The reason that advice was given to idle a turbo engine before shutting down was not specifically lubrication but more associated with the temperature of the exhaust and the heat soak of the exhaust going through the main bearing housing of the turbo, the problem being that the excesive heat was carbonising oil at the piston ring seals at the turbine end and also "heat treating" the piston ring seal reducing the spring effect and encouraging either lub oil getting into theexhaust or exhaust gasses getting into the crankcase.

In an earlier life I was involved in development for one of the leading turbo manufacturers and we always used to let exhaust temps drop to 300 deg C before shutting down test bed engines.

This problem has very largly been overcome in recent years by water cooling bearing housings.

Turbos require lubrication when you stop so its worth waiting for a short while if you can.

Last edited by The Doc on 29th Nov 2009 2:10 pm. Edited 1 time in total

piston ring seal, in the turbo????? At work
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"I can't always believe facts I read on the web" - Charles Dickens

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the problem being that the excesive heat was carbonising oil at the piston ring seals at the turbine end and also "heat treating" the piston ring seal reducing the spring effect and encouraging either lub oil getting into the exhaust or exhaust gasses getting into the crankcase.

I’m sorry but I’m lost, I have re-built lots of engine (big and small) and never come across this problem.

A lot of the above would be caused by glazed piston bores/very high mileage engines and engines worked hard from cold (any moving part can wear out) hence combustion pressure passing the piston rings, causing high/excess crankcase pressure. (Turbo or none turbo engines all the same)

I have come across (carbonising oil) – oil being burnt on the turbo bearings because of too much heat (which or floating bearings because of the speed they spin at.), hence letting the turbo cool at low engine speed, letting cooler/fresher oil help to cool the turbo bearings for a short time after a time of hard engine work is always advisable.

Never race, high rev or work any engine hard until it’s fully warmed up and after hard work give it time to cool down.

(Nobody works hard in the gym when cold and after a hard work out its always advisable to cool down)
An engine is the same if you what it to last ???

Looks like I confused some folks with piston ring seals win the turbo, at the turbine end of most turbo's there is a groove in the shaft which a square section spring seal, which looks like a minature piston ring, is fitted and makes a labyrinth seal to avoid oil getting in the exhaust and seal the high pressure exhaust from the crankcase, excessive exhaust temperature at shutdown can A; clog this with carbonised oil and B; make it lose tension so it leaks.

Problem was more acute with the higher exhaust temps on petrol engines, but as said is mainly cured with water cooled bearing housings nowadays.

Now I understand what your saying, I have just never new it was called a (piston ring seal) your spot on in what you saying 7Iron. Sorry me getting confused.

I had a tractor turbo recondition at the cost of £500 so do look after yours  At work
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"I can't always believe facts I read on the web" - Charles Dickens

winner by default of the tractor vs caravan race