[Godzilx]

Hello,

I am chasing a 2E81 code that is causing my car to constantly overheat. I installed a brand new water pump, thermostat, and coolant reservoir 2 months ago and this started happening immediately after, got progressively worse and the problem started changing. I also have a CSF radiator.

Car is a 2007 E90 335i

TLDR:

ONLY getting 2E81
New WP, thermostat, CSF radiator and reservoir
Car used to instantly go straight to shutdown and spray coolant out cap, now only limp mode and no spray
System was bled multiple times
Fuse for thermostat and WP are good
No heat coming from interior vents
NOT losing coolant
Coolant pipings not overly hot, oil temps normal
Pump command on Protools works for ~20s then shuts off
Running EFan and pump on Protools also shuts both off after ~20s
No white smoke out exhaust or coolant on oil cap

My next step is to replace the WP and thermostat again, but the issues Im having are strange, and I need to drive the car over an hour to work on it. It’s looking like it’ll need a tow, so looking into other suggestions before I do that.

How I got here:

In May I had a track day where the car did great. Once I drove the 3 hours home, as soon as I got into my town the car threw a ton of codes regarding the water pump and BSD system.

Upon looking at the WP, the housing was cracked and coolant leaked into the connector. This BSD fault would also cause my battery to drain completely so I replaced that as well.

So I replaced the WP and thermostat and bled system multiple times (fan low, temp high, foot on pedal). After that the car would occasionally still overheat (Once every ~2 weeks), skipping the yellow warning and going straight to red. By the time I restarted the car coolant had dropped from 255° down to 210°. I took off the connector and cleaned up the terminals plus checked fuses, and the problem seemed to occur less, but could be placebo as it was rare at the time.

Fast forward to August I had another track day. Three sessions in everything is working great. On my fourth, I instantly go into red limp mode and coolant starts spraying out of coolant reservoir cap. I let it cool and I was still able to drive it home, again another 3 hours without any overheating or more spilling. Never got above 210 on that drive home.

After that track day, I replaced the reservoir.

After replacing it, the instant shutdown mode only happened one time a few days later. Then, it stopped shutting down and spraying, and changed to only going into limp mode without any spray, but way more often.

Fast forward to now, if the car is totally cool I can make it 20-30 minutes on the highway before it goes into limp mode. Before the 20 minutes mark, coolant will bounce up and down between 220 and 180°F. As soon as it goes over ~230°, it can’t be stopped and it continues to rise to 250+ and send the car into limp mode.

I am also now noticing, my car will not blow hot air out the vents. I have tried 70-84°F, with the dial by the hazards button on the hot setting.

Also when the car overheats, the reservoir and other lines are not extremely hot, they’re almost touchable. Pressure is built up in the reservoir and I am NOT losing any coolant.

When I use protools and command 50 or 95% pump speed, it goes at the commanded speed for about 20 seconds then just shuts off. It used to run indefinitely between my two track days (After replacing WP/Thermostat, before reservoir). Also, I tried running the pump and EFan at the same time, and they then both will shut off after 20s.

Another thing I’ve noticed, is that when around 250° and coming to a stop, the temperature will drastically decrease 10°, then as I wait stopped will shoot back up to 250.

Just before writing this, I couldn't get the WP to turn on with protools. I simply took the WP fuse out, and put it back in, and it works again in 20s intervals.

So the pump turns on and off, but seems to time out when asked to maintain speed. I have a feeling there is an issue with the BSD system or something electrical over the pump itself. Temperature outside seems to have little to no affect on overheating.

My working theory is the pump is hitting a certain duty cycle, and then shuts off after the 20s as seen with protools. So when the car hits the 230ºF threshold, maximum duty cycle is commanded until it cools, and since it shuts off after the 20s, it cannot return to below 230 and this leads to overheating.

My next step is just to ahead and replace the WP and thermostat, but does anyone have any other suggestions?

Thank you for your time.