large white blast of smoke on overrun

[GeoffSmith]

As the theories for explaining coolant leak under lift off are getting more convoluted, why not consider that the blue smoke is being mistaken for white smoke and the explanations become a whole lot simpler?

[Simon_P]

As the theories for explaining coolant leak under lift off are getting more convoluted, why not consider that the blue smoke is being mistaken for white smoke and the explanations become a whole lot simpler?

Good idea ...so on complete lift off it would usually indicate valve guides and crank case breather.

(2) The 'obvious' way for coolant to get into the exhaust is because of a failed head gasket (or crack in the head or block) - as to how the pressures affect when it makes such a trip, and gets burnt at a closed throttle situation, I haven't thought through yet!!!!

or oil for that matter ... on the intake stroke with the throttle closed the vacuum is scavenge from anywhere it can - see above plus any HGF leaks to cylinder. Oil or water it wouldn't burn it would vaporise on contact with the very hot bits in the exhaust and turn into steam - white and dissipates quickly or smoke - white/blue hangs around and stinks.

Following on from Phil's comment the check that the drain back to the sump isn't blocked. and someone also had a blocked turbo oil drain.

[kbee]

Sorry just spotted this thread if the oil vaporises rather than burns the vapour will be white . It did when I blew a turbo.