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Discussion Starter · #1 · (Edited)
So this has been an ongoing problem for a fair few months now... when my R53 is idling (parked up, in traffic etc.) the coolant temp is reaching 120+ constantly. Sometimes it'll drop down to normal temps once moving, but often it'll only drop to about 115 and then rise again.

Water pump has been replaced. Thermostat & gasket replaced, and today I replaced the housing because I noticed it had a hairline crack in it, but still no luck. Expansion tank has been replaced, I've got two caps that I've tried in case one of those was faulty, but nothing solves the problem. Radiator hoses replaced & no visible leaks anywhere now.

Interestingly there's no cabin heat, but both of the pipes into the heater core in the cabin are scalding hot. Get up to speed and you'll get heat coming through, but then it vanishes again.

Obviously I'm tempted to consider the head gasket, but I can't see any symptoms of it. Oil looks fine (did an oil change about a month ago, nothing untoward in the oil then or now), no visible oil in the coolant, no signs of any misfires. Surely a bad head gasket would mean temperatures skyrocket and don't come down, correct?

I really am stumped with the thing now. If anyone has any suggestions or knows someone reasonable in the Hull area who could take a look I'd be grateful, before the bloody thing pushes me over the edge! :cursing:

EDIT: On a side note, I'm using this coolant from EuroCarParts as it's what the geezer recommended to me. I was previously using Comma Xstream G48 which I've seen recommended as the only coolant to be using. I'm wondering if I've been mugged off in the coolant department here?
 

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I had similar issues with mine a few years ago. Tried all sorts (repeated bleeding, flushes etc)but there were two issues that sorted it out eventually.
The first was the heater matrix which seemed to have sludge build up in it and took ages to get any heat out. I replaced it with a new one and that resolved the heat issue and cut down on how often I’d get an overheat.
The other thing which eventually sorted the problems for good was replacing the expansion tank cap. I’d tried two new ones which were aftermarket, and changed the tank for an alloy one but still got overheating. Eventually I just went and got a new OEM cap from BMW and that has solved it, never had any overheating since.
 

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I use the blue ECP coolant without a problem just so you know.

Is the bleed screw tight?

Is your expansion tank leaking?

Is your fan functioning?

Maybe your heater matrix needs attention as that seems to be the only thing left to check.

Sent from my SM-G935F using Tapatalk
 

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Discussion Starter · #5 ·
I use the blue ECP coolant without a problem just so you know.

Is the bleed screw tight?

Is your expansion tank leaking?

Is your fan functioning?

Maybe your heater matrix needs attention as that seems to be the only thing left to check.

Sent from my SM-G935F using Tapatalk
Fair enough, couldn't find any data for ECP's coolant so at least I can rule that out. Bleed screw is tight, no leaks from the expansion tank, fan seems to be good.

I had similar issues with mine a few years ago. Tried all sorts (repeated bleeding, flushes etc)but there were two issues that sorted it out eventually.
The first was the heater matrix which seemed to have sludge build up in it and took ages to get any heat out. I replaced it with a new one and that resolved the heat issue and cut down on how often I’d get an overheat.
The other thing which eventually sorted the problems for good was replacing the expansion tank cap. I’d tried two new ones which were aftermarket, and changed the tank for an alloy one but still got overheating. Eventually I just went and got a new OEM cap from BMW and that has solved it, never had any overheating since.
Heater core seems to be a common suggestion so I'll look at that next. I'll bear the expansion cap in mind and order one from BMW if I can't resolve it with the heater core.

You've already diagnosed the heater matrix as being clogged up, so id change that next!
Just made a start on pulling the matrix out - why the f*** did they make it so difficult to get at? Don't fancy trying to get it out without spilling anything in the dark so I'll attack that tomorrow. Fingers crossed I find it clogged and that's the problem!
 

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If there is no cabin heat but both hoses to and from it are hot the water circulation is being restricted and that is almost certainly the cause of the over heating.
 

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Check the low speed fan is working, very common fault.

Put the air con on and see if the low speed fan comes on. If it doesn't then the high speed comes on later, it's fucked and needs a repair kit.
 

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How is it getting up to 120 degC? You're above both cooling fan stages - first at 106 and second at around 112 (I think). Are you hearing any fans coming on?
 

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Perhaps......if the water isn't circulating, the temp sender in the head is doing it's job telling the ecu to put the fan on, but that isn't cooling the water 'from' the engine, just that in the radiator, so it gets hotter

Fix the matrix if it's a blockage.
 

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Discussion Starter · #11 ·
Perhaps......if the water isn't circulating, the temp sender in the head is doing it's job telling the ecu to put the fan on, but that isn't cooling the water 'from' the engine, just that in the radiator, so it gets hotter

Fix the matrix if it's a blockage.
I think this is the one. The fan is kicking in as it should but it's not effective enough at cooling the whole system, just the coolant in the radiator which isn't flowing anywhere.

Took the matrix out this morning and put it under the tap - lo and behold, barely a trickle out of the other end. Ordered a replacement from ECP, should be able to fit it next week, hopefully solving the problems once and for all.

Fingers crossed now that the overheating hasn't done any damage to the head...
 

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you might be lucky, as whilst you've been running hot you haven't been running without coolant from an overheat caused by coolant loss or airlock etc, so with coolant all around the head galleries, albeit very hot, it is 'there' so keep your fingers crossed.

my 2p is just use BMW coolant, it's cheap.
 

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Scruff, did you ever solve your issue?

I have very similar symptoms on my car and can’t figure out what is causing it!

Started to suspect the heater matrix and came across your thread.
 
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