Thought I'd make a new thread for this topic instead of bombarding OldSchool's overhead diy thread with it. There seems to be an ongoing debate about the accuracy of the overhead computer, and MPG in general, so this is the place to talk about them.

 

Here's my most recent experience with the overhead computer's accuracy. Usually it seemed like mine was pretty accurate, but this last trip not so much. I had to drive from Columbia, SC to Princeton, WV (making a stop for gas in Wytheville, VA both ways) and back to Columbia. It was a straight shot along I-77 the whole way, and is just barely over a 500 mile round trip.

I filled up in the morning before I left (left receipt), in Wytheville (middle receipt), and again in Wytheville on the way back (right receipt). According to the overhead I was doing 17.5mpg when I filled up the first time in Wytheville, but according to my math (211mi on 11.567gal) I was doing 18.24mpg. I topped off in Wytheville on the way back through and this time did 18.27mpg (80mi on 4.378gal) for that stint and 18.25mpg (291mi on 15.945gal) overall, the overhead still said 17.5mpg. I didn't fill up again when I got back to Columbia, but by the time I got back the overhead was at 18.1mpg, so assuming that the mileage did increase half an mpg or so that's around 18.75mpg for the whole trip and 19.25mpg for the stint from Wytheville back to Columbia. I reset the trip computer when I filled up the first time in Columbia, and then let it go for the rest of the trip. So it seems like my overhead was off by 3/4 (4%) of an mpg for this trip.

Receipts.


Overhead readout at first fillup in Wytheville.



I'd say 18.25-18.5mpg is pretty damn good for a 5.2L, especially since the factory rating is 15mpg or so. I was pleasantly surprised when I did the maths and found out that I used less than $90 of gas to do the whole 502 mile trip.

 

Holy Sheet! you paid $3.19 per gallon.....

 

Yep, gas is cheaper in VA so I stopped in Wytheville instead of Princeton in WV because it's $3.50 a gallon there. I think it was right under $3.60 a gallon when I was in Pittsburgh a few weeks ago.

 

I have a gas filling issue with my truck so I barely put more then 20 bucks in at a time cause it takes so long, With that being said does the cpu readings differ from say just under a half tank compared to a full tank?

Reason I ask is I have a 98 with the Smaller V* in it & mines reading 10.1,lol now when I first got it it was in the 9mpg area and has slowly but steadily been raising over them months, I also tend to see numbers change when Im on the breezeway on say a 30 mile trip.

I also had this thing recently tuned up.

 

I usually just don't fill the tank either, and it seems like my average doing that is between 12 and 14mpg. Not sure how accurate that it since I didn't do the math to check it.

If you hold down both buttons on your computer for a second or two it'll reset the numbers so that you can see what you're currently doing instead of since you got it.

 

Thought I'd add to this again since I just filled up my tank again. I did 292.3mi on 20.381gal ($65 @ $3.189 per gallon) which comes out to 14.34mpg. My overhead computer said 14.4mpg, so it was pretty close. I made one 150mi round trip on the highway (a/c was on since it was 98 degrees) and the rest was driving around town with occasional short trips on the highway, all with the a/c on.

 

Thought I'd update this thread again. I made an excel sheet to keep track of my gas mileage, and difference between the actual and computer mpgs.

 

Damn...since installing my cosole...I haven't seen anything over 14MPG on the DC Beltway. I haven't taken it more than 40 miles in any one direction for years though. LOL. I just replaced the TPS/IAC and did a full Throttlebody cleaning...combined with new spark plugs. She starts nice in the cold now...drops right down to 700 rpms immediately now....no more wacky reving up and down. I don't expect much better having the 3.92 rear end and 4x4.

 

Mine is usually within .5 of what the math comes out to be.

Though honestly, I don’t give a shat about gas anymore. I don’t even look at the pump. I just put the nozzle in one of four vehicles and pump away.