35d Normal Thermostat Operation
 

It's been 3 weeks since I replaced my thermostat in my 2011 X5 35d. This morning it was -20°c so I thought I'd monitor my temperatures a bit.
My morning commute is 60 km highway driving, it took 20 km for the engine temperature to reach 75°c, 35 to reach 84°c and as soon as I coasted down to 50 kph the temperature dropped to 73°c.
Around town I saw 70°c to 73°c.
This is on a new OEM thermostat, so just keep in mind if you're checking thermostat condition in the winter you're going to need a long highway drive to get a good reading.

In "normal land" I would conclude that thermostat is not closing completely. Somebody out there with another oil burner to act as a control.

"New doesn't mean fixed" I say all three time. You could pull the heater wire on the thermostat and confirm if the engine is deciding it wants to new cooler and determine what the natural open temp is for the thermostat. On gas 3.0, I'm used to seeing about 90-95C which is a lot different from your numbers.

Its gonna take me a good 20 hours of driving to get to -20F temps!


:cool:

It's an 88°c thermostat and I see that all the time in fair weather. The cold will be different as most of the heat goes to warning the cabin.

I would check the output radiator temp and would like to see some other d driver feedback. The ECT seems way too low. Unless the d needs lower temp and the DME is forcing tstat open it seems very suspect to me

I'm not familiar with temps lower than 20*F soooo take this with a large grain of salt. At -20*C would it be beneficial to block the front grille with cardboard or something?

Living where 0c is the norm for 2-3mo and -35c is occasional, the radiator cardboard situation only helps the heat up time. I've driven my X5 at -25c and it will get the engine to normal operating temps in 10-15 minutes. The cardboard helps the speed at which the cabin heat is effective and I will usually put some in about Dec 1 and leave until feb.

I just did a little test, heater off and engine temperature had no problem getting up to 88°c. I turned the heater back on and the engine temperature dropped to 80°c within 2 minutes. The thermostat is just fine, everything is working like it was designed, but heating up the cabin is a lot to ask from a diesel.

In that case, cardboard. Sounds like the engine just doesn't make as much heat to dump as petrol powered models.

Where are you located? -20c is chilly for early November. It was 22c here yesterday (though that's was a crazy fluke it is 3c today)

I live in southeast Saskatchewan, and it's usually not this cold in November but we just had a storm go through. I'm not a huge fan of cardboard, I don't think it's necessary. My engine temp was low because of heating the cabin, not because of flow through the radiator. I also prefer to leave the radiator free to do its job if needed.
I'm also not concerned with the temperatures I saw. I just wanted to make a point that sometimes the thermostat is working properly but the engine temperature is still low due to other conditions.

I thought the movable flaps in front of the radiator act as 'automatic cardboard'?

Aren't sustained low temps bad for the glow plugs and eventually module? I had a failed thermostat without knowing it and needed to also replace glow plugs and the module. The only indication of a thermostat problem was the code for glow plug fault.

Negative those flaps are to allow more air to flow though the radiator when moving but keep all aux fan air going back vs out the front when not moving.

I know my gas engine didn't operate properly when ECT stayed below 80 and when it's below zero F I definitely block my radiator to help keep ECT in the operating range of the m thermostat. I will cover just half the radiator for temps under 10-20F but below 10F or -12c I'll switch to full coverage. I've never seen ECT get over tstat control when radiator is blocked and temps are super cold. I intentionally don't make a perfect seal so some air always gets to the radiator.

The thermostat is not electronic on the D. Heater operation does drop temperatures and cardboard/ plastic helps in the winter. When you realize that 35d can do 34 mpg at 60mph, you see that there's not much heat wasted.