Let me see if I can add my .02$ here. I wouldn't drill anything?!? I don;t know the purpose of doing that because the only way I know how to close it up is to tap the hole and then plug it with a screw, but that's a lot of unnecessary work IMHO. Frankly, it could be a number of things. The most sever is a cracked head. A cracked head allows more heat to enter the motor, triggering the switch to read hotter, but you can tell if there is oil in the water. Another thing could be timing, off timing makes the motor run hotter. Or when you disconnected the plug to the T-stat, you might have slightly damaged the connector, which gives a false reading. Try cleaning the connector with contact cleaner, let it dry and see what happens. Like Weasel said, I don't think its the sensor itself only because, as you drive faster, the engine gets hotter, but you are also introducing more cool air in the system, which balances it out. Just like if you have a known temp problem, sitting in traffic compared to driving, the temp gauge rises faster sitting than driving because there isn't any air passing through the system.

Well as of now, no water in the oil(deepstick or cap)nor oil in coolant. I've never messed with the timing. Just after I replaced the waterpump, I made like 145-150mph and everything was perfect. Since that little hose got cut off by the fan, I've been having this problem. It's really getting hot because it would spill the coolant from the expansion tank and also that rad hose is getting hard, so I don't think it's a faulty thermostat sw or wire. Correct me if im wrong. I could try that to see what happens. Also it would sit there idling 30-45 mins( that I've done) and wouldn't get hot......... This thing is driving me crazy!!!!!! Guys, I really appreciate your'll looking out for me.

May be a debris from the hose went into the cooling system and blocking partially a passage.
...just in case;
don't take this as an insult.
Did you put rags in holes to keep debris from falling in during the water pump replacement? If yes, did you remove all of them?

It couldn't have been debris from the hose cause the fan rub off on the hose until there was a little hole where coolant would just be spraying under pressure(when at oper temp). No I didn't use rags to block any holes, I cleaned everything perfectly before installation. (not a messy diy, lol). The only thing I could think of right now us that aux pump. I'm not too sure what exactly is it's function and how it operates. What do you think?

OK guys, I back with this problem again. I don't drive my X5 often that's why it took a little while to respond. I replaced the aux water pump and the problem went away for a while. The pump was faulty, it would work only when i shake it. I took it to almost 150mph twice and everything was ok. Here is the problem now, after driving for a few times, it's doing the same thing again, once i accelerate to over 80mph, the temp gauge will go up to red and right back to normal(half) the coolant will spill all over the left side of the engine from the expansion tank. It's a new(genuine) cap, expansion tank, radiator, fan, clutch, aux water pump, thermostat, water pump. Recently it sat there for about three weeks, and when I started it, I saw the left exhaust steaming out a bit, it lasted for about 20-30 seconds. Now i'm thinking I may have to replace the head gasket. No signs of coolant in the oil and or oil in the coolant yet. I've read a few posts concerning the oil seperator and its effects, I'm really not sure whether i should do the head job which I know will cost some good $$$ OR is there something else I can do. Any ideas will be greatly appreciated.

You could test for a blown head gasket. Go to the local parts store. It will probably be called a bock tester. Looks like a huge dropper and includes some fluid that changes color in the presence of hydrocarbons(fuel)

Sounds like a text book head gasket or cracked head issue.


Sent from my SGH-i917 using Board Express