on the 300D. After reading/thinking about this thread for awhile I got out there and started nosing around under the hood. What I found was that if I opened the reservoir cap and squeezed the top radiator hose it actually felt and gave indications that it had air in it. In addition, I did not have the reservoir up to the "full" line and looking closely it seemed the top radiator hose was higher than the coolent level that I was running in the reservoir. I topped the reservoir up to the full line, squeezed the top hose alot to insure that it was full of coolant and now when it cools off there is absolutely no pressure in the reservoir just like some of you suggested on a properly working system. Oh yea, my aux water pump does not leak anymore either.

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Jim