So just thought I'd pass this along.

My ACD is malfunctioning in some way and it has all three lights on. After researching in here I learned I didn't need to worry as it won't damage anything if I continue to drive this way for a bit. Well, procrastination has turned that 'for a bit' into a few months.

But here's the fun part. With my ACD in this condition, I get 10-15% better fuel mileage.
I don't think this is very surprising, but I didn't think it would be this much.

Comparison. (I keep track of every gallon of fuel I put in my car.)

Both examples are 100% highway.
Date Tripometer Gallons Price Odometer $PG MPG
6/11/07 300 12.641 $41.20 19490.3 $3.26 23.73
After ACD issue.
6/23/2012 308 11.214 $41.48 46272.2 $3.70 27.47

Also, if I had to guess. City MPG has gone from a rough average of 18mpg to 22mpg.

Of course, I'm going to get my ACD fixed. But it would kind of be nice to switch it off to save fuel when I'm not doing any 'spirited' driving.

 

My acd has that on too. I'm bringing it in to get the lights turned off but i'm pretty sure it locks the center diff 50/50.

 

Isn't that just like tarmac mode?

I dunno, I think the op might of just driven really slow being careful because something is wrong with his car. But if he keeps really good track of his mileage and drives the same as before, then that's a pretty suprising difference.

 

I haven't changed my driving style at all. These are pretty close to apple-to-apples.