How tightly sealed should the dipstick be?

I recently replaced the o-ring on my dipstick. It doesn’t really seal very tightly. It got me wondering; does the dipstick o-ring need to seal against pressure/vacuum?

Until I changed the o-ring, I had never really thought about this deep erudite topic before.

 

It's a light seal. The oil is actually doing the job. At the bottom of the tube where it inserts into the block/pan volume there's another tube the runs into the oil reservoir, it does two things. Provides a stable area to read the oil level from without splashing etc... And a column of oil that blocks air from moving in/out of the crankcase.

TLDR... The tube is effectively submerged in the oil so the seal isn't very tight at the top.

 

Excellent explanation. I never thought of it like that and it makes perfect sense.

 

You should see the mess when pukes!
Had an engine that the injector stuck open... Killed the seal on the rings, boost pressurized the case real fast... POP! And puke... Rebuild time! Ahhh Dyno stories...

 

Usually a little of both at different times -- as the column of oil in the tube that SMG mentioned will fluctuate up and down dynamically with the oil level in the sump during driving/cornering/going over bumps/etc.. Are you having a problem with the dipstick popping up out of the tube, or just wondering about a mystery of the Universe?

 

I am just pondering the universe.

The long version of my question comes from returning home from the Virginia City Hill Climb and discovering that half of the aluminum dipstick handle below the o-ring had broken off and (gulp) fallen into the oil pan. I don't know if it broke 100 miles ago or 700 miles ago. I have a vague recollection of something seeming weird when I checked the oil at the hill climb. I have an oil pan gasket arriving next week to begin the treasure hunt. Anyhoo ... I already got a used replacement dipstick (the used dipstick vendor, who shall remain nameless, forgot to ship a gasket) and when I stuck it in the hole its petrified o-ring was so tight it only went in with a shove. It got me wondering if it was supposed to be like that.

 

I must be the winner of some sort of freak incident contest. Image Unavailable, Please Login

 

You must have pissed off some gods somewhere in order for your dip stick to fall into the oil pan. That is actually a curse I use on people.

 

That is pretty unusual/bizarre, but I wouldn't worry about it too much -- plenty of 3.0L and 3.2L engines running OK with a cam cap nut, or washer, down in the sump .

 

Found a crescent wrench in an oil pan once...