My Big block engine seems to be running hot. When stopped at a red light the temperature guage will go up to around 220 and the car will start to run rough. At other times it seems to run around 200 and that seems to be high because it will start to run differently then as well. I have made sure that there is enough anti freeze in the system and have changed the thermostat twice. The most recent Thermostat I purchased was a 180 degree thermostat. I have purchased a new radiator cap and run a cleaner through the radiator to ensure it is not stopped up. It is a 4 row radiator and a flex fan so it should be able to keep the car cool. Interestingly, the fluids have never gotten so hot that they boil out of the radiator nor has it ever seemed to be overly hot when we have opened the cap. Yesterday was the last day we worked on it and we let it idle for approximately an hour. The temperature guage slowly went up to around 205 and stayed there. The car did begin the run differently around 190/200. At no time during this trial did the temperature fall but it did seem to stay between 200 and 205 for a very long time. I revved the engine several times and the temperature would increase slightly but not much. I also opened and closed the hood a few times to see if that caused a change. It didn't. I tried turning the AC on Cold and Hot to see if that made a change but it didn't.

Does anyone have any ideas what could be going on?

 

,, check for glazed or loose belts first ,, test your cap pressure,, then maybe a flush

 

Fuel boiling? 190/200 shouldnt be hot enough to cause any issues. I never had true vapor lock, but at red lights in the summer my temps would get uo around 200, and the engine would start running rough. An extra thick carb to manifold gasket fixed the problem. I have an edlebrock so i went with an eddy square bore 1/4 inch gasket

 

Post pics of flex fan and shrouding and inside radiator tubes..
what is timing set to?

 

Check your timing, set it for 36 total, and verify you end up with initial in the mid-teen range. Make sure you have an operational vacuum advance, and hook it up to manifold vacuum so you end up with actual timing at idle around 28-30 degrees. This is imperative for a cool-running engine at idle and low speed operations.

Running a flex-fan is a horrible idea, and is not helping your problem. Install the stock fan with the clutch.

Lars

 

Add some redline Water Wetter.Chit works. Any auto parts warehouse will have it

 

The factory never used "Water Wetter" or any magic snake oil ingredients to make these cars operate at normal operating temperature. All you have to do is tune the car correctly and get rid of all the junk, inappropriate parts that have been installed and make the car operate correctly. These cars were production vehicles, designed to operate flawlessly in Phoenix in the summertime with the A/C turned on in traffic. Once you fix the problems, the car will not overheat.

Lars

 

Your '74 LS-4 came with a 195°F thermostat. From my compilation research below, GM indicated that a 195° stat was fully open by 227°F. I don't think 220° would be considered overheating by GM's design parameters when the thermostat wasn't fully open yet.

 

Have to agree, chevy running at 200 - 205 does NOT constitute overheating.
But also agree with Lars , loose that horrible flex fan!

 

Thanks. I will try to work on it more today and tomorrow and let you know how it goes. The flex fan came with the car I had no idea it was inferior to a clutch fan. Had read just the opposite.

 

Not overheating.

Water boiling point is 212F, at 15 psi that boiling point is increased to 249.8F. A 50/50 mix of water and antifreeze will add 11F buffer to those number so in reality when the car pukes out the overflow the water temp is 260F or higher.

 

I am and have been using a 70/30 combination in my high compression (HOT Running) 427 and this combination works better than 50/50 because the anti-freeze in not as good as water is in transferring heat out of the radiator. I would like to run 100% distilled water in my system if there was no chance of freezing. 100% water and a bottle of Water Wetter would be even better. The higher the concentration of anti-freeze the hotter the engine will run so I intentionally use as little anti-freeze as needed. In the Northern areas you might need the freeze protection but where I live we don't so why handicap the cooling system? Running 100% water is not a practical idea as your water pump needs lubrication as well. Anti-freeze does provide some lubrication which is good for a long lasting water pump.

Lars is right about GM not using water wetter or anything because the stock engines could handle the heat they generated with their cooling systems in good working condition. Over the years the seals and gaskets around the radiator get worn and no longer seal the radiator system to ensure that most of the air is going through the radiator instead of getting pulled around it. The factory Fan with the thermal clutch and a good shroud go far to keeping your engine cooler. If the radiator seals are kept in good condition and the other parts work then the original cooling system is sufficient for most cars. I saw a guy with a car that was overheating that had more than 80% anti-freeze in it as every time it leaked he just added more anti-freeze. I was so happy when they started selling the anti-freeze in the pre-mixed configuration as this really helps some people.

Many problems arise when people without the expertise of the GM engineers start making modifications to these engines cooling systems. When people get rid of the thermal clutch and start making changes to look "cooler" then problems can start. A Flex fan can pull more air if used with the shroud that came on the engine. When the shroud is gone and a Flex fan is there you have the perfect settings for an overly hot running engine. The Thermal clutches work very well and can last a long time with a good factory fan. Frequently people remove the factory shrouds and change fans and then problems start. The fancy flex fans are neat looking and come with all colors and shaped blades and many of them are installed to make the engine compartment look better/cleaner. They might use less power than the thermal clutch did but they don't operate as well as a factory designed cooling system with it's solid fan. I have a feeling that many of the high temperature running problems are owner induced at times by trying to improve on the "original design".

A majority of problems we see are because someone has "modified" the cooling system or do not have the engine "set up" properly. With the initial timing right, a good vacuum advance along with a proper timing curve similar to the factories the engine is much easier to keep cool. My engine ran warmer than it should have for a while and it turned out that my distributor's Vacuum advance hose was leaking and the advance was not working. A vacuum hose replacement and the vacuum kept my timing where it was designed to be and the engine ran cooler as a result. When I installed a new distributor I made sure it had the same curve as what the car came with. Those guys at GM had some idea of what they were doing and few of us know what they did well enough to "improve" on their designs. I am an Engineer but I didn't do their job and don't have their experiences.

A lot of cars have radiator expansion/overflow jars that require a good working radiator cap that holds pressure along with good hoses that connect the overflow to the overflow reservoir. this allows the expanding coolant to get to a reservoir while the engine is hot and then allowing it to be pulled back into the radiator as the engine cools. On cars without good overflow reservoirs the coolant expands and is then lost and then as the engine cools it draws air back into the radiator which seriously impairs the cooling ability. Again I have seen this happen on my own Corvettes so I am always checking to be sure that all the parts are there and working correctly.
I personally replace the thermostat and radiator cap every so often to ensure that the systems are working properly when I replace the coolant. Electric fans are really cool to have but often the original cooling fans and the thermal clutches the car came with was more than sufficient for most applications.