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Old 17-02-2017, 09:50   #1
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Decarbonizing Universal Diesel w/Mystery Oil?

Hi,
I've observed a little film of soot over the boat's stern. I am planning to replace the 3 injectors on my 1989 M25XP universal diesel, as it's cheaper than a rebuild. Since I'll have direct access to the combusion chambers, I been considering a decarbonizing process used on Atomic 4 engines
1.pouring 1/4 cup or so of mystery oil into each chamber.
2. rotate engine by hand and let it sit for a day
3. repeat once
4. run engine till expected smoke clears up

Has anyone used Mystery oil to decarbonize a diesel? Any concerns or advice. My thought is that after 25 years at 160F, the rings may not be sealing as well.
There's no risk and the downside is smoke on the initial startup.

Thanks,
Chris
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Old 17-02-2017, 11:54   #2
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Re: Decarbonizing Universal Diesel w/Mystery Oil?

Quote:
Originally Posted by chrisyse View Post
Hi,
I've observed a little film of soot over the boat's stern. I am planning to replace the 3 injectors on my 1989 M25XP universal diesel, as it's cheaper than a rebuild. Since I'll have direct access to the combusion chambers, I been considering a decarbonizing process used on Atomic 4 engines
1.pouring 1/4 cup or so of mystery oil into each chamber.
2. rotate engine by hand and let it sit for a day
3. repeat once
4. run engine till expected smoke clears up

Has anyone used Mystery oil to decarbonize a diesel? Any concerns or advice. My thought is that after 25 years at 160F, the rings may not be sealing as well.
There's no risk and the downside is smoke on the initial startup.

Thanks,
Chris
I love Marvel Mystery Oil for freeing up sticky (stuck) hydraulic lifters on auto engines. However I think burning it in a combustion chamber could lead to even more carbon deposits. Many high performance gas engines have used water injection to aid with detonation and reduce deposits. If your going to pull the injectors take a look at the tips and determine how much soot build up is present. Do you run the engine with a good load on it or just loaf it at lower RPMs? If the tips are not coated with hard carbon but just soft soot it will burn off with a good load on the engine running for a while.
I think there are some products you can add to the fuel that claim to reduce soot and carbon build up. Others will chime in and offer other tips and tricks.
If the engine runs good and uses no oil I would just wash the stains off the stern and call it good.
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Old 17-02-2017, 12:04   #3
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Re: Decarbonizing Universal Diesel w/Mystery Oil?

I am also a fan of MMO, however I would not do it, you could wash some carbon into the rings and carbon is extremely abrasive and could scratch the cylinders, and what are you fixing?
possible downside, no up side
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