Smoking Downhill

95 4.6 hse petrol
Was going down a very steep hill in 1st gear using the engine to brake but also used the brakes now and then, after a mile or so looked back and saw smoke big time - stopped and just smoked like mad on tick-over.
Went onto a main road shortly after and smoking stopped after a a short while.

Wonder if it's fuel still going in or oil? Smoke was gray. No problems now apart from it uses a lot of fuel as usual, brim-brim about 12 mpg mixed use - lot of town though.

grey smoke is usually oil. only guessing, but you might of been so steep it all collected at the front of the sump and got back past a ring into the chamber. dont quote me though LOL

Closing the throttle for extended periods with the engine being forcibly turned over by engine braking would have caused significantly lower air pressure in the inlet tract - this would have encouraged engine oil to be sucked past the valve stem seals into the combustion chambers. No harm done.

Oh well - glad no harm done - higher gear & more braking next time then...

Smoking on or after overrun with throttle closed, is oil being sucked in past the valve guides.

wammers said:

Smoking on or after overrun with throttle closed, is oil being sucked in past the valve guides.

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oh, cos it's a pushrod motor. Was wondering what could cause oil to be pushed up past the piston into the head :scratching_chin:

JerryXt said:

oh, cos it's a pushrod motor. Was wondering what could cause oil to be pushed up past the piston into the head :scratching_chin:

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Does not matter what type of engine it is, if the valve stem oil seals are duff and guides are worn this can happen. Same if the rings are worn. If rings are worn and oil control ring is duff with throttle shut on overrun oil can be sucked up past rings on the induction stroke. If this is happening you would also have high crankcase pressure as gas passes rings on combustion stroke. Far more likely to be valve guides.

Most probably valve stem oil seals. Relatively simple repair as these can be replaced without removng the engine or heads.

So it's an oil-sucker at the moment going downhill in low gear anyway.

Tappets are a bit noisy so one day i may have to do something about it but it runs fine right now and who knows when much more serious things happens

Only ever rebuilt one engine, it was my old long gone twin 750 cc bike & a success (5 weeks touring Europe was the test drive)

That bike engine should have set you up a treat-750 twin, must have had pushrods and ohv, so your rangie plant is only 4x as much, bigger gaskets, no pushrod towers, head gaskets you only use once-don't put them in the oven like your old copper ones, monster fuel injection system to remove; it's an absolute piece of p***-not!

Went down the same hill today also in first gear lots of engine braking - No smoke at all.
Must be my new Lambda sensors working and not flooding the cylinders & spewing out lots of petrol, also doing about 2-3 miles more per gallon so far.
Thought the car ran fine before new sensors but now its noticeable better - got a nice result presenting it at the MOT - £140 for 2 OEM Sensors incl. fitting and reset of faults/adaptive values and a glance to see there's absolutely no faults to be dealt with - knock wood hope to keep it like that (Still a P38 so expecting something soon)