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View Full Version : Intermittent lumpy running with white smoke?


Andy M
01-04-2009, 04:41 AM
540i Touring 90k miles owned 8 years
Recent PAS leak fixed by pressure switch being replaced
and Coolant leak cured by recrimping small hose at top of radiator
Since then getting intermittent white smoke in exhaust and loss of one or more cylinders and possible PAS crunchy noise
Coolant level is perfect and Carbon Monoxide in coolant test is also perfect
PAS fluid level also good
After 10 minutes rest car starts and runs perfectly with no smoke
Is there any route for PAS fluid to be vacuumed into the block/inlet/exhaust manifold?
My mechanic says V8's can have weird vacuum faults and he's even heard of Gearbox fluid being vacuumed into cylinders to give appearance of blown engine on a V8 that just needed an autobox seal replacing
Any ideas?

Andy M
02-21-2009, 03:54 PM
After my intermittent white smoke question, the coolant light started to come on every now and then. This needed a pint of water one week then a litre of water a fortnight later. Then one night, I came home and I thought my wife had washed the car as there was a large amount of water running down the drive which appeared to come from the n/s front wheel area.
I suspected a water pump leak and took off the engine cover panel and the top of the air filter and the corrugated pipe that links the air filter to the inlet manifold to get a closer look.
I then noticed that the underside of the corrugated pipe had fluid on it - the water pump leak was being thrown up by the fan and aux belts. Then Eureka! I realised that the corrugated plastic had two massive splits/holes between the ridges of the corrugation on the underside which you would never see from above.
So just like a broken pipe on a Henry hoover, raw ice cold damp air (during the recent snowy period) together with splashes of coolant leaking from the gradually failing water pump were being drawn directly into the inlet manifold!
Once the engine was warm and the engine bay air around the cracked pipe was heated, the drips of coolant were evaporated and the raw air being drawn was dry enough to stop the exhaust gas appearing white, and the engine ran smoothly. If I had not had a water pump failure I would never have found the problem!

Andy M
02-21-2009, 04:03 PM
If you have a 12 year old BMW, I would urge you to remove your air intake pipe work and inspect the underside for cracks and splits - The under side gets crisped by the engine heat and eventually disintegrates. And every time your mechanic swings it out of the way to change the air filter, the plastic cracking gets worse - and unless you take it completely off to inspect the under side - and lets face it, why would you - you will never find the problem.
If you get white smoke do you really want to pay for head gasket work?