Running cold on motorway, not thermostat :/

[porka]

Hi guys, I have a strange problem with my 04 3.0d.

Arround town, the temperature very slowly gets to normal, about 88c and on the motorway it drops down to barely over 60c.

Simple I thought, dodgy thermostat, so I replaced it today and no change !

Whilst driving and keeping an eye on the digital temp. readout under option 7 I noticed something very strange.

Below 2200 rpm, the temperature gets to normal and above that it shoots down

Basically just under 70mph normal temp. and at 75 its gets down to 60 odd, crazy !

It's as though the thermostat is opening at higher revs, but how is that possible ??

Maybe someone has come across this before ?

Thanks for any help !

[emil]

similar to my -01, 3.0i

anyone?

[ArtMan]

Interesting....I m having the same problem as in if i drive slow it heats back up and on freeway it will cool down...I just assumed that the Thermostat was just busted but if yours still active like that its really odd.....ill be changing mine soon but ive read that if you change that its time to change the water pump also...and im a little tied down with money so maybe next month...but ill post how mine goes once i do it.

[amacman]

I am making a wild guess that the viscous fan clutch is not disengaging causing the fan to run constantly .
if this is the problem it needs fixed quickly .

[m5james]

The fan clutch would sound like an engine taking off, so I would hope that people would notice the sound differences and pedal feel via the parasitic drag. A seized fan can break under all that force, enough to the point where people weren't fixing them soon enough and the broken blades went through everything from hoses to the hood itself. A simple test is to open the hood and spin the fan...if it doesn't, you literally need to stop driving it now before the blades break.

If that's not it, id say to rebleed the cooling system. If there isn't enough coolant or air bubbles in the system, you'll get wrong readings and could be overheating your engine without even knowing it because the coolant isn't even touching the temp sensor.

[porka]

Thanks for the replies guys.

I took the viscous fan out all together last night and went for a quick drive. No difference. Something happens at 2200 rpm and the temp. goes down, regardles of gear. Below that, it is normal.

I have found more references to this problem with 5 series owners:

BMWLand: Where Power Meets Control - UK BMW - 530D E61 - what temperature is normal?

The only trouble is that the fix is the EGR thermostat and I don't actually have one on mine. There seem to be two versions according to realoem.

Another possibility are cooling flaps which open and close electronically. Can't find anthing on realoem for my car but will go and have good look soon.

[radaddict]

Perhaps it's the temperature sensor. I don't know about the diesel, but on the gas engines, the sensor is hot and gets cooled by the coolant (this way, if the coolant is too low or isn't flowing for some reason, the temperature gauge will show hot before the engine actually overheats - hopefully). If the sensor is malfunctioning and not getting hot enough, the coolant will cool it down below what is normal.

This is mere speculation on my part. However, the cooling system is pretty simple and if it's not the thermostat, there's precious little else it could be.

Good luck!

[porka]

I guess it's possible, but it's strange that it happens at 2200 rpm, below that it stays warm, even at 2100 rpm, then if I take it to 2300 rpm it starts to cool. Back down to 2100 and it starts warming again.

Had a look at the flaps but they are not electronic so can't be that.

I had a play with the old thermostat in a pan of boiling water and it opens, then closes as the water cools so basically it was working fine. There is however also a top part to the thermostat which doesn't move with the bottom part but is spring loaded. Just curious what that part is for.

[radaddict]

Originally Posted by porka

I guess it's possible, but it's strange that it happens at 2200 rpm, below that it stays warm, even at 2100 rpm, then if I take it to 2300 rpm it starts to cool. Back down to 2100 and it starts warming again.

Had a look at the flaps but they are not electronic so can't be that.

I had a play with the old thermostat in a pan of boiling water and it opens, then closes as the water cools so basically it was working fine. There is however also a top part to the thermostat which doesn't move with the bottom part but is spring loaded. Just curious what that part is for.

Well, higher engine speed circulates coolant more quickly. Coolant circulating more quickly would have a greater cooling affect.

[radaddict]

Do you notice a difference in cabin heater output when the temp gauge drops? Does the heat coming out of your vents also get cooler? This would give an indication of whether the engine is actually operating at a lower temperature or if the gauge is not accurately showing engine temp.