I'm cutting and pasting a lengthy post I put on the Ericson list back in 2019. It concerns my Yanmar 1GM and an issue with oil consumption, as well as some smoking. You may find it applicable here.
Executive summary: The post is long, so if you don't want to read it all then here is the executive summary: Run the heck out of your engine for about 10 hours or so in case your issue is caused by stuck rings or whatever. By "run the heck out of," I mean 3400 RPM, which is probably a lot harder than you may have been running it. And no, you won't blow up your engine, because 3400 is the continuous rating for the GM-series of engines.
***** WARNING: LONG POST FOLLOWS *****
Oil consumption and running a diesel hard enough
In 2017 I replaced my well-running Yanmar 1GM with another 1GM that I got for a steal on eBay. This one had been run only in fresh water (a great thing for a raw water cooled engine), had zero surface rust, and was just too good of a bargain to pass up. So I bought it, tested it in my garage, and then swapped engines in June of 2017. The original engine is in my garage and I plan to rebuild it in my leisure, or just keep it as is for a spare.
Anyway, the "new" engine started right up, had good compression (which I verified with a compression tester), ran very well, but did smoke a small amount. Because of family commitments, I had very little occasion to run it in 2018. But after putting only about 20 of my own hours on the engine, I began to observe that it was consuming some oil. The Yanmar manual says that some oil consumption is normal, being greatest when the engine is brand new and also toward the end of its useful life. However, the numbers I was seeing were more than I was comfortable with. Specifically, I was observing around 0.4 to 0.5 oz./hour. This may not seem like much, but that little engine only holds 1.4 qts. total in its baby oil sump to begin with! Plus, my original engine consumed little if any oil--certainly nothing like this. I was not happy.
Knowing that the compression is good, I was thinking it might be the valve seals, or possibly the oil ring. It was not leaking oil, so the oil had to be going out the exhaust. So even though it was not smoking much, I figured the amount it was smoking had to be enough to account for this amount of consumption.
I was considering swapping back to the original engine and then tearing down this one for a rebuild. But I first decided to give a call to Scott at S&W Diesel in Wilmington to see what he thought. He wondered if perhaps the engine had been run too lightly or not under enough of a load for prolonged periods. He said that he often talks to customers who baby their engines (thinking that's a great thing to do) and then encounter increased oil consumption from things like stuck rings, etc. He mentioned that it's especially bad with generators because it's often difficult to load those up. He said that he will tell such customers to run the crap out of their engine for several hours and see if the problem doesn't fix itself. He mentioned one fellow who did this, motoring from San Diego to L.A. Harbor (I think it was), and by the time he put 10 hours of hard running on it the problem vanished. He suggested I give that a try.
I already knew that a diesel ought not to be babied, and I have never done that with any of the ones I've owned. But with this engine I don't really know how the previous owner may have run it in the past. I do know that he used to race his boat and it could be that he just fired it up to get to the starting line and then to get back into the slip. I'm just speculating here, of course. I do not really know the total number of hours on this engine as the previous owner did not have an hour meter on it, nor do I know his usage pattern. It looks to have had light use, and if so, that's not necessarily a great thing.
So, I decided to follow Scott's advice and run the heck out of it. I put a little over 10 such hours on it, running it at about 3300 rpm. This is above its normal cruising rpm but within the continuous rpm rating of the engine, and is about the max I can get with my particular prop in any case. (I am slightly overpropped.) This was a really good, hard run. When I did this, the oil consumption shot up to over 2 oz. per hour! Yikes! But after this I also noticed that the smoke I had been seeing pretty much disappeared when I ran it at a more reasonable cruising rpm (e.g., around 2800). Something clearly had changed.
Since putting those hard-running hours on the engine, I've been running it at 2850-2925 rpm since mid-February. This is a good, stout cruising rpm for this engine and puts it under a decent load. (I confirmed actual engine rpm with an optical tach; my Yanmar tach reads about 200 rpm too low in this range.) I would carefully check the dipstick after every run.
Well, guess what? On April 13, after 27.2 hours, I could finally discern a very slight decrease in oil level on the disptick! So I carefully added a small amount of oil until I brought it right up to the full line again. It took all of 2 oz.! Doing the math, this is only 0.07 oz./hour! And the engine no longer smokes. I can sometimes get a small amount of steam, depending on the outside air temperature/dew point. Sometimes I don't even get the steam. But as for the smoke, it is gone.
Scott's suggestion paid off. I'm guessing there may have been some carbon causing a stuck ring or something. The engine runs great--though to be honest, I would have thought all was well before had I not observed the oil consumption.
My plan is to run it at WOT for an hour or two here and there, to keep everything blown out. I've also added a nice solar panel setup so I can keep up with my electrical loads without having to idle the engine. (As I mentioned, I didn't tend to do that too often before anyway, but now I'm being very punctilious about avoiding that completely.)
I hope this info may be helpful to someone else.
