I've seen this behavior before. Guess what it was? A plugged radiator. It flows enough coolant to keep the engine cool at slower speeds, but can't flow enough to cool the engine at highway speeds. It's either that or your lower radiator hose is collapsing.
Good luck,
-Mitch
> Date: Mon, 10 Jul 2000 18:20:46 EDT
> From: ABeerCan@aol.com
> Subject: DML: Truck running hot
>
> OK, this is kinda weird. I know that usually when an auto acts up like mine
> is, then it runs just fine on the interstate or when moving along, but heats
> up when stopped at a red light. Mine is just bass-ackwards as it can be. In
> town it is fine, on the interstate, after about 4 or 5 miles, it starts to
> warm up. I just changed the t-stat, it is a 180. Water pump is new, along
> with hoses and a large three row radiator. I run 65/45 prestone/water.
> After it gets hot, like around 215 to 220, I turn off the ac, drive about 5
> more miles and it cools back down. Then it is just fine unless I get down on
> it. The oil is clean Mobil 1, the coolant doesn't show any signs of oil, so
> I believe the head gaskets are fine. Any ideas? It has been fine the past
> three summers since I hopped up the V-6 in it. Thanks for any help.
>
> Will
> Cylindrically Challenged V-6
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