E30 325i M20B25 Cooling system issues…

[Arata 30]

Hi team. 
 

It’s time for me to start attacking on maintenance/repairs on my E30.

Long story short, my heater core valve (or water valve, whatever it’s called) gave up couple of weeks ago, decided to go over and replace what I should be replacing for the cooling system.

I’ve just replaced the radiator, heater core, heater core valve, new o rings for fitting, 2 temperature sensors on top of the thermostat housing, expansion tank and level sensor.

Please note that I’ll do the water pump and timing belt at the same time soon. Thermostat is less than 1 year old and all parts are OEM from FCP Euro.

Have bled the system multiple times with front of the engine up on jack stands, and it seemed that I didn’t overheat the engine which is good relief, no leaking. However, there’s little cold to warm air from the vent at full hot setting. I’m getting hot at upper and lower heater core pipes, and the heater core of course is getting hot, all other coolant hoses are hot as well.

The other things I’ve noticed was the temperature gauge on dash is now 1/4 to 2/3 towards coldest mark, which indicating that the it’s not getting at full operational temperature.

I have gone for test drive for good 4 hours today, still no sign of overheating but the gauge never got in the middle, and no change of heater bringing hot air. It’s staying like warm to cold.

I have spare old thermostat which I’ll swap them over and see if it changes anything but I doubt it. 
 

Any suggestions? 
Thanks in advance.

[Arata 30]

I’ve put the spare thermostat in, and this time I’m just struggling to bleed as it tries to overheat this time. I think there’s still a lot of air trapped and the way those coolant hoses go I believe I have to manually bleed by disconnecting the each hoses at a time and add the coolant directly to try get as much as air I can?

[Driftit 2078]

It does indeed sound like a bleeding issue.  They can be a pain to bleed.  Especially if you have changed the heater core.  Have you tried priming the heater core?  Disconnect the hoses and jam the garden hose into it.  Run water through it while slightly restricting the outlet so it builds a little pressure.  I've done this to a couple of cars.

If you have an airlock the thermostat may never open.

If you suspect the heater core is still the problem you can join the two hoses bypassing it.  Test to see if it is still occurring.

Also have you replaced the viscous fan clutch?  If not you should.

[Arata 30]

Thanks Driftit. So that’s what I’m gonna do after work today. Pre-fill the coolant with one by one and heater core and try bleed it and see if I can have my heater back.
And no but now you mentioned it I’ll add the viscous fan clutch with the timing job too. 

[C-130 Hercules 571]

Do you have an electric fan sitting in front of the radiator? In that case check fuses and operation of that fan... 

[Arata 30]

No it’s the manual fan with clutch.

[Eagle 1662]

A poor man or rugged mans way to bleed the system is to put your mouth over the expansion tank hole and use it to pressurize the system. You block the vent hose with finger etc and use the other hand the open and close the bleeder between breathes. I usually crack the bleeder when its upto operating temperature just be sure sure but there is rarely any significant amounts of air.

Lost count of how many M20 and M30 engines ive done like this before i had a cooling system pressurizer.  

You can also drill a 2mm hole in the thermostat arrow to help bleeding but ive never needed to doing the above

[Arata 30]

Thanks again Eagle, you always help me.

So far this is what I’ve done…

I’ve swapped the old thermostat which only to find out it’s not opening. I’ve done multiple bleeding, and let it cool, tried again. 
so have put the one I recently changed couple of months back, and took 3 times to get it calm. But I’m back to where I was, it’s not overheating and seems like I have got the air out, but the needle is never in the middle, more towards colder mark and little heat from heater.

I think what I’m gonna do is to look for another thermostat and do water pump/timing belt and do the bleeding again and see what happens.

With the heater core valve, it shouldn’t matter whether is on or not as when it’s not connected it should be open anyway? So I can just leave the wires as I’m not getting any power regardless.

 

[e30ftw 410]

1 hour ago, Eagle said:

A poor man or rugged mans way to bleed the system is to put your mouth over the expansion tank hole and use it to pressurize the system. You block the vent hose with finger etc and use the other hand the open and close the bleeder between breathes. I usually crack the bleeder when its upto operating temperature just be sure sure but there is rarely any significant amounts of air.

Lost count of how many M20 and M30 engines ive done like this before i had a cooling system pressurizer.  

You can also drill a 2mm hole in the thermostat arrow to help bleeding but ive never needed to doing the above

I thought I was the only who did this bleed procedure lol. 

I went through this recently, although m5x swapped but I replaced heater core and had to fill up from a completely dry coolant system.

What worked for me and has worked in the past is jack the front left up and only that side. Seal your mouth on the expansion tank and blow down hard to force the coolant down. You'll hear bubbles when you release your mouth lol. Seems retarded but it works. 

Also give the upper hoses and squeezing to get any extra bubbles out. Do this all while it's not running by the way.

Keep filling and then once full put the cap on and run the engine. You're supposed to have the heater on and fan at full. Having the heater on is enough though, just to make sure the valve is open and coolant can circulate the core. I kept the fan on so I knew once it was hot and hot air was blowing that it was bled properly.

[Eagle 1662]

With heater valve disconnected if should default to open\hot. You should be able to hear it clicking if its working when moving the temperature knob from full cold to hot. If all parts you replaced are working, the system is bled and all hoses are proper hot (you can verify actual temperature with infrared thermometer) then it maybe check the heater flap\cable is moving when going from cold to hot. Never done an E30 but its im assuming its located around the heater box like most vehicles. If its in the closed (forward position?) if will be bypassing the core and not heating air. 

Not sure what sensors you used but i dont trust aftermarket ones myself. Never heard or seen any BMW OE coolant temp sensors fail tbh. My E30 temperature gauge never read right (think it read low or high)and it turned out to be due to bad ground or something loose in the instrument cluster, cant quite recall (If it was ok before then its probably not that though)

12 minutes ago, e30ftw said:

I thought I was the only who did this bleed procedure lol

Haha Ive used it ever since my first E34 in 2005. Probably a old timer BMW trick i saw somewhere.

[e30ftw 410]

There are also different temperature thermostats. Depends where you get it from, FCP has 71C and 80C. If you run a lower temp one, your temp gauge will only get to the first white mark, not the middle. 

 

[Arata 30]

Thanks guys. I believe I may found the issue.

I’ll have to order new thermostat for the right opening temperature as the current one is set to 78 degrees where original one is 85 degrees. That will sort out the temperature gauge below half way.

I just removed the lower panel and the pipe towards the heater core is nice and hot, on the other hand the heater core valve pipe is luke warm. So that’s what’s blocking the flow of the coolant. I’ve looked again but I think it needs to have 12v to open the valve? My next question is can I feed 12v directly to make it open? (I’ll have to do some wiring job) because I don’t really want to open the entire dash if I don’t need to…

[e30ftw 410]

Yeah it's 12v.

https://www.e30zone.net/e30wiki/index.php/Wiring_Diagrams

Look at the A/C Temperature Control wiring if you want to do some wire tracing. I'm pretty sure the whole heater core loom connects via one big white connector to the chassis loom which you will see under the dash behind the brake booster somewhere. 

[Arata 30]

e30ftw, you are legend. I’ll have a look into this weekend.

[Arata 30]

So I’ve tested the wirings/fuses/relay and funny enough the relay might have gone as I’m not getting any power. Luckily I had spare relay so I’ve replaced it and I’ve got power coming to the heater valve, run the car and turned the temperature knob from full cold to full hot and back and forth and I could feel the heater valve moving so confirmed it’s working. 

If the information is correct to get the heater valve open I have to set the temperature setting to cold to make the valve open and bleed the coolant? I’ve done once after I’ve sorted the power issue and seems it’s getting a lot warmer than before, not quite as hot as before but definitely getting hotter.

I guess I’ll continued to bleed and check coolant level but for now it’s not overheating and somewhat heater is coming back so it’s good for me.

[e30ftw 410]

The valve is open when you have it set to hot. That is when the valve is open and coolant is able to flow into the core and back to the engine so you are getting heat.

Setting it to cold will close the valve and you won't be flowing coolant through the core so any air won't be bleeding out of that part of the system.

[E30 325i Rag-Top 2956]

A couple of tricks and tips I was given for bleeding an M20…

1. Make sure the hole under the bleed screw on the thermostat is clear.. this often gets blocked and then doesn’t bleed the air.

2. To get air out of some of the odd places in the cooling system it can help to have the front of the car jacked up so it’s sitting on an angle. 
 

Good luck, it can be a real pain to get all the air out and stop it blowing all the coolant out the expansion tank.

[Arata 30]

Thanks Rag-Top,

I’m just waiting for new thermostat and will do another attack on bleeding. Hopefully comes out alright.