1GM10 burning oil. Problem? Not a problem?

My situation

the 1gm10 came with the boat. In its past life, the PO had all the oil fall out and an alarm failure, so he bricked the old block.  He found a used block, machined the head, mated the two and off she went. The problem is, now the engine burns some oil.  Not a whole lot, say around a quart every 10/20 hours, but the engine only holds 1.5 quarts, so I'm doing a lot of refilling.  I was sort of content to just live with it and be mindful of the oil level but yesterday I changed the oil filter for the first time after about a year, Shitty access and such,  but after an accidental flush and an hour or so of running through the rpms the oil is still squeaky clean.  I assumed that the oil was getting past the rings and burning, and that if that was happening, soot would be getting into the oil, turning it black fairly quickly but maybe that's not how it works? 

Any thoughts? The clean oil piece is giving me some hope that maybe its an issue that wouldn't require a full rebuild? Is that just wishful thinking? Any ideas on what else might be going on here?

 

MiddayGun

Super Anarchist
1,094
404
Yorkshire
Unless there's a big puddle of oil under the engine then its almost certainly burning it, you'd know if the head gasket had gone and it oil was getting into the seawater you'd see it with the engine running at the dock.
Personally I'd just keep topping it up, since fixing it will probably necessitate a rebuild, if it was something easy like a seal then you'd have oil under / on the engine.

If you do want to know more then as Jon said, a compression test is probably the next stop.

 

Zonker

Super Anarchist
9,127
5,041
Canada
I spoke to a Yanmar person in San Francisco who sold parts for decades. I purchased new valve seals because our 3GM was burning oil. She said forget them; it's not the valve seals. She said she never sold them because it just doesn't leak oil there. But she was happy to take my money in case she was wrong.

My engine had been babied by the previous owner (run at 2000 RPM all the time) and the bores were a bit polished. I ran it hard 3400 for a few hours, 3600 RPM for 1 hour and this reduced the oil consumption considerably. Mine used to use about 1 L every 15-20 hours.

 

Blue Crab

benthivore
15,080
2,239
Outer Banks
I spoke to a Yanmar person in San Francisco who sold parts for decades. I purchased new valve seals because our 3GM was burning oil. She said forget them; it's not the valve seals. She said she never sold them because it just doesn't leak oil there. But she was happy to take my money in case she was wrong.

My engine had been babied by the previous owner (run at 2000 RPM all the time) and the bores were a bit polished. I ran it hard 3400 for a few hours, 3600 RPM for 1 hour and this reduced the oil consumption considerably. Mine used to use about 1 L every 15-20 hours.
Dunno why this is so hard to do... but it is.

 
I spoke to a Yanmar person in San Francisco who sold parts for decades. I purchased new valve seals because our 3GM was burning oil. She said forget them; it's not the valve seals. She said she never sold them because it just doesn't leak oil there. But she was happy to take my money in case she was wrong.

My engine had been babied by the previous owner (run at 2000 RPM all the time) and the bores were a bit polished. I ran it hard 3400 for a few hours, 3600 RPM for 1 hour and this reduced the oil consumption considerably. Mine used to use about 1 L every 15-20 hours.
I run at ~3200 anything less is painfully slow.  I'll give it a go at 3600 for a while, see how that shakes out.

 
I used some of this stuff

https://www.restoreusa.com/index.php

didn't seem to have much or any effect
I just had a look at the Restore website and it seems that the two products, CEM and RESTORE, are formulated with different ends in mind. I'm a bit sceptical that you can "chemically" repair a worn engine as RESTORE seems to claim. 

As I understand it CEM is formulated to remove the deposits left behind when the engine is run at low loads and under optimum temp. As others have said a good, hard, full operating temperature, run should achieve the same end. It wasn't cheap and was sold as a three part treatment, one to add to the oil prior to changing. One to add to the fuel. And one to add to the new oil after an initial clean wit a double change using the first product. 

 

Crazy Horse

Member
227
33
Queensland
A compression test is not going to prove much because it's most likely oil control rings that are suffering rather than the compression rings, if it is starting ok. It is using a lot of oil for the small sump and practically emptying it in the time you say. Engine overhaul may be the only longterm option.

 

El Borracho

Sam’s friend
6,345
2,383
Pacific Rim
Some ring leakage is caused by carbon (burned oil) jamming up the rings so they don't seal vertically. The solvents for carbon are concentrated sulfuric acid or hydrogen peroxide. Neither are very good for an engine :)

Other leakage is from cylinder glazing. If the rings and piston flying up and down doesn't remove glazing I doubt any snake oil will. That idea, above, of running at high rpm might well work.

If cleaning rings and restoring the cylinder walls is desired it is a relatively simple matter to tear down the engine just for that. Especially so with a one-lung engine. Put all the same parts back in. Used to be standard procedure back in the good old days. A morning job for a shadetree guy like me.

 
There are a couple shade tree mechanics who have gotten gunked up old truck engines running a lot better using seafoam in the gas, in the oil (prior to a change/flush) and with a spray that goes up the air intake.  There are a few tales like this with YouTube videos to match... Never tried that approach with a diesel but it's my go-to for keeping diesel gunk and water in the fuel to a minimum. 

 

Ishmael

Granfallooner
49,585
10,291
Fuctifino
I use Sea Foam as a fuel stabilizer for gasoline, among other things. Works well as an ongoing carburetor cleaner too. 

 
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