Hi all,

My first post here after getting an LCI 530d touring a few weeks back.

I have pretty bad mpg at the moment. iDrive indicates 26.7 mpg and I have calculated around 33mpg over a tank.
Thanks to good advice on here I found out about the thermostat issues. I was initially getting around 60-65 degrees even on a long run. After replacing I am getting around 82 degrees with some fluctuation.

I have taken the main stat out tonight and I am getting a new one in the morning. Out of interest I popped mine in a saucepan with a jam thermometer and popped some water into the radiator side of the stat housing. I then turned on the gas and waited for the water to drop in the stat. It started to open at about 84-85 degrees and was fully open by 88 (which is the stat's rating). I then cooled it down and kept putting water in the rad side until it stopped draining. The stat closed fully at around 84 again.

So this doesnt seem a hundred miles away from 88 and I am now wondering if anyone knows what the 88 degree rating actually means. Is this the temp that the stat begins to open or the temp it should be fully open?
Also can a few degrees really make the difference between 33mpg and 40-45mpg which is what I expected to get on this car over a tankful with largely motorway driving.

An interesting test and I will post my results as others have. The behaviour of mine seems so so similar to many other posts I have read on this and other forums so I am quite hopeful that the main stat will fix the issue. However 3/4 degrees really does seem a very small margin for that level of mpg difference dont you think?

Thanks all


Tim

 

I don't think you'll see a huge MPG improvement if your car is running at 82C.

In winter the MPG on these cars drops dramatically (they take ages to warm up).

Having both stats in tip top condition does get the car to temperature quickly and holds it there and that seems to make the difference in MPG especially when going from say 70C to the full 92C.

 

My 535d averages 29mpg - 12 mile spirited commute so your 33 isn't bad.

 

Thanks for the replies guys.

the car is now getting up to 92 degrees odd (96 on one run) and staying there pretty well.
latest MPG calc from brim to brim (changed the thermostat around half way through the tank) was 35mpg. Much happier with that. I have a long run this weekend so will update next week with a full motorways cruise.

iDrive still only reports 27 mpg which seems a bit off. Does anyone know if there have been any software updates which may affect this?



Thanks

Tim

 

Two things:
1. Check your iDrive is set to UK gallons amd not US gallons.
2. There is a transmission oil cooler stat as well that will delay your engine getting up to full temperature if it is faulty.

There are quite a few threads online on the various forums re: No. 2 (Google is your friend).

 

No.2 is assuming you have an auto of course.

 

I don't know about you guys but my car has a faulty thermostat that keeps minimum of 70ºC (instead of 90ºC) and i feel a lot more confident with it like this. It allows longer runs at wot before reaching excessive high temps. It is also a lot better for dyno runs.