Hello,

My stock L98 is making some strange noises,

when warm (close to 220 on the gauge) and sitting for a period, the engine will begin to randomly knock, at different intervals, and not with RPM. its relatively loud, since people next to my car can sometimes hear it. my oil seems fine, and doesn't appear to have any metal flakes and such in it. However when the car is off it can sometimes still make this noise, (though is subsides), it is not dieseling btw.

Also my radiator cap has been hissing lately, usually in the same trips as the knocks it will hiss as if releasing air, under pressure though.I can't tell if its actually on the cap or elsewhere on the Radiator. I think its air because in the Coolant bottle many bubbles will appear after with the noise and the engine being off. What is going on? is this really a rod knock? some other knock? radiator cap on the fritz?
any help would be appreciated.

 

Predetonation ? (Timing) lean running condition
Exhaust leak ?
Rod knock ?
Connecting rod bearing ?

 

Sounds like it's over heating, check to see that it's full of coolant and the system is functioning normally. Check the radiator cap, it may not be pressurizing the system, which would allow it to boil off at too low a temperature. Make sure the thermostat is not stuck closed. Worse case scenario, it could be a blown head gasket, blowing compression into the system.