Ford Lehman 120 oil dipstick level.

Something to think about, especially those with one engine.

These new to me twins had different oil level marks on the sticks. One was scratched higher than the stamped full mark, otherwise they were the same, look original.

port engine stick is on starboard side, SB is on port side, so I dismissed it as a location thing at first.

I watch engine temp and oil pressure, sync by ear and tach.
What I observed was that SB with fill to stamped full mark would slowly have less pressure and temp would rise.

I added oil to the mark on the other stick. Now both are same pressure and temp. Running within spec range.

The tip I am passing on is think about this for your own and not just follow what the stick says. I know, fill with the recommended amount of oil and then mark the stick, I will next time. But if is lower than the scratch???

I ran twin 120s for almost three decades, and one of them was removed and rebuilt early on. The rebuilt one was done by a Lehman dealer in San Diego, and the dip stick was "indexed" after the engine was re-installed. The engine had zero oil in it when it went back in. The mechanic added the required amount of oil minus one quart and marked the stick. He added the last quart and marked the stick again. I pulled the other engine's stick and copied the marks, which because the engine was tilted aft, were lower than the factory level-on the-ground marks. BTW, the oil filter retains very little after shutdown.

I found over the years that the engines seemed to like to run at the low indexed mark. If I added to the full, the oil found it way into the drip pan. I never had oil in the drip pan when running a "quart low."

Rich, It is not one size fits all. You found your spot again not the stamped mark.

BTW, the oil filter retains very little after shutdown.
another difference, mine stay full as they are not inverted.

I found over the years that the engines seemed to like to run at the low indexed mark
To be clear the lower mark the mechanic marked, or the stamped mark. Sounds like you were running a quart low, whatever works.

Soo-Valley said:

BTW, the oil filter retains very little after shutdown.
another difference, mine stay full as they are not inverted.

I found over the years that the engines seemed to like to run at the low indexed mark
To be clear the lower mark the mechanic marked, or the stamped mark. Sounds like you were running a quart low, whatever works.

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Yes, indexed = mechanic's mark. Yup, very likely a quart low.

According to Bob Smith that is the way to figure out how to measure the oil, drain the oil, fill to low oil and mark the dipstick fill to the correct full amount of oil and mark the full on the dipstick. He said not to trust the dipstick as it came from the factory. When we got our current boat I would fill to the full mark each day and the oil would always be down the next day. After several days of filling to the full mark and the oil would be consistently low the next day I decided to run a day with the oil at the lower level. It never went any lower even after multiple days running without any refill. So I decided that was the level the engine liked and now I don’t top off the oil since it just goes out the exhaust apparently.

Comodave said:

According to Bob Smith that is the way to figure out how to measure the oil, drain the oil, fill to low oil and mark the dipstick fill to the correct full amount of oil and mark the full on the dipstick. He said not to trust the dipstick as it came from the factory. When we got our current boat I would fill to the full mark each day and the oil would always be down the next day. After several days of filling to the full mark and the oil would be consistently low the next day I decided to run a day with the oil at the lower level. It never went any lower even after multiple days running without any refill. So I decided that was the level the engine liked and now I don’t top off the oil since it just goes out the exhaust apparently.

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Engines DO talk to us; we don't always understand them the first time.

Yes, I figured out that it wanted the oil level at the lower end so that is where I always check for. I may be somewhat slow but eventually I get it...

After 5 hours running the oil level did not adjust as would be expected if overfilled. Of course more monitoring after more hours of operation but in my case the SB was running low due to a missing index like the port engine.
Both ran with same pressure and both had steady same temps.

These engines were originally used as generators and combine motors, where they worked just fine. They were not a success in trucks.

The original engines were mounted horizontally and the dipsticks were correctly marked. In our boats, they are tilted back and many dipsticks were not remarked.

I spoke to Bob Smith at a GB Rendezvous and Rich is correct, the only way to correctly fill the crankcase is to drain it and refill with the measured amount of oil (as per the manual) and then mark the dipstick.

Tilted back, the excess oil is splashed about by the number 6 conrod journal which vaporizes it and sends a lot of it out the breather which, depending upon your configuration, is sent back into the intake. If you fill to the proper level you will not "use" oil.

rgano said:

Yes, indexed = mechanic's mark. Yup, very likely a quart low.

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Perhaps I was not clear. The indexed mark on port engine was above the full mark, in fact it is a hair above the word 'FULL' I did not put it there. The SB is factory stamp. So they were getting filled to different level.

I will have to start a close watch/record any changes going forward this season to see where it settles.