No heat, what could it be?

[Joey Link]

I have no heat in my '89 325ic. Since the fan blows, I was thinking the likely culprit would be the heater core but neither of the heater hoses running into the firewall from the engine are warm to the touch either. I noticed a valve down below that one of those hoses connects to, then another hose comes off it into the head and a small hose going somewhere else. What is this? Do any of you have any ideas? Coolant system was just filled and properly bled.

[KenC]

After driving the car around for 30+ minutes, does the return line to the radiator get warm?

[Joey Link]

I don't want to drive it around without bumpers yet, but after idling for 20 minutes it's still only barely warm.

[jlevie]

Does the temp gauge show that the engine reaches normal temperature? The needle should be at 11-12 o'clock?

If the engine reaches normal temperature there could be an air bubble in the heater core, meaning that you need to bleed the cooling system, the heater valve may not be working, one of the heater hoses could be plugged, or the heater core could be plugged

[Joey Link]

Yep, the engine reaches normal operating temperature. Unless there's some way to bleed the system incorrectly, that was done today by following the steps in the Chilton manual (forgot my Bentley at home).

Because it was working before it sat for almost two years, and because the heater hoses are new, my guess is it's the valve. Is there any way to 'test' it? That wouldn't cause the heater hoses running into the firewall to not heat up though, would it?

[ethirdy]

There's NO air coming out when you bleed the system? As in, car running at idle, crack bleeder, trickle of ONLY coolant coming out? Are you running the defrost on high at the warmest setting while doing so? This will help encourage the constant flow through the heater core.

Is the engine itself getting hot to the touch? Valve cover, intake mani? If not - replace the t-stat. I had this happen, fixed everything.

Did you maybe hook the intake/outlet hoses to the wrong spots on the heater core inlet/outlets? Can't say for sure it'd keep it from heating up...but the valve is only on one side, so it makes sense...

[Joey Link]

Yeah when I cracked it I didn't hear or see any air at all, just the coolant trickle. The heater was set on high heat, fan setting 4, with all sliders to the open position. The intake manifold was not hot to the touch, even though the gauge was at the 12 o'clock position. Mr. Copperwheat suggested the car probably wasn't warmed up enough, though the gauge indicated it was at the proper temperature and it had been running for 20 minutes.

[CorvallisBMW]

20 minutes should be enough to warm up an m20 at idle. Did you bleed it with the front end raised up on some jack stand or a jack? First thing I'd try in replacing the t-stat, it's a quick $10. That or stop by Funk's on Thursday and Kenny and I can try to help you out :)

[Fidhle007]

You should have heat just above the blue and it should be very hot by the time the gauge is in the middle. I'd be suspect of your heater valve but having the hoses from the head to the body reversed can also cause heating issues. If these have been off at all since you last knew the heat worked, I'd start there but beyond that the heater valve would be the most logical dart to throw.

[Joey Link]

20 minutes should be enough to warm up an m20 at idle. Did you bleed it with the front end raised up on some jack stand or a jack? First thing I'd try in replacing the t-stat, it's a quick $10. That or stop by Funk's on Thursday and Kenny and I can try to help you out :)

Nope, it was flat on the ground. The thermostat is my guess, it just doesn't seem like it's opening. It's supposed to be new, but I'm sure it's not entirely unheard of to have a new part not work properly. I'd love to meet up with you guys but the cabby needs tires before it can move. It literally has four different sizes! I still might drop in and see if you guys need a hand though ;)

You should have heat just above the blue and it should be very hot by the time the gauge is in the middle. I'd be suspect of your heater valve but having the hoses from the head to the body reversed can also cause heating issues. If these have been off at all since you last knew the heat worked, I'd start there but beyond that the heater valve would be the most logical dart to throw.

The heater valve is my next guess after the thermostat. Is the heater valve attached to the heater core or is it independent? There's some sort of valve in the engine bay between the firewall heater hose and the head, what's that for? is that the valve you're referring to, or is it a different one?

[KenC]

If the coolant return line isn't hot, then your thermostat isn't open.

[george graves]

If the coolant return line isn't hot, then your thermostat isn't open.

Or there is something messed up. I'm really paranoid about my m30- even thought it's a m30b35 and the head is not suppose to crack, I know it can. No heat when driving means you have a massive air bubble, or are running on steam. Either way, not good.

[ethirdy]

No heat/engine not getting hot = thermostat stuck OPEN, not closed. With it stuck open, the engine consistently circulates the coolant, instead of holding it and letting it warm up. I just worked on an 89 325i that no matter how long we ran it or how hard we beat on it, the engine was cool to the touch. Talk about confusing - it was defying physics :) The car was INSIDE a garage, so it didn't even have wind to cool it off, yet it wouldn't get warm to the touch.

We took the t-stat out, and held it in front of my propane heater, no change. Let it cool off....no change. It was stuck open, and wasn't closing. New t-stat - engine got warm, we got heat :)

The other thing I'd try is swap the inlet and outlet hoses to the heater core. 10 minute fix, right on the firewall. You get heat back, you know they were backwards. You don't get heat back...well...maybe it is the valve like others suggested, but the engine being cool leads me to believe otherwise.

Let us know what happens!

[Joey Link]

Can anyone tell me what this valve is and what it does? It's #8 in the picture and labeled thermostat on RealOEM. I'm wondering if it's connected correctly. Since it's between the coolant line from the firewall to the head, I suppose it could effect the flow. For some reason my dad is extremely suspicious about this part being faulty. Seems like there are other more obvious things, but he's right nine times out of ten so I've learned not to argue :)



So here's my checklist for tomorrow:

1. Bleed - I'm going to re-bleed the system to make sure it was done properly the first time I did it.
2. Thermostat - I guess there's some way to test with a heat gun to see if it's opening and closing properly?
3. Heater Valve - Is there any way to test this? I would think if the lines going into the firewall aren't warm then the valve wouldn't be the culprit, or does the valve somehow control flow through those hoses as well?

[Joey Link]

Double post :(