Author Topic: Can I make the radiator self-bleed?? (Read 4880 times)

iamcreepingdeath · « **on:** October 08, 2009, 02:36:28 PM »

I see everyone going through hell to bleed the air out of the coolant on their M42s, and i heard somewhere that the M20 has a self-bleeding system, where all you have to to is rev the engine and the coolant is continually self-bleeding, so you never get any air bubbles in the system, causing a bouncing temp gauge.

Can you somehow make it so that the M42 does that?

So i thought of something, and i am not sure if it will work or not. What if i was to get rid of the bleed screw and somehow attach a fitting in its place with a small teflon tube and run the tube back into the coolant reservoir? (see image below)

What would happen? as the engine runs, the coolant (and air bubbles) would continuously run through the tube from the bleed hole back into the reservoir. No coolant would be lost, but would that screw up the system? would that prevent coolant from flowing through the radiator?

monty23psk · « **Reply #1 on:** October 08, 2009, 03:51:16 PM »

I know on my M5 is it self bleeding. The trick is that the expansion tank is seperate from the radiator. Believe so with the m20. Also under the cap, would be a hose heading down which would let the air escape. I am not sure, but from your design air would still be kept in the system. I would think that adding something of a t fitting to that new hose way under the path of coolan might work. The problem I think would be in the height above the radiator that you would need and with the hood, wouldnt think possible.

Great idea though if you make it work.

iamcreepingdeath · « **Reply #2 on:** October 08, 2009, 04:00:40 PM »

hmm... the air will be kept in the system, but it would be routed into the air space inside the expansion tank, and therefore would not get back into the coolant stream. You know what i mean?

tjts1 · « **Reply #3 on:** October 08, 2009, 04:08:08 PM »

I don't get it. You have air going into one end of the hose and water coming out o the other?

iamcreepingdeath · « **Reply #4 on:** October 08, 2009, 04:15:17 PM »

Quote from: tjts1;79628

I don't get it. You have air going into one end of the hose and water coming out o the other?

air and coolant. Have you ever bled your coolant before? coolant and air bubbles come out of the bleed valve, and when the system is bled completely, only coolant comes out. The point is, with the bleed valve re-routed into the expansion tank, coolant will constantly be flowing from the bleed hole to the expansion tank, and the occasional air bubble with it, which will just join the air that is already in the expansion tank.

does that make better sense?

tjts1 · « **Reply #5 on:** October 08, 2009, 04:38:09 PM »

The bleed screw on the M42 radiator goes directly into the radiator core. The radiator already has a connecting pipe between the top of the overflow tank and the top of the core so the system is already self bleeding as is. You can try opening the bleed screw to the core but I think you're better off leaving it closed and simply opening the radiator cap on the expansion tank with the front tires parked up hill.

iamcreepingdeath · « **Reply #6 on:** October 08, 2009, 05:28:36 PM »

actually, according to this schematic, the bleed line doesn't go into the rad core, it goes into the overflow tank. but that is confusing, because doesn't the bleed screw open right into the upper rad hose? And the connecting pipe from the core to the tank goes from the bottom of the core to the top of the tank, not from top to top, so there is no way for air in the rad core to be released into the tank.

the system is not self-bleeding, that is why there is a bleed screw. for it to be self-bleeding, there would have to be a path for air to take from the rad core (or hose) to open atmosphere or the air inside the overflow tank.

monty23psk · « **Reply #7 on:** October 08, 2009, 05:58:52 PM »

You are correct but if the air can't escape you will build up extra pressure. This is why the m5 one was designed with the bleeder hose, above the coolant line. Air will alway go up.

iamcreepingdeath · « **Reply #8 on:** October 08, 2009, 07:18:23 PM »

It says above in the schematic that "The cooling system is protected against excessive operating pressure by registering the radiator feed pressure."

besides, re-routing air from one part of the system to another cannot increase the overall pressure in the system, because the air is neither leaving or entering the closed system.

The only thing i can think of at the moment is that if re-route the bleed hole into the expansion tank, too much coolant will bypass the main radiator via the bleed line, and therefore lessen flow through the radiator, causing the engine to heat up. There is only one way to find out...

monty23psk · « **Reply #9 on:** October 08, 2009, 08:44:27 PM »

very true and keep us posted.

qualicas · « **Reply #10 on:** October 10, 2009, 05:25:07 PM »

I'm beginning to think that all this bleeding problem is largely due to poor circulation through the oldrad. Also, when the water pump is running with the rad cap off, there is no pressure. This will cause the water pump to cavitate on the suction side. What cavitation does is lower the pressure, lowered pressure causes the water to flash to steam at low water temperatures with the resultant bleeding problems. I had no problems with bleeding at all. All the cooling system was new. Has anyone ever had bleeding problems with new rads?