I have a 2016 Suburban and had recently done a cam swap/DoD delete. I had finished up and when I was tuning it I noticed the knock retard kept kicking on infrequently at idle. I tried to listen to where it was coming from and it was from the front of the engine. I originally thought it was chain slap or a bad pump/pulley but after further investigation via stethoscope it is coming directly from the thermostat housing. I plan to replace the thermostat and hopefully fix the problem but I would like to know if anyone else had similar problems or other possibilities if this isn’t the problem.

 

I replaced the thermostat with no change, going to check under timing cover to see if there is any indication of chain slap. The reason I initially believed it was the water pump was because I had a high fluctuation of coolant in the reservoir at idle. I now realize it is probably due to the frequency of power spikes from the cam not being very consistent. If the timing chain is not the problem then I suppose I’ll be pulling the heads to inspect my valves and pistons.