Radiator Bleed Setup Question

Joel K

Supporter
Hi,

looking for some recommendations with regard to the following

1)Is it necessary to run a bleeder line from the top of the radiator back to the header tank? Is it sufficient to just bleed the system on setup by opening the top drain valve slightly connect a hose temporarily, bleed the system and close the valve and your all set?
2)If running a line is preferred, what size and type of hose is recommended? Just looking for some standard black rubber hose, nothing fancy.

As always. Thanks for the help.

Joel
 

Ian Anderson

Lifetime Supporter
I do not have bleed lines on my DAX.
start of each drive season part of check over is crack bleed and see if air escapes. Most years 14 now on the road perhaps a few ml of air escape and needs topped up in the header tank.

Easy enough to check before heading out on a trip like to Le Mans and back about 1400 to 1500 mile round trip. And no doubt you would check the car over before heading out!

ian
 
I am building A SGT and have put a brake line hose from the top of the radiator to the header tank as recommended by Mick
 

Bill Kearley

Supporter
Yes, use a bleed line. No need to run a line back to the tank. I simply used a pet cock at the top of the rad and a line down below to let air out. Also have a second one at top of thermostat housing. Easy to bleed.
 
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Scott

Lifetime Supporter
I have a radiator bleed on on my car, but I have no practical experience -- the engine would have to be running for that. Air seeks the highest point, but the bleed line must be routed down to pass under the door before it can go up into the expansion tank. It's not clear to me how well air will flow to the expansion tank. For this reason I kept the bleed line at the height of the port as long as possible (I'd estimate 4 feet) before it dives down... worst case the air gets stuck there rather than in the top of the radiator. I had Abe weld a speed bleeder into that line so that I could see if any air is trapped there without making a mess.

The radiator that came with the kit had the bleed on the pressure side. My understanding is that it's preferable to have it on the low-pressure side so that's where I put mine when I had the custom radiator fabricated. If yours is on the pressure side, it's bypassing the radiator so you don't want it too large. I have seen others using a brake line as Alex suggested and that seems good to me. I think I read somewhere that Carroll Smith would use compressed air to ensure that those thin bleed lines weren't clogged when prepping a car for a race.
 
I have never found it necessary to fit or use a coolant bleed system to the radiator, once its bled properly and thoroughly should always by OK. BUT what essential in my opinion to install bleed lines from the rear of the inlet manifold directly to the expansion tank, using pipes no greater in size than the standard 3/16 brake pipe. In a 40 this is ( again in my opinion ) essential, and exhausts any trapped air or steam pockets from the rear of the engine, where it is farthest from all of the main coolant connections to the engine from the coolant system. Frank
 
Joel,
I run a -4AN from the top of the radiator to the expansion tank, it makes it very easy to bleed the system if you have to drain it.(I already done it twice). When I refill the system I just disconnect the bleed lines from the tank (both radiator and engine steam vents) and use my vacuum brake bleeder and that fills the system in no time and getting most of the air out.
Every time I’m getting home after driven the car I let the elec waterpump run for a while and you can hear it’s a lot of air in the system, so I think it’s a good idea to have a bleed line on the radiator top.
 
Johan.
can you go into more detail about refilling the system ( I am almost there) and have both a radiator bleed line and a steam vent line connected to the surge tank. I left a drain plug next to the radiator. I also have a vacuum brake bleeder. Where do you connect the vacuum brake bleeder and how much coolant does the system usually take? thank you very much
 
Joel, this is a quote from Howard:
"You should vent the system from the high points, rear of cylinder heads, top of radiator (both), and the thermostat housing back to the expansion tank. Place the expansion tank as high as possible as well and run the line to it from the lowest pressure point in the system. That would be the cold side return from the radiator and input to the pump. If you have a heater core then you may need to vent it also if it is trapping air.

Both my cars the SLC and the GT40 are done like this, the system will bleed itself. Nothing else needs to be done as the air must return back to the expansion tank and has no other place to accumulate. If you are fighting air in the system then it isn't designed correctly and there is a place where the air is being trapped. A proper self bleed system will correct this and once you have done that you will never have a air in the system problem again.

Then you can control water temp with a thermostat."
 

Joel K

Supporter
Joel, this is a quote from Howard:
"You should vent the system from the high points, rear of cylinder heads, top of radiator (both), and the thermostat housing back to the expansion tank. Place the expansion tank as high as possible as well and run the line to it from the lowest pressure point in the system. That would be the cold side return from the radiator and input to the pump. If you have a heater core then you may need to vent it also if it is trapping air.

Both my cars the SLC and the GT40 are done like this, the system will bleed itself. Nothing else needs to be done as the air must return back to the expansion tank and has no other place to accumulate. If you are fighting air in the system then it isn't designed correctly and there is a place where the air is being trapped. A proper self bleed system will correct this and once you have done that you will never have a air in the system problem again.

Then you can control water temp with a thermostat."
Thanks Hector, yes. I want to make this as simple to run and maintain as possible. I haven’t gotten that far yet, but based on my setup I think I’ll do the radiator bleed line, HCV bleed line, and thermostat bleed line all into the expansion tank. The LT4 does not have steam vents and based on the crate engine instructions air in the heads will be expelled via the thermostat bleed line.
 
Johan.
can you go into more detail about refilling the system ( I am almost there) and have both a radiator bleed line and a steam vent line connected to the surge tank. I left a drain plug next to the radiator. I also have a vacuum brake bleeder. Where do you connect the vacuum brake bleeder and how much coolant does the system usually take? thank you very much
Hector,
I have a 3/4” hose from the bottom of the expansion tank to the low pressure side of the system just before the WP inlet. It also works if connected to the heater inlet.
I unscrew the radiator steam line and cyl head steam vent and apply the vacuum , one line at a time and it will fill your system, just make sure you have fluid in tank at all time.
 
Hector,
I have a 3/4” hose from the bottom of the expansion tank to the low pressure side of the system just before the WP inlet. It also works if connected to the heater inlet.
I unscrew the radiator steam line and cyl head steam vent and apply the vacuum , one line at a time and it will fill your system, just make sure you have fluid in tank at all time.
Great!! That makes perfect sense. Thanks for the tip Johan.
 
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