Hello,
I was showing my car to some one to sell, and while he was looking at the engine bay, he opened the oil fill cap and held his hand over it. First of all, I did not know you could open that cap while the engine is running, I always thought that it will spray hot engine oil over you... Anyhow, he held his hand there, and then said, " oh... this is not good" and then when I asked him about it, he explained that that air blowing out of that hole is called a "blow-by". He said that that is an indication that the engine has lived its life and is about to die... the rings have worn out too much, and that stream of air coming out is a sizable leakage.

I did not know what to say, I had never heard that term before. But after Googling it for a little bit, I figured that it could also mean the PCV valve is plugged and needs to be replaced. Of course, I have no means to quantify the air flowing out of the fill hole, but the question is how serious is this? and was he telling me half-truth to get me to go down on the price of the car?

 

I don't think that his test was definitive. I never did that test on my 95, so I don't know if that is normal.

A compression test would give you some idea of an engine problem, if one cylinder was much lower than the others, or all cylinders were too low.

A leak-down test is much more informative on the engine's condition. That test would help identify the percentage of compression loss and the location of leakage in each cylinder (intake valve, exhaust valve, head gasket, or piston rings).

 

It reminds me of many years ago, I was selling my Civic GL (great car) had a guy look at it, he started the car, revved it up a bunch of times, turned to me and said "Oh, the engine is stringing, I'm not interested in it".

I was thinking... "what is he talking about?" Never heard the term before or since.

Sometimes guys are their own worst enemy.

 

You'll feel some of that (at the oil cap) regardless of blowby. As the pistons move up & down, the crankcase pressure pulsates up & down. You'll feel the pulses flowing out of the oil cap, but you won't feel the pulses sucking in. So even if the net is zero, it still feels like it's blowing air out.

Is there oil from the crankcase getting into the intake duct - through the crankcase breather tube? That would indicate more blowby than the PCV system can handle.

But a compression test is the proper way...

 

Im laughing at this chumps ploy. He's full of crap! Just be sure your pcv is working and your oil level is good. Its Ok to take cap off while idleing . But next time just slap his hand and say I Don't want you stringing my engine or just make up your own crap that sounds confusing. LOL