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Old 31st July 2021, 20:16   #1
mgb66
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Default KV6 190 persistent overheating

Having spent a good few hours reading all the posts on this subject I hesitate to write another one on this thorny subject. However I'm at a bit of a loss and don't want to go off in some wildy wrong direction with the overheating problem I'm having.
My ZT-T had been running fine until a week or so ago the temperature guage started fluctuating upwards, and then went all the way up with the red light showing and ENGINE OVERHEAT coming up on the trip computer.
I must admit I do not check the coolant level often enough, especially as when I do, the header tank always seems to require some topping up.
In fact I do always carry some coolant in the car just in case.
On this occasion it took at least a litre and a half.

However on my next trip out, the temperature guage went into the red after a mile or so.
I decided to check everything as best I could and particularly the thermostat and associated pipework. Having taken the engine cover off I had a good look in the V and although I could see some liquid it was more oily than evidence of coolant. I cleaned this up and it has not returned. The area immediately by the thermostat was completely dry.

Given that air locks seem to be an issue I decided I had better go through the recommended procedure for filling the system.
With the help of a neighbour I duly re-filled the system according to the Haynes manual. Two concerns during this process were that as soon as the engine started the expansion tank overflowed, plus the engine cooling fan did not come on when the temperature guage was indicating normal temperature.
I let the engine cool down and took the car on a short drive. Same story. At about a mile the temperature guage shot up and the red light came on.
I thought that the re-filling procedure might have been done incorrectly so I decided to do it again. I asked my son to help and following the procedure he kept the revs up until the fan cut in.
I then left the car for an hour and checked the expansion tank level which was a bit high. I syringed about 300mml out to just reveal the ribs.
I waited another four hours or so and took the car for a short drive. After a mile the temperature guage once more shot up and the ENGINE OVERHEAT warning appeared.
I was on a dual carriageway and so gingerly drove to somewhere I could stop with plenty of steam from under the bonnet and evidence that the cap was letting out coolant. After half an hour or so I filled the tank with about 2 litres of coolant ( I've got through about fifteen litres so far in this sorry tale) and limped home.
I have checked again and again for any sign of leaks but connot see any. The water pump was replaced along with the cambelt at 97,450 miles and the car has now done 107296. The thermostat is a plastic one and was replaced in 2017 at 90220 miles.

The oil on the dipstick is clean and there is no emulsion under the oil filler cap and no sign of steam from the exhaust.
I have not been able to check the engine temperature via the trip diagnostics as I daren't run the engine long enough.

Given loss of coolant seems to be via the expansion tank pressure cap and there is no evidence anywhere else of leaks I would be grateful for any thoughts. I'm wondering about a failed water pump or a sticking thermostat.
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Old 31st July 2021, 20:35   #2
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Check your fan is working using the demister test, aircon off, press the demist button, the low speed fan should kick in and run continuously. If it starts and stops there's a problem, cause varies depending on what type of fan you have.

Re ejecting coolant, how much coolant are you putting in? "I syringed about 300mml out to just reveal the ribs.", that's way too high. The max level is right at the bottom of the tank. If the tank is overfilled the excess will be spat out. You can see the max and min levels at the bottom of the tank in the pic below.

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Old 1st August 2021, 07:05   #3
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Whereabouts are you in London Peter?

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Old 1st August 2021, 08:15   #4
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Hi Peter
After a quick read of your story i suspect that either the cap seals are faulty or more likely is that the oil cooler is blocked which then stops the coolant flow around the engine

I would bypass the oil cooler with a piece of pipe fill system and bleed it then try it, i have known quite a few oil coolers fail causing this problem, I also notice Simon has asked where in London you are if you are stuck perhaps he will come over and take a look at it for you

Dave

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Old 1st August 2021, 10:35   #5
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Quote:
Originally Posted by mgb66 View Post
Given loss of coolant seems to be via the expansion tank pressure cap and there is no evidence anywhere else of leaks I would be grateful for any thoughts.
Failed thermostat? If the wax capsule has leaked, it will remain shut. These stats don't fail 'safe', so will inevitably will cause overheating/boiling.



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Old 1st August 2021, 12:05   #6
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Simon, thanks for your interest. I'm in SW18.
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Old 1st August 2021, 12:22   #7
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Simon, thanks for your interest. I'm in SW18.
Peter
Lets hope Simon will come and take a look for you
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Old 1st August 2021, 12:33   #8
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Thanks very much for all your thoughts.

Given that the bottom hose from the radiator does not appear to get very warm at all, and there are gurgling noises from the thermostat piping once the engine is switched off, I did wonder if the thermostat is stuck shut, so no circulation and therefore boiling over.
I did the demist test and the fan appears to be working. Also the fan comes on at full blast once the gauge hits the red.

I went to and got some more OAT mixture this morning pending further attempts at re-filling and that's now the fourth 5l canister I've bought in this process. Mad!
Bypassing the oil cooler as a test sounds a good plan.
I would pass this problem on to the small local garage I use but with wonderful timing they closed for their annual fortnight holiday on Friday.
Ironically there was also an MG Rover dealer locally but they went over to Skoda years ago, I may call in and see if any of the MG Rover experienced mechanics are still there. I do feel though that this problem should not be beyond some DIY.

I had to fire up the MGB this morning to go to Halfords. Good as gold needless to say. Changing the thermostat on that would be a 10 minute job...
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Old 2nd August 2021, 07:03   #9
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Originally Posted by mgb66 View Post
Given that the bottom hose from the radiator does not appear to get very warm at all ...
That's an important piece of evidence Peter. Thanks for your PM.

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Old 2nd August 2021, 08:10   #10
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Quote:
Quote:
Originally Posted by stevestrat View Post
Check your fan is working using the demister test, aircon off, press the demist button, the low speed fan should kick in and run continuously. If it starts and stops there's a problem, cause varies depending on what type of fan you have.

Re ejecting coolant, how much coolant are you putting in? "I syringed about 300mml out to just reveal the ribs.", that's way too high. The max level is right at the bottom of the tank. If the tank is overfilled the excess will be spat out. You can see the max and min levels at the bottom of the tank in the pic below.

As above make sure you have the right coolant level, and the O-rings on the cap should be round not flat, you can replace them with Viton ones.

1

2

The O-rings on the caps difference.

Flat.
3

Domed
4

Side by side.
5
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