[lowonthetotem]

I have a 2006 325i E90. Just this morning the temp light started coming on and going to red if I drive the car more than a minute or two.

I am in FL so it is 90+ degrees outside and the heat in the car only goes to 85, so it is difficult to say, but I as far as I can tell, I am getting no heat.

My question is how can I tell if it is the thermostat or the water pump or something further up the electrical stream? Should I just start with the cheapest thing and move from there? I've never owned a car this electronic. Is there a way to ask the car what is wrong? Seems like there should be, but maybe I don't have the equipment to do it.

I would appreciate any insight that anyone could provide.

[Outlaw 06]

It could be that one of the items you described is faulty, but I wouldn't troubleshoot it unless you're absolutely sure the car isn't about to overheat.

The M54B25 has an aluminum-alloy block and head. If it overheats the results can be catastrophic because the block warps quickly. If this happens, then you'll need to replace the entire engine instead of just re-surfacing the head and replacing the head gasket (ask me how I know).

[lowonthetotem]

Maybe I should qualify it a little more. When the light came on the first time, I pulled over within minutes to a gas station and checked the coolant after the car cooled. It was a little low, but nothing drastic. I topped it off and drove to work. The yellow light came on within a few minutes. It stayed yellow for the half mile or so to work. After the car cooled for a few hours I checked the coolant again, and it was fine.

I managed to get it home by driving a minute or two and stopping as soon as the light came on (I don't live far from work). I let it cool down for five minutes or so and then drive another minute. At home, I put it up on ramps and took off the mud shield(s). There is no leakage. All the hoses are intact. I checked the fuses for the engine and for the temperature control, and they are intact. I don't see any leaks in the radiator.

I will check the heat again tonight when it will be more evident if it is working, but it seems that very little or no coolant is getting into the engine. The pump and the thermostat seem to be the likely culprits. I just never had a car with a thermostat that cost more than $15 or an electric water pump ($500+ wtf?), so I never worried much about just buying parts and trying them one by one starting with the cheapest. I guess I could try that, or should I just bite the bullet and replace both? I've read several accounts of thermostats and pumps being replaced at about 40,000, which is where I am. I haven't read too much about other electrical problems that could cause this. I am just wondering if anyone else has.

[Chriztofor]

1)See my sig.
2) How many miles?
3) Did you ever change the coolant?
4) Probably water-pump and thermostat (If you change the water-pump might as well replace the thermostat.

[lowonthetotem]

1. Yes, I am thinking I need to get one of those.
2. I am at 35,000
3. It has been getting the dealer maintenance for the last four years. I don't think they ever changed that. I haven't.

Thanks

[ENINTY]

I think it is the water pump. The thermostat, according to the Bentley repair manual, only fails in the open position as to not cause the engine to overheat if it breaks. Maybe a water pump test is in order here. I'd do the the air bleed procedure for coolant replacement and see if the water pump fully cycles. The pump will run for approximately 12 mintues during the test and it sounds like a mini washing machine in opeation. To activate the procedure, set the ignition to on (instert the key fob and press the start button without pressing the clutch or brake), then set the heater to the highest temerature setting the the fan setting to low, then press the acceleration pedal for 10 seconds and the water pump will activate. It is best to add a battery to the jumper points under the hood to prevent the battery in the car from running down. Also, scan the ECU and see if there are any error codes for the water pump, but I'm not sure it throws codes when it fails anyway.

[Express]

water pump

[lowonthetotem]

Thanks ENINTY. I did that procedure and got no response from the water pump. Thanks for the adcice on the thermostat, but since I have to replace the pump, I am going to replace both. Just waiting on the parts to arrive now.

Get to drive my Dad's '93 325i (E36) while I wait. That thing sounds like a cross between a harley and a jet.

[GMWNashville]

id go head and replace both-but know that sometimes if you have a waterpump fault code ive had issues getting the car to bleed after replacement without clearing the codes first...only happened once out of the prob 20-30 ive done so idk?

[lowonthetotem]

Just to let you guys know, I replaced the water pump and the thermostat and everything works good now, it seems. I had to take off the coolant overflow to get to anything. That is something that isn't mentioned in the mannual or on the DIY on this. Maybe it isn't necessary, but it made things easier.

It seems like the tell tale on this was that the heat stopped getting hot. As soon as the new pump and thermostat was in the heat come on and was noticably hot, even here in FL.

[lowonthetotem]

Oh, and I did not get any fault codes. I guess maybe I never let the engine get hot enough to cause one, but it seems pretty lame that they did not register.

[bmw6953]

its the water pump most of the overheating issues on the E90 have come from the water pump. Replace it but its not a cheap part its like $600