First few runs after engine rebuild and she over heats
Still pulling my hair out trying to figure out why she overheats after driving 20 minutes. Temperature gauge climbs to about 85% and goes to 90% before call it quits to prevent it from overheating. Steam comes out of the backflow tube from radiator cap when I shut it down. I suspected air trapped in the engine and proceeded to get that out.

I tried burping the system to let air out. I did this about half a dozen times. I also opening the temperature sensor while i filled radiator to get air out. That didn't work so i started thinking that i could have a head gasket leak into coolant. I checked tested for gases leaking in from gasket with "Lisle Combustion Leak Detector". I put the tester in with blue liquid filled to line as soon as tstat kicked in. I kept squeezing the rubber ball to suck gases in and the color stayed blue. The temp gauge climbed to about 85% and the color still stayed blue so I dont think its a head gasket leak. I also do not see any white smoke from exhaust. I really cant figure this one out.

I also change tstats to mr. gasked Mr Gasket 4363 T-Stat. There's no room to drill 1/8" hole. I also have a spare 160 and 180 degree t-stat where I do have room to drill a 1/8 hole.
If you look close, you'll notice the Mr. Gasket already has a bleed opening built into it.

Does it continue to create air bubbles in the coolant? Did you install the head gaskets correctly? The front marking toward the front of the engine on both sides. I know when both are installed correctly, one looks like it's upside down. Were the heads resurfaced? Was the block surface pitted much? Was the block surface flat?

I don't think the head gaskets are leaking. But here is another way to check for a leaking head gasket is:
1) Pressurize the cooling system to 15 psi with a cooling system pressure tester.

2) Remove the spark plugs and let it sit for at least 30 minutes with the cooling system pressurized. If there is a leak you will need to pump up the pressure periodically.

3) With the cooling system still pressurized, disable the ignition system and crank over the engine. If there is a leak, the coolant will spray out of a spark plug hole in the cylinder head.

Is the radiator partially plugged? Normally, a radiator has to be "Rodded Out" to be certain they are clean. Simply, both tanks are removed and a rod is run through each tube to clean it.

I don't want to tell you to buy a new radiator. But your radiator is small. I wouldn't spend money to clean it or replace it with the same size radiator. My 351W would never survive with a radiator that small.

Is you gauge accurate? have you checked the temp any other way?

FYI: Fel-Pro tech recommended the head gasket P/N 9333 PT-1. It's an original replacement Perma-torque style, but a heavier duty version and holds up well to higher compression or turbo charged engines. I think it is sold for the late model Lightening trucks. They told me todays stock replacement head gaskets are not designed to hold up to the higher compression of these older engines. I don't know how true that is but I followed their advise.

Edit: Just another thought. When I used to work as a mechanic. Every time an engine was rebuild, or head gaskets replaced the radiator was sent to a radiator shop to be rodded out or it was replaced. I still question the radiator size in your car and if its partially plugged.

Today i measure it with a thermal gun. I pointed the laser at the tem send unit screw and it read 190 - 195 degrees. I think its getting better but not 100% sure yet. I also agree that maybe the long tube headers are adding extra heat which is too much for the small radiator to handle.
That sounds about right for the gauge readings you are seeing. Some people don't mind 195 deg coolant temps on older cars but I like to see lower temps. Much higher and I start thinking about pinging, fuel percolating in the carb bowls, vapor lock, and on and on.

Yeah, I understand headers will add heat to the engine compartment. But I think your radiator is just too small for sufficient cooling. The temps shouldn't climb that far above the thermostat temperature rating. Unfortunately, a good quality radiator today is not near as inexpensive as it use to be.

I'll start shopping for one. What radiator do you recommend that will fit? 24"?
Sine yours is marginal now, you can probably use another copper brass style and don't need aluminum. The 24" wide 3-row radiators National Parts Depot sells look nice but seem very expensive. I think I would search elsewhere and NPD would be a last resort.

Pay attention to what side of the radiator the lower hose attaches to. 1969 and earlier the lower hose attaches to the passenger side (right hand side). 70 and later (sometimes late 1969) the lower hose attaches to the drivers side. Ford made the change for slightly better cooling. But it takes a lot of parts to switch over from right to left side hose attachment. It's not a simple radiator and water pump change.

Since the 24" wide radiators are a saddle mount you will need the one upper and two lower mounts and the rubber inserts for the mounts. Fortunately all the mounts bolt in. Although you may need to drill two holes for 5/16" bolts to attach the lower mounts. The upper mount attached to the radiator support using existing bolts at the hood latch area. A fan shroud is always a great help as well. The saddle mounting brackets and fan shrouds are being reproduced if you cannot find them used.

I am not familiar with the current brands on the market today for OEM replacement copper brass radiators. It used to be Modine. Then I think Modine switched to Proliance and now I don't know.

Lastly, what kind of fan does your car have with the smaller radiator? For original, I have only seen the 5 blade, I think 17" diameter fans with the 24" wide radiators.

I have a 4 blade fan. The blade measured 4.5x8 inches. I do gave the fan sgroud. I'd imagine that the car has a reproduced Original style fan/radiator/shroud since the car is mostly Original
Not sure how your measuring your fan as 8 inches seems very small. I would assume measured all the way across the fan, it should come out to about 16 inches for the old style fixed fan. With a shroud it should be adequate. I'm not sure what the 69's had for a fan I know the 71 had the 5 blade flex fan. As Mike was pointing to, it could be you have the wrong setup. I'm not sure. Lastly with the shroud fitted correctly, there should be roughly 1/2" to 3/4" clearance between the tips of the fan blade and the edge of the shroud. Much more then that and you don't get the pull through the radiator like you should. Just a couple thoughts, hope it helps. JTS 71 Mach1
Yeah, I also believe that is the wrong fan regardless of the radiator. Although they existed, I have never seen a Mach 1 with that small of a radiator. Regarding the fan, I double checked, the smallest fan Ford installed is a 5 blade 17.56" diameter flex fan. For aftermarket I think the closest will be 17" or 18" diameter.

The 5 blade reproduction fan is nothing like the original so I installed a 6 blade Flex fan from Derale. I believe it was 17". I think 18" was too close to hitting the fan shroud because the fan was not centered top to bottom in the shroud opening on my car. If you can fit an 18" fan on yours that would be a little better. Here is a link to the one I used, they also have an 18 inch version.

Flex-A-Lite also has one but the Derale brand is made with slightly thicker blades. Derale also does a very good job of deburring and smoothing edges so you won't cut your hands installing it unlike with Flex-A-Lite.

Just looked at the fan you listed. Looks like a good quality piece should work very well with a good shroud. JTS 71 Mach1

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