Do Not Overfill

[StephenSanchez]

Question:

When looking through threads about different crankcase oils I came across people writing "do not overfill" a lot. The only thing I really know about why to not overfill is that the oil can come up and shoot out through the dipstick holder. I also assume it could affect seals and gaskets, but I don't exactly know how or to what extent. Given the repetition of this warning/advice what are the other mechanical, technical, and/or performance problems that could arise if you overfill your crankcase?

Thanks

 

[ThreeJs]

besides the seals and gaskets possibly leaking you can aerate, foam up, the oil causing cavitation, reducing oil flow and reducing the lubrication qualities of the oil.

 

[StephenSanchez]

That's helpful. I didn't think of it but it makes absolute sense. Thanks. Not to be overly obsessional and detail-fixated but how much would you have to overfill to get that negative effect?

 

[bill06447]

The dipstick is an approximation-7 quarts in a 6 quart capacity pan won't be the end of the world, but generally try and add oil in quart increments, which should bring from the add line to the full line.

Bill

 

[koda2000]

there's also something called hydraulic lock. if you severely overfill an engine with oil it can prevent the pistons from moving up and down. this can even bend a connecting rod, although this condition is more common when you get water in the cylinders.

 

[masospaghetti]

Cavitation and the possibility of damaging your main seals are the two main reasons.

 

[SoNic67]

Aeration and foaming lead to all other ill effects. Aeration happens because of the crankshaft counter-weights slushing in the overfilled oil.

http://dspace.mit.edu/bitstream/handle/1721.1/38713/166145859.pdf

 

[StephenSanchez]

Thanks to everyone for your input. And what a great master's thesis that gal wrote!

 

[Flash]

I heard somewhere that if you're taking oxycontin for back pain there's a possibility that you might try to fill up the transmission through the oil dipstick hole which would overfill the engine.

I also heard that that will cause the engine to blow much, much more smoke than a seafoam treatment and cause a heavy knock that sounds like a main bearing.

I heard.