1992 E34 535i with cooling problems

[The Dark Side of Will]

I just replaced the head gasket in my '92 535i. With 258,000 miles, it was due for some major maintenance. I had the head resurfaced and replaced the cam and rockers as they were worn. I used an MLS gasket at .051 thick with some gasket sealer and ARP head studs to hold it together.

So now I have a mystery cooling system problem.

I put the engine back together and the only extra parts I had were the ones I deliberately left out (the injector electrical connector clips).

I refilled the cooling system by leaving the bleeder open, filling the reservoir until coolant came out the bleeder, then closing the bleeder and continuing to fill the reservoir until it wouldn't take any more.

I turned the heat on and started the car. It warmed up and the needle stayed at the middle mark for "a little while", but I wasn't getting any heat. Then in a period of about 10 seconds the needle went up to the red mark and I shut the car off. I left the key on and the temp was back to normal within a couple of minutes, but all subsequent attempts to run the car had the same result.

I was not getting heat from the vents. The radiator and the radiator hoses were cold, but the short hose from the thermostat housing to the waterpump was hot. I didn't hear the heater circulation pump and couldn't tell if the heater valves were operating. I replaced the heater valves a couple of months ago and had heat until I had to replace the head gasket (although the system was a bit flaky and would sometimes "forget" that I had the heat on until I moved the temp dial again.). I've heard the heater circulation pump run before, but don't hear it now, so I suspect it's not running. I have not yet probed the electrical connectors for voltage to see if the valves and pump are energized.

Due to the temp gauge's rapid return to normal once the engine is shut down, I believe I'm getting an air bubble in the thermostat, BUT bleeding doesn't give me anything but coolant. At first I thought it was a bad thermostat, but I replaced the thermostat and the problem persisted. I put the first thermostat in a pan of boiling water on the stove and it operated.

The system *should* function properly when completely stock (which it is, except for the MLS head gasket).

So...

How hard are E34/M30 cooling systems to bleed, normally?
Is the best bleeding procedure just to bleed it, or does it need to purge via multiple thermal cycles?
Can an empty heater circuit cause the behavior I described?
Do the heater valves make noise when they operate?
Has anyone ever tried "hot wiring" the heater valves and pump?
Has anyone had good results drilling a vent hole through the thermostat?

[Tiger]

I don't have M30 but I do have alot of experience on cooling system. First of all, how much coolant did you fill into system? Usually it takes at least 1.5 gallon of 50/50 mix.

Secondly. with reservoir cap off, did you squeeze the top radiator hose repeatedly until the air are burped though your reservoir? When you got all the air out, the coolant in the reservoir will overflow as you squeeze the upper radiator hose. Alot of people don't do this.

Third, yes, it is most likely your heater system is dry but it takes a while for the system to burp itself clean with the cap on the reservoir so the system can build up pressure to bleed the air out of heater system. Alot of people simply leave the reservoir cap off to try to bleed the system.

[The Dark Side of Will]

I had drained the block to replace the head gasket, so the system was completely dry. The Bentley manual says 12.7 qts and it took about 2.5 gal, which is consistent with the idea that the heater core is still dry.

I have not tried incorporating squeezing the upper radiator hose into the bleeding process. If the initial thermal cycling hasn't pulled enough fluid into the system from the reservoir, I'll try that. I won't get to do anything further with the car until this weekend, as I'm on Navy duty right now.

[myles]

My 535 is the most difficult of any BMW I've worked on to bleed, but once you know the trick, its quite easy. M20, M40 and M50s are easy, but the M30 is harder.

Use the bleed screw to get air out, but also disconnect the small coolant line from the top left of the radiator (just near where the main top radiator hose connects to the radiator). That acts as an excellent air bleed location, and once you've got liquid coming out of that point on the radiator, you should have very little air left in the system.

To your other questions, the heater valves to click as they pulse open and closed, but if you've got it on full hot, it won't pulse as it just stays open. I've never needed fiddle around much with the heater to bleed the air. I've never tried hot wiring the valves, bit I did blow a fuse once playing around there with a multimeter.

I've never heard good things about drilling a hole in the thermostat on these beasts.

[The Dark Side of Will]

What about the aux coolant pump? I should hear that and it should be on when I have the system turned to full hot, right?

[myles]

Yes, you should hear it hum and feel it vibrate when you've got the heat set on full hot. I had mine disconnected for quite a long time because it was causing a fuse to blow. It didn't make any noticible difference to the bleeding process when it was disconnected.

[The Dark Side of Will]

Hmm... but if the valves were closed, there would be significant problems bleeding the system. Hmm... I'll check the fuses supplying those two components this weekend.

[The Dark Side of Will]

Use the bleed screw to get air out, but also disconnect the small coolant line from the top left of the radiator (just near where the main top radiator hose connects to the radiator). That acts as an excellent air bleed location, and once you've got liquid coming out of that point on the radiator, you should have very little air left in the system.


Cool. Thanks for the info. There's always a trick to German machinery. If you don't know the trick, it's impossible; if you know the trick, it's cake.

Well... except for putting reinstalling the intake manifold on an M30 in the car. There is no trick to that and it's a pain in the @$$ no matter how good a mechanic you are.

[The Dark Side of Will]

Use the bleed screw to get air out, but also disconnect the small coolant line from the top left of the radiator (just near where the main top radiator hose connects to the radiator). That acts as an excellent air bleed location, and once you've got liquid coming out of that point on the radiator, you should have very little air left in the system.


Bingo.
I had read on a write up elsewhere that the orifice from the bleed hose into the reservoir can become plugged. Mine was. Since I was away for the week, I relayed your advice to my dad, who disconnected the hose and the radiator and couldn't blow through it. I used an air gun to blow compressed air through it and a bunch (well, considering the size of the orifice...) of junk came out at the reservoir end. He filled until coolant came out both bleed locations (maybe 1 cup), closed the bleeder and reconnected the hose, then filled until it was done, which was another couple of quarts.

It sounds like it was mostly the radiator bleed, but some coolant may have made its way into the heater circuit during cool down following the initial thermal cycle.

Fixed now. Thanks!