Engine Temperature Fluctuates , Roadmaster

He did say it smells hot at times when the temperature is up. That leaves out just a bad sending unit wire.
I've had cars run hotter on the highway also. Still could be the fan clutch or water pump. We still think it's the thermostat. We've driven on the highway with no fan.
Remember at slow speeds a restricted thermostat is letting less water thru but the engine needs less to keep cool. At high speeds a restricted thermostat is still restricting water but needs more cooling.

 

Fan clutches can fail and cause your symptoms No mention of air temps when this happened. High speeds don't cool a motor working hard to maintain that speed without a fan and good radiator. I've never had a thermostat cause this for they usually stick open or closed.

 

The two cars I remember driving with no fan at highway speeds were both 350 Chevys in old cars. My 55 Chevy wagon with mechanical fan only, no clutch, broke a belt and I drove with our car club at least 50 miles to the nearest town to get a new belt. It ran cool until I stopped at NAPA, and this was Florida in summer.
The other identical drive train and same type radiator was my yellow 1941 Ford. Yes it has a 57 Chevy desert cooler radiator. I drove it probably 50 miles to a car show and it didn't get hot until I got in the line to register.
My son has driven several cars with no belt or fan and never had heat problems until slowing down.
So we feel under normal conditions an engine will cool without a fan while driving if everything else is in good shape. After all, that's the principal of the clutch fan made to slip.
That leaves a plugged radiator, not likely if it is cooling in city driving, or a bad thermostat or water pump.

 

The fact is, cooling at speed is done from ramming air through the radiator. The clutch, on cars equipped with one, disengages from centrifugal force on the fluid inside. Now, t-stats can open only partway, and that's caused by the wax pellet inside partially melting, so it doesn't push as far. This is what I think is wrong with her car's t-stat.

 

I agree. We shall soon find out.

 

fixed, pretty sure

I replaced the thermostat today, very easy. I used a Stant Superstat 180' , their upgraded thermostat and a premium gasket. The old one was a 195', maybe OE? I also took the opportunity the change the air filter element to a K&N. I tested for leaks in the driveway and with none spotted geared up and went to check the surf. This is a 20 minute interstate ride each way. I still got minor fluctuations but it never went into the red zone and fluctuated at a slower rate. The temp did not stay rock steady but varied in a smaller safe zone. So I am calling it fixed and will keep an eye on it for now

 

Good luck on a job well done. Ain't it great we can still check out the surf while those other poor people shovel snow?

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Warmer

thanks, it was good to fix my wagon. The surf was too small to ride, sunny and calm winds but real cold air temps. No snow here, for this I am thankful, looks like a warm day down in Florida.

 

Not really. That photo is a few weeks old. Our birdbath was frozen solid and it's been under 50 degrees all day. Warm again next week.

 

Cold

It got up to 35' for today's high, about 20 degrees colder then normal. With a new high tech wetsuit, no air or water temp is too cold. Last winter I went surfing in 37' water and 38' air temp and was warm. It was a sunny day and light winds, you get a lot of solar gain when wearing a black wetsuit. My Roadmaster is getting well known to the local surfers. The third row seat Is perfect of changing into a wetsuit.

 

When they make wet suits with heaters maybe I'll go in in 37 degree temps.

We live near a lot of 72 degree springs and I discovered that's too cold.
However we have swam at Christmas and Thanksgiving in the ocean. I was younger and dumber back then when we first moved to Florida.