Odd bleeding behavior

[LivingLegend06]

I'm having a hell of a time getting my cooling system bled. I have an M50NV with an M42 rad. Stock thermostat (I think) which I drilled a small hole in at the 12 o'clock position.

My procedure:
Jacked the front end in the air about 18" then filled the rad until it wouldn't take any more (approx 2 gallons). I'm running the car with the bleeder closed and the cap off the radiator.

I start the car and let it get to temp (3/4 mark on the dash, infrared temp gun shows the head being right around 200) at this point the expansion tank starts bubbling and the level rises greatly. Ive been placing a large funnel on top of the rad fill and I'm probably getting 2 quarts of coolant in the funnel, the level continues to rise and I turn the car off for fear of overheating. within two minutes of turning the car off the level abruptly drops all the excess it has risen, and when I say abruptly I mean like you just pulled the drain plug in the tub. As the level is rising in the exp tank I'm hearing popping noises and they are clearly felt by putting your hand on the radiator. sounds like a pissed off monster inside the rad is trying to get out.

Through this process I'm not getting any hot air inside the car and the radiator is still cool to the touch. Both upper and lower radiator hoses are quite hot and the line coming from the exp tank is scorching hot.

Ive tried keeping the radiator closed up with the cap on and seemingly nothing happens. Opening the bleeder only gives my coolant and the car just continues to get hot. No bubbling occurs with the cap on and the level can't rise. I tested the thermostat in a pot of boiling water for proper operation and everything checked out okay.

What am I doing wrong?

[Matt-B]

are your heater core hoses backwards?

[LivingLegend06]

Car was properly bled and maintaining constant temperature (working heat etc.) with an m20 radiator. If the hoses are backwards now then they were previously too. All I did was swap out the radiator.

[hwy84]

My procedure:
I'm running the car with the bleeder closed and the cap off the radiator.

What am I doing wrong?

I think you answered your own question. Cooling systems require pressure to work. Running a hot motor with the cap off means you can't build pressure, which means that your coolant boils at a significantly lower temperature.

Based on your description, you are basically boiling the coolant in the motor, which expands as it changes to gas, and bubbles (making the noises you hear). When you stop the car, you stop builidng heat, which stops boiling the coolant, and the level recedes.

When you say "nothing happens" when you run the car with the cap on, does the car overheat?

This is basically why you never remove the radiator cap on a warm engine. Doing so immediately relieves the pressure in the system, and you'll boil over right there and then.

Follow the standard bleeding procedure (using the aptly named bleeder screw ;)) and you should be fine.

[LivingLegend06]

When I Leave the cap on the car continues to build heat beyond the 3/4 mark on the gauge and I turn off the car because I'm uncomfortable with how hot its getting. I have not been able to get any air out of the breather in any of my attempts, it seems to only spew coolant.

[ck_taft325is]

Keep the cap on the M42 radiator and pop the bleeder screw out until you get some coolant then give it a bit of gas with the heater on full hot and the fan on all the way. Start from Cold. Give it some time to heat up and give the top hose a few squeezes to push water through it a bit. Continue to give it a few revs now and again. You sure your thermostat is opening up?

[LivingLegend06]

It opened in a pot of boiling water, I didn't check what temp it opened at though. The car used to cool properly, all that was changed was the radiator. If I can't figure it out in the next day or too ill buy a lower temp thermostat.

[LivingLegend06]

Car now has a brand new 80* thermostat. Still no progress has been made. Car gets really hot, no air comes out of the system and the rad and heat inside in the car are both still cold. Maybe a bad waterpump? I was told the car got a new waterpump by the PO when the swap was done but so far 95% of what he has told me about the car has not been true.

[LivingLegend06]

The car now has a new waterpump too.

I no longer feel that this is a bleeding issue, something else has got to be wrong.

On occasion I can get some heat in the rad near the upper hose but it isn't happening until the car is already too hot and the heat isn't traveling across the radiator, opening the cap or bleeder at this stage just spews mountains of coolant but no air. Still no heat inside the car.

[samiam3356]

With the car off..do you hear the valve open and close when you switch to from cold to full heat?

[ScHpAnKy]

just wondering if anybody has any ideas on this as I'm now having the same trouble

[LivingLegend06]

Nope, car is still in the garage. I have been working on other areas of the car for the last year and have not messed with trying to get it bled again.

and in response to samiam from 11months ago, yes, i can hear/feel the valve moving that directs air through/around the heater core.

[328ijunkie]

m42 rad fail.

[gp.plus]

I had the exact same problem with my swap using an m20 rad, I tried everything mentioned above with the same results. In the end a friend of mine came by with a tool called an "air lift" it connects to the overflow bottle and an air compressor, it then changes the pressure to a vacuum and sucks the cooling system completely down to the point that the hoses collapse. Once you reach the point you flip the valve and draw fresh coolant in through a hose, we used a bucket to hold the fresh coolant. This fixed my bleeding woes within 5 min. Maybe you can find a local radiator shop that may have the tool, or buy one.

http://www.amazon.com/gp/aw/d/B000IHK1VI/ref=aw_d_detail?pd=1

[eurosport22]

i had the same trouble the first time i bled my system it got hot and i had to shut the car off before i could even get the thermostat to open and fill the rest of the radiator. i filled the reservoir up and burped the top rad hose until i couldnt feel my arm any longer. added more coolant or water and did it again until the level stopped going down. started the car after about 20 30 mins of burping and it was cooling eh o.k. so i let it run longer to check the fan switch i installed and it never went to the 3/4 mark anymore. as i drove it it took more and more coolant until the final time i filled it up i t stayed at the full mark. i had all that trouble until ii squeezed the HELL out of the top hose and it burped all the air out. it also helps if you kinda get a rhythm going with the movement of the coolant going up and down.