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?

[Tom_T]

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?

Yes on the valve adj. & the other things mentioned above Bryan.

Also, we've switched the winter/summer blends here, so that could be some of it.

Also, if you use ARCO or TOTAL (new name they're going to since BP sold-out), they over-oxygenate their gas, so it gets slightly less mpg than the majors & Valero - according to some out here I know.

I don't know of any stations selling 100% gas around OC nor SoCal in general, but you might find some race fuel or avgas to use, but they may have other problems if not unleaded & proper octane & whatever additives CA makes them add. There was another topic on the 100% gas stations topic on here a week or so ago, but SLITS only found a couple up in NoCal, & I'd think he'd know of any down here...if there were any. (IMG:style_emoticons/default/sad.gif)

Lastly, inspect your right foot....carefully - have you changed driving habits any in that time? (IMG:style_emoticons/default/biggrin.gif)

Also, if you want to max mpg in a 2L Djet, IIRC around 2800 & 65-67 will get you best at perhaps 36-39 on100% gas in the old days - less than today with 10-15% ethanol. That's from my personal experience steady cruising SoCal to SFO area on I-5 back in the late 70's & early 80's - when CHP still pulled you over too regularly over 55 there back then - so 65-67 was pushing your luck.

BTW - 55 is NOT the best mpg on our 914s & esp not for the 2L Djet in stock form, even though mandated back then! (IMG:style_emoticons/default/dry.gif)

Rick - CA switched from MTBE for smog reduction additive in gas about 10 years ago, over to the ethanol instead - after they found out it was a possible carcinogen that went through the soils on spills/leaks like greased lightening & into the water table. Ethanol is the lesser of 2 evils for CA gas additives in this case. (IMG:style_emoticons/default/dry.gif)

Of course for years before that they ignored complaints that MTBE ate thru rubber hoses/ect. & caused more leaks than the emissions of VOCs it saved, & we were replacing the gas tank seals/hoses on our 88 Westy every other year at $200+ a pop back then! (IMG:style_emoticons/default/mad.gif)