Radiator bleed line size

[Alex]

for the air bleeds at the top of the radiator (that I'm running to my remote fill/expansion tank ... highest point in the system) is there a minimum line size to use?

normally I use -8, but in this case -6 would be more ideal for routing. Then I began thinking why I used -8 for my other cars and I can't remember .... overkill maybe? But if the outlet port on the raidators is only 1/4'' NPT, then -6 should be fine, right? (because the npt port is the smallest piece of the system and thus most restrictive)

 

[Graham Endeacott]

I don't think it really matters bearing in mind that many cars don't utilise the bleed line at all.

Regards,


Graham.

 

[Paulbav]

I'm using -3, as I understand it if you use a large diameter hose it will allow water to flow through easily and bypassing the radiator therefore reducing the cooling efficiency, not what you want in a GT40....

 

[Jack]

Use a -3 Alex..

 

[Alex]

-3, haha, wow, sounds like I've been supersizing it for no reason. FWIW, I never had any cooling issues with -8. Infact my cooling setups have worked 100% flawlessly in front and rear-engine cars, but it sounds like I should step it down to a smaller more-recommended size (which it good for me for routing purposes!)

 

[Mike Pass]

Here is a pic of the air bleed on the engine which is at an angle on my car. Manifold is an Edelbrock Performer RPM. Works well.
Cheers
Mike

 

[Alex]

Next bleed question - I've got 3 radiators (2 rear, 1 front). I t the front and run it to its own fitting at my remote fill/expansion tank.

for my 2 rear radiators, should each radiator be t'd and then run to its own bung on the remote fill/expansion tank (so 2 separate rear bungs on my tank), or can i T each radiator together and then T those 2 lines together such that 1 line supports both rear radiators?

 

[Alex]

Still not sure if i can/should T the air bleed lines from 2 radiators together, or keep them separate and run 1 line per radiator to my remote fill/expansion tank to bleed the air....

 

[Ian Anderson]

I don't see it would make any difference so long as your header tank is at a lower pressure (Botton of tank feeds to inlet hose to waterpump) than the top of the radiator pressure it will move air back to the header

Ian

 

[Alex]

that's my setup (-10 line from bottom of tank to inlet side) but i just wonder if i T 2 radiator air bleed lines together, what happens if one is pushing out air at the same time that one is pushing out fluid? Grid-lock l ike in a fuel system?

 

[Howard Jones]

Alex, the idea is to provide a route for all the air in the system to return to the expansion tank (highest point in the system) from all the other high points in the system such as the back of the heads and the top of the radiator(s). Only one route is necessary so there's no reason not to "T" the distant ones like at the top of the radiator. I used AN4 for these and I think bigger would not be better in this case. Smaller will work but I have iron blocks and they tend to produce crud over time that might obstruct a small port opening. AN3 would be fine also.

I have done my GT40 this way and never had a air in the system issue since. Just fill it up with coolent and it will self bleed in a few minues. I also did my SBC in the SLC the same way. 2 AN4 lines, one from each side of the radiator T'ed together and then a 1/4 inch alum tube run back to the expansion tank. Also the engine has three vent points. Two at the rear of the intake manifold on each head, and the third at the front of the intake manifold using a spare coolent sensor port. All three are "T'ed" there and a second 1/4 inch AN line is run to the expansion tank.

The expansion tank is located as high as possible in the engine room and the cap is within a inch of the highest point on the car just under the rear body work. The radiator cap vent line goes (port right at the cap bung) from there to a over flow catch can located lower in the engine room and it can be drained from under the car from a pet cock.

I used a AN8 line from the return (inlet from radiator) side of the water pump to the bottom of the expansion tank to vent the system.

The only other thing to think about would be a heater core if you have one, I don't. It it doesn't bleed itself when the lines to it are fully open, I don't think so but maybe, then a bleed line might be used at the higest point in the heater system also.

Check out my SLC thread for clear pictures.

 

[Alex]

The expansion tank is located as high as possible in the engine room and the cap is within a inch of the highest point on the car just under the rear body work. The radiator cap vent line goes (port right at the cap bung) from there to a over flow catch can located lower in the engine room and it can be drained from under the car from a pet cock.

I thought you ideally wanted the catch can mounted around the same level as the expansion tank to allow the tank to suck back any fluid that gets puked out easily?

 

[Howard Jones]

I put mine below the expansion tank for packaging purposes. The closer the better, with a little vertical delta as possible. Especially important is the the length of the connecting tubing should be as short as possible.

Right next to the expansion tank or slightly below it with a very short line would be ideal.

Really both could be built as one part with the lower compartment being the catch can and the higher one being the expansion tank................hummmmmmmmmm.......maybe I'll do that.

 

[Howard Jones]

I put mine below the expansion tank for packaging purposes. The closer the better, with a little vertical delta as possible. Especially important is that the length of the connecting tubing should be as short as possible.

Right next to the expansion tank or slightly below it with a very short line would ideal.

Really both could be built as one part with the lower compartment being the catch can and the higher one being the expansion tank................hummmmmmmmmm.......maybe I'll do that.