Is that a steady 90c, no matter what? Mine currently settles at 83/84c and I'm debating whether I should change the main one as well...

Also, theo, what year e60 do you have?

 

They are the same temps as mine was. I would try the EGR first as mine was wide open. My temps now sit between 90 and 94 all the time.

 

'04 530d.

The temperature moves within a range from 88 to 92 when it has reached its operating temperature, 88 on constant high speed (lots of air cooling) and up to 92 when stationary in traffic after higher speeds.
I would replace it within the coming months, your fuel efficiency is probably not suffering yet but DPF regeneration might. And in any case, these thermostats do deteriorate over time. Yours is on its way so it's only postponing the inevitable.

 

I have seen the DIY you tube vid for the egr one, is there a tutorial for replacing the main one?

 

Also very similar.

 

In terms of Mpg, a lot depends on your mileage, an extra 3-4mpg will save you money, but the cost of replacing the thermostats can be quite high.

In terms of this alone you need to balance how long it will take the increased mpg to pay back the cost of the fix.

 

You would really only see a significant increase in MPG after changing the T stat if the check engine light was on. When the check engine light is on, the computer is programmed to run on 1 set of operating values, thereby not constantly changing the operating values based on a variety of conditions to optimize fuel consumption.

 

I have changed my thermostats twice. Really both of them twice and I still can't reach the correct temperature. But there seems to be different modes to it:
When I start the car first thing in the morning and drive the car for example 30 minutes, let?s say 20 miles without any traffic I can get about 80?C as a maximum and I can?t really feel worm in the car.
If I stop for a coffee or some shopping, than the car is reaching 90?C without any problem and you can feel really worm, even I would say hot, than I need to change the setting of the knobs to maximum cooling.

If I?m in the traffic, and my A/C is off (does not matter summer or winter) the temperature is going up to 97?C and then it drops and it is between 87-94?C.

And as I said, I have changed both thermostats twice and it seems to be almost same.

 

You might find this thread interesting, member Milko75 mentioned a third thermostat there which could also influence your operating temps. Never knew that before.

 

Thats not true at all. Poor MPG is one of the reasons many people find that the thermostats are knackered. With a cold running engine the its like running on choke so needs more fuel. The ecu isn't that intelligent to know what the thermostat is doing it just knows what fuel it needs when the engine is running at X temp. Some of the petrols now have electronic thermostats then the ecu can tell if the engine should be a what temp but that's not the case with the diesels.