Head gasket ??

[BLZN4FN]

Ok I should know this answer but i'm drawing a blank here. I just bought a 89k5 350 for 50 bucks.

It's blowing white smoke. I checked the oil and its full of antifreeze how do I tell which side headgasket is bad? I think I will replace both while i'm in there
but just want to figure which side is bad or maybe a bad block but cant remember how to check.

Also will a blown head gasket cause the engine to have a ruff idle?

 

[diesel4me]

Yup--

Do a compression or leakdown test...yes,a blown head gasket usually causes a rough idle,but so can spark plugs fouled with tranny fluid from a blown modulator valve,which also makes white smoke!..(if you have a 700R4 tranny,it has no modulator,so disregard that if you do!)..

It would be easy to tell which bank has the blown gasket if it has dual exhaust..but the spark plug will be super clean in the cylinder thats leaky,and will likely have prestone on it..

I've found a few bad head gaskets with a vacuum gauge,and others by watching for coolant to be blown out of the spark plug hole in the suspect cylinder..sometimes it'll blow between 2 cylinders,and both suffer compression loss..I've seen blocks eroded and rendered useless from the flame travelling between the 2 cylinders on a few motors..