HELP! Brief temp gauge fluctuation?

[mige39]

03' E39 @ 115k and have never had a "real" cooling issue before this.

I have, however, had a check coolant level happening intermittently since I got the car and have just topped it off whenever it came up. Well, about a week ago I got the coolant check message again and tonight I had some temperature fluctuation on the analog gauge. I checked the coolant level as soon as I got home and topped her off, but it was only low a tiny amount. I'm fairly confident I wasn't low enough on coolant that the car would overheat from not having enough coolant.

What happened to me tonight:


I had my engine temperature gauge go passed the middle mark this evening. I first noticed it after the car had been on for 5 minutes and I was sitting at a light.

The gauge appeared to creep to the 3/4 mark but would not go passed it, it was fluctuating a bit as if it was fighting to hold the temperature steady at that mark. This lasted about 20 seconds and I drove off.

When I drove off, the temperature went back to the middle and held there for the rest of the trip. I was a long way from home and went through some stop/go but the temp held steady.


I'm home now and haven't been able to reproduce the problem. It sits fine at idle and I drove about 15 miles without issue but i'm obviously still uneasy.

What do you all think? Coolant Temperature Sensor failing?

Could this be a bubble since I didn't bleed the system the last time I added coolant? Should I be bleeding the system every time I pull the cap and add in coolant?

[jamesdc4]

I'm not sure about bleeding the system every time you top off, but the fact that you have to top off at all can indicate a possible impending cooling system failure.
Also, the involvement of the temp gauge is suspect and would lead me to believe that you may have a small leak.
I would thoroughly check for leaks including checking your water pump weep hole and additionally, your oil for signs of coolant.
When was the cooling system last overhauled?

[deathwarden5]

Although slight temp gauge fluctuations aren't major or unheard of, in your case I would look into it. If there was no coolant loss and a fresh cooling system, I would worry about it. Since you are losing coolant, I would look into a leak somewhere, and try to fix it as soon as you can.

[TheMatrixz]

I think I top off my coolant every 4 months or so, though I don't have any leak. I think it's normal as I had to do the same for other cars too.

The E39 temp gauge has a buffer to hold it at normal display range, it's not a real time gauge. That said, if you see any fluctuation, it could be air trapped inside the system, just bleed it see if that goes away.

The cooling system (hoses, water pump, radiator, expansion tank and cap) normally fail at around 90k miles - 110k miles. Get ready to replace. It will happen.

About bleeding every time you top off, I don't think it's needed unless the coolant level was lower than the bottom of the expansion tank.

Tan

[Wolfen]

Coolant loss it means it's going somewhere. You may be burning it and in need of a valley pan gasket.

[ataie]

what is the normal coolant temp reading? mine never reaches the center (about 11 o'clock). I just changed the thermostat and still not in the middle. is that where it should be?

thanks,
02 M5

[mattmartindrift]

M5s are not dampered as severly as non-M cars. So, your temp gauge will read more accurately what is happening - it will move around more.

My 540 will be dead-nuts center from 75*C through 112*C. If you're concerned you can unlock your High OBC and use Test 07 to get an exact temp numer.

[ataie]

how do I unlock High OBC to check temp?
thanks

[mattmartindrift]

How do I unlock the OBC (Low and High)? (http://forums.bimmerforums.com/forum/showthread.php?p=14994497#post14994497)

[Tim Mclaughlin]

Does the expansion tank have a vent in the top of it my father in laws is leaking out the top near the rim replace or is this normal vent anyone thanks

[ataie]

expansion tank is about $60 new, so you can change it as they can just crack as they age. you also have a bleeder screw on top of the expansion valve which is about $3. that often brakes as well.

[Vatoman]

can you add a aftermaket temp gauge since this is such a issue with our cars seems like it would be a good thing to do for more accurate numbers.

[sovietbmw]

I had the same exact problem. It was the fan clutch failing. replaced it and the needle was rock solid in the middle. Couple of months later I had developed a radiator leak so i said screw it and did what everyone here always recommended - COMPLETE cooling system change. It's not even that expensive to do.