temperature needle jumps to hot after a second

[manjitr]

upon startup the needle is little lower than the middle (as the car has been stading for approx 3 hours) but then in a second it jumps to hot. I don't think my engine is hot. what could it be? how do i check the water pump ?

btw.. it's a 2000 740il

[libertylover]

Sounds like a temperature sensor problem to me but please clarify your description. So you ...??
1) Drive around and the needle is in the ... middle?
2) You stop for 3 hours.
3) You restart the engine and the needle is a bit below the middle, then suddenly jumps to hot after a second. Then what? After 5 seconds? After 30 seconds, etc.??

Did you drive it after the restart? If so, what happened? Is the coolant level OK?

[manjitr]

ok i used to get the check coolant level when i did a cold start for the past 3-4 days. my brother had taken the car in the morning and after 2 hours of him coming back home i cranked and the temp needle was on the hot side. so i let the car stand for approx 3 hours and filled in some coolant. then on start it stays below the middle line for a second and then jumps to hot. Didn't leave it on for a long time coz i didn't want to mess anything up.

Interesting note : Radiator fan start up at high speed but then changes speed to idle. shouldn't it be at high rev coz the temp is high.

Coolant level seems to be ok now.

thanx for helping.

[libertylover]

Well, hmmm. The fan thing does seem odd but...?? Have you quizzed your brother-was it running hot when he had it? Also, how much coolant did you have to add? If you had to add more than say, 1 quart/liter, you probably have a leak somewhere and the overheating was real. It's cooled by now, so restart and report results please.

[manjitr]

well the temperature has gone back to normal after a 3 minute drive... and has been that way the whole day. i think BMW should improve the engine cooling system if they haven't already in the 745.
We have had cooling problems twice in a year.

[libertylover]

Let's see, you live in Nevada-very hot in the summer, cold in the winter? The car is about 4 years old and no longer under warranty I'm assuming. Hmmm.

If you haven't already done so, you should probably flush the cooling system and replace the coolant since those high temperatures do a number on it. Also, you might consider replacing your hoses that go to/from the radiator, the heater core, and to the engine of course. At least inspect them to make sure they are not all cracked and brittle. The hoses themselves won't cost much but they're probably a pain in the butt to change. Failure mode for a water pump is that they start to leak pretty obviously. Maybe have the radiator pressure checked at a radiator shop. Check the coolant level once/week to see if it needs to be topped off. Good luck.

[manjitr]

cold in the winter ??
it just snowed here last month !!


ok i have changed coolants for other cars(honda) as they don't happen to have their underneaths covered so it's easy to find the drain plug..
so u have any idea where the drain plug for the 740 is ??

[libertylover]

Sorry, I don't really know where the drain plug is. I'd have to search for it as well. I can tell you that most of those plastic covers underneath come off easily and may make access to the drain plug a whole lot better.

[libertylover]

I was underneath my car today so I took a look. The radiator drain plug on my '93 740iL is on the left side at the bottom of the radiator and it's a blue plastic plug. Hope this helps.

[manjitr]

thanx. i let the air bleed and cooland level went way down and i filled it up.. no check coolant warnings now and temperature is normal.

[manjitr]

had a expansion tank explode a day later.. but thanx to extended warranty it was replaced and two months later i get the check coolant warning again and temperature started going up.. took it to BMW and they kept it for 2 days still have no idea were the leak is .. !!

[libertylover]

Sounds like the problem is better at least. As I understand it, it's OK until the coolant level leaks out too much.

For what it's worth, my car's coolant "disappears" as well and I have to add about 1 quart/month here in hot hot Florida. On the underside I've seen a few drops of coolant but I've never figured out where the source is - I just top it off as needed. On my car the "Low Coolant" warning will come on without the slightest hint of overheating but my radiator is brand new thanks to the previous owner.

[manjitr]

well at least u don't overheat..
try driving around in nevada with a car that heats up when you turn the a/c on.