Smoking heavily when cold

Smoking heavily when cold

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Mulsanne-Speed

Original Poster:

569 posts

154 months

Friday 2nd October 2020
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I followed my wife to drop off our 2016/66 L405 for an MOT yesterday. While driving behind her having just started the car, going up a slight hill, the car was smoking very heavily. It's only done 31,000 miles and was last serviced 3 months ago, just over 1,000 miles ago.

The car doesn't get that much use and has been stood for exactly 30 days (having just looked on the in-control app).

The only time it came out of the garage between then, was for a wash - The engine was sat running on that day for about 20 minutes, don't know if that could be a factor, perhaps causing some kind of build up?

The smoke did completely vanish after a few minutes of driving, but was definitely very heavy.

Any advice or thoughts would be much appreciated

Shanksy87

381 posts

129 months

Friday 2nd October 2020
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What colour was the smoke? If white'ish I would go on the assumption that when the exhaust got hot enough it vapourised all the moisture lingering in the exhaust from its layup

Mulsanne-Speed

Original Poster:

569 posts

154 months

Friday 2nd October 2020
quotequote all
Good morning Shanksy87 and thank you for your prompt reply.

Yes, I guess it was whiteish in colour, although not steam, it had a definite smoke element to it.

Strange how it burnt off though, which I suppose could well point towards what you suggest. I'm guessing if it were anything more sinister the smoke would continue. There were no emission issues at the subsequent MOT Station anyway.

What you suggest probably makes sense.

Many thanks for your help and have a good Friday

A.J.M

8,012 posts

193 months

Friday 2nd October 2020
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If it cleared off then I wouldn’t worry about it.

Maybe take it a longer trip along a motorway to get it fully warmed up.

paintman

7,764 posts

197 months

Friday 2nd October 2020
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Burning a gallon of petrol/diesel produces amongst other things a considerable quantity of water.
This condenses inside a cold exhaust system.
Cars used for sort journeys where the exhaust never gets hot enough to boil the water off generally go through exhausts faster than those used for long journeys as they rot out from inside.
You'll often see it dripping from the tailpipe.
Also a cause of mayo in oil filler caps - which isn't the surefire indicator of hgf that some seem to think & I sometimes wonder how many have had their trousers pulled down by unscrupulous garages.
If you're not losing any coolant then nothing to worry about.
As the weather gets colder it becomes much more noticable.

Edited by paintman on Friday 2nd October 18:07

Mulsanne-Speed

Original Poster:

569 posts

154 months

Friday 2nd October 2020
quotequote all
Thank you AJM for your comments and in particular Paintman for your detailed reply, with some good points made.

If I understand Paintman correctly, I'm wondering if because the last time I started the car, I left the engine running and the car stationary for 20 minutes, whether moisture has accumulated within the exhaust, then burnt off when next driven.

This I suspect would make sense.

Many thanks

Andy RV

306 posts

137 months

Saturday 3rd October 2020
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Is it diesel? Does it have a dpf? If so it may be part of the regen cycle?

Mulsanne-Speed

Original Poster:

569 posts

154 months

Tuesday 6th October 2020
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Hi Andy

Sorry, not logged in for a couple of days.

Yes. it's a 4.4 V8 diesel, so yes could be this. It seemed fine when I drove it this morning from what I could see out the back. I rev'd it hard when I came back home and checked what was coming out the exhaust, it wasn't heavy smoke, just what I'd describe as a blast of diesel smoke at peak rev