Oil drain assembly question - trying to fix leak

timsch said:
No leaks around the drain valve, or anywhere else. However, I noticed today after mowing a heavy film of oil residue on the engine cover coming from what must be the oil dipstick cap.

So, I've got pressure in the crankcase. I hope that's not as bad as it seems it could be. It starts easily enough and runs well....
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Of course there is excess pressure. When the crankcase is not sealed ie dipstick not sealed, every time the pistons moves up and down it can suck in excess air and then blows it back out along with some oil. To prove this just leave the dipstick out and start the engine if really see a mess. Or operate a sink plunger and how pushing it down creates pressure and then a vacuum as you pull it back up.

Even when the engine is sealed up there will be both pressure and vacuum pulse thus this why vacuum fuel pumps works. Of course when the engine sealed these fairly close to zero as crankcase valve vents any excess pressure then closes creating a vacuum.
 
Hmmm... I've got plenty of older vehicles that have dipsticks that don't seal and those don't seem to have this issue.
 
there are three pages to re-read so I will just comment. The way to use the dye is to clean the area off completely with some brake cleaner etc., and maybe even the pressure washer. Then add the dye to the oil and run it for a couple minutes. Inspect. If nothing, run it again a little longer. The idea is that the dye makes it very easy to see where the leak is. The dye will be visible long before you can see an oil drip.

Excessive blowby can be caused by bad valve guides, a blown head gasket between the head and a passage leading to oil, or worn rings. Even a cracked piston. However the pressure can also be caused by bad timing, or a blocked breather hose. Wrong timing can cause excessive crankcase pressure, and a blocked breather hose forces the engine to find other ways to vent crankcase fumes. Gasoline in the oil can also boil off, so can water, causing excess pressure.
 
sgkent said:
Excessive blowby can be caused by bad valve guides, a blown head gasket between the head and a passage leading to oil, or worn rings. Even a cracked piston. However the pressure can also be caused by bad timing, or a blocked breather hose. Wrong timing can cause excessive crankcase pressure, and a blocked breather hose forces the engine to find other ways to vent crankcase fumes. Gasoline in the oil can also boil off, so can water, causing excess pressure.
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Thanks. If it is excessive, which I'll have to look into how to check that, I hope it is a blocked breather hose. It runs too well otherwise for me to think about tearing into the engine for all of those other possibilities.
 
A new dipstick should come with the O-ring already in place under the lid.

If you had a block breather, the entire engine would be an oily mess because oil would be forced past every seal and gasket
 
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