MPG change, where to start looking? Options

[914Bryan]

I know this isn't an exciting high performance question, but a question just the same.

I'm having an issue with the mileage my 74 2.0 DJet and am wondering where to start looking for the problem. I commute 60 miles each way to work (120 total). My driving is 98% freeway, non rush hours so a steady 75 mph, motor is turning 3200.

I could always count on 32mpg, day in, day out. Over the last two months, it has slipped to 28mpg. I burn a tank a week, so this has been about 8 tanks of gas that I have noticed this.

Engine is running fine, no change in performance.

Would a tardy valve adjustment cause this? I'm a little over 6k since my last one.

Any ideas?

[jonvo4591]

To do a down and drity alcohol content test, you'll need a few things.

A water bottle, a sharpie, a fuel sample and a little water.

Make 10 marks in equal increments on the side of the bottle with the sharpie. Then pour some fuel in the water bottle till it reaches the 9th mark. Take the amount of water it would take to fill the bottle up to the last mark, and pour it in. you should have the bottle full up to the last mark.

Now, shake the bottle up for a bit, and then let it sit for 5 minutes or so. The water will combine with the alcohol and the parting line should raise between the fuel and the water/alcohol mixture. This will give you an idea of how much alcohol the fuel contains.

This test is probably best used as a comparison test between different fuels.