Hey all. I was just gifted a 98 K2500 7.4L.
It has this strange dull knocking sound at all speeds, even stopped. I cannot figure out where it's coming from. It obviously is coming from the front of the car, but thats as much as I can figure out. The really weird thing is that the rate of knock is constant at all speeds. It's random, its not even or smooth. It is a low, dull knock. Does not sound anything like valves or piston (I've had both).

Also the engine temp will not go over say 120 or so. What is the normal engine temp on these? I know the previous owner just had the water pump and radiator replaced, is it possible they screwed up the thermostat?

 

Welcome to the forum.

The low temp could be either a bad thermostat or temp sender. I'd check t-stat first.

The knocking sound is constant and doesn't change w/ engine rpm?

 

Ill check the t-stat. Thanks.

Yes, the knock is more or less constant. Its not always there, but it does NOT change with RPM.

 

yeah t-stat or sending unit... might try to verify engine temp if you got a thermometer.

as for the noise, doe it do it at idle? does it only do it under load? I know you say stopped but I guess I'm wondering if it's doing it in park or neutral.

with it staying the same speed regardless of RPM seems odd.

 

It does it regardless of it being in neutral or drive. Sometimes. Sometimes I drop it into neutral and it stops. Does not matter if under load or not.

Im going to pull it into my garage and just start going over it with a fine tooth comb. It needs a tune up bad, no idea when the plugs or wires were last changed. It does idle a little rough but I was told that it was normal for these engines. I was also thinking maybe a loose transmission or engine mount? But I would think it would sound different depending on situation.

I know the transmission was replaced a couple of years ago, maybe the torque converter bolts are loose? I would think it would be a more constant sound if that was is.