smoke from air filter

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XVC375
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Joined: Thu Mar 09, 2017 5:59 pm

smoke from air filter

Post by XVC375 »

Hello All

After a short but intensive run (some hills and relatively high speed running) I noticed what looked like steam coming from the front grille once I had parked up. Upon investigation there appeared to be oil smoke rising from the air filter apertures (the filter is of the later gauze type). It was not billowing out and only lasted around 15-20 seconds before stopping but it did look a bit worrying.

Since then, it has done this periodically. Cleaning the air filter didn't seem to make any difference. Oil and water were both changed within the last couple of months and the engine does not appear to be running hot.

I do get some running-on but not on a regular basis. Could this be a contributory factor?

Thanks

Dan
earthhist
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Re: smoke from air filter

Post by earthhist »

A fairly common problem, the consequence of the pipe that connects the rocker cover to the air filter. When the engine is running there is vacuum within the filter from the induction system and this draws air from the valve chest. This air bears some oil vapour. When the engine stops, that vapour will then tend to diffuse away including through the input holes as you stated.

If the engine is worn, either at the valve guides or at the pistons, then there is additional pressure within this engine which makes the rate of transfer of oily air into the oil filter much worse. Normally if this is happening, then you will also be losing oil (as drips) via the the crankcase vent that has its outlet pointing down next to the engine on the nearside side of the car.

If the oil is very old it is more inclined to vaporise.

Having significant quantities of such oily smoke does suggest engine wear, but it is not in itself dangerous. When the engine is running the oil vapur is drawn into the engine where it is burned.
Richard Johnston, Plymtree Devon, formerly A30/A35 Club Technical Officer and President
XVC375
Posts: 38
Joined: Thu Mar 09, 2017 5:59 pm

Re: smoke from air filter

Post by XVC375 »

Thank you for your comprehensive reply, Richard.
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