nzi95001

I have my suspicions but wanted to see what everyone thought. 2003 Suburban 5.3L Vortec at highway speeds once engine has been running for some time and I step on gas/increase load on engine I get code p300 multiple misfires and the truck runs terrible after that with a squeaking noise coming from the engine (it's not a belt). I attached a short clip of the sound. I am also losing coolant slowly (about 1/2-1 gallon every 750 miles or so). I cannot find any evidence of a coolant leak (I did the dye but not a pressure test). I also changed the coils, and the plugs/wires are fairly new. Not sure the two issues are related, but my hunch is they are. After the engine has cooled down everything seems to run great again. Please any thoughts appreciated!

V12TT

My thoughts: You have a bad radiator.
Check your transmission fluid level to see if it's overfilled.

nzi95001

I'm not sure, there's no evidence of leaks/no coolant on the ground and the noise is a loud clacking which dies down to a squeak after a while. It's the same frequency as the engine RPM. I'm wondering if coolant was seeping into the combustion chamber if it could cause this?

V12TT

Oh. If there are sounds in the engine then that might be it. It's also possible that you have a small leak on the water pump. It will be squeaky if coolant get to the serpentine belt and burned off. I guess it's depending on where the sound comes from.

kevinkpk

Does this water pump have a weep hole?

V12TT

Also, is there a way to test for coolant in the oil like a test strips or something similar?

nzi95001

Yes it has a weep hole. I put it in myself 3-4 years ago. I don't see any coolant leaking from it and even did the dye but no evidence it has been leaking.