Where is the oil going?

We have two Perkins 6.354 naturally aspirated engines in the museum that is our 1975 engine room. Hours unknown but estimated to be 6000 – 8000. The port engine does not use more oil than the width of the “Max” scratch line on the dipstick between 100 hour changes. The starboard takes about a gallon and a half between changes and needs top ups every 3 – 4 days when traveling.

Aside from the mystery of why two engines with identical service profiles are so different, there is the bigger mystery of where the oil is going. The drip pan of the starboard engine shows some leaks but not enough to account for more than a small portion of the lost oil. The exhaust smoke from the two engines is identical, the area around the outlets cleaner than I have seen on any boat, and both start instantly, even with weak batteries. I sometimes see a sheen in the water on startup or long idling periods forced by locks or no wake zones but, these are Perkins after all. Interestingly, this problem has gotten steadily better over the thousands of miles we have run since buying the boat last year. More interestingly, there is no visible difference between the two engines’ occasional exhaust sheens. The only difference I can detect is the amount of oil I am pouring through one engine and a tiny amount of oil in the starboard drip pan.

Both engines are under oil analysis showing normal wear for their age. Although I try to run them up to near WOT for 5 - 10 minutes every day or two, these engines are run very lightly in the 1400 – 1600 rpm range most of the time which gives us 7 knots. My GPS shows that our moving average over 1258 miles was 7.0 knots. We burned 448 gallons during that time which works out to 179 hours so 2.8 GPH. 2.8 / .056 = 50 HP or just 25 HP per engine on average. These 130 HP engines are running very lightly indeed but they seem happy.

Thoughts?

It should be very easy to check blowby by pulling the dipstick or removing the oil cap. See if there is a large smoke diff port to stb.

When the engine reaches operating temperature, I doubt you would see any smoke from that amount of oil being burned with the fuel. I wouldn't worry about it.

Ted

Assuming 200 gallons of diesel burned on that engine between changes, 0.75% oil burn is not too bad for a nearly half century old high hour diesel. As Diver Dave suggests check blow by.

BTW, what oil are you using?

This is a somewhat radical suggestion, and maybe you are better off letting sleeping dogs lie, but maybe you have a bit of cylinder glaze on the oil burning engine. With twins you can easily (but check if your transmission can take the freewheeling- Velvet Drives are ok) shut one down and run the other hard, maybe 2,000 rpm for a day of cruising to attempt to burn off the glaze. Then check the oil consumption.

David

I burn and drip about 6 quarts for every 100 hrs.

so every 200 gallons or so.

I run at 45 to 50 hp I guess as I run 6.3 knots from 1700 rpm.

Ford Lehman 120.

sunchaser said:

As Diver Dave suggests check blow by.
BTW, what oil are you using?

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Rotella 15W40. There were several bottles Lucas oil leak stopper in the boat. I used up the last two full ones in the engine but and then stopped using it and have noticed no change in consumption.

The dipstick on this engine doesn't permit checking blow by since it is the type that has a tube down into the sump. I hadn't thought to check via the oil cap. I'll check when we get back to the boat.

The little Yanmar on my sailboat was the same way on the dipstick and interesting in the blow by department. At idle, taking the filler cap off was like there was a hair dryer on low setting blowing out of the engine. At cruise, you could just feel the faintest pulse, like a baby's breath. That engine didn't burn a bit of oil between changes.

1.5 gal over 100hr is nothing to worry about, even though it is different than the other. Make sure you have the right amount of oil in the sump by measuring at next change. Some engines burn off oil faster if level is too high, you can try leaving it toward the add mark.

Second Dave on next run, run the stbd hard like 2000, 2100 and shut port down or leave it idling in N if gear can't freewheel. Run it hard a few hours.

Some rings are designed to put more pressure on the cylinder walls and seal better when the combustion pressures increase under load. That might be why you see blowby at idle but very little underway and no oil burning on your sailboat engine.

David

If the dip stick sticks down in a tube that ends in the oil, be sure to check the oil level a couple of times .

The oil can climb up inside the tube giving a false reading.

The only difference I can detect is the amount of oil I am pouring through one engine and a tiny amount of oil in the starboard drip pan.

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On those old Perkins engines, the starboard forward engine mount bolts are threaded thru into an oil gallery. A very common nuisance on those is leaking thru those bolts (actually they are studs).
This is easily stopped by removing the studs one at a time, cleaning and using sealant on the threads.
I solved my oil leak issue by doing this on the old Perk that was in my "ex" old Mainship model 1.
Perhaps not the major part of your disappearing oil, but maybe worth one minute of time to investigate.

FF said:

The oil can climb up inside the tube giving a false reading.

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On one of my cars, there is zero oil on the dipstick, until I remove and re-insert the stick. Viola! now normal. There is an O ring seal at the handle, and it keeps the oil totally out of the tube.

jleonard said:

On those old Perkins engines, the starboard forward engine mount bolts are threaded thru into an oil gallery. A very common nuisance on those is leaking thru those bolts (actually they are studs).

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That's interesting. Either a last minute design compromise or some cool way of insuring the bolts don't seize to the block.

diver dave said:

That's interesting. Either a last minute design compromise or some cool way of insuring the bolts don't seize to the block.

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British engineering at it's finest. Actually only 2 of the 3 are affected.
Probably too difficult or impractical to blind drill/tap the holes. I can understand why they are drilled thru.
In my case, the engine was what was called a "CKD" engine which stands for Complete Knock Down. This means the engine came over the US in parts and was assembled locally, possible by Mainship or one of it's local suppliers. The purpose was to beat import duties.
Perhaps the "seal the bolt threads" operation was skipped. But since I bought the boat used I'll never know.

FF said:

If the dip stick sticks down in a tube that ends in the oil, be sure to check the oil level a couple of times .

The oil can climb up inside the tube giving a false reading.

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Also just the opposite can take place. When checking oil pull the stick and wait a few minutes especially with cold engine. It takes time for the oil to rise up inside the tube. If you don’t wait you can get a false low reading

Might be the same issue as some Lehmans, the dipstick is marked for use in a combine or tractor or some such, then its tipped back and stuck in a boat. This usually means the rear crank journals are submerged and the oil gets thrashed and consumed until the journals are not so deep anymore. Then the oil consumption stops. Try swapping dipsticks and see what you have? The next oil change, carefully measure the proper oil amount and see how the level compares with the dipstick. You might only have a measuring issue.

When one of my Perkins started using oil, I found that I had an oil cooler leak that passed oil through to the cooling raw water which was exiting the exhaust. It appeared as oily droplets in the water.

Changed the oil cooler and problem solved. Hope yours is as simple.

FlyWright said:

When one of my Perkins started using oil, I found that I had an oil cooler leak that passed oil through to the cooling raw water which was exiting the exhaust. It appeared as oily droplets in the water.

Changed the oil cooler and problem solved. Hope yours is as simple.

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Note that simple does not mean cheap!

kapnd said:

Note that simple does not mean cheap!

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In my case, they're $300 a piece. In boat terms, that ain't bad.

I know b/c I've gone through 3 of them in the last year due to wear (2) plus a 3rd loss due to a broken bracket that wore a groove into the outer case of one of the new ones. I'm getting pretty good at changing one out in about 30 mins.

Roger,

If you ever do injector service, be sure to check compression.
BTW, thanks for sharing the long run fuel consumption numbers.

If this is really bothering you, do a leak down compression test. That will allow you to isolate any issue to intake valve, exhaust valve or piston rings. It is nice to have a fancy differential pressure gauge to be able to compare cylinders, but just pressurizing the cylinders individually and listening for air leaks will tell you where the weak link may be.

I have a Perkins 6354 natural in my 1975 Defever passage maker and it used a lot of oil . I had the the head rebuilt and was told by a Perkins dealer to use straight 40 wt. oil. They said using multi grad could actually make your oil consumption worse.Doing this fixed my oil use almost to nothing. Good luck they are great engines .

"They said using multi grad could actually make your oil consumption worse."

Multi grade oil is very thin oil with a reversing flour like material that thickens it up with Enough heat.

Most displacement boats engines are at 1/2 power or less , the block thermostat may keep the water temp up, but not the oil temp.

In a car or truck the water may be 180-200 F and the oil will be at 240 or so.

This activates the thickening process , 180F may not.

Many of our antique engines are far happier with single weight oil.

IF Da Book (the maint manual) gives a choice , IMO , chose the single weight.