Bleeding the cooling system / barfing coolant

[Theotherotter]

Last year I had to replace my water pump and a lower radiator hose (I posted about it), and found that it was a bit of a pain to get the cooling system bled. I did find and read the procedure that is posted somewhere about it; I found that the only way I could get the system bled was by bleeding it both from the bleed screw and from the unused sensor port on the other side of the thermostat (I have a three-port stat housing). But I did get it bled and all was good.

This spring, the heater valve failed. The car is an E12 with a B35 powertrain swap, so replacing that valve was a pain in the ass, but surprisingly not as big of a pain as I was expecting, and I got it done. This obviously required bleeding the cooling system again, which I did the same way I did previously. Like before, I could only get the air out and a normal temp needle if I also bled it / filled it from the sensor port on the stat housing. I took the car on a trip this weekend that involved around a thousand miles of freeway driving. Everything was perfect - needle in normal position, etc. This morning, as I was arriving back to work, at the very end of my trip, I noticed that when I got to a toll booth the needle would climb, then go back when I started moving. When I got to work, I looked under the car and opened the hood, and sure enough, it was barfing coolant onto the ground from the overflow hose in the reservoir. It was running hot because it had barfed out enough that there was now air in the system again.

What am I doing wrong when I refill and bleed the system? It seemed to be bled just fine, and behaved fine for around a thousand miles of driving, the large majority of which was 80mph on the freeway in hot weather. Now it isn't. It did puke a little bit after the last refill/bleed in the fall, but was then fine. My first assumption is that this is user error and there is something I'm not doing right. It should not be this hard.

[Chimi-Changa]

For the M30-My favorite is slightly elevate drivers front side, have a rag and extra hose for the top of radiator to the expansion tank. Pull that original hose from the tank end and hold completely vertical holding it with the rag around the top. Your other hand attach the extra hose to the tank nipple, then blow through the other end with long low volume breaths (key). You should hear any system air escaping through the radiator side hose, and keep going until you see the coolant eventually bubbling up out of the hose.

[Theotherotter]

Interesting! I'll try that.

After work yesterday I found a nearby FLAPS and added more coolant and bled it a bit more (guy in parking lot complimented its 'old-school cool'), it was running hot on the way home but cool enough, only dribbled a little on the garage floor when I parked. Drove it again after dinner, no problems.

[Mike W.]

I've had to do it twice one or twice, but I've bled M30s lots and lots of times. Here's what I do.

Bleeder open, fill slowly. Maybe run it some. Heater open. Watch the gauge. If the heater works, it's bled. Conversely, if it's low on coolant, even just from a minor ongoing leak, the first thing that happens is the heater stops working. Fill slowly. Not stupid slowly, and it'll go up and down some as it expands and finally the 'stat opens up. While I've had relatively few problems bleeding the cooling system, trust me, you have lots of company, many have been frustrated over the years.

Also keep in mind, the coolant tank, when cold, is only roughly half full. Any more than that and it will bleed out when it gets up to temp anything above that level. Speaking of the coolant tank, make sure the little vent tube that goes to the radiator isn't collapsed. There's supposed to be a metal bushing in there to prevent that, if it's missing you can tighten the hose clamp enough that you close off that passage and it's not going to be right. Fought that one on an E24 long ago banging my head against the wall for a while until I figured it out. Might even be worth pulling that hose off just to make sure.

[Theotherotter]

I’ve finally got the damn thing almost completely bled. Left for MI yesterday, was running hot in traffic getting downtown so I pulled over and bled it more by just opening the bleed screw and waiting…waiting….waiting. GHave it some throttle and eventually it started dumping coolant out the bleed screw, tightened it and off I went. Later aborted trip and when I stopped to turn around, again running hot, so I did the same thing, opened the bleed screw and waited…and waited…finally started dumping coolant out the port and I closed it. Might need one more round but finally it runs at needle-almost-in-the-middle in traffic. As if this isn’t fun enough I’ve got another car getting a cooling system service later this year.

[gadget73]

just out of curiosity have any of you tried one of those vacuum bleeder systems on these? I've used them on other vehicles with very good results. Its an air powered vac pump that sucks down the system, then you stick a hose into a bucket of coolant and open the valve to let it pull in. I liked the one my friend had so much that I bought one for myself when I found one at a flea market for 30 bucks. Mine is an Airlift but the same basic tool exists in other brands.

It also serves as a leak checker, if it won't hold vacuum its not going to hold pressure.

[Theotherotter]

Finally it’s 100%, and this is what i did:

Jack up the front, put it on jack stands. Open bleed screw. Remove coolant reservoir from bracket, raise high and pour coolant in until it comes out the bleed screw. Close screw, reattach tank, top off to appropriate cold level, start and run car until hot. Seems so simple but it took me this long. Drove it tonight and temp was perfect. Thanks to a Kamil for the suggestion.