Mercruiser Dirty Oil

[Alumarine]

A friend just picked up a boat with a 78 mercruiser 140hp 3 liter in it.

The engine runs well and compression is good, but I haven't seen oil this dirty on the dipstick for years.

We've changed the oil and filter twice but it's still black on the dipstick after it runs for a bit.

Can anyone recommend a product to help clean out the crank case?

I'm reluctant to use any snake oil without a credible recommendation,

Also, does it matter if the oils black on the dipstick?

thanks

 

[180shabah]

Re: Mercruiser Dirty Oil

I would continue with what you are doing....frequent oil changes with a good detergent oil.

There are many products that will CLEAN the engine out, but you increase the chance that a large "chunk of sludge" will be dislodged and end up blocking an oil passage completely. So use at your own risk.

Winter is coming, any chance of pulling the engine and doing a quick rebuild?

 

[mthieme]

Re: Mercruiser Dirty Oil

You could add a quart of ATF Dextron in there just before the next oil change.
This is very high detergent. It is also low viscosity, so use the throttle with moderation.

 

[chiefalen]

Re: Mercruiser Dirty Oil

You don't want to run it with a overflowing oil pan.

Drain a quart for every quart you add.

Short of pulling the motor and the oil pan this is really all you can do.

 

[HT32BSX115]

Re: Mercruiser Dirty Oil

There are many products that will CLEAN the engine out, but you increase the chance that a large "chunk of sludge" will be dislodged and end up blocking an oil passage completely. So use at your own risk.

Absolutely. You run a huge risk of breaking something loose large enough to block a down stream passage to say, a main bearing. Once it starts spinning you'll destroy the crankshaft etc.

Just change the oil frequently and you'll clean out the engine over a few oil changes. If it's a freshwater boat you could put a slightly warmer T-stat in it and you'll dissolve the "stuff" a little quicker.

I would not dilute the oil with anything.


Regards,


Rick

 

[Alumarine]

Re: Mercruiser Dirty Oil

Thanks for the advice guys.

For now at least, I'll just change it a couple more times.

 

[chiefalen]

Re: Mercruiser Dirty Oil

You do know that you need straight 30 weight oil in that motor?

 

[Alumarine]

Re: Mercruiser Dirty Oil

You do know that you need straight 30 weight oil in that motor?

Yes, thanks. I use 30 weight or 25W40 in them.