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3-Series (E36) Chat relating to the BMW 3-Series from 1992-1999. Autodoodad Specific models include: BMW 316i, BMW 318i, BMW 318iS/ti, BMW 320, BMW 323, BMW 320, BMW 324, BMW 325, BMW 328.

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Old 11-01-2006, 04:21 PM   #1 (permalink)
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Heater's only hot while driving?

My heater only blows out hot air if i am driving. Even if the engine is totally warmed up its not hot unless im moving. I usually have to keep the RPMs up to keep it blowing hot. So ill drive around in 2 or 3 gear with the RPMs up. Anyone have any idea whats going on?

Please help, Rexburg ID is getting really cold!
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Old 11-01-2006, 05:02 PM   #2 (permalink)
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How healthy is your water pump? What model car do you drive?
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Old 11-01-2006, 06:06 PM   #3 (permalink)
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Sorry....forgot about that minor detail. It is a 93 325is. The water pump is fairly new. I replaced it less than a year ago.
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Old 11-01-2006, 10:06 PM   #4 (permalink)
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Thermostat? Maybe not the right temp.?
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Old 11-01-2006, 10:13 PM   #5 (permalink)
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Quote:
Originally Posted by foxrace8
...Rexburg ID is getting really cold!
sounds like you need to move....Idaho isn't that great of a state anyways.....ha ha just kidding dude...

I'm in northern Utah so I understand the bitter cold winters...I'm thinking of moving to a warmer climate....

but sorry I can't be of real help...
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Old 11-02-2006, 02:13 AM   #6 (permalink)
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A few possibilities I could think of off the top of my head. None of which are easy to check.
- Clogged Heater Core water passages
- Heater Core exterior is clogged and dirty
- Heater control door is not staying open for some odd reason
It's late, I'll post more if I can think of anything while at work. But until then bundle up and keep that car moving!
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Old 11-02-2006, 08:35 AM   #7 (permalink)
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There are separate controls for the large vent just to the right of the driver position. Make sure that the controls are set for heat and air flow.

If that doesn't help, try replacing the cabin filter.
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Old 11-02-2006, 08:48 AM   #8 (permalink)
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It's blowing air, just not warm air?

How's the airflow from the vents and such? Is the blower pushing good airflow out the vents? Its just that the air isn't warm? Feel the heater hoses at the firewall and see if they're hot going into the firewall (and thus heater core...). I assume your motor is warming up alright?
If you're not getting good airflow out of the vents and the blower motor is running then yes check the cabin air filter. If your heater hoses aren't warm or hot then you have to start looking at those and why they're not hot. Run your heater in the recirculate mode for max heating too. The AC compressor should be off as well.





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Old 11-02-2006, 09:36 AM   #9 (permalink)
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Thanks guys. Yes the blower is pushing a good amount of air through the vents. And the car warms up just like it should. I guess i'll check the hoses going into the firewall and see whats going on.
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Old 11-06-2006, 03:40 PM   #10 (permalink)
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UPDATE: I checked the heater hoses at the firewall and they feel hot. Any ideas?
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Old 11-06-2006, 04:31 PM   #11 (permalink)
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Heater core, water valve, thermostat....

What's the temperature on your instrument panel gauge look like? Is it in the middle of the gauge? Has this hot air problem just started? Or has it been this way for a long time? The TIS manual says look at the thermostat (should be p/n 11 53 1 743 542 and have a small bleed hole in it...). Then look at the water valve (should be p/n 64 11 8 375 792) and replace as necessary. Do you have an IR Temperature Probe? The infrared probes allow you to point and shoot to take temperature readings. Very helpful in diagnosing these problems. You can point it at the hoses, at the heater core itself, the vents, etc...
That way you can get a more accurate reading of the actual temps of the hoses feeding the heater core. I'm kinda suspecting the water valve if you're getting good airflow from the vents and your engine temps are warmed up.


Water Valve.... p/n 64 11 8 375 792 from BavAuto.com ($129) p.640-3 in Bentley Manual. The valve is actually upside down in this picture....








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Old 11-06-2006, 04:43 PM   #12 (permalink)
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Hey man,

The heater valve is a very good posibility but I'd say that a good backflush would do you good. When was the last time you had your coolant changed?
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Old 11-06-2006, 09:49 PM   #13 (permalink)
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Yes the temp gauge is right in the middle, that looks normal. Thanks for the part numbers. I don't have an IR temp probe. I should though. I think ill look into the water valve. And to Dirte30, i changed the coolant about a year ago, or a little longer. Is there anyway to tell if the water valve is bad? Or do i just need to replace it to see?
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Old 11-07-2006, 08:39 PM   #14 (permalink)
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No test...

I don't know of a good way to test it because of the extremely cramped quarters there to work with. The old domestic cars had them out where you could get to them easily but not these. The valve is electrically operated with two solenoids (to feed the two chamber heater core...), probably one or both solenoids have crapped out. Pretty good guess that it's the culprit. I guess you could unplug the harness from the valve and take voltage readings while moving the temperature selector on the dash, to see if the valve is getting voltage commands, but other than that I don't know of a legit test.







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Old 11-08-2006, 01:48 AM   #15 (permalink)
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Hold on tiger, before you do anything else, Bleed your radiator.

Get the car on a very steep incline, front of the car up high (you want the top of the radiator above the heater core in the cabin. This way, gravity helps you get the air to the front of the system.), start the engine, put heater on MAX heat w/ all vents open, and open the bleeder screw right next to the radiator fill cap. After the engine is warmed up (water temp needle vertical) rev the engine to 2.5-3.5K rpm to get the water pump spinning fast enough. (you may want a friend to do this and watch your temps, unless you don't care and feel comfy reaching under the throttle body and rotating the cable cams - NOTE: Careful, the rev limiter may not be able to stop you from over-revving manually! I do not know if the ECU will kill the injectors and spark or just cut the throttle) You need to bleed the engine until no more bubbles are coming out of the bleeder port and the hoses feel firm (careful they get *HOT*) - IE: don't have any air bubbles in them. (mainly the return hose on the driver's side of the car, if your facing the engine bay, the right hose) This process can take some time, you will probably make a mess and use lots of 50/50 mix of antifreeze. It's ok to have the radiator cap off before you start the procedure and probably a good idea since doing this will suck lots of coolant into the system when the air gets replaced and you will need to replenish the reservoir. (BE CAREFUL opening the cap if it is hot, the system is designed to be able to run under pressure - so open it slowly and listen to any hisses - wait for any hiss to stop before you unscrew further)

Trust me on this one, if your system is NOT bled correctly, hot coolant will not reach the heater core until the engine is rotating fast enough to push water through the heater core. Coolant wont flow through there on it's own if there is air trapped in the system and requires the extra minute pressure that is created when the pump spins faster. If your engine got a little to hot and boiled off some coolant, even if you replaced it, it can most definitely have ingested some air. You can't just fill the expansion tank until it stays full and be done with it, unfortunately our cars are a little to complex for that >: |

After your system is bled properly, and this STILL happens, THEN begin looking to replace parts. Start with the basics. Besides, if you replace a part, you have to bleed the coolant again anyways which will most likely fix the problem when you thought it was the part all along.

note: the PLASTIC water pumps fail catastrophically, they don't slowly wear down. Also, the plastic impeller water pumps were only put on early model cars. Since you said yours is definately metal, your ok on that)

I can't believe you guys already started to tell him to replace parts...
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Last edited by bitcore; 11-08-2006 at 01:59 AM.
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