Hello fellow truck guys and gals,
I hope someone can help me out. I have a 76 Bronco Sport with a 302 and C4. I've had the Bronco since last August and have put about 3,000 miles on it in that time. The previous owner only had the truck about 3 years and had taken it as payment for a debt, so he knew very little about it. Based on the idle, I believe that it has a mild cam in it. He told me that he knows the heads are from an earlier year (71?) because the spark plugs from a 76 didn't fit. The truck also has an Edelbrock Performer intake and 4 barrlel carb.

Under normal conditions, in town or on the highway, the truck runs at 190*F according to the factory temp gage. When I come to a stop, the truck maintains that temperature. When I turn the Bronco off, then turn the key back ON (so the gages work) the temperature quickly climbs all of the way to the peg on the hot side. If I start the truck with the temperature elevated above about 220*F on the gage, it is noticeably harder to start, and runs rough until the temperature comes back down to 190*F. The temp comes back down pretty quickly once the truck is running.
I have not flushed the cooling system, but the coolant looks to be in good shape; clean and green.

Am I damaging the truck by letting it get this hot?
What are the potential causes and solutions?

Thanks in advance for any thoughts.

Steve

 

It's normal for the coolant temp to climb when you shut off the engine (and the "temp" gage is measuring coolant temp, not engine temp). When the engine stops the water pump stops, so the coolant stops flowing through the engine and radiator. The engine (which is hotter than the coolant) keeps dumping heat into the coolant which can't get to the radiator to cool back off, so the coolant temp goes up. The temp sensor is in the intake manifold, at the top of the engine. Since heat rises, that will be the hottest place after the engine stops (until it's able to cool back down again). As long as you aren't boiling over when it "heat soaks" after shut-down I'd say it's normal and nothing to worry about.

The hard start and rough running on hot restarts might have nothing to do with the coolant temp, at least directly. I've had two carbureted Ford trucks, including my current '71 Bronco. Both of them would transfer a significant amount of heat to the carb when the engine was shut down. The fuel in the carb would expand and overflow out of the float bowl and down the throat. The engine would then essentially flood. On my Bronco I have an electric fuel pump with a shutoff switch. I can completely eliminate the hard hot starts if I shut off the fuel pump a little before the engine so the carb isn't full of gas.

By the way, adding heat to the coolant after shut-down does mean that if the engine is overheating while running (for instance if you are running a high load) you shouldn't shut it off to let it cool. If you do you will boil coolant as it heat soaks. A better bet is to let it idle, preferably facing into the wind, with the hood open. This will let everything cool down.

 

I have this exact same issue on my 1970 Bronco. (This is my second; I previously had a 74 that would run much longer before having this issue kick in, but same thing). You drive a bit, drives well, but once you make a stop, it will then hard start and bog down with decreased horsepower; almost like the timing is way off. This happened when I first got it, but has persisted even now after replacing many things (upgrading to headers, new radiator, water pump, fuel pump, 4 barrel, etc, etc.), but still same issue. I'm considering getting an additional electric fan that runs on temp and can stay on when parked, but I'm not sure this will do the trick. Wondering if @fyreduck1921 has found a solution?

 

bronks R notorious 4 under hood heat. The louvered inner fenders, hood scoops, ele thermo fans, even phenolic spacers under the carb or heat shields R all work around strategies some have used.
The concern would B 'wash down' where the gas penetrates down the cyl walls and removes oil so that there's no lube on start ups. Nonea dez sound that extreme.
I like the fan upgrade as it has multiple benies...

 

Put an elec ct stat controlled fan to stay running and shut off when is hits the temp you set.

 

I put an Edelbrock phenolic spacer between the carb and intake and that helped the hard starting and rough idle situations.

 

It's normal....................

 

not now, upgrade!:
"...which heat shields and/or spacers can significantly reduce."

 

Any engine, when the engine is shut off will see temps climb.......even if you have an e-fan running, the only temp that will effectively drop is in the radiator...... the coolant inside the engine and heater will take hours through conduction, to transfer out............ take an IR gun and check....it's just the law of latent heat transfer.....this does not damage any engine component but it can cause the fuel to get hot which heat shields and/or spacers can significantly reduce.