Engine knock after over heating. Only knocking  when under load. What could it be?


Asked by Feb 02, 2016 at 07:34 PM about the 1993 Chevrolet C/K 2500 Silverado Extended Cab SB 4WD

Question type: Maintenance & Repair

Engine knock after over heating. Only knocking 
when under load. What could it be?

My friend bought a truck from another friend of 
mine. Long story short he sold it because he blew 
a lower radiator hose and overheated and now it 
knocks when under load/accelerating. It doesn't 
knock if it's parked and you revv it or if it's in 
neutral and you revv it. Only happens while driving. 
The friend that bought it has another motor to put 
in if he has to. But we want to see if we can fix this 
one first. What could the problem be? Thanks in 

2 Answers


Is the check engine or service engine soon light on while it's knocking? I'm thinking it's the knock sensor. On some GMs the knock sensor(s) screw into the cooling jacket. If the truck was overheated it may have damaged the knock sensor. The knock sensor listens for spark/knock and retards the ignition timing until the spark/knock stops. If the knock sensor is damaged and not "hearing" the spark/knock it won't retard the ignition timing and the engine will continue to knock. Spark/knock will usually only occur under load. You may be able to test this theory by filling up one time with premium gasoline. If the knocking stops or is not as bad, there you go. It's probably going to be the knock sensor. Some engines use 2. If yours does, replace them both. Also inspect the wiring going to the knock sensor(s). Make sure they didn't get burned or otherwise damaged by the overheating. HTH. -Jim

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Andrew Olsen

Or you blew up the motor. If you overheated it enough to damage the knock sensor then you defiantly ruined the engine. It would have to be on fire.

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