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Old 14-08-2016, 09:40   #1
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2GM20 Smoking on StartUp

When I started my Yanmar 2GM20F (fresh water cooled) yesterday it started smoking like heck in the engine compartment & the low oil pressure warning light came on. It wasn't even warm yet & when I shut it off & the smoke cleared there were no obvious signs of problem so I started it again & it ran fine all day. Is it possible that the exhaust backed up somehow on initial startup? Thanks for any & all suggestions!
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Old 14-08-2016, 10:30   #2
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Re: 2GM20 Smoking on StartUp

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Originally Posted by merrytimer View Post
When I started my Yanmar 2GM20F (fresh water cooled) yesterday it started smoking like heck in the engine compartment & the low oil pressure warning light came on. It wasn't even warm yet & when I shut it off & the smoke cleared there were no obvious signs of problem so I started it again & it ran fine all day. Is it possible that the exhaust backed up somehow on initial startup? Thanks for any & all suggestions!
===

Smoke in the engine compartment is frequently caused by combustion products blowing by the piston rings on one cylinder and being forced into the crankcase where they exit through the vent. You quite possibly have sticky rings on one of your two pistons. Have you changed your oil recently and is it the correct type and weight for your operating conditions?
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Old 14-08-2016, 10:48   #3
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Re: 2GM20 Smoking on StartUp

Yes, I did change the oil but not the filter about 3 months ago. It was very dirty & hadn't been changed for a while so I was planning to do it again this time with a new filter. I believe it is the right type of oil. It might be slightly overfilled too. Thanks for your reply by the way!
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Old 14-08-2016, 11:00   #4
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Re: 2GM20 Smoking on StartUp

Check your dipstick, make sure it doesn't have added volume for some reason, water or fuel going in there. It's a weird one for sure. Like you I wonder if a blocked exhaust would do that... but the oil light coming on.. hmm... not sure that makes sense.
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Old 14-08-2016, 11:01   #5
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Re: 2GM20 Smoking on StartUp

This will sound crazy. But it happened to me last week.

I started my Yanmar with speed set to idle. It didn't start up right away so just as I released the start button, the engine kicked back and started in reverse rotation.

I'm not kidding.

Unburned combustion mix poured out the intake, because the valve timing was off. The overlap was during the wrong part of the cycle.

The oil pressure warning came on because the pump was running backwards.

Took me a few seconds to comprehend the situation, so it ran for maybe 30 seconds before I shut it down.

Started it again a few minutes later and all was fine.
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Old 14-08-2016, 11:12   #6
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Re: 2GM20 Smoking on StartUp

Good thought, as four winds says. Or a piece of carbon got stuck in an intake valve, or the valve stuck, so when combusting it came out the intake.
Still cant figure the oil alarm lite though. Maybe it was running backwards!
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Old 14-08-2016, 11:14   #7
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Re: 2GM20 Smoking on StartUp

That sounds very similar to what happened to me, four winds. I also started on idle & it almost caught but when I pressed the button again is when it started & began to smoke & the oil pressure warning came on. It's not possible for it to run in reverse rotation though is it?

Cheechako I was wondering about the blocked exhaust too & will check my dipstick.
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Old 14-08-2016, 11:19   #8
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Re: 2GM20 Smoking on StartUp

Yes, I've heard of diesels starting backwards before.
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Old 14-08-2016, 11:41   #9
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Re: 2GM20 Smoking on StartUp

I feel better knowing some possible causes so thanks for the input. I guess all I (we) can do is keep the oil clean, monitor the dipstick, & re-start if it runs backwards! Making a little shrine to god of Yanmar wouldn't hurt either.
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Old 14-08-2016, 11:45   #10
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Re: 2GM20 Smoking on StartUp

Yes, almost any engine can run in both directions.

Some do by design, with change of camshaft, starter rotation, etc. Like twin engines boats with counter rotating engines.

BTW, you may have noticed the exhaust being louder, since some of it was exiting the breather.

And again, the oil light came on because the oil pump was running backwards.

Mine did it last week, freaked me out for a while until I understood what happened.
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Old 14-08-2016, 11:51   #11
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Re: 2GM20 Smoking on StartUp

Don't start the engine at idle speed. And always keep the battery hot so it spins fast and strong.

The manual says start the engine with the speed control set to medium speed, then reduce after starting.

I was lazy, and just reached out over the bridgedeck and pressed the button, and the battery was down a little. I think this and the timing of releasing the start button caused my event.
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Old 14-08-2016, 12:01   #12
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Re: 2GM20 Smoking on StartUp

OK but sometimes when I start it with some throttle it seems to flood.
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Old 14-08-2016, 12:33   #13
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Re: 2GM20 Smoking on StartUp

Not sure if it was said, but we had a exhaust hose that had a inner layer on one of our 2gms that was coming apart and blocking exhaust causing a great deal of back pressure and smoke. The low oil psi may be too low rpms ?

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Old 14-08-2016, 13:23   #14
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Re: 2GM20 Smoking on StartUp

Thanks for your post Dulcesuenos. I will check that out as well.
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Old 15-08-2016, 09:36   #15
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Re: 2GM20 Smoking on StartUp

I think you experienced running backwards as a result of releasing the starter just as a cylinder was about to fire and did just before the top of the stoke. Don't worry about it, probably a one in a million. I had it happen once and never again. Don't get ulcers over it.
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