John Deere 318 Engine oil level

[thelonepatriot]

When I check the engine oil level it nearly always reads about 3 inches above the full mark. It doesn't seem to matter if it has set for a few minutes or a few days. After I remove and reinstall the dipstick It will give me the actual reading. Is there a plugged vent somewhere that would cause this or is it normal? The tractor is a 1988 model.

 

[wore out]

When I check the engine oil level it nearly always reads about 3 inches above the full mark. It doesn't seem to matter if it has set for a few minutes or a few days. After I remove and reinstall the dipstick It will give me the actual reading. Is there a plugged vent somewhere that would cause this or is it normal? The tractor is a 1988 model.

It's an Onan quirk and completely normal.

Oil works it's way up the tube when the engine is in operation and gets "vacuum locked" up there.

Loosen the dipstick to allow air in and the oil to drop to the level in the crankcase (as you've discovered) wait a couple of minutes and check the oil as you normally would.

I have wondered if replacing the O-ring on the dipstick "plug" would help, but I have never tried that. One would ASSUME that if it was leaking crankcase vapors OUTWARD, allowing the oil column to rise it would allow air back in after shutdown so the oil level would drop, but that doesn't seem to be the case.

 

[T.R.K.]

Lots of small engines give an over-full reading if you just 'pull' the dipstick. Wipe the dipstick off and then check.
Also, the dipstcks in some engines are bead blasted or have something done to them to roughen up the finish and if the mower has just run, the oil will look much higher on the dipstick than what is actually in the crankcase.
Please note, on Kawasaki and Honda, you don't screw the cap down to determine the oil level. On the larger engines it makes about 4 oz. difference in the amount of oil actually in there.