine is cool, the header tank is full even if I have had to release the air pressure after about five miles. It seems as though, once this air pressure is released, the problem goes away until the engine cools down and the whole thing starts all over again. So long as the engine remains hot, once the pressurised air is release, the problem goes away.
I think it's going to have to be a heads off job.
I think it's going to have to be a heads off job.
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