When my Z-28 heats up for about 20 min. It smokes pretty bad. It doesn't smoke on start up, and the smoke is white. So i'm guessing it is blow by since ZZ4 uses low tension oil rings anyways. I'm gonna change rings in the spring or summer, among other things. But i'm using 10W-40 oil now, you think 20W-50 will stop the smoking (blow by) for now?

 

Pull the pcv after you get it warmed up..
does it look like you got a fire in there?

If yes, run a leakdown test.

 

white smoke is coolant, not oil, youve probley got a blown head gasket, start the car and look in the radator cap, if its bubbleing you forsure have a blown gasket. and if no bubble look to see if the coolant is going down and look at the dipstick to see if any in the oil, it will be pretty runny if its in there.

 

oh you'll have to let the car warm up first to get it circulating threw the system before looking for the bubbles, just let it idle with the cap off untill its warmed up then look

 

Agreed, white smoke = coolant. Since it doesn't happen right away, you probably have a crack that is opening up as the engine warms up. I'd suspect head first, rather than a gasket.

Has it ever overheated on you?

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No the car has never overheated that I know of. The reason I think it might be blowby. When your giving it a little gas like backing it in it will smoke pretty bad, but just at idle it just smokes a little, again when warmed up. And I noticed one of the plugs always has oil on it, well what I think is oil. I think my best bet is to run a leakdown and compression test, would that tell if the head, or gasket is cracked too?

 

yes it will a leakdown test is great, run it and look at the radiator, bubbles and its a blown gasket.