GMC Repair: engine problems, blown head gasket, radiator cap

Question
I have a 97 chevy truck with a 350 motor.  When I give it gas there is a knocking sound but when I have it at idle it sounds normal.  Also when I maitain speed limits it sounds normal too.  And white smoke comes out of the driver side exhaust.  I think its a valve.  

Answer
Greg,

Valve ?. Possible.

Blown head gasket ?. Most probable.

Want to know for SURE ?.

1. Perform a compression test on ALL cylinders.

2. Perform a compression leakage test on ALL cylinders.

3. Run a cooling system pressure tset.


QUESTION: Can you see bubbles in the radiator cap area when the radiator cap is removed and the engine is at normal operating temp ?.

CAUTION: Be CAREFUL as NOT to get BURNED by HOT COOLANT when removing the radiator cap.

let me know.


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