MaxD

In late October I undertook the DIY timing belt/water pump replacement. It was a battle, but I successfully completed the job and everything is working well (although I wake up some mornings with the cold shakes worried I might not have tightened something down enough )

I had a hell of a time getting the timing belt over the pulleys, etc. It seemed an incredibly tight fit considering I assumed the tensioner was supposed to allow some slack prior to releasing the spring. Anyway, it doesn't make any noise or anything, but I've noticed my fuel economy has dropped by about 2 mpg ever since I completed the job. I'm not relying on the computer economy values - I track it myself with a handy iPhone app. I usually average 23, and now I'm averaging 21 on the same daily commute.

Any chance the two are related? Is it normal to see a temporary drop until the belt stretches a little?

Catamount90

It certainly make sense that the added tension on a fresh belt & new tensioner would create more drag on the rotational forces.

However, I think I'd sleep better at night knowing that I had a fresh belt & stuff tensioner rather than a sloppy belt and +2 mpg.

As long as you tensioned correctly I'd say you're all set. (I'm doing my TB + WP now and am slightly confused about setting the correction tension myself... which brings me to AW this evening).

lyleswk

Maybe the tension. Could also be something much less obvious and not related...like fuel blends. Not sure when Denver switches or if you do, but in areas where this does occur, winter fuel blends result in 1 or 2 mpg drop in mileage. In Texas, the switch happens about 1 December. Might want to do some research on that and see if that occurs in Denver.

MaxD

That's an interesting possibility — I hadn't considered fuel blends. That's probably what I'm seeing.

Just out of an abundance of caution: Is there any way to tell if the timing belt is "too tight"? I took the cover off the other day and checked it, and although it's nice and taut, there is about 1/4" of play... that is, you can push down without exerting too much pressure on the exposed area of belt between the cam and the water pump about 1/4". As I said, it doesn't squeal or anything. Car cranks easily, and starts as usual.

lyleswk

That sounds about right but do not exactly remember from 2 years ago...

mikeyspeed

As long as you DOUBLE checked the cam timing when you completed the job, I would say the belt has nothing to do with your fuel economy. But, if one of the cams is off a tooth, your mileage will definately fall.