I'm trying to understand my cooling system, and maybe I'm the one that's broken

[herwawan]

Hey,


I've been trying to fix my cooling system since the day I've got the M3 (04 convertible) and I can't seem to be able to properly do so - or maybe I don't fully understand how it's supposed to work. First up a disclaimer: I'm not trying to have my coolant to remain at one exact temperature (just to be clear). I'm just trying to avoid overheating and overcooling. In normal conditions (highway, no dense traffic) the operating temperature seems to fluctuate between 80C (176F) and 90C (194F) - roughly 12 o'clock on the dash.

Context and parts changed, in the right order:

• 1st, Water pump - right before I bought the car last September, the PO ran into an issue with his old water pump, full steam under the hood and belt on the ground. So they replaced it with a new one from Geba, never heard of that brand before, part number W0133 1974939).
• 2nd, Thermostat - I noticed the car never reached 12 o'clock ont he car when I got it, and as surprising as it is, the PO didn't feel like changing the thermostat with the water pump despite the thermostat being pretty old. Replaced it with a new one from Whaler, part number 11531318274
• 3rd, Fan clutch - when driving up a pretty steep canyon in traffic, the coolant temperature needle hit the second dot on the dash and was about to keep going up until I shut off the car. I waited for the car to cool down, the traffic to get better and off to the garage, who found out that the fan clutch was leaking and not working. Replaced with a new one from Whaler, part number 11527831619
• 4th, Radiator - when the heat got back to California a few weeks ago, I ended up having the coolant temperature hitting the second dot on the dash while driving on the freeway with no traffic. I knew the radiator had never been replaced (had the 04 model year on it when replaced, pretty long life for a radiator!), so I went ahead with that. Replaced with a new one from Nissens, part number NSN-60806.

After all of that, you would expect everything to work fine, right? Well.

The overcooling problem: when the car goes up to temperature after startup, it ends up hitting 84C (183F) before cooling down to roughly 76C (168F). Good news is, thermostat seems to be doing the job. After that, it goes up again and stabilize between 80C (176F) and 90C (194F) when highway with no traffic. But somehow, in certain conditions (going downhill, going through colder area), the temperature keeps dropping up until the needle hits roughly around the first dot.

The overheating problem: when driving up slow and steep canyon, the temperature hits almost 100C (212F), bringing the needle up to the second dot. I considered switching to an electric fan, but at this point with all those parts new, it should for now work correctly. I'm not driving it hard, really. In normal conditions, I would expect it to work.

Anyways, as you can see I'm struggling. Maybe all of this is perfectly normal. Or not. I don't know but this is driving me crazy haha!

Help!

[Obioban]

Replace everything again... and this time use OE parts.

What you're describing is not normal/healthy behavior at all.

[Icecream]

Replace everything again... and this time use OE parts.

lol, sucks but probably true. The OEM parts are very good.

[Ramps]

The stock cooling system works very well on these cars, I second the recommendation to replace everything with OE parts, make sure the AC condenser is clean, make sure the aux fan works, use a vacuum bleeder on the cooling system. You’ll be as good as new.

[Slideways]

It's worth changing the coolant temp sensor located under the intake manifold. It is the sensor that is supplying signal to the needle in the cluster gauge. My sensor went bad without throwing an error code and it would dip down to the first dot under the same overcooling conditions you are describing.

[dl.m3]

Everything you described sounds perfectly normal.

[Obioban]

Everything you described sounds perfectly normal.

Not with healthy stock parts.

[Titaniu//M]

I agree with everyone's opinions of using stock parts. Replacing everything at once is probably easiest, but if you want to experiment I would start with the water pump first. That is one part where the aftermarket and OE are not equivalent.

[Tbonem3]

I believe the Wahler parts you have are OE quality. I believe at least the thermo is OES by Wahler. Not sure on fan clutch. Rad is Modine if you want to save some $, but Nissen is very good quality, common on Asian cars. Honestly didn't know they had a e46 m3 application tho. Of what you listed, I really only have pause with the WP. Though, even lower quality WPs should still work ok enough at least at first before exploding lol. Perhaps the cheaper impeller design or material doesn't flow/spin as well?

I suspect something blocking the rad or a better job flushing/filling coolant or maybe the fan clutch isn't working properly.

What's your coolant mix, what brand of coolant and what ratio? Did you open the heater core and check the exp tank after it cooled overnight? System is self bleeding, but you usually do have to add more fluid the day after the first drive, after it cools completely.

[enjoy_m3]

I would check the temp sensor. Are you 100% sure system has been bled of air pockets? Even the heater core? Might want to re-bleed. Have you monitored coolant consumption/? It's also possible to have a defective thermosat.

[Tbonem3]

Cooling system is self bleeding, but still a good idea to open heater. When air does escape, the water level will then drop (check the next morning), so you'll need to add (to exp tank).

[Obioban]

I believe the Wahler parts you have are OE quality. I believe at least the thermo is OES by Wahler. Not sure on fan clutch. Rad is Modine if you want to save some $, but Nissen is very good quality, common on Asian cars. Honestly didn't know they had a e46 m3 application tho. Of what you listed, I really only have pause with the WP. Though, even lower quality WPs should still work ok enough at least at first before exploding lol. Perhaps the cheaper impeller design or material doesn't flow/spin as well?

I suspect something blocking the rad or a better job flushing/filling coolant or maybe the fan clutch isn't working properly.

What's your coolant mix, what brand of coolant and what ratio? Did you open the heater core and check the exp tank after it cooled overnight? System is self bleeding, but you usually do have to add more fluid the day after the first drive, after it cools completely.

IIRC the Geba water pump uses a metal impeller.. and none of the metal impeller pumps flow as well as stock (BMW used the composite impeller stock because it allowed them the flow the engine required, that they were unable to get from the shapes that could be created on a metal impeller).

[old///MFanatic]

The good news is you have replaced things so you can proceed from there. Had you used some junk brands it might be of some concern but you've used solid brands.
Before you go and replace parts that you probably don't need to you diagnose as best you can permitting. First I would check the codes with something like PA Soft 1.4 and see if there's anythng with temp reading inplausible. If noting odd in code readings I would replace the fan temp switch (lower radiator hose) and the temp sensor (by the t-stat). This can be your issue and these are inexpensive. Clean the contacts while doing this. I have seen these get coolant on them from prior system work and it messes with the readings.
You should also do the biggest issue after someone has done work on the system and bleed it of possible pockets.
I mean as of now the only thing giving you the impression something is off is the gauge you're reading. So you need to make sure those readings are correct before you replace new parts over again.

[eacmen]

IIRC the Geba water pump uses a metal impeller.. and none of the metal impeller pumps flow as well as stock (BMW used the composite impeller stock because it allowed them the flow the engine required, that they were unable to get from a metal impeller).

Ran the Geba water pump with metal impeller on our track car. Water temps were stable on track in 100+ deg F events. Granted that is high RPM and high airflow. Street driven car may have different experience.

[old///MFanatic]

Ran the Geba water pump with metal impeller on our track car. Water temps were stable on track in 100+ deg F events. Granted that is high RPM and high airflow. Street driven car may have different experience.

Yep sounds about right. I ran the Geba brand on my FI Coupe for a long time and no issues at all.

OP: Geba been around for over 50 years in Germany making water pumps, they're not an inferior quality brand. FCP Euro carries it and gives it their Lifetime Warranty.

In regards to BMW's pump issues. BMW had major issues with the plastic impellers breaking and coming apart from the WP shaft. Don't get me wrong composite WP are good now a days. They allow for a lighter balanced impeller and it's easier on the pump roational load and the pump's bearings.
"Cast metal" impellers aren't going to shaft strip or break apart though. But being heavier they don't have the advantage of being less fatiguing on the bearings.

So a composite style pump more often goes bad and you don't have any signs before hand. While a cast style WP will shows signs from the "weep hole" leaking and or the bearings making noise.