No heat at idle and water pump whistling

[Chebyshev]

My '89 325iX doesn't put out much heat at idle, but as soon as I rev it to 2000 rpm, the heat starts coming out of the vents. At idle it is around 65°F air and at 2000 rpm it goes up to around 95°F (it is ~35°F outside today).

I read that this could be caused by air in the cooling system, so I went to bleed it again and noticed a whistling noise that seems to come from the water pump at idle. I took a video of the noise: https://youtu.be/0VO2dgQ2P2g. While I was bleeding it, I noticed that when I opened the bleeder screw, the noise would go away (most of the time) and then start back up a few seconds after closing the screw. Once the car got to normal operating temperature, I noticed that at idle coolant stopped coming out of the bleed hole. I could have the screw all the way out and no coolant would flow from the hole. If I revved the engine a bit, coolant would flow. I had the heat on full blast during this entire operation.

I should also note that the temperature gauge goes down a little bit if I rev the car to 2000 rpm and hold it there for a bit, not moving the car.

I replaced the water pump (Graf) and thermostat (Mahle Behr) as part of the normal timing belt job 2900 miles and 3.5 months ago.

My intuition is that the water pump isn't generating sufficient pressure at idle to move the coolant through the heater core (or past the bleeder screw apparently). Does the whistling noise mean anything to anyone? Is my intuition about the coolant pressure at idle off? Why would an essentially brand new water pump fail (if that is what is going on)?

[roguetoaster]

I don't hear the WP whistle, but I could see a new WP separating the impeller from the shaft. Perhaps when you rev it the shaft does start to spin the impeller, but at idle it does not.

[Chebyshev]

You don't hear the whistling noise in the video? Or is that an expected noise that I've somehow tuned out over the years?

[roguetoaster]

It sounds like normal E30 noises to me, but we all know our own cars best, so if there's something new only you could really say. I was also listening on a phone, so it could be out of range for the speaker.

[Chebyshev]

I replaced the gasket on the throttle body heater and it is no longer leaking air.

I bled the system again, following the above procedure, but the behavior remains: no heat at idle and a whistling or whining noise from the water pump area that goes away when I release the bleed screw when I'm first bleeding the system. The noise remains constant once it seems like all the bubbles are out regardless of what I do with the screw. At that point barely any coolant flows from the bleed hole at idle.

Is there a diagram of the coolant flow path somewhere so I can understand where the suction and pressure sides are? I suspect that maybe there's a leak on the suction side that is entraining air. I'm basing this on my knowledge of how my pool pump system works, so maybe I'm off base, but it seems like a similar system.

[redlightpete]

It sounds like there’s way too little coolant. A leak at the throttle body gasket should not be leaking air, it should be spewing coolant. Are you filling the system with the bleeder screw open and the car level or with the front higher than the rear? The heater should be set to full hot during filling also.

[JehTehsus]

Not necessarily an issue, but worth noting - the heater core solenoid can jam shut. I have had no heat for a while now, just drilled my solenoid out and the heat is working again (yes, I had it unplugged and everything, it had siezed closed).

That being said, I agree with redlightpete. Sounds like there is not enough coolant in the system, not even close.

[Chebyshev]

The throttle body heater was leaking air into the system when the car was off and cooling down - I could hear it and the system would occasionally gurgle like it was filling with air.

Over the past couple days I've tried bleeding it twice and each time I only add about as much coolant as comes out of the bleed screw, so it seems like it is full to me. Wouldn't it overheat when running if it was way low on coolant?

I'll give it another go today. I left the fill cap and bleed screw open last night, maybe something bubbled up.

[Chebyshev]

Not necessarily an issue, but worth noting - the heater core solenoid can jam shut. I have had no heat for a while now, just drilled my solenoid out and the heat is working again (yes, I had it unplugged and everything, it had siezed closed).

That being said, I agree with redlightpete. Sounds like there is not enough coolant in the system, not even close.

Well I get heat when the RPMs are up around 2000 and the dial works to vary the amount of heat, so I think the solenoid is working ok.

[Chebyshev]

I just went out again to try to fill/bleed the system with the front end of the car jacked up. Same basic behavior as before - coolant runs from the bleed screw when I add it to the reservoir. I turned it on, let it get to temperature then: https://youtu.be/zckRVe6Mnzw

Is that too little coolant flowing out when the engine is idling? There's still that whistling noise and I'm starting to think I just got a bad water pump when I replaced it earlier this year. Maybe it isn't creating enough pressure?

I also checked the temperature of the block with an IR thermometer while idling and it was 210°F. Is that a reasonable temperature?

I'm getting pretty frustrated with this since I'm making no progress!

[Chebyshev]

Figured it out - dug that plastic plug out of the heater valve pipe, right by the elbow coming from the heater core.

[JehTehsus]

Figured it out - dug that plastic plug out of the heater valve pipe, right by the elbow coming from the heater core.

So. stuck solenoid after all?

If you have A/C, deleting that may cause some issues.

[Chebyshev]

So. stuck solenoid after all?

If you have A/C, deleting that may cause some issues.

No, the solenoid is fine, I bench tested it. The pipe leading to it was clogged. I'm not deleting anything, I just dug out that clog with a screwdriver and reinstalled everything.

[JehTehsus]

No, the solenoid is fine, I bench tested it. The pipe leading to it was clogged. I'm not deleting anything, I just dug out that clog with a screwdriver and reinstalled everything.

Ahh, I see, thought that was a piece of the solenoid. Where did a plastic chunk that size get into the system from?

[Chebyshev]

Ahh, I see, thought that was a piece of the solenoid. Where did a plastic chunk that size get into the system from?

Yeah, I wonder about that too. I don't know the full history of the engine unfortunately, so I can only guess. My guess is that at some point something plastic got shredded up (crappy water pump impeller maybe?) and the little shards of plastic built up in that spot and melted together in the heat and pressure of the coolant over time, forming that plastic chunk. It didn't have a defined shape, but rather was formed to the inside of the pipe.