This would be temp sensor, correct?

That's where rubber band was changed a while ago but I put on one that looked similar so I'm pretty sure that's where I'm loosing coolant (reason why I changed it before).

I assume if that band is bad (or the sensor) that would explain why my engine temp gauge would jump up from time to time (almost to the red) and then come back down (all this in 10-15 seconds)..?

Dealer only part (meaning no way to get it before Tuesday)? I assume rubber band comes with it?

Isn't that temp sensor for the Fuel Injection? I thought the gauge temp sensor was on the thermostat? Someone else me know for sure.

Isn't that temp sensor for the Fuel Injection? I thought the gauge temp sensor was on the thermostat? Someone else me know for sure.

It seems to be plugged into one of the coolant hoses..??

I forgot to mention, this is on a 99 540i

ttt

ttt

That is indeed one of the temperature sensors. There is also one on the thermostat. Both are labeled "temp sensor". I assume the rubber band you're referring to is the o-ring on the sensor itself. Yes, it comes with it. The o-ring is only a problem if you have a leak.

Yes I had a leak there before, o-ring was replaced but not with one from the dealer. That was about 2-3 months ago and I believe I have a leak there again

Would that same sensor be able to cause temp gauge to jump up & down sometimes? or maybe if the leak is there it can create air bubble(s) in the system causing temp to jump?

Yes I had a leak there before, o-ring was replaced but not with one from the dealer. That was about 2-3 months ago and I believe I have a leak there again

Would that same sensor be able to cause temp gauge to jump up & down sometimes? or maybe if the leak is there it can create air bubble(s) in the system causing temp to jump?

It's plausible. Unfortunately, the only way to know for sure is to swap in a 'known good' or new sensor. If there is a leak again, you'll have to pull it and check the o-ring to see if it's damaged. If it's not, check the orifice that it goes into for damage. If still no damage (and assuming the o-ring is of the correct size), you can try using some o-ring lube on it to help it seal. I use stuff from the pool supply stores called Aladdin Magic Lube. It's specifically for o-rings and it works great. In fact, I would use it on a new one I was replacing as well. It really helps prevent damage on reassembly.

It's frustrating that every time I have a problem with the car it's either Friday and shops are closed or day before long weekend (like now).

Last time I had a leak it turned out to be because of that o-ring, I should've went back to the dealer later and changed it or at least made sure I change the o-ring to one that's the same as oem.

So that sensor can cause engine temp gauge to jump, what about t-stat?

I'm thinking that it has to be an error because it doesn't make sense that the engine really overheats (almost into the red) in 5-10 seconds and then cools down in 5 seconds (without aux fan coming on).

I'm guessing your temperature jumps are because there is air in the system. You need to fix your leak and then purge your system of air.