I didn't see any fault codes related to the thermostat. But I can definitely look again. That's a good idea - it hadn't occurred to me to check for that.

The coolant level sensor is installed in the expansion tank, but nothing is plugged into it. And I can't find a connector nearby. It should be right in the immediate area because there usually isn't any extra slack in the wiring. I'm going to unplug the sensor in my E39 528iT and see if it triggers the low coolant warning light. Then I'll know if that's causing a problem or not.

The wire that plugs into the expansion tank runs behind the tank and into the firewall.

What is this FFT-FFF-FFT Sound?
 

My most recent project-within-a-project has been to overhaul the cooling system in the X5. It has a new radiator, water pump, thermostat, expansion tank, expansion tank cap, upper/lower radiator hoses, and fresh BMW coolant.

I was having a problem with it running hot, but have not gotten it out on the road yet to see if the cooling system overhaul did the trick. The last time I drove it, I noticed a strange sound but thought it was a bad idler pulley on the serpentine belt. I replaced the pulley when I did the cooling overhaul, but noticed the sound was still there so I listened a little closer.

I have my suspicion of what it might be, but I want to get some other input before I go there. I shot a quick video with my phone and the noise can be heard every time I rev the engine. I'll quickly rev it to 2,000-2,500 RPM and you can hear the "FFT-FFT-FFT" sound each time? Any theories about what it might be?

I tried to embed a video I uploaded to YouTube, but can't get it to work. So here's a direct link: https://www.youtube.com/watch?v=v_5gQpTYfzE

Well boys and girls, it looks like I'm going to be replacing the head gasket on this project car after all.

When I bought it, I knew this might be a possibility and figured it into my offer price. I just hoped I could avoid it.

After installing all the new cooling system parts, I took it for a test drive. I just drove back and forth on the street in front of my neighborhood. After about 10 minutes everything was looking good and I thought I was golden. As I turned back into my subdivision, the temp gauge started to climb and just hit the red as I pulled into the driveway.

I popped the hood and could hear the coolant boiling in the expansion tank. And even though it was tightly capped, coolant had still sprayed past the cap. There is no doubt that the cooling system is being pressurized. The FFT-FFT-FFT sound also got worse as the engine warmed up.

I did go ahead and drain the oil, though. Lots of water in it. It was very thin and runny, too. I changed the oil filter and filled it with fresh oil. It's probably going to take a couple of oil changes to get it cleared out.

Next week I'll get the head pulled and take it to a machine shop. I'm interested to see what it looks like since it's already been off recently. And to be on the safe side, I'm going to Timesert the block while I'm waiting for the head to come back from the machine shop. Fun, fun, fun!

:/

Going to have a look at a rod bearing? Good luck.

Jeez, I hope not! :)

I assume you will be checking the block for cracks and flatness?

You assume correctly! I'm not taking any chances!

Alex, I'll take "Who Needs a Head Gasket for $1,000", please:
http://www.creative-pro.net/cars/x5/VC_Yuck.jpg

Yuck!

Not pretty