Re: Cooling system K2500 What's normal?

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Posted by Frankenbiker ( on 23:16:54 03/01/08

In Reply to: Re: Cooling system K2500 What's normal? posted by Ben

: Assume the parts person gave you the right one. When they went from V-Belt to Serpentine belt, the pump rotation switched. I don't know HOW2 tell, but maybe someone can post. An arrow on the case would be too much to expect'm to do.

On the 350's, you could NOT tell the difference externally. The only way to tell was to open the thing up and look at the impeller. I suspect the big-blocks are the same way.

However, I thought that by 1999, the systems were ALL reverse rotation (ccw) pumps, so it wasn't an issue any more... was it? Were there still CW pumps running around in the refurb market?

It was a BIG issue in the transition years, 1988-1991, when many of the R/V series trucks still had V-belt drives, not serpentine drives.

One thing to check is whether or not your radiator cap is holding pressure correctly. It was never an issue on my Chevy, but my Freightliner likes a new cap every year as a maintenance item. It's extraordinarly sensitive to cap "tightness".

My '89 truck started having these kinds of problems after the water pump was replaced with either an incorrect rotation, or a "bidirectional" rotation pump was installed in it's place, without my knowledge. It was exacerbated by an unknown heavy rust problem. It eventually wound up killing the head gaskets because I could not for the life of me find the correct water pump without ordering online (an impossibility at the time).


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