70 mustang 302 overheating problems

Make sure it is not running too lean or rich. Purge air out of the cooling system. A product I use called Water Wetter will reduce operating temperatures several degrees. I would also make sure the water pump fan belt is not slipping.

I have not taken the intake off to check the gaskets. I have had this car for several years. When I changed it over to the 4V several years ago, the car sat in my garage for a long time before I started working on it again. I put new belts on it just to make sure they were not slipping. Was told about a flow restrictor that goes behind the thermostat, but I think that may only be on the 351C and not the 302. Guess I need to pull the intake and check those gaskets. It seems like the overheating issues came up after I made the change. But like I said before, the car sat for several years in between the times I would work on it.

Sounds like a coolant circulation problem. Yes, double check the intake manifold and gaskets. Plus, since the vehicle sat it wouldn't hurt to flush out the cooling system using a chemical cleaner. You might have rust and sediment in the cooling system passages. A lean air to fuel mixture will cause it to run hot as well. Make sure the vacuum advance is working and the centrifugal advance is working. Hope that helps! Jim

I flushed the system with a radiator flush chemical. It was pretty clean for sitting all that time. Starting to think the intake gaskets MSU be the problem.

Got the new heater core put in today. Ran the car for one hour in that garage and it never got over 172*. Wasn't able to get the car out and drive it yet, got to finish putting the dash back together. I'm hoping this will take care of the problem. If not, next step is to remove the intake and check for correct gaskets. Thanks for all of the input, it is greatly appreciated.

Thanks for letting us know! Looking forward to your progress! Jim

Got the car put back together with the new heater core in. Let it idle for one hour in the garage. Temp got up to 172* and stayed steady. Drove the car today about 8 miles and it went up to 215*. Going to pull the intake and check the gaskets, if that’s not it I don’t know what else to do. This problem is killing me !!!

I pulled the intake today, the gaskets were correct. I tested the thermostat on the stove and it opens and closes as it should. I did find the wire for the digital temp gauge was loose. But I don't think that is the problem cause the car does overheat. Was going to run it without the thermostat in it, but I think that would be a waste of time since I know the thermostat is working properly. Anybody got any other suggestions ????

Perhaps you should test for exhaust gases in the coolant.

Check for a restricted exhaust system. Critters like to climb into the tailpipe and build a nest in the muffler sometimes when a vehicle sits. Also check your base ignition timing and be sure the advance mechanisms are working. The vacuum advance should be plugged into carburetor vacuum, not intake manifold vacuum. There's a difference. Intake manifold vacuum is strongest at idle and decreases on acceleration. But carburetor vacuum is the exact opposite. Remove and inspect the spark plugs. If the tips are white it's running too lean. That will cause the engine to run hot as well. Hope that helps! Jim

UPDATE : after the latest work, I changed the radiator cap from a 13lb to a 16lb cap. Also realized I had spark plugs in it when it was a 2V car. Changed those out to plugs for a 4V. Also retimed the car just to make sure that wasn't an issue. The car still has a 160* thermostat in it. I test drove it today, the temp got up to 204* while driving and the cooled back down to 188* while sitting in the garage idling. My thinking is he car still shouldn't be getting that hot with a 160* thermostat. The water in the radiator stayed at 180*-190*. I have a radiator cap that has the thermometer in it. I wanted to be able to compare radiator temp to engine temp. The car is running great, just going to take it on a long drive in the next day or so and see just how hot it will get up to. Thanks for all the info, it was very helpful.

I thought about that as well. I did the paper test on it and it is pulling air thru the radiator. This has been a tough one to figure out.

Did you try the Water Wetter? It should drop the temp several degrees. Do you have a fan shroud?

Never heard of a Water Wetter.....lol... And yes it does have a shroud.

It does not have a fan clutch.

Water Wetter is a product that lowers operating temperatures by improving the heat transfer from the coolant to the radiator. You can buy it at any auto parts store.

Well I took t out for a test run today. Same results, temp is fine at idle but when you drive the car it went up to 230*. It was 220* on the radiator cap gauge and 230 inside the car. I added the coolant to it today. I have wasted so much coolant I was wanting to see if I was getting close to finding the problem before I put anymore in it. Well I thought i had it figured out yesterday and thought by adding the coolant today that it would bring the temp on down. But nope, that didn't happen. I don't know what else to do, I am totally lost now.

No laser heat sensor gun. I bought the Mr Gasket thermostat radiator cap just so i could compare engine water temp vs radiator water temp. Both temps are running within 15* of each other, with radiator being cooler of the two.

Ok just a new update. The car is doing better but still running a bit warm. Riding around on backroads car get up to 190-195 and thats with a 160* thermostat. But when I take it out to the fourlane hwy and run it hard the temp goes up slowly and got as high as 215*. I have put in a new temp gauge. It is a mechanical/digital readout gauge. The radiator is running 10-15* cooler than the engine (190*) avg. The timing was off a little. My question is this, with the 160* thermostat in it could it be letting the water flow to quickly and not having time to cool off ? I have a 16lb cap on it now and its not spewing over. But i'm thinking that the thermostat is basically staying open and not letting water stay in the radiator long enough to cool it down. what do ya'll think ?

Just running regular 87 as bad as I hate to with ethanol.

I was just thinking with the 160* the water would not have time to really cool down because the thermostat would basically be staying open.

I didn't realize there was a difference between the 2v and 4v plugs in it either. I was running the 2v plugs until i read my old manual for the engine. I changed the plugs out and seems to have helped some. I will try the higher octane gas and see what that does. Its just odd that normal slow driving and it runs ok, but if you get on it up to higher speeds it goes up. Ran the car @100mph for over 3 miles and it shot up pretty fast.

It has a 2 core on it, but it is the same as the small 3 core that was on it. The cores on this one are large cores. Doesn’t make sense that the radiator would all of a sudden be to small. It is all still factory with the exception of the 4v intake and shorty headers.

For some reason my answers/questions will not post to the thread.

I think I may go back with the small 3 core that was on it and see what happens. I hate throwing more money out on another new radiator. I looked at a new aluminum 24" 3 core radiator, and thought about getting it. But I just don't see how it can all of a sudden be the radiator. Unless like your friend said the large 2 cores are flowing too much water. How would you slow down the water pump ?

Final update : The overheating problem has been fixed. I went back to the 190* thermostat, also shortened my upper and lower hoses to give a better flow, new digital/mechanical gauge with a new sensor. Car runs at 205* steady. I can 75mph or 110mph, temp runs at 205*. it will drop down to 200* when just cruising around. Have run the car for a few day now and it is doing great. I guess it was a culmination of little things that fixed it. But I am satisfied it is good to go now. Thanks for all the input.

Congratulations!