Porch

So I took my 06 530xi touring in for a coolant flush as preventative maintenance, because the coolant wasn't blue, and I figured I was doing the right thing. That same day, the car got too hot on a fast drive through the mountains, for the first time since I've had it. Took it back to the shop next day, they shrugged their shoulders and said "need new water pump/thermostat, $1400", which I can't afford. Took car to my friend who's a "retired" vw mechanic, we tested water pump, seems to be working fine, and he diagnosed the thermostat as being stuck closed. I got a tstat locally and with very much of his help, installed it, which was a fairly miserable job. Got the car back together, filled the coolant properly with a vacuum(the shop that did the coolant flush did also), got the car up to temp, tstat opened at like 245f, fan kicked on, temp plummeted, gave my buddy a high five, and took off up a hill, and... car got too warm again. Note- I haven't kept the car under a load after getting the temp warnings, so I don't fear engine damage.

Here's my long-winded question- I have a bimmergeeks protool bluetooth scan guage thing so I can have guages like oil/coolant temp, knock sensors, and any number of other things, all on my phone while I'm driving. After the temp thing started happening, I set one of the guages for water pump speed, and it seems to be operating properly during driving- it speeds up under acceleration, slows down after, etc, but with one caveat- it only usually slows down to 194rpm. That's been its default speed since I set up the guage, with the exception of early on after the tstat replacement, where it was running at sub-100 speeds all the way up to 250...

So finally my question is, may this just be an electrical problem with the water pump? I ordered a graf pump, but would LOVE to send it back if I can solve this issue with a fuse or something like that, because replacing the thermostat was a huge job that I don't want to do again if at all possible!

Notes- the coolant system has no leaks, not before/after the flush, nor after tstat replacement. The shop that did the flush did not use any kind of detergent or stop-leak products for that service.

Also, just realized that 194rpm is baseline speed for the wp, with the heat on. Turn the heat off, and slows to 53 at idle, but fluctuates with driving.

habbyguy

Same car I had. When I swapped my pump and thermostat, I was shocked to see how much debris had accumulated between the A/C condenser and the radiator. It literally obscured the lower half of both of them (maybe a bit more).

To me, it sounds like your pump is doing the right thing, and assuming your T-stat is opening as designed, I'd start looking elsewhere for the problem, including a gunked-up radiator (possible since someone previously used questionable maintenance practices).

FWIW, you can see a video on the pump / T-stat replacement, as well as cleaning out the space between the condenser and radiator here (the portion showing the debris starts around 8:15):

Porch

Yeah, I left a fair amount of debris in the bottom of the radiator due to time constraints, but got a lot out with the vacuum. That space was like 2/3 full of crap. Was wondering/hoping that I could remove the plastic tray under the radiator to get the rest of the debris out, or maybe get the radiator loose from the condenser without undoing any hoses...

habbyguy

In the video, I worked the radiator up a bit (IIRC) and got enough space to force out the debris, using a vacuum and compressed air (and a long stick). Amazing how much accumulates there, given the relative inaccessibility of the area to human view / touch!

Porch

yeah, I don't get it at all! Same with all the leaves, etc that I found in the cabin air filter areas when I first opened them up...

Porch

So I got all the crap out of the bottom of the space between the radiator and ac condenser with an air compressor, stick, and vacuum(tons of debris down there), and went for a drive. The car is more drivable now, like the temp drops more quickly when you unload it, but it still gets hot when I go up a long hill. The temp is more reactive to the water pump spooling up, but sustained load on the engine still makes it get too hot.

in the mornings I've been opening the coolant cap and starting the car to check that the wp is pumping, and with the heat off and wp going at like 50-60rpm, it's like barely a trickle, but when I turn on the heat and wp is going 194rpm, it's a steady stream, but not as strong as I've seen in some videos. That suggests low water flow, but why would this happen all of a sudden, the same day of a coolant flush(which was very expensive btw)?
something got stuck in the water pump maybe? Or the radiator? When we drained the radiator to replace the thermostat, the coolant was quite dirty(thought I got my coolant flushed?), so I don't know. Wp seems to be working according to scan tool, but maybe it decided to check out the same day of the flush? In any case I have a graf water pump and behr radiator coming soon, but want to rule out other things before installing these- fuses, relays? If nothing else, I'll install the radiator first because it's easy, and will exchange more dirty coolant, then if still acting up, the water pump, which will exchange more coolant.

Wish I never got my coolant flushed. I'm missing peak fall colors in NC because I can't drive into the mountains. And I don't have any faith in the local bmw specialty shop anymore.

habbyguy

My guess is that the new radiator will take care of the problem. I'd bet that the flush liberated some "big chunks" which are large enough to clog the passage entries in the core.

Out of curiosity, what brand water pump did you use? I've heard nothing but horror stories with anything other than OEM (Piersburg, and I guess Graf).

There are also those who claim that a vacuum fill for the coolant is necessary after the water pump change, though it's hard for me to imagine that the pump isn't fully "wet" with a normal fill, being approximately the low spot in the cooling system... but that's using logic, and often BMWs are immune to that.

Porch

I bought a graf pump, behr radiator. We did use a vacuum to fill the coolant system when we replaced the thermostat, my buddy is a former vw mechanic so he has every tool. so did the shop that did the "flush". Next step is radiator replace, then if need be, water pump. Wish me luck.

habbyguy

My money's on the radiator being the source of the problem. For your sake, I hope I'm right! ;-)

Porch

New Radiator solved the problem baby! What a joy to look at the temps now! And that's an easy repair- that's the first place I'd start, for anyone else having cooling issues. Only caveat is the new mahle-behr Radiator doesn't have a drain hole, but I guess that's probably why it was $130 at autohausaz.com, rather than the prices I was seeing elsewhere. But I wouldn't flinch at replacing it again, if the car lasts long enough to need it!