Having no thermostat can be worse than a bad one as far as overheating is concerned, but, heating under load is more often a sign of a partially plugged radiator. Have the radiator "flow tested" at a reputable radiator shop. Sometimes the radiator can be rodded out, but for trailer towing I would install the biggest new radiator that can fit.

Eric

Glen Cymbalist wrote:

> Rich,
> I think you just solved a problem our old Chevy ('76 400CID) wagon has.
>
> A couple summers ago, I installed a new 180 thermostat in it. This
> thermostat is supposed to be for trailer towing. It has an opening about
> 30% larger than a normal one.
> Last summer cruising at 60mph, 90 degree weather, with AC on, and no
> trailer, the temp guage would slowly start climbing up to 210-215 degrees.
> If I slowed down, the temp would drop to about 190 degrees.
>
> Could it be this "extra flow" thermostat allows the hot coolant through
> the radiator too fast? ie.: doesn't allow it to cool at higher speeds?
>
> Glen Cymbalist
>
> On Mon, 1 Feb 1999, Rich Walbridge wrote:
>
> > In later years, when towing the Airstream, the coolant didn't get a
> > chance to cool off in the radiator because the thermostat would open at 160
> > and call for coolant from the radiator which hadn't had the opportunity to
> > cool off. So, I went back to the 210. Never overheated once!
> >
> > With the 160 thermostat, I would get heat pretty quick-but it wasn't
> > really hot like it gets with the 210. But you have to wait a bit longer
> > for the heater to give off some of that heat on the colder days.
> >
> > My guess Melissa: is that there is a thermostat problem. Could be that
> > the gauge is in trouble too.
> >
> > I had a 1969 428cu" Mustang that had a cooling problem. It had a stuck
> > thermostat. When we took out the thermostat to let it run without it, it
> > overheated very quickly because the coolant was being pumped too fast
> > throughout the system and never cooled in the radiator.
> >
> > Rich Walbridge
> > WBCCI#3371
> > '73 Excella 500