Blowby or not Blowby

[edrrt]

I took the filler cap off a 80hp Yanmar at low idle and could feel very strong puff/puff/puff against my hand. When I covered the hole with my hand there was not pressure though. In fact it seemed to be sucking on my hand gently. No gas forces past my palm. But if I lift the hand up the puffs are there. If I go to high idle I can not percieve the puffs anymore. No mist or smoke. Nothing splashing up the dipstick. Seems to run really well.

A mechanic recently went through the machine and told me there was no blowby. So whats this puffing at low idle? Is it just the eb and flow of the air in the crank case due to the piston travel?

 

[Scrub Puller]

Yair . . .

Is it just the eb and flow of the air in the crank case due to the piston travel?

Yup.

Cheers.

 

[Delmer]

Yuppers, look for blowby at the vent tube, and don't be concerned if you can see some mist when it's cold. As the manuals say "blowby is a subjective measure".

 

[John C.]

You didn't say how old the engine was or if it has a turbo charger. Lots of those engines have positive crankcase ventilation now days and that can make a difference in what you are describing. If it has a turbo it likely won't have PCV installed.

 

[edrrt]

You didn't say how old the engine was or if it has a turbo charger. Lots of those engines have positive crankcase ventilation now days and that can make a difference in what you are describing. If it has a turbo it likely won't have PCV installed.

2005, no turbo.