Stupid friggin heater problems

[Mad_Max 231]

So I picked up a 94 325i coupe the other weekend, auto with M50B25TU. Told it supposedly had a cracked head as it was overheating when driven, but didn't overheat while idling.

Got it home, checked the water pump, that was all good. Thermostat in two pieces, so replaced that. So since then, the motor itself is running great, temp is normal.

Problem is I can't get the heater to work. Bled the system, several times. No air bubbles. Have confirmed heater valve opens and closes properly (have tried 3 separate valves as well), no change. Removed and flushed the heater core, so no blockage. And yes the little round dial below the centre vent is set to hot.

Any new suggestions on where best to start looking? I've never had this problem before, heater isn't even lukewarm. Thinking to pull the heater core again  tomorrow to see if it's even getting coolant flow, to make sure water is circulating through the head.

Edited August 2, 2017 by Mad_Max
Stupid autocorrect on my phone, edited on laptop where I can type properly.

[KwS 2425]

Can you feel if the inlet and outlet hoses of the heater core are getting hot when the coolant is?

[allan 295]

Is the vehicle an import? as have had similar problem turned out that the hoses from the heater core had been blocked off with two solid pieces of aluminum bar just were they  enter the heater core itself. Took me ages to track it down and a real pain in the butt to pull out. Although once removed presto heat from the heater all fixed or so i thought. If this turns out to be the problem just keep an eye on the carpets as the core could fail still not having coolant running through it for a length of time

[Mad_Max 231]

I didn't think of that tonight, was getting late (and me frustrated after mucking around with heater valves to ensure they are working properly).

I did check the other day (when it had a suspect valve in it) and the one from the back of the head to the bottom of the valve was lukewarm, the hoses from the valve to the heater core were cold - but that valve turned out to be suspect and I can't guarantee it wasn't stuck closed.

Am assuming it's a lack of water flow causing it. I've also checked the basics (no water in the oil, or oil in the water, car runs too smooth to have dropped two cylinders, no signs of cracked head or blown head gasket, etc), if I can't get the heater sorted might just end up scrapping it and concentrating on repairing the Alpina instead (which coincidentally also has a water leak, determined where that was today, not a hard fix in theory).

[Mad_Max 231]

2 minutes ago, allan said:

Is the vehicle an import? as have had similar problem turned out that the hoses from the heater core had been blocked off with two solid pieces of aluminum bar just were they  enter the heater core itself. Took me ages to track it down and a real pain in the butt to pull out. Although once removed presto heat from the heater all fixed or so i thought. If this turns out to be the problem just keep an eye on the carpets as the core could fail still not having coolant running through it for a length of time

Hi Allan, sorry didn't see your post appear (was typing my reply above)...... not sure if it's an import, though would probably pay to remove all the hoses and flush them, see if there's a blockage anywhere there - that would explain it alright, and would be easy enough to swap another hose onto it. Will look into that more tomorrow, thanks

[Mad_Max 231]

So to add to the confusion over this one, today I have:

• Verified there is water flow from the expansion tank through the heater core and back out, so that's not blocked.
• Found it was missing a thermostat inside the airbox (part #11 here), have refitted from another 325I
• Removed thermostat and replaced with a different one in case the other one was actually faulty
• Removed and rechecked the water pump in case it decided to break yesterday (Murphy's Law)
• Bled the system countless times to no avail

When running, the bottom radiator hose remains cold for what I'd say would be an extremely long time.

20 hours ago, KwS said:

Can you feel if the inlet and outlet hoses of the heater core are getting hot when the coolant is?

All 3 hoses to the heater valve are quite cool to the touch, there is no blockage but I'm suspecting there's also no flow. So water pump, thermostat, heater valve and core are all ok, I'm now thinking either the radiator is blocked, or there's a blockage in the head or block somewhere that's stopping water flow as there is not even a steady trickle from the radiator into the expansion tank.

Will try changing radiators if I get time tomorrow, see if that changes anything. Starting to run out of places to look now.

Edited August 3, 2017 by Mad_Max
Adding more info

[Mad_Max 231]

So it looks like I've found the true problem. This is what's left of the thermostat, there's one small piece missing, which I'm presuming has gotten wedged in one of the water jackets inside the head, stopping water flow to the back 2 cylinders.......

Either I'm going to have to find a way to reverse flush this loose, or the head will have to come off and see if I can remove it that way. Not a job I wanted to be doing on this thing.......