Cooling system acting very strange

[lolcantturn]

I'm not sure what it is. This is an M20B25 It overheats on idle intermittently, but it takes a very long time for it to overheat on idle. If I'm driving around it's fine. And no, it's not the fan clutch, as it has adequate resistance. Once it's gone past the mid point on idle, there's nothing I can do to cool it down except turn the engine off. Then it won't overheat on idle anymore until the next random occurrence.

Yes, it's bled as much as I can bleed it. The strange thing is though, when I try to bleed it, I open up the bleed screw to relieve all the pressure from the system, and coolant flys straight up into the air. You would think the system isn't under pressure anymore, and that I could open up the coolant tank cap with no problem? Nope. When I have the bleed screw off and open up the coolant tank cap, it starts to fountain! So now I have coolant spraying from both the bleed screw and the tank. When it all finally calms down and I still have the engine running, I try to top off the tank, but I see no evidence of coolant coming out of the bleed screw after I top off the tank. I closed both the bleed screw and the coolant tank, and I keep the engine running, and I see coolant just flying out of my overflow tube on the coolant expansion tank. WTF? I turn my engine off, and I can hear the tank go "Gurp gurp gurp gurp" with coolant just emptying itself.

Another thing, when I parked today, I saw coolant on the floor and it was coming out of the expansion tank overflow tube. It's almost as if my system is very very pressurized.


Cliff Notes:

• Car overheats on idle RANDOMLY, it's not the fan clutch, it's not the thermostat (changed it out twice, same results).
• Headgasket was done <200 miles ago, compression is great on all cylinders.
• System is bled properly
• Sometimes I can't bleed the system at all because when I top off the coolant tank, there is no coolant arriving at the bleed screw.
• System seems pretty pressurized for no reason

I mean, I can drive like this, but I'd rather not worry about it at all. Help!

[StereoInstaller1]

Go to a radiator shop, ask them to do a pressure test, most do it free.

Did you have the head pressure tested before you put it back on?

What you are talking about sounds like a cracked head, where exhaust gasses pressurize the cooling system.

Go get a pressure test. Watch if you can.

GL, and HTH,
Luke

[lolcantturn]

Go to a radiator shop, ask them to do a pressure test, most do it free.

Did you have the head pressure tested before you put it back on?

What you are talking about sounds like a cracked head, where exhaust gasses pressurize the cooling system.

Go get a pressure test. Watch if you can.

GL, and HTH,
Luke

That's the thing though. I made sure to do this headgasket right, I have an 80k head and it's probably the only perfect condition part on my car. I remember when my headgasket first failed in novemeber, it was evident exhaust gasses were building up in the system because it was bubbling through the coolant, kind of when you blow through a straw into a cup of water. Here, there is no bubbling at all, the coolant just rises and overflows from the expansion tank.

If anyone needs a video I can get one to make things a little more clear..

[lolcantturn]

Like it's almost as if something's blocked..but I'm sure my cooling system lines are all in the right direction.. If I squeeze the hose directly in front of the thermostat housing (the one that goes off the therm housing through the fan clutch), I can get coolant to come out of the top of the bleed screw..

Totally clueless man.

[gp.plus]

I know you said you bled properly but may I ask anyway, did you lift the front of the car to bleed it, I skipped this step after doing a headgasket and had all the same symptoms. Another thing that I did to fix it was to remove the top hose on the thermostat housing and pour as much coolant in there as it would take (engine cold,front jacked up). It was like I had an air bubble trapped down low in the system, but doing the above fixed it and it's been perfect since. Good luck.

[lolcantturn]

I know you said you bled properly but may I ask anyway, did you lift the front of the car to bleed it, I skipped this step after doing a headgasket and had all the same symptoms. Another thing that I did to fix it was to remove the top hose on the thermostat housing and pour as much coolant in there as it would take (engine cold,front jacked up). It was like I had an air bubble trapped down low in the system, but doing the above fixed it and it's been perfect since. Good luck.

I had the car lifted, not lifted as much as I could have though.

And good idea with the hose taken off. I took the hose off from the side of the thermostat housing, but taking it off from the top seems a bit more logical.

I feel like I do have a HUGE ASS air bubble somewhere. This didn't happen prior to me changing my thermostat housing gasket 2 weeks ago. My heat is fucking ridiculously hot and my car warms up normally. I just don't get it man. I'll try to rebleed it and see results.

[StereoInstaller1]

Don't lift the front of the car when bleeding a stock M20.

Go get your shit tested, quit fucking around.

[gp.plus]

Yea I feel ya man, it was driving me nuts, I started trying to follow the path of coolant through the system and even that still doesn't make complete sense to me. It gets really odd at the WP and Therm housing, seems like there are junctions with opposing pressure when the thermo is open. Idk maybe my mind was just worked that night. Be sure to update.

[jlevie]

The description of this problem practically screams "failed head gasket to me". That is especially likely if the cooling system is still under pressure if the car has completely cooled off.

[lolcantturn]

Don't lift the front of the car when bleeding a stock M20.

Go get your shit tested, quit fucking around.

Time to find a radiator shop.

Yea I feel ya man, it was driving me nuts, I started trying to follow the path of coolant through the system and even that still doesn't make complete sense to me. It gets really odd at the WP and Therm housing, seems like there are junctions with opposing pressure when the thermo is open. Idk maybe my mind was just worked that night. Be sure to update.

As many times as I've fucked around with the M20's cooling system, it still doesn't make sense to me where the damn hoses go haha.

The description of this problem practically screams "failed head gasket to me". That is especially likely if the cooling system is still under pressure if the car has completely cooled off.

Oh no, it's not under pressure when the car is completely cool, but it is when I turn it right off. When it's cool, theres no problem.

[StereoInstaller1]

It is supposed to maintain pressure until it cools off

[lolcantturn]

Took it to a local shop where they test the coolant to see if exhaust is present.

No exhaust is present.
My compression numbers are all uniform 160psi
There is no milkshake in the oil, no milkshake on the oil cap, my exhaust fumes are normal (not white).

One thing I noticed though, is when I changed out the intake manifold gasket, I put the coolant line next to the bitch tube BEHIND the bitch tube, crushing it between the long block and the bitch tube. There was no way for coolant to pass by there virtually, as it was real tight.
I moved it from there and now the coolant has room to freely flow, but my problem hasn't gone away. Maybe running it the coolant hose so restricted liek that could have ruined the pump??
It's raining now so I can't work on my car, but I'm going to see what effect removing my thermostat temporarily has. One thing I noticed is that when I was trying to bleed the car, my radiator was UNTOUCHABLY hot, and the lines coming from it, while the heater hose line coming off the firewall wasn't hot at all. Heat was present, but it was warm at best.

Maybe I should do a complete flush from the block? There has to be a blockage, this doesn't seem to make much sense.
Also when I say my car "overheats," it'll never go over to the red zone, but it'll hover between halfway and 3/4ths. Not a complete disaster.

[lolcantturn]

Drained my coolant from the block and refilled.
My bleed screw is still gushing out coolant, not like a slow dribble, but just shooting extremely fucking hot coolant.
I drove around and managed to get really hot heat back. Still lingering between 1/2 and 3/4ths.
Sometimes coolant arrives at the bleed screw, sometimes not. It'll just be steam.
Gahhhhhhh..

[lolcantturn]

The only good thing I noticed is that the coolant doesn't empty itself from the coolant overflow anymore................grr

[lolcantturn]

Would it matter if I'm running water or just coolant?
My system is 1000000% water right now.