Overheating

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   I have a BMW F Reg 520 SE E34
After a long journey parked the car came out to drive 2 hours later and coolant all over the drive appears to be coming from the radiator cap. When I parked the car temp was normal. Took the thermostat out refilled and bled the system (Expert at this now) and drove it for about 2 hrs. Temp consistent at the quarter mark so fine. Checked thermostat in boiling water- O.K. So I am totally baffled unless the radiator cap failed when stationary but its only 2 years old.
Anyone any ideas ?  

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iang Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 22-July-2003 Location: United Kingdom Status: Offline Points: 21	Topic: Overheating Posted: 13-September-2004 at 06:48
	I have a BMW F Reg 520 SE E34 After a long journey parked the car came out to drive 2 hours later and coolant all over the drive appears to be coming from the radiator cap. When I parked the car temp was normal. Took the thermostat out refilled and bled the system (Expert at this now) and drove it for about 2 hrs. Temp consistent at the quarter mark so fine. Checked thermostat in boiling water- O.K. So I am totally baffled unless the radiator cap failed when stationary but its only 2 years old. Anyone any ideas ?

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Andrew Rolland Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Go away rain Joined: 19-August-2004 Location: Scotland Status: Offline Points: 6579	Posted: 13-September-2004 at 07:27
	I don't know much about E34's but if it is a traditional style rad cap then sounds like you have the wrong one. Cooling systems work under a lowish pressure and therefore the rad cap must be able to withstand that pressure. If the rad cap can't take the pressure it will blow and hey presto the ground beneath your 6 pot gets a showering of coolant. Years ago when I drove a Mini the rad cap had the pressure stamped on it (15psi) which meant it would blow and let out the coolant when the pressure exceeded 15 psi. BMW should be able to tell you what pressure rating your rad cap needs to be and also be able to supply you with a correct rad cap. Sounds like she maybe got a bit hot on your 2hr drive and that was enough to increase the cooling system pressure enough to blow the cap. Something must be causing the pressure to rise to get too high without it over heating. Try flushing out the system as it may be blocked. Also make sure the system isn't overfilled otherwise you will get coolant escaping from the rad cap as it expands and flows up the rad and out thru the cap. Don't run without the stat for too long otherwise you will suffer from over cooling. Hope this helps Andrew
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Ian :0 Members Profile Send Private Message Find Members Posts Add to Buddy List Groupie Joined: 11-August-2003 Location: United Kingdom Status: Offline Points: 92	Posted: 13-September-2004 at 08:10
	Ian, My 1992 518 was part of a recall for a change of radiator cap due to pressure leakage. Perhaps your fell into this category also ? There's a web-address for recall details. I've lost it, but I'm sure someone will post.
	Ian

iang Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 22-July-2003 Location: United Kingdom Status: Offline Points: 21	Posted: 13-September-2004 at 09:56
	The radiator cap is newish one from BMW which i got from a product recall so i am pretty sure its the correct one. I had cooling problems 2 years ago so i replaced Fan Clutch, Thermostat, Water pump, Radiator and flushed the system and the cooling has been perfect since. The temperature was fine when i parked so the problem has occured whilst the engine was not running this is what totally baffles me. I will replace the radiator cap and flush the system again and see what happens

Andrew Rolland Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Go away rain Joined: 19-August-2004 Location: Scotland Status: Offline Points: 6579	Posted: 14-September-2004 at 03:16
	Ian Yeah the coolant temp may be perfectly well but if you have overfilled the system you will get a bigger volume leaking out due to expansion of the coolant when it is hot. I used to get this on my Mini yonks ago. Fill her up a bit too full with coolant, drive, temp gauge normal, park, return - big puddle of coolant on the floor. It would then find its own level by expanding out if too full when hot. If BMW parts are anything like the Vauxhall parts dept I used to get spares from for my last car then you may just have the wrong rad cap! Things like having air con etc could mean that the cooling system is slightly more beefed up and will have a different operating pressure and hence a different rad cap. Andrew
	Be exclusive and drive a Petrol 5 Series! Current '13 62 F10 535i MSport Auto Previous '04 04 E60 545i SE Auto '03 53 E60 545i SE Auto (Stolen) '98 S E39 523i SE Auto

iang Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 22-July-2003 Location: United Kingdom Status: Offline Points: 21	Posted: 14-September-2004 at 05:29
	I have discovered the problem there is the tiniest of leaks where the expansion tank joins the radiator near the bottom it only leaks when hot and under pressure. I cannot believe i did not spot it. I reckon the seal must of failed when i had stopped causing the coolant to leak. Running without the thermostat kept the temp / pressure down so the leak was minimal. Annoyed as the radiator is only 2 years old but relieved as the problem is solved.

Andrew Rolland Members Profile Send Private Message Find Members Posts Add to Buddy List Moderator Group Go away rain Joined: 19-August-2004 Location: Scotland Status: Offline Points: 6579	Posted: 14-September-2004 at 06:39
	Ouch How much will a new rad be? Last rad I did was a genuine Vauxhall Part for my 3.0i 24 v Senator and it was I think �230. Mind it was a big big rad! Can the expansion tank come away from the rad or is it a combined unit? My E39 appears to be a combined rad and expansion tank but I'm not so sure as I am new to all things BMW and the Haynes manual for the Series 3 (98 ownwards) is as clear as mud for the M52 engines. Keep us posted Andrew
	Be exclusive and drive a Petrol 5 Series! Current '13 62 F10 535i MSport Auto Previous '04 04 E60 545i SE Auto '03 53 E60 545i SE Auto (Stolen) '98 S E39 523i SE Auto

iang Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 22-July-2003 Location: United Kingdom Status: Offline Points: 21	Posted: 14-September-2004 at 08:25
	�95 from GSF in Greenford London. I find parts for my BMW are cheaper than parts for a ford fiesta which i also have thanks to GSF and Europarts. (Sounds like an advert for them)