large white blast of smoke on overrun

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large white blast of smoke on overrun

Postby gaskethead » Thu 29.04.2021, 15:31

I've had a look at the various smoke threads and wonder if anyone can suggest order of items to remove and check with this problem... (I was about to start with turbo removal - but really hoping to avoid that having read more).

If I run up to max revs in gears up to 4th and then back off on the throttle I get an enormous white cloud, and obscure anyone behind

I have noticed over the last few years a lot of oil in the rubber intake to the turbo - as in drops rather than a coating.

Whenever running gently up to 4000rpm I can't see any smoke behind?

Otherwise engine runs well (v close on emissions for MOT tho')

Any ideas gratefully received
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Re: large white blast of smoke on overrun

Postby esprit888 » Thu 29.04.2021, 18:23

gaskethead wrote:I've had a look at the various smoke threads and wonder if anyone can suggest order of items to remove and check with this problem... (I was about to start with turbo removal - but really hoping to avoid that having read more).

If I run up to max revs in gears up to 4th and then back off on the throttle I get an enormous white cloud, and obscure anyone behind

I have noticed over the last few years a lot of oil in the rubber intake to the turbo - as in drops rather than a coating.

Whenever running gently up to 4000rpm I can't see any smoke behind?

Otherwise engine runs well (v close on emissions for MOT tho')

Any ideas gratefully received
Chris

White smoke typically indicates coolant loss, blue ish smoke indicates oil. Check the levels of both, had a similar experience once when a previous owner decided to change the oil, added the 4 quarts of new oil, but.....forgot that he didnt drain the old oil! A grossly overfilled M100 spits it out the crank and into the intake
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Re: large white blast of smoke on overrun

Postby Rocklobster » Thu 29.04.2021, 22:05

:agree:

If the turbo shaft seals are tired, they'll allow coolant (and probably oil) to be drawn through when you come off throttle because the turbo will suddenly go from positive to negative pressure. This coolant will exit through the hot exhaust and will boil, so you get steam out of the back. Any oil that also gets through will probably not get hot enough to burn, so you won't get any blue smoke.

If you're getting excessive oil deposits in the turbo inlet, that could be from a slight pressurisation of the crankcase making the breather work overtime (again due to tired turbo seals). Although you will always get oil deposits here, so this may not be connected.

Engine ok. Turbo needs a rebuild.

Give Midland turbo a ring on 01159 752458. They rebuilt mine for £200 + vat & I got it back in 3 days. It's a pig to remove, but it's worth it.
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Re: large white blast of smoke on overrun

Postby Simon_P » Fri 30.04.2021, 09:03

When you say back off do you mean ease off slightly, or do you mean almost completely or foot off the pedal.
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Re: large white blast of smoke on overrun

Postby Rocklobster » Fri 30.04.2021, 16:32

Gradually easing off the throttle will cause a more gentle pressure change than just removing your foot from it altogether, so I'd expect the most severe whiteout when you lift off altogether, reducing to no smoke (or at least much less smoke) from easing off gently.
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Re: large white blast of smoke on overrun

Postby sideways » Fri 30.04.2021, 16:39

As Rocklobster said, turbo seals - sounds fishy I know (Lobster and seals) but... :D
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Re: large white blast of smoke on overrun

Postby HJ2 » Fri 30.04.2021, 17:10

Seals? Jaimy the fisherman wrangler to the rescue!
I vote seals as well. Been there, got the T-shirt….
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Re: large white blast of smoke on overrun

Postby Rocklobster » Sat 01.05.2021, 12:24

Unanimous then, it's the turbot. (See what I did there?) :bananasex:
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Re: large white blast of smoke on overrun

Postby RonR » Sat 01.05.2021, 12:36

Could you check that the vacuum take-off for the brake servo isn't sucking in fluid? Easier to do than removing the turbo.
Many years ago I had a servo failure on a Lancia that produced a thick white smoke screen on overrun.
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Re: large white blast of smoke on overrun

Postby Simon_P » Sat 01.05.2021, 15:35

Rocklobster wrote:Unanimous then, it's the turbot.
ok I 'll take the bait - I'd cast the net a little wider than the turbot sea RonR's sugestion that it could be the Hake servo. :roll:

Would be interesting to know if it is arfter light or complete back-off ie throttle closed.
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Re: large white blast of smoke on overrun

Postby lotusflasherman » Sat 01.05.2021, 19:44

RonR wrote:Could you check that the vacuum take-off for the brake servo isn't sucking in fluid? Easier to do than removing the turbo.
Many years ago I had a servo failure on a Lancia that produced a thick white smoke screen on overrun.


Agree. Had the same on my Eclat - but that was after braking for a corner, as I powered into it I'd emit thick white smoke ... bit dangerous for following cars when they ran into 'fog. A replacement servo from Lotusbits was a cheap and quick fix.
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Re: large white blast of smoke on overrun

Postby gaskethead » Tue 04.05.2021, 16:30

Many thanks for all the suggestions.

Smoke/cloud is very bad with total shut off on throttle suddenly, but still there if I ease off more gently.

Checked servo pipe - unfortunately dry.

SO turbo bolts/nuts soaking in plus gas. From the comments looking forward to the job! Thanks for tip on Midland turbos - I expected twice that price.

Does anyone recommend a gasket assembly paste for the hot exhaust/turbo joints please?
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Re: large white blast of smoke on overrun

Postby HJ2 » Tue 04.05.2021, 17:05

gaskethead wrote:Many thanks for all the suggestions.

Smoke/cloud is very bad with total shut off on throttle suddenly, but still there if I ease off more gently.

Checked servo pipe - unfortunately dry.

SO turbo bolts/nuts soaking in plus gas. From the comments looking forward to the job! Thanks for tip on Midland turbos - I expected twice that price.

Does anyone recommend a gasket assembly paste for the hot exhaust/turbo joints please?


The metal to metal seals can be re-used. I use a light smear of Copaslip after thorough cleaning of the mating surfaces.
The exhaust manifold gasket needs to be replaced though.
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Re: large white blast of smoke on overrun

Postby Simon_P » Tue 04.05.2021, 17:33

gaskethead wrote:Smoke/cloud is very bad with total shut off on throttle suddenly, but still there if I ease off more gently.


The throttle closed means that the vacuum is inside the the Inlet Manifold and not the turbo side, so it might not be the turbo. I'd check a few more things first.

If you disconnect the Inlet and rig up a suitable filter you could prove one way or another.

The turbo gaskets are metal so no sealant required.

The nuts on the Turbo are one way so they likley won't come undone/the stud will break - find out which bits you can't get before you start.
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Re: large white blast of smoke on overrun

Postby GeoffSmith » Tue 04.05.2021, 18:38

Simon_P wrote:
gaskethead wrote:Smoke/cloud is very bad with total shut off on throttle suddenly, but still there if I ease off more gently.


The throttle closed means that the vacuum is inside the the Inlet Manifold and not the turbo side, so it might not be the turbo. I'd check a few more things first.

Try the PCV valve.
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Re: large white blast of smoke on overrun

Postby lotusflasherman » Wed 05.05.2021, 11:03

I agree with Geoff... and Simon.

Also check the Oil Seperator - the black box above the Cam Angle Sensor with cover held on by 6 setscews. If that is clogged up engine might be breathing in oil.

Always check simple things first. At full throttle the turbo is putting positive pressure in the plenum, with sudden shutoff that will go high negative (vacuum) and start sucking at the crankcase ventilation system and other vacuum connections. If you get smoke then, those are the components to check.

But if you only get smoke when you go back on the throttle again and the plenum is then fed through the turbo, suspect the turbo seals. From what I've read, I wouldn't be touching the turbo ... yet!
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Re: large white blast of smoke on overrun

Postby Rocklobster » Thu 06.05.2021, 21:25

Just remember guys, it's white smoke, not blue, so it's not oil, it's coolant.

I'm not arguing with anyone that suggests checking the simple things first, that's sensible, but
The throttle closed means that the vacuum is inside the Inlet Manifold and not the turbo side
isn't entirely correct.

The primary vacuum will be inside the plenum, but the turbo is still spinning (fast) and trying to pump. This creates a secondary vacuum between the exhaust valves (when closed) and the impellor. If you have a weak shaft seal, this will draw either oil or water or both through.

My money's still on the turbo, but do check as many simpler things as you can think of first.
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Re: large white blast of smoke on overrun

Postby esprit888 » Fri 07.05.2021, 00:54

:agree:
Mostly :D White smoke, especially if it dissipates quickly, indicates coolant but we didn't hear back from the OP as to whether there is coolant loss or oil loss? The turbo does not have a coolant seal as it circulates through the casting within the housing and back out the return pipe, never entering the pressure or vacuum sides of the turbo itself. if coolant is getting in to the turbo then its cracked and it will also be leaking in to the oil pan, not unheard of but unlikely.
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Re: large white blast of smoke on overrun

Postby Rocklobster » Fri 07.05.2021, 08:49

That's very true actually, well spotted and you may have just disproved my turbo theory.

The puzzle is, where does the coolant get the opportunity to enter either the intake charge or the exhaust? It's clearly being drawn in by vacuum when off throttle.

Grasping at straws then, you could try disconnecting the heater control vacuum pipe from the throttle body and then go for a drive. This will rule out a heater matrix or seal leak.
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Re: large white blast of smoke on overrun

Postby dapinky » Fri 07.05.2021, 10:32

I have no technical observations to add to this thread, as the things I could add have already been said......

.... but I do have 2 'way out' thoughts (which have previously been hinted at) as it is now getting to a point where the "obvious" answers don't fit the symptoms.

(1) A damaged & leaking brake master cylinder will allow brake fluid to go into the servo, which could get sucked into the inlet manifold, and then burnt. This would give smoke of the observed colour, but probably not a large cloud of it on throttle closure, so may best be ignored.

(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!!!!
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