Hot Rods Modern Radiator Expansion Tank Theory

Hey guys, I did search but didn't find the exact same topic as this, so please correct me if i'm wrong.

I am in the process of planning my cooling system. Small block dodge, installed as Good Lord intended under the hood of 1960 Ford Falcon solid axle gasser.

This is a 90% street car that will have the radiator/fan module under the trunk floor. The radiator will be positioned with a Non-vented cap towards the rear bumper and with the true bottom of the radiator facing the front bumper, but tilted down 20-30degrees for that scoop effect to help the fan out at speed.

I've been researching the drag/drive racers as well as the drift cars that mount radiators in or under the trunk. They all have problems purging air unless an expansion tank is used between the radiator and the overflow catch can. The expansion tank has the standard, vented radiator cap. I can easily run a T fitting from the upper radiator hose up into the trunk and mount an Expansion Tank inside the trunk as the top of the system to purge air.

Here's the concern:

All the true expansion tanks with rad caps have both an Inlet AND Outlet port (along with the brass barb nipple at the rad cap).
Evidently the OEM uses expansion tanks as part of the circulation and connect one port to a rad hose and the other tank port to the heater return or other location.

My question: can I just plug the upper port on the expansion tank, use the T fitting at the upper rad hose to purge air up to the tank and not worry about true circulation through the tank? It will still have the vented radiator cap on the tank (most racers simply weld shut the cap location on the rad itself).

I understand it would not benefit from additional purging that true flow in/out of the tank will provide, but it should still purge air, yes?

Does anyone think I'd still need to run the second fitting on the expansion tank all the way up to the heater hose on the engine at the front of the car? This would provide true circulation. The LA mopar does have the bypass hose that could accept a T, but who wants to run another 18 foot of coolant hose?

Either way, the 1/4 fitting at the tank's vented cap will go to a standard catch can.

Thanks,
-rick

 

My uncle worked at modine forever he was an engineer. Lost him in 2013. He made this drawing. Hope it helps.

 

That is exactly what I needed.

Many thanks to you and your dad. He obviously knew his stuff and enjoyed sharing that knowledge. My dad was an engineer and also loved to share the stuff he thought was cool.

-rick

 

One could also apply some newer techniques to the air lock problem.

A lot of newer cars/trucks have this issue and it's solved most times by recommending a vacuum fill of the system. I think that is the standard factory process for a lot of them. Pull a vacuum in the cooling system, and introduce the coolant. No air to purge, vacuum 'sucks' the fluid in. Not useful for topping off if needed, but for initial fill it's great.

 

Those drawings are correct as far as they go, but that's not quite what you'll have. Note that in each case, it's an always-upward path to the expansion tank. If at any point that path goes down then back up, you'll have an air trap. Unless you're planning on running that line through the car at the lower of the two connections on each end. I went through this on a LT4 swap into a Jag....

Crude drawing, but you can see the issue. If you run the front-to-rear piping low, you'll have traps at both higher ends. The expansion tank will cover one, but you'll still need a way to bleed the air out at the other end. Wherever you mount the expansion tank, it'll need to be the highest point and I suspect the front will be best. I'd also drill a 1/8" hole in the thermostat to allow easier initial filling; that won't affect cooling. Do run a coolant recovery tank. I'd run the expansion tank inline with the upper radiator hose, that will make it easier to fill/purge the system.

Hope this helps...

 

yes yes. This is basically my plan, with a twist.

Dont laugh, but if i run the hot water into the bottom of the radiator, the flow will help bubbles rise along with the coolant. If the radiator cap is welded shut or has a very high pound unvented cap, then there is no difference between top and bottom, except that the upper connection is 1.5" and the lower is 1.75. So by flipping the radiator, i keep the suction side on the 1.75" (now at the top) and the pressure side is on the 1.5" now at the bottom- so the fittings are sized as intended by OEMs.

The expansion tank (and catch can) will be above the radiator (in the trunk, instead of under it) and there will be a bleeder and/or another high # non vented cap just off the water neck to alleviate air pockets at the front of the system. Both coolant hoses will go down from engine to run side by side under floor, then dip right into radiator (should all just be below trunk flow, unlike my world class art included)

So I have purging at both ends of car, The radiator cap is blocked and rad is flipped, leaving the hose bungs correct for suction/pressure, the flow through the radiator is UP, carrying air to the T fitting to the expansion tank, and that cap controls the pressure. The fan mounts below the rad and pulls air down and back to spit gravel on people behind me.

-rick

 

One thing missing from my drawing is a way to actually fully drain the system if need be. If your radiator has the same size inlet and outlet, mount it with the radiator drain at the top. That gives you your bleed point, then weld a bung onto the water pump-to-radiator line for the actual drain.

 

Good catch! My rad is an aluminum BeCool universal and I dont think it even has a drain, but I can install an inline drain in the lowest part of the hose.

-rick