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From 20.4mpg to 15.8mpg in one tank...

heyjpark1

NAXJA Forum User
Location
Oakesdale, WA
I got an interesting problem...I've averaged 20.4 mpg now for as long as I can remember (and before you ask, yes, I know how to properly calculate mpg:looney:).

Two weeks ago I did two things to my daily driver that I think could have affected my mileage:

1) Went from 215 75R 15 tires to 235 70R 16 tires. The 235's are about 1.8 inches taller then the 215's. Could this be the problem (by the way, I am adjusting my mileage for the small speedo change)?

2) I've been driving with a cracked coolant pressure bottle forever now. I replaced it with a new one, which I'm assuming brought the temp on the heep down. Could I be spending more time in closed loop mode?

I've got about 40,000 miles on the spark plugs, but they are 5 years old. I don't think the spark plugs could go to hell in one tank of gas, but that is the only other think I can think of.
 
I'd get at least half a dozen pump to pump mileage readings before I started chasing this; larger sample size may show less of a swing. What temp is your engine running at? If its in the 200-210 range, you're good. I don't see any correlation in the coolant bottle but I definitely would swap in a new set of plugs; they're cheap.
 
1) I physically measured the tires. The tire size difference doesn't make that much of a difference in speedo readings.

2) So far, I've measured the gas mileage over 3 tanks with consistent results.

3) With the POS factory gauge that the jeeps come with, its tough to tell what my exact temp is. I could shoot my infared gun at the radiator hose. I know its running a little cooler, however, now that I've replaced the bottle.

4) I can't imagine that the tire size increase would make that much of a difference, but maybe someone else has some ideas.
 
Ideal driving conditions: 40 miles to and from work, no stop and go, 60 mph.

If the 235's are going to cost me 5mpg, I'll go back to my 215's even though they look stupid.
 
15 is a bit low for 235's, you should be 19mpg. What year ? manual or stick ?
My 98 gets 19-22, 98, 5 speed, 3:07 gears, the difference is I hardly ever use 5th gear unless I'm over 65mph, I keep the engine in the 2200-2400rpm range and that helps. If I use 5th and keep the engine at 1800-2000rpm my mileage takes a dump big time. Also what is the air pressure, I run my BFG AT/KO's at 40psi.
 
15 is a bit low for 235's, you should be 19mpg. What year ? manual or stick ?
My 98 gets 19-22, 98, 5 speed, 3:07 gears, the difference is I hardly ever use 5th gear unless I'm over 65mph, I keep the engine in the 2200-2400rpm range and that helps. If I use 5th and keep the engine at 1800-2000rpm my mileage takes a dump big time. Also what is the air pressure, I run my BFG AT/KO's at 40psi.

Sorry...its an '89 Auto. The air pressure is 35psi. I was running my 215's at 40 psi. Could that 5psi difference cause that much mileage loss?
 
Yea, it could, especially if you put that 35 lbs in on a warm day and the weather cooled down which will generally put them around 32psi.
 
They might have switched to winter blend fuels in that timespan too.

I usually get 12-13 but this last tank which was apparently winter fuel brought it down to about 10. Terrible.

With 15 you are still in the green I'd say!
 
Winter blend? Never really knew about this but my mileage took a huge crap last week too. I dont get good mileage as it is due to probably a few reasons, but generally I'm getting about 200 miles out of a tank, last time I filled up I was stretching it to get to around 170 out of the tank (I'm using examples not exacts) So your not alone in the recent loss of MPGs

....Or on a total side note, maybe gas is all watered the hell down since they are only getting $2.50 a gallon now instead of $4.00 we were paying 6 months ago?!?!?!?!?!?!?!?!
 
Winter blend? Never really knew about this but my mileage took a huge crap last week too. I dont get good mileage as it is due to probably a few reasons, but generally I'm getting about 200 miles out of a tank, last time I filled up I was stretching it to get to around 170 out of the tank (I'm using examples not exacts) So your not alone in the recent loss of MPGs

....Or on a total side note, maybe gas is all watered the hell down since they are only getting $2.50 a gallon now instead of $4.00 we were paying 6 months ago?!?!?!?!?!?!?!?!

Thats one of the downsides of PA, I know the suppliers screw with the gas, I've experienced it a few times when I worked in NJ and commuted. Every time I would get gas in the pokes and drive to NJ, back and forth for 2 or 3 days, my mileage would drop, when I filled up in NJ and drove home for 2 or 3 days my mileage went back up, now NJ has stricter rules on winter gas than the boonies in PA, we don't have emissions testing up here in this area, so the suppliers could be 'cutting' the gas with whatever will burn and not be grossly obvious, it sure would show up during inspections when they stick that sniffer in the tail pipe. I'm just more sensitive to mileage due to commuting and I keep an eye on my jeep. NJ also has stricter gas inspection people that drive around sampling, I've never seen one of those in PA, I've seen quite a few in NJ over the years. I think they screw with it because they can and get away with it, they could also be buying older gas from other areas and mixing it with newer stuff, for many years PA has been a dumping ground for the cities east of us.
 
I had A/T Cooper 235-70-15's on my 96, and I was getting about 16-17 MPG in mixed driving.
I swapped my wheels and tires from my 95 Grand Caravan, Blizzak Snow tires @ 205-70-15's.
Accounting for the revs per mile difference of the newer smaller tires, I am getting 19 - 20 MPG.
The main difference for the improvement I think is the switch from A/T to passenger car snow tires.
Must be a big difference in rolling resistance.
Since this is strictly a on-road vehicle for the snow season, I am also experiencing smoother and quiter ride with improved handling.
 
Thats one of the downsides of PA, I know the suppliers screw with the gas, I've experienced it a few times when I worked in NJ and commuted. Every time I would get gas in the pokes and drive to NJ, back and forth for 2 or 3 days, my mileage would drop, when I filled up in NJ and drove home for 2 or 3 days my mileage went back up, now NJ has stricter rules on winter gas than the boonies in PA, we don't have emissions testing up here in this area, so the suppliers could be 'cutting' the gas with whatever will burn and not be grossly obvious, it sure would show up during inspections when they stick that sniffer in the tail pipe. I'm just more sensitive to mileage due to commuting and I keep an eye on my jeep. NJ also has stricter gas inspection people that drive around sampling, I've never seen one of those in PA, I've seen quite a few in NJ over the years. I think they screw with it because they can and get away with it, they could also be buying older gas from other areas and mixing it with newer stuff, for many years PA has been a dumping ground for the cities east of us.


I could completely agree with this. Especially when it comes to crappy 'box' gas stations like sheetz and wawa. Doesnt matter what car I'm driving, whether its a riceburner honda, or my jeep I've ALWAYS ALWAYS gotten terrible mileage from their gas. And wouldn't ya know they are always cheaper than the competition, needless to say unless I run out of gas in front of their station I never use it!!!
 
I was also going to suggest the winter additives in the gas. Starting to notice my mpg's go down slowly now that it's getting colder. Used to average around 17-18mpg on the highway (31's and 3.55 gearing) and now it's falling down to around 16-17 on the highway. Combination of the additives being put in gasoline for colder months, and also from letting it warm up a few extra minutes in the mornings.
 
I could completely agree with this. Especially when it comes to crappy 'box' gas stations like sheetz and wawa. Doesnt matter what car I'm driving, whether its a riceburner honda, or my jeep I've ALWAYS ALWAYS gotten terrible mileage from their gas. And wouldn't ya know they are always cheaper than the competition, needless to say unless I run out of gas in front of their station I never use it!!!

Thats not valid, at least in my area, the gas stations in this area get their generic gas from the same terminal, it's behind Sams Club in Whitehall, ALL the gas trucks fill their tankers from there, they all get the same regular from the same 3 story tank and add their individual mojo juice to make their 'brand name' gas just before they dump the gas into the tankers. The stations like Sheetz and Turkey Hill pump the same gas. I buy from both or in some cases all three discount stations. As near as I can tell the only thing missing is the cleaning additives, they pump the generic gas which has both federally and state mandated levels, brands like Sunoco, Shell, BP, etc add other cleaners and enhancers but not always. I got curious one day and got gas in a Sunoco on McArthur Blvd near the lehigh valley mall where a truck had just filled the tanks, his next stop was a Turkey Hill about 5 miles up the road towards blue mountain ski area. That said there is no real way to tell if there were some kinds of old gas or other bulk filler so to say in the tanker before it got there.
Gas stations and business's that have their own gas and go out of business or close many times have to have the fuel pumped out and removed which they pay for, nothing to stop the company that recovers that fuel from 'disposing' of it by reselling it to a greedy supplier that figures no one will notice if he mixes it will enough with new gas. Just my observations.
 
Thats not valid, at least in my area, the gas stations in this area get their generic gas from the same terminal, it's behind Sams Club in Whitehall, ALL the gas trucks fill their tankers from there, they all get the same regular from the same 3 story tank and add their individual mojo juice to make their 'brand name' gas just before they dump the gas into the tankers. The stations like Sheetz and Turkey Hill pump the same gas. I buy from both or in some cases all three discount stations. As near as I can tell the only thing missing is the cleaning additives, they pump the generic gas which has both federally and state mandated levels, brands like Sunoco, Shell, BP, etc add other cleaners and enhancers but not always. I got curious one day and got gas in a Sunoco on McArthur Blvd near the lehigh valley mall where a truck had just filled the tanks, his next stop was a Turkey Hill about 5 miles up the road towards blue mountain ski area. That said there is no real way to tell if there were some kinds of old gas or other bulk filler so to say in the tanker before it got there.
Gas stations and business's that have their own gas and go out of business or close many times have to have the fuel pumped out and removed which they pay for, nothing to stop the company that recovers that fuel from 'disposing' of it by reselling it to a greedy supplier that figures no one will notice if he mixes it will enough with new gas. Just my observations.

Well sounds more evidence proven than my butt dyno observation. Now that you bring the point up, it makes more sense that they get gas from the same initial 'tank'. So I'll say your right, but I still won't buy gas from them :eeks1:

I'll buy gas from the little guy at ____ station down the road thats losing business over a few cents! No pun intended to you, just when big and mighty wawa came into our town (eagle) a few years back, it was in a way a turning point of what used to be, and whats become...and along with its presence it took out 2 small gas stations that had been operating as long as my dads store. Completely un-related to all this but just wanted to say where my opinion comes from on that.
 
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