750i 5.4 v12 coolant loss

Cooksta
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Car model: 1997 BMW 750i 5.4 v12
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750i 5.4 v12 coolant loss

Post by Cooksta » 27 Feb 2014, 17:09

Hi. I have a 1997 750i 5.4 v12. The water pump went so had to replace pump,rad,fan & header tank etc. Since then it loses about half a litre of coolant no matter how far I go. I've had it pressure tested and all seems ok. No signs of leak and never overheats and doesn't boil up or seem to lose coolant if left idling. Any ideas please..?

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M60NJP
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Re: 750i 5.4 v12 coolant loss

Post by M60NJP » 27 Feb 2014, 17:48

Dumb question..........surely it must overheat if it loses coolant? Or are you topping up every journey?

Cooksta
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Re: 750i 5.4 v12 coolant loss

Post by Cooksta » 27 Feb 2014, 19:17

It only loses less than a litre. Enough to bring on check coolant level warning.

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M60NJP
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Re: 750i 5.4 v12 coolant loss

Post by M60NJP » 27 Feb 2014, 19:54

How recently were the repairs done? If you've only done a few miles since it may still be venting air. Otherwise it reads like a hose has perished or is leaking at the clip.......

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DeeDee
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Re: 750i 5.4 v12 coolant loss

Post by DeeDee » 27 Feb 2014, 22:33

dont these leak in the valley manifold gaskets on the engine or is that the V8???

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Re: 750i 5.4 v12 coolant loss

Post by M60NJP » 27 Feb 2014, 22:46

DeeDee wrote:dont these leak in the valley manifold gaskets on the engine or is that the V8???
AFAIK it's only the. V8s...

Cooksta
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Car model: 1997 BMW 750i 5.4 v12
Location: Gillingham. Kent

Re: 750i 5.4 v12 coolant loss

Post by Cooksta » 27 Feb 2014, 23:23

Repairs were done about a year ago. I did have trouble initially with air locks but got that sorted. I've probably done 1000 miles max since the repairs. I don't use it on a daily basis.

Cooksta
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Car model: 1997 BMW 750i 5.4 v12
Location: Gillingham. Kent

Re: 750i 5.4 v12 coolant loss

Post by Cooksta » 27 Feb 2014, 23:27

I replaced all the hoses & clips etc when the pump was done. No sign of leaks. I don't understand why it always loses the same amount of coolant whether I do 20 miles or 100. Could the expansion tank be too small?

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Re: 750i 5.4 v12 coolant loss

Post by M60NJP » 28 Feb 2014, 07:49

Cooksta wrote:I replaced all the hoses & clips etc when the pump was done. No sign of leaks. I don't understand why it always loses the same amount of coolant whether I do 20 miles or 100. Could the expansion tank be too small?
Shouldn't make any/much difference - the challenge is why additonal coolant is being needed every time you use it! Was the exp tank brand new? It could be leaking.....

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Stratts
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Re: 750i 5.4 v12 coolant loss

Post by Stratts » 28 Feb 2014, 10:02

You'll have to look for the visual signs of coolant leakage in the engine, or check the carpets on the passenger side to see of the heater matrix is leaking.

Assuming you have bled the system properly, and you can't find any signs of leaking, I would question the validity of the pressure test you had done or check if you are loosing coolant internally, but that sort of loss would cause masses of water vapour from the exhaust.

Bleeding of these engines takes ages, it is possible you still haven't done it properly. I was at a 7 Series club meeting last year and some of the guys there mentioned it takes hours to bleed properly. It's a massive lump and takes something like 15 litres of coolant in total.
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