5.0 Overheating Under Load
 

Hi
I have a question that I hope someone will have an answer
I recently took advantage of a clear & cold sunny day to give my, new to me, 83 Mustang a good highway run before putting her into the stable for the winter. While on the run I noticed that while running on the recently repaired Cruise Control in 5th gear going up a steep or long hill the engine temperature began to climb on the temperature gauge to high and when after breaking the crest of the hill the temperature would go back to normal. At the time I was driving at 110km/hr, engine RPM was 2000 - 2100, the outside air temperature was +3 deg C and the cabin heater was throwing lots of heat. There also seemed to be no loss of oil pressure, another possible indicator of excessive heat in the cylinder block

Where this is the first car I have ever owned or driven with the 5.0 engine, 4 barrel carburetor, 5 speed manual transmission and the first time I've driven the car on the highway with a now functioning cruise control. Is it normal to have the water temperature to rise and spike like this with the engine under load going up hill?

The car has a relatively new 4 row aluminum rad (installed in 2017), it looks like the thermostat has been changed at sometime in the past, and there is no indication that there is an issue with what looks like to be the original water pump (shaft movement or seal leakage).

I also checked the function of the thermostat with a heat gun on the cylinder block closer to the thermostat housing. The thermostat seems to be opening around 90 Deg C or 195 Deg F and maintaining at temperature of 94 - 95 Deg C or 202 - 205 Deg F.

My questions are the following
Should I consider replacing the thermostat with a 180 Deg Thermostat?
Where the Cruise Control will pull the throttle wide open in order to maintain speed going uphill. Will the Cruise Control pulling the throttle enough to open all 4 barrels on the carburetor dumping extra fuel, at a relatively low RPM to maintain the set speed cause this overheating? Is there any way to adjust the throttle or the carburetor linkage to prevent this from happening without sacrificing performance?
note: Prior to fixing the cruise I never experienced any kind of overheating issues when driving up hills in 5th gear while manually controlling the throttle to maintain speed in summertime conditions.

Should I change my driving habits to not use the cruise and drop a gear when going up a hill?
Should I be looking deeper like checking for a cracked or blown head gasket or could this be just a bad temperature sensor?

Thanks

A couple of things: The thermostat is factory set at 195 F. That's OK. Check your coolant level. Could be a tired water pump, impeller rusted, slipping,(won't show up without removing pump) belt slipping. Are the rad fans working? Could be as simple as a bad rad cap, not building enough pressure.
If it was a head gasket you would get water vapour in the exhaust(White smoke) or coolant in the oil, (milky oil) or bubbles and over pressure in the cooling system.
You should be able to drive the car without concern if everything is OK. Get the cooling system pressure checked for leaks, including the rad cap. Go from there. If the water pump is original, I'd change it. (35 years old!) Could be the temperature sensor, but it doesn't sound like it off the get go. Good luck.

PS I got my 08 Bullit from Dartmouth NS.

Thanks for your response
Quite frankly I never even thought of a bad radiator cap and I should have considering a gentle squeeze on the top rad hose with the engine cold & stopped air could be heard bubbling in the overflow tank. I checked the cap and the rubber valve disk on the cap was hard, badly grooved and cracked. The seat inside the rad is not damaged so a new cap is definitely in order
I also agree that, because of its age, the water pump probably should also be changed. I did do a stethoscope ( actually a very long screwdriver) noise check on the pump and everything sounded pretty good, nothing rattling or a lot of cavitation noise. I know sound check doesn't prove much but a loose or damaged impeller is easy to detect sometimes.

Did you have your Bullit shipped from Dartmouth or did you come down and get it? If you came down I hope you had a chance to sample some fine East Coast Food, Drink and hospitality while you were here

I bought it from Carson exports and had it shipped by Mackie Transport. They were both awesome, and the car arrived in mint condition. All original with 30 K, never seen winter, stored indoors in the off season.

Took the Rad Cap to the local Ford Dealer to check the Part #. It dated back to the 80's and is no longer current so the cap could possibly be the original. Definitely time for a change but will hold on to it as a souvenir