Any mechanics know why gen 4 Prius (and other models) have tons of blowby from oil cap?

Hm, thoughts but no replies. I'm not a mechanic, and I don't play one on TV. I might be able to tell you what it isn't. The Prius engine is an Atkinson cycle which allows some of the compression stroke to vent back into the intake manifold. That would (should) not affect pressures inside the engine. The engine itself has a rather high compression ratio, like 13:1. My thinking is high compression and excessive blow-by are mutually exclusive. The cylinder timing 1-3-4-2 should even out any interior volume changes, something you would see in any engine with an even number of cylinders. I can't think of any other source, other than the proposed leakage past the piston rings. I guess the next logical step would be to analyze the gas escaping at the oil cap for exhaust components.

 

The PCV is what draws vapors out of the engine and into the intake manifold. But the PCV only works when there is a pressure drop across it. Maybe this combined with the momentary loss of vacuum when regurgitating air is what causes the pulsing you are noticing.

 

Please let me know when your find a car engine that doesn't spray an oil cloud out or an uncapped oil fill hole while running.

 

Vvillovv has two typos in his post. I think it should be "Please let me know when you find a car engine that doesn't spray an oil cloud out of an uncapped oil fill hole while running."

 

No. He is saying that all cars are like that.