Heat doesn't really work

[2ruble]

If I leave the temp dial on hot and open the vents it'll come out hot for about four to five seconds and then pretty quickly cool off. If I close the vents for a few minutes and then open them back up the same thing will happen. If I leave the vents open the air coming out will cool almost to outside temperature while driving, if I come to a stop it will be outside temp coming out the vents.

If I run the 'recycle' button it'll stay warmer (not sure how long, seemed to be at least the last five-seven minutes of my trip to work this morning) - but it's still not hot. Again, while sitting stopped it'll cool down, but not get outside temp with the recycle button on.

Any ideas? The head has previously been off for, what I was told, a timing chain and it looks like green coolant was used. I took the throttle body heater thing (dumb) off and put in all new heater hose and flushed most of it and used zerez g05 (still some green).

Also, both hoses coming from/to the heater core are hot...

[DesktopDave]

I'd suspect the heater valve.  Seems like it's partially obstructed.  Something is not permitting warm coolant to circulate.

[2ruble]

without being able to look at my car for the next 7 hours... where is the heater valve? (picture would be awesome as all I can find online is for e36s - unless it's in the same location, lol); I'm thinking it's in the cabin under the dash next to the core though (awesome.......)

Edit: Think I found it on realoem - looks like yea, it's under the dash and I guess it's the aluminum inlets. Hate to be cheap - but looks like they're about 175 each (if I had to replace them).

Question - on e30tech someone stated switching the hoses; if they weren't changed during the latest replacements what would reversing them do? does the heater/water valve have a check valve in it? does the flow matter? or should I just take apart stuff and try and see if the valve is clogged?

Also, is the valve necessary? if I somehow determine the valve is bad/clogged (can I open it and clean it?) and the core is good, can I just use a piece of heater hose and run it without the valve? or will that affect the cool/cold air?

[DesktopDave]

I have a few good spares, no need to spend $175 for a new one.

They rarely go bad though - it might be as simple as a plugged heater core.  Those do go bad, pretty commonly.

There might also be a bypass in the two heater hoses.  Look in front of the firewall to see if you have a connecting hose running between the two.  It was put there as a bandaid by BMW.  That little bypass has a tendency to die too...

[2ruble]

so, when I can get at the car I'm looking for a connecting hose between the two before the firewall.
Need to check the hose/pipes before and after the valve for heat to see if it's passing through the valve... anything else?

Is there a way to test the valve or if the core is clogged?

And I'm assuming the symptoms of heat for several seconds and 'warm' when recirculating are potentially due to all those listed?

[DesktopDave]

This picture is really hard to make out - but here's mine with the bypass valve.  It's in the middle of the picture - those hose clamps in the middle of the upper hose:


This mod was an official BMW TSB.  Dealers would cut both hoses and put this little release valve in the middle.  It's just a waxstat, designed to prevent high temperatures from bursting the heater core.  It was calibrated to open only if the car was seriously overheating, but who knows when it opens 20 years later?  If it's partially blocking up the system, you'd get symptoms like you're experiencing.

I've been thinking too (dangerous, I know).  It's possible for both hoses to be hot, even if the valve is completely sealed.  Warm coolant can flow up the return pipe.

[2ruble]

what should I be looking for/doing with that bypass valve exactly if its there?

[DesktopDave]

I'd remove it, if the pipes inside the car aren't getting hot.  Buy a few nylon hose repair kits/extenders & splice them in.

[2ruble]

cool - sounds good... I appreciate it... I'll look into it within the next two days; I'll let you know - thanks a bunch



Edit: as a note before I can get back to the car... I know the heater hoses going in to the firewall are getting hot as hell... if that makes a difference

[2ruble]

So I get to my car in the parking garage last night to drive home - and the heat works 

It'll get pretty hot while driving but when sitting at a stop it starts to gradually cool down - unless I have it on recirculation; then it stays hot.... ideas on this?

[DesktopDave]

Still sounds like low flow through the heater core to me.  Could potentially be a water pump issue as well.  BMW used a composite impeller in the pump that has a limited service life.

If a PO had sealed up the system with some stop-leak, it tends to accumulate in the core and the bottom of the rad.

[2ruble]

cool cool - I'll check all the heater stuff out within the next couple days... and hopefully it's not a water pump...

thanks again

[DRTE30]

Here is a thread I recently started about two weeks ago regarding more or less the same issue you are dealing with along with a few trouble shooting ideas:
http://www.m42club.com/forum/index.php?topic=17936.0

For starters and as suggested, I would get rid of the old bypass valve.  For my car, that thing was leaking at every hose clamp and I suspected it also to be malfunctioning.  Secondly, in spite of spending the cash to replace all the hoses you just did, you may want to do the entire "Mess Under The Intake" modification and streamline the whole vacuum/coolant system down to only a few key hoses.  This drastically simplifies a complex system, saves you money in the long run, and gives you a bit of a piece of mind knowing that the system is as simple as possible and less prone to errors: http://www.m42club.com/forum/index.php?topic=2742.0

...and while you're in there, you may want to throw in some fresh fuel injectors!  Look at that, your next free day is all spoken for!  There is A LOT of info in this thread, so read carefully and research carefully to mitigate incorrectly purchased injectors.  I am personally using 21# Volvo Turbo injectors for the last three years, along with a Mark D chip and getting around 33mpg, up from around 27-28mpg originally:
http://www.m42club.com/forum/index.php?topic=233.0

[2ruble]

Awesome - thanks for the links I'll definitely be taking a look over the next couple days. I did just recently do that throttle body delete which is why several of the hoses were replaced. So that instead of a forest of hoses that look like a redundant mess (especially in GA) there's one hose coming form the head to that coolant/heater tube thing... lol

unfortunately the injectors weren't replaced and are now ticking    but I'll be taking care of that within the next couple weeks hopefully - pretty proficient at removing all intake parts now - lol; going to start timing myself I think j/k).

In looking for that bypass I can't honestly tell if it's there based on what pictures I've seen, but I think it is... So when I got a few more bucks and a free da I'll be diving in to that for removal.

Thanks again for the help - as it stands the heat works very good with recirc on - and still works well without, just an obvious temp drop at stops - but is almost immediate in return once moving again.

[DesktopDave]

I wonder if the control unit is shutting off the heater valve when the recirc flaps open?

I'm not even sure it's possible, but it does match the symptoms, doesn't it?