[TDF10]

Hey everyone, first time poster but long time lurker (both here and on E46 Fanatics [when I had one]). I just finished a major overhaul on my car (2014 535d) as I crossed the 85k threshold. I had a coolant leak coming from the coolant flange and given the work required to access it, decided to replace a lot of items on a preventative maintenance basis. I replaced water pump, engine thermostat, transmission oil cooler housing + thermostat, all associated gaskets and seals, serpentine belt, tensioner, 5-6 coolant hoses, cleaned out my intake manifold, replaced every gasket and seal in the manifold, replaced the coolant reservoir, changed my oil, cleaned out my cabin blower (there were some leaves causing noise), and replaced the windshield cowl.

Prior to working on the intake manifold, I replaced the water pump, thermostat, and several hoses. I took the car for a test drive and noticed that it was not getting up to temperature. It was about 50 degrees outside and as I got on the highway, the car actually want from about 1/8 warm down to cold. When I got back, I noticed I still had the coolant leak and figured that maybe there was air in the system (despite bleeding it) or the thermostat was bad. I replaced the thermostat again and then did the intake manifold work. I fixed the leak and put everything back together.

The car is running great except for the fact that it now won't get to normal operating temperature. I had to run it hard on the highway (90 MPH at a low gear with the turbos spooling) just to get it to normal temp. As soon as I left of the gas and cruised, the car once again started cooling. In the morning, driving it on the roads, it won't warm up normally. I'm at a total loss as to what could be causing this. Since I replaced the new thermostat with one from BMW, I don't think it's that (I tested the old replacement thermostat and it functions fine). I'm wondering if there is any way that a bad battery could cause a poor temperature reading (I've noticed my battery is getting weak)? Aside from that, I'm wondering if coolant got on one of the electrical connectors and is now causing issues? The caveat to both those issues is that the water pump and thermostat are mechanical so the only issue from an electrical perspective would be the dials in the car. I made sure to install the thermostat with the pin down at the 6:00 position (as outlines by BMW) so I don't think that's the issue either. To bleed the system, I just let it burp itself and went through the normal coolant filling procedure.

If anyone can point me in the right direction, I'd sure appreciate it. I'm pretty good with cars and mechanically inclined but this one has me stumped.

[bk_mike]

Did you follow the coolant bleed procedure in TIS? I suspect you still have air in the system.

[TDF10]

Thanks for that info. How would that cause the system to run cold? I didn’t use a pressurized bleeder. But, I do think I followed the appropriate procedure (saw it on Bimmer Post) for venting the cooling system. I noticed the return line in the coolant reservoir was returning coolant without bubbles. See below for what I followed. If the issue is related to air in the system, would the solution simply be to hook up the pressurized system and draw out air or would I need to drain and refill?

1. Switch ignition on.

2. Set heating to maximum temperature and fan to low (heater valves are open and auxiliary water pump starts).

3. Add coolant slowly. Fill expansion tank to maximum cold level.

4. Start engine and run at idle for 5 minutes (top up coolant to maximum cold fill level if required).

5. Close cap on expansion tank, press accelerator peda!
several times to approx. 2500 rpm

6. Open cap on expansion tank, run engine at idle for another 5 minutes (bubble free coolant will emerge from return line in reservoir tank).

7. Fill to maximum cold level. Top up expansion tank with an additional 250ml.

8. Close expansion tank.

9. Drive vehicle and monitor coolant level. Top off as necessary.

[bk_mike]

That's the procedure I was referring to. Usually air would make the engine overheat not overcool as you mentioned. It sounds like the thermostat is stuck open. Do you have ISTA? Have you pulled the codes?

Also any chance you replaced the coolant temp sensor?

[TDF10]

My understanding as well was that trapped air would cause overheating. It does seem like the thermostat is stuck open but I don’t know how that could be the case given it’s new, and since I screwed in the thermostat housing which can only be screwed in once the thermostat is properly seated. I had the same issue with the other (brand new Febi) thermostat that I removed. I’d figured that one was a dud but after testing it with boiling water, I confirmed that it was in fact working. I’m so confused and wondering if I ought to just remove the water pump and thermostat and reinstall. Any other ideas?

[TDF10]

To everyone who chimed in, thank you.

I wanted to close the loop here in the hopes that this can help someone out in the future. I got my car back from the body/windshield shop after some minor repairs to clean up the front bumper and install a new windshield. While the car was in the shop, I purchased a coolant vacuum filling kit, new coolant, and a new temperature sensor. I installed the new temperature sensor with no positive effect. I was able to get into the secret menu and see that my car was cooling very slowly and even once it had a bit of heat, as soon as I started cruising or coasting, the temperatures were dropping. So that wasn't the problem. I then proceeded to remove the thermostat. To avoid any install issues, I also removed the water pump entirely so that I could clearly see whether the thermostat was properly seated and sealing. While I had the thermostat out, I also tested it by throwing it into some boiling water. That test confirmed the thermostat was indeed working. I installed it carefully, torqued everything down to the proper specs (EGR cooler, thermostat housing, water pump) and then proceeded to refill the coolant. I was able to get a really good vacuum on the system and let it sit for 5 minutes to confirm there were no leaks. I filled up with about 1.75 gallons of coolant and then reinstalled everything. I took the car for a test drive a the problem was fixed! I don't know whether it was the thermostat or an air bubble but it was definitely one of those two things. The car now heats up perfectly. I guess what they say about "third time's a charm" is based on at least some truth...

After all the work I did (new belts, washed in intake manifold, oil change, new water pump and idler pulley, coolant flange, oil cooler + oil thermostat, new coolant thermostat, cleaned out leaves from the cabin blower, new windshield, resprayed front bumper, ceramic coating), the car drives incredibly well. Sitting at 82k miles and it feels better than when I bought it was 22k miles.

Cheers

[ezaircon4jc]

Originally Posted by TDF10

... minor repairs to clean up the front bumper...

Cheers

Can I ask where you had your bumper done? Cost? Satisfied? My front bumper has severe road rash from a trip to Texas and I'd like to get the license plate holes filled. THANKS!

[TDF10]

Originally Posted by ezaircon4jc

Can I ask where you had your bumper done? Cost? Satisfied? My front bumper has severe road rash from a trip to Texas and I'd like to get the license plate holes filled. THANKS!

Ikon Auto Collision in Temecula. They are great. $650 all in.