I've never heard of that technique. I can't say. Traditional compression tests measure PSI buildup on the compression stroke. It's a test for proper sealing of the valves and compression rings.
"Normal" Oil Usage by Diesels?
- Thread starter Kings Gambit
- Start date
Yeah, w/o a pressure gauge, there's no direct measurement. But you would not expect all cylinders to be low on compression at the same time to the same degree; so, if one is not weak then--big conclusion--they must all be at spec., etc., if I follow the logic.
That sounds logical. Hypothetically speaking though, one cylinder could have sucked up something and scratched a ring or cylinder wall. Chances are remote.
Another possibility is that the compression rings are fine but the oil rings aren't working right. Again I'd recommend something like Seafoam first. I expect others to give an opinion on this before you act on it.
You could do a cylinder comparison test by measuring starter current. Measure current with all injectors installed then other measurements with each injector removed one at a time. You always have two injectors installed. Compare results. This would be comparison only with no absolute compression numbers.
So, we're safe in concluding that if the serial cylinder test reveals no evidence of relative loss of cylinder compression, then the oil consumption is probably not due to seepage past the rings?
Well I hate to say it, but that will only test the compression rings, not the oil rings. Not much help is it? It's probably not a stretch to say if the compression is good, the other (oil) rings should be in similar condition.
If compression is really needed, why not just buy/borrow a compression gauge and the correct adapter for your engine. Then you have a direct measurement and the assumptions go away.
Mine has 1300 hours, so it much less. I use about a quart in 6 quart or in a season of about 250 hours.
I would presume it is piston ring wear which decides the major consumption .
Just for the math that was about 1/8th teaspoon per engine hour or so.
Jim...
Hard to believe it’s been more than 5 yr since I raised this question. Change in usage patterns brought on by COVID and other variables has diverted my attention. I chatted with a Yanmar technician last fall who told me the critical measure for excessive use of motor oil is based on diesel fuel consumption. Say, 0.5% might be regarded as within average tolerances. That would be 125 ml of motor oil burned with 25,000 milliliters (25 liters) of fuel, so with about 6.6 US gallons of fuel. Sole consideration of the number of engine hours offers much less precision since fuel consumption rate varies with RPMs in the same time.
It’s easier for me measure motor oil use than liters of fuel consumed in the short-term; but with repeated fill-ups (toppings off) during travel it would be straight-forward. The bad news appears to be that I’m near or slightly above the “acceptable average”, which does not correct for total engine hours. That average is 0.5% or less.Thirty hours of motoring at 3,000 rpm should consume 135 liters of fuel (35.7 US gallons) in my 3JH3E. So135,000 ml x 0.005= 675 ml, about 0.7 US quart of oil maximum. I may have my own final estimate soon! It seems I’m somewhere near that however; much above what you folks have reported earlier in the thread. My up-tick in oil burn is relatively recent; this was not the case when I bought the boat in 2004.
It’s easier for me measure motor oil use than liters of fuel consumed in the short-term; but with repeated fill-ups (toppings off) during travel it would be straight-forward. The bad news appears to be that I’m near or slightly above the “acceptable average”, which does not correct for total engine hours. That average is 0.5% or less.Thirty hours of motoring at 3,000 rpm should consume 135 liters of fuel (35.7 US gallons) in my 3JH3E. So135,000 ml x 0.005= 675 ml, about 0.7 US quart of oil maximum. I may have my own final estimate soon! It seems I’m somewhere near that however; much above what you folks have reported earlier in the thread. My up-tick in oil burn is relatively recent; this was not the case when I bought the boat in 2004.
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Here is something I posted on the Ericson list that might be of help. I'm copying it below.
Alan
Alan
2008 Yanmar 3YM30 with around 600 hours of run time, and I typically cruise at ~2,900rpm. We do sail a lot, rather than motor, so on most trips the Yanmar doesn't get much of a workout. I follow the manual's instructions to race the engine to max RPM several times before shut down at the end of a day or multi-day trip to blow any carbon/deposits out that may have accumulated from idling. I check levels every day on the boat, and typically the motor burns no discernable oil, which gets changed at the end of every season.
But a few weeks ago I took the boat on a 400nm circumnavigation of the DelMarVa peninsula, and without wind we had to continuously motor the entire offshore leg, which took roughly 27 hours, which I did at 2,500 RPM both to conserve fuel and to maintain position with a flotilla. When I checked the oil after that leg I had to add roughly 4-6 ounces of oil. That's the only time in 4 years of owning the boat I've ever had to add oil, and in the intervening weeks I haven't had to add any more (Rotella 15W-40).
But a few weeks ago I took the boat on a 400nm circumnavigation of the DelMarVa peninsula, and without wind we had to continuously motor the entire offshore leg, which took roughly 27 hours, which I did at 2,500 RPM both to conserve fuel and to maintain position with a flotilla. When I checked the oil after that leg I had to add roughly 4-6 ounces of oil. That's the only time in 4 years of owning the boat I've ever had to add oil, and in the intervening weeks I haven't had to add any more (Rotella 15W-40).
Thanks for your report, Alan. I can see where something similar makes sense in my situation. The diesel did not noticeably burn motor oil in about the first 1000 to 1200 h of its operation. I’ve generally run it 3000 rpm at “full speed” whereas it could do 3200 rpm when full out. So, I’ll start running it full out the next few hundred hours. I see the same slight amount of smoke at times; maybe that will go away as well.
KG
KG
Doing a bit of math on @Alan Gomes 9HP motor vs my 50 HP Volvo Penta, but I do not run WOT. [ 2200/3000 RPM ]
I never see smoke after start up.
Jim...
PS: Engine oils DO break down after many cycles, thus we have Oil Filters.
I use much less oil or 0.02 oz/engine hour versus his 0.07 oz.
I never see smoke after start up.
Jim...
PS: Engine oils DO break down after many cycles, thus we have Oil Filters.
Do you need to cruise @ 3000 RPM? Suggest you back off to 2600 or so for continuous multi hour use. Cheers/Len
Our 3YM30 burns a little. I usually add somewhere between 50 and 150 mL over the course of a season. Looking at my logs it looks like I burn oil at just over 0.1% of my fuel burn rate, so well within the tolerance KG posted. The engine has 500 hours, with a mix of cruising at 2800 RPM’s and short runs to get in and out of the slip.
Yeah. The acceptable range I saw was 0 (nil) to 0.5%. Unfortunately, I have not kept a good log of diesel fuel consumption; but it’s likely reconstructable from CC purchase records. Probably not more than two tanks (= 40 x 2 gal)/yr in most years based on engine hrs.
For what it's worth, here's a data point, based on my personal experience and fastidious engine logg keeping.
On my 1984 Catalina 36 with Universal M25 (Kubota D850), I very carefully kept the sump full, up to the top mark on the dipstick, and had to add oil kind of frequently. I noticed that no matter when I checked it, it was down to about the 3/4 mark. So, I decided to leave it, and found that the engine would toss the top 1/4, and then wouldn't use any oil - at all! I could run it for 100 hours, until my scheduled oil change, and it hadn't budged from the initial depletion to the 3/4 mark. So, I only filled it to 3/4, and it used NO NOTICEABLE OIL. Go figure. Burnt none, tossed none, nothing.
On my 1984 Catalina 36 with Universal M25 (Kubota D850), I very carefully kept the sump full, up to the top mark on the dipstick, and had to add oil kind of frequently. I noticed that no matter when I checked it, it was down to about the 3/4 mark. So, I decided to leave it, and found that the engine would toss the top 1/4, and then wouldn't use any oil - at all! I could run it for 100 hours, until my scheduled oil change, and it hadn't budged from the initial depletion to the 3/4 mark. So, I only filled it to 3/4, and it used NO NOTICEABLE OIL. Go figure. Burnt none, tossed none, nothing.