1996 2.5 diesel Transit (170k miles on the clock). Starting with the engine cold, if I brake to a standstill in the first 2 or 3 miles of driving, immediately after braking the van starts smoking very badly (black / blue - definitely oil) and banging loudly from the engine. The engine tries to stall, but with a bit of gas it sorts itself out after a few seconds. This will generally only happen once per trip, but smokes so badly as to blind anything behind me. I'm also concerned about the banging since it sounds pretty violent. Once up to temperature, the engine runs fine and doesn't cause any problems at all. The engine is using oil at slightly higher than normal rate. Once the oil level starts to get a little low, the fault doesn't happen so often unless I brake hard. I'm certain the problem is oil getting into one of the cylinders, but how? My best guess is that one of the valve stem seals has failed, but any other thoughts would be appreciated before I take the head off.

Keith, January 2007

Problem turned out to be the diaphragm in the oil filler cap / crankcase breather being a little bit sticky. New oil filler cap and all is well...

Keith, February 2007

It's very rare for a valve stem oil seal to fail on a trusty Di, check the easy things first like the air filter and inlet manifold for oil, if they don't seem to bad then carry out a compression test on each cylinder.

MrMPuk, January 2007