I have a 2002 1/2 ton 2wd 4.3L automatic with 50k miles.

There is noise at about 1500rpm that sounds similar to valve knock, but I ran some 93 octane fuel in it and it did not seem to change. I had a Chevy mechanic listen to it and he seems to think that it is the coolant circulating through the heater core, he said it is common with the 4.3L. He is probably right because it is louder when it is cold.

Has anyone else noticed this?

I've driven alot ofC1500s, but this is the first 6 cylinder I've ever owned.

 

coolant sounding like a valve knock?..I dunno...I'd have to hear it...

 

Actually valve knock isn't a good discription. It sounds more like pump cavatation. It was occurring at point when an engine would knock (lower rpm loading), that's why I thought it might be valve knock, and since the 4.3 apparently has roller rocker arms,maybe that's why it sounded different.

I've heard alot of different noises in a lot of V8 chevys/gmc, but this is a new one.

Thanks for the reply.

 

heater cores make "gurgling" noises...thats about it...if your gm guy heard it though,maybe he knows

 

I had this very same noise exactly as you describe it at the same RPM range. My truck was a 2000 silvy 4x4 with the 4.3. I tried everything to get rid of the noise. I even tried using 10w-30 instead of the reccomended 5w-30. The noise just got worse and happened more frequently hot or cold. After running it this way for about 6 months I noticed metal shavings in the oil. TRADED IT IN AND NEVER LOOKED BACK!!!!!!!!

Oh yeah my engine had only 62,000 miles on it.

 

I'm really don't think this noise is coming from the engine. At first I thought it was valve knock, but it's not consistant.

I took a vise grip and clamped the heater hose andit reduced the noise. I also bypassed the heater core and it reduced itmore, but it was still there, I really think it is turbulence within the engine coolant system. How or why who knows. The GM guy said the some of late 80's V8s alsomade that noise.