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Discussion Starter #1
Hi everybody I have a BMW 318 E36 convertible which was given too me by my best friends family as he died last year. Me and my mate went to have a look at it and everything was fine gave it a look over test drove I ect ect and ended it buying it. Around a month later if that the pressure in the water system got ridiculously high but didn't come up on dash as over heating, no white smoke, no water or oil convert contamination just a lot of pressure any ways since then we ask a few people what they thought it could be and all came back with HG failuer so we got head looked at the gasket and it looked fine no cacks was a heat spot on first cylinder but nothing major at all. We then send the head off to be pressure tested all ok nothing with it at all so we then got it skimmed it then came back to us and we put all new cam seals valve seals ect ect full top end rebuild and build it all back and running no problems we then took it out for a drive and next thing same happened again! Massive pressure built up but with no symptoms of HG failure only the pressure so he decided to stick it in his garage and fix it when he had enough money by this time he was skint. Not so long after this he was involved in a accident and died and now the car has been given to me and I want to get it back on the road for summer and I can not for the life of my think it was could be :( so can some one please please help me I'm stuck.
 

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BMWCCA HPDE Instructor
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If it isn't overheating, losing coolant, or mixing oil & coolant, how are you coming to the conclusion that it has excessive pressure in the cooling system?
 

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Discussion Starter #3
You could hear it making like a bubble noise if I remember correctly and the water pipes are absolutely solid there is well over a bar off pressure. Went to open expansion bottle slowly and it all overflowed (after I turned engine off) and lost huge amount of coolent.
 

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The Canadian Prick.
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1. You have air in the system.
2. You MIGHT need a new rad cap.
 

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Discussion Starter #5
No bleed the system so there was no are in the system
Normally if the cap is knackered it would release pressure all the time and not keep holding it so I've been told :/
 

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The Canadian Prick.
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A rad cap is what? 15-20 quid?
Bleeding the air out of the system is free.

But hey, it's your car.
 

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Discussion Starter #7
No I meant it as in I've bled the system so there isn't any air in it and I was saying I got told if the caps are faulty they normally don't hold any pressure at all I wasn't trying me to rude :(
 

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D'oh, You Kids!
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If you could hear it gurgling, there was still air in the system. Air pockets create hot spots that boil the coolant. Boiling coolant drives the pressure up.

Bleed the system. There are at least a dozen write-ups about how to do it in this forum. Condensed version: raise the front of the car. with the engine cool, the key on but the engine off, the heater set to full-on heat, and the vent screw out (it's in the top of the expansion tank) VERY SLOWLY pour the 50/50 antifreeze-distilled water mix into the expansion tank. It will fill nearly to the top, then bubbles will start to come out through the return port in the tank. Keep pouring until no more bubbles, not even champagne-size tiny one, come out, and the expansion tank will take no more coolant. Replace the bleed screw, replace the pressure cap, and start the car. Let it run until it gets to operating temperature. You should have HOT air coming from the heater vents. If not, bleed it again. If you do have heat, turn it off and let it cool down for at least an hour. Check the coolant level in the expansion tank. Top up as needed. Take it for a short drive. Closely observe the temperature needle. If it goes ANY above the center mark STOP, shut it off and let it cool. You have more bleeding to do. If it stays centered, congratulations, you've successfully bled the cooling system.

This is a VERY common problem with new BMW owners and mechanics who've never worked on BMWs before.
 
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