Hmmm.... When you replaced the thermo, did you flush and clean the system? If not, perhaps some more, what did you call it, "bits jammed in it..."

Otherwise, I would have to suspect the new thermo as questionable. I am not aware if the 6cyl engines utilize a bypass arrangement for water flow like the V8's, so ambient temp may have a greater affect on the 6cyls.

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RM Smith
1988 560SL

"Where is it again that we are going, and why are we in this handbasket"?