Cure for Yanmar diesel engine smoke?

[Waterant]

I wanted to share my solution for Yanmar (and maybe other makes as well) engine smoke, which I have had since I got the boat three years ago.

My setup:

- 2002 Mainship 430
- 2x 200gal tanks
- 2x Yanmar 6LYA-STP 370 hp diesels with ~320 hours on them
- 5gal of new Rotella T3 diesel engine oil in each engine
- The starboard engine has turbo replaced with a brand-new one
- The port engine was completely rebuilt, and the new turbo was installed. ~50 hours after rebuild
- Both engines had injectors replaced with new
- Cooling system was pressure tested

Symptoms:

- Both engines smoked heavily after a cold start while idling in the marina, any RPM, heavy grey smock (I believe it had bluesh tint to it)
- No smoke in gear up to 2100 RPM
- As soon as the turbo kicks in at 2100 RPM and up, heavy grey smoke is on both engines; amount and color are the same on both engines

Cure:

- I added 64 oz bottle of Howes Diesel Treat, Conditioner, and Anti-Gel in each fuel tank: https://www.tractorsupply.com/tsc/product/howes-lubricator-diesel-treat-64-oz

- I removed 2 gallons of oil from each engine, and in each, I added 1 quart of Lucas Heavy Duty Oil Stabilizer
so my oil level is around 50% now - on another forum, I found this being mentioned a few times as a possible cure for the smoke problem. The reason was the uneven installation of the engines in the boats, and the "full" level shown on the stick was for the horizontal installation. So basically, if you have it at the full mark, you overfilled the oil pan.

The result on both engines:

so far, ~10 hours after this was done
- Very little noticeable smoke on idle after a cold start
- No visible smoke at any RPM while running
- Engines sound happy, oil pressure is normal (I have a mechanical pressure gauge installed on each engine to confirm), temperature is normal

That issue bothered me since last summer after the port engine rebuild, and it was puzzling why both engines had the same symptoms even after both turbos were replaced and one engine was completely rebuilt and new injectors installed.
I hope this helps someone.

 

[Waterant]

Some pictures of the smoke before

No pictures "after" as there are no smoke so far

 

[DavidM]

You might have gotten the same result by running them hard- 200 rpm off of top for 6-8 hours.

David

 

[Waterant]

You might have gotten the same result by running them hard- 200 rpm off of top for 6-8 hours.

David

Not sure if that would help as I had the same issue with old and new turbos on the starboard engine. So it's not like there was some residual oil in the turbo.

What else running them at max rpms for 8 hours would accomplish?

 

[BruceK]

When you add 2 additives simultaneously, one to fuel, one to engine oil, it`s difficult to know which if either caused the improvement. The bottles of Lucas oil additive you identify as "Oil Stabilizer" say the product is "Stop Leak".I`m wondering if it might be an oil thickener,increasing viscosity. From your smoke color not being blue it doesn`t seem you were burning oil.
I suppose the main/good thing is it worked somehow, but nice to know how,for future reference.

 

[Waterant]

The smoke had bluesh tint to it but it's hard to tell without me having experience with other kind of smoke to compare.

Both engines had injectors replaced with new and cooling system pressure tested.

I'm not sure which one helped but it's probably oil stabilizer (I originally posted a wrong link, I did not add "stop leak") or even simply reducing the amount of oil in the pan.

With those products costing only $13 per bottle, not much reason not to use both with draining some oil if you are trying to fix the same issue.

 

[porman]

I have the same boat, same engines with 2200 hours on them. They had 800 hours on them when we bought it. The engines smoke a little on cold start up but it goes away soon after. They will start smoking if I let them idle too long, but it stops after running them hard for a little while. The oil levels are at the top of the dipsticks. I use Valvetech fuel that already has additives in it. We cruise mostly at 1600 to 1800 rpm with an occasional run up to keep them cleaned out.

 

[BruceK]

I looked at Lucas Oil Stabilizer online, it has admirers and haters. Seems to be an oil thickener, to stop oil losing viscosity when hot, good for reducing oil consumption in worn engines and reducing blow-by but,yours are 320 hour engines. Engines idled a lot without load can glaze the bores, leading to oil getting past the rings and burnt, so idling at the dock for longer than it takes to leave is contraindicated.
I had success using an oil additive product at double strength as advised by the mfr to unglaze the bores after I accidentally ran the genset no load for a long while, the cold plate compressor died without me realizing, removing the only load. It definitely worked, blue smoke stopped and the genset ran happily ever after.

 

[Waterant]

I have the same boat, same engines with 2200 hours on them. They had 800 hours on them when we bought it. The engines smoke a little on cold start up but it goes away soon after. They will start smoking if I let them idle too long, but it stops after running them hard for a little while. The oil levels are at the top of the dipsticks. I use Valvetech fuel that already has additives in it. We cruise mostly at 1600 to 1800 rpm with an occasional run up to keep them cleaned out.

I suspected the fuel quality, which is why I added Howes Diesel Treat. Maybe this fixed the smoke.
I should try one thing at a time, but I was eager to fix that issue as soon as possible, so I threw everything I could find during the long winter wait at it at once.

I looked at Lucas Oil Stabilizer online, it has admirers and haters. Seems to be an oil thickener, to stop oil losing viscosity when hot, good for reducing oil consumption in worn engines and reducing blow-by but,yours are 320 hour engines. Engines idled a lot without load can glaze the bores, leading to oil getting past the rings and burnt, so idling at the dock for longer than it takes to leave is contraindicated.
I had success using an oil additive product at double strength as advised by the mfr to unglaze the bores after I accidentally ran the genset no load for a long while, the cold plate compressor died without me realizing, removing the only load. It definitely worked, blue smoke stopped and the genset ran happily ever after.

The only disadvantage of using Lucas Oil Stabilizer, that I could find, was harder starts and possible oil starvation when using at cold temperatures, and we didn't run the engines or use the boat in those conditions.

 

[DavidM]

Not sure if that would help as I had the same issue with old and new turbos on the starboard engine. So it's not like there was some residual oil in the turbo.

What else running them at max rpms for 8 hours would accomplish?

It has worked for me in the past, both for turbo and non turbo engines.

If you run at low loads for an extended period, unburned fuel and soot builds up on the rings and cylinder walls which causes them to stick and you lose compression.

Heavy loads for 6-8 hours burns that soot off and frees up the rings so it will run clean at low loads.

Tony Athens, the marine engine guru on Sbmar.com, recommends the heavy load procedure for genset that are all sooted up from running a long period at very low loads.

The additives do much the same.

David

 

[Waterant]

It has worked for me in the past, both for turbo and non turbo engines.

If you run at low loads for an extended period, unburned fuel and soot builds up on the rings and cylinder walls which causes them to stick and you lose compression.

Heavy loads for 6-8 hours burns that soot off and frees up the rings so it will run clean at low loads.

Right, but the port engine was completely rebuilt with new cylinder liners and pistons. Brand new cylinders and pistons with no build-up but still getting heavy smoke.
The compression was checked and normal in every cylinder on both engines.

 

[lwarden]

My boat with 370 Cummins 6BT smoked a fair bit when starting cold, neither engine smokes when under way. During the winter I have pan heaters, even though it really doesn't get very cold here in San Diego. The pan heaters helped the smoke on startup during the winter. I do run both engines at the bottom of the oil level dipstick running the recommended amount of oil per Tony Athens. Also, I run Stanadayne fuel stabilizer in each tank and this seemed to help with faster starts year round and less smoke during summer months.

 

[Dougcole]

My motors (Yanmar 4LHA-STP) used to "burn" oil when I first bought the boat, I never noticed much smoke, but there must have been some as the oil has to go somewhere. I was keeping the oil level near the top mark on the dipstick. One of the mechanics at the local Yanmar dealership told me to keep the oil midway between the marks. I started doing that and miraculously, I stopped losing oil. They never burn a drop now unless I accidentally put in a little too much when refilling after an oil change.