Engine/Transmission (1998.5 - 2002) Could this be the problem???

[marksmith]

I replaced my fuel filter about a thousand miles ago and ever since I haven't been getting decent fuel mileage. Around the same time I slapped on a set of 285's but I didn't think that the mileage would drop that much. I have gone from a solid 19mpg to about 14. 5 to 15. That isn't taking tire difference in to account. What is the problem? I am stumped and want my mileage back.



Thanks for any suggestions.

BTW the filter is a NAPA filter.



Mark

 

[Sky]

Hey Mark,



When I put on my 33's I lost about 2mpg also. Another guy here in Medford just put on 35's and he said he lost like 6mpg. We were just talking about that a few days ago. If you want the bigger tires your gonna pay for it in fuel milage.



I dont think its the filter. I would use Fleetguard filters though. Go to a cummins shop and pick one up or call Genos.

 

[Bob Wagner]

and don't forget the change over to winter blend fuel , that will really decrease your mileage

 

[LSMITH]

I run 285's and get 16-18 in town and 20 at 75-80 mph on the freeway normally. I do not think it is the tires, nor is it the fuel filter. Winter fuel drops me about 2 mpg across the board, and colder temps can take another 1-2 mpg off.



With highs here at 30 or so I am getting 18 on the highway and 15 in town.

 

[Pit Bull]

I think it is the winter fuel and the larger tires combined. Winter fuel maybe a little bit more of the equation then the tires but they both count.

 

[Gary - K7GLD]

Don't forget to factor in loss of speedo accuracy with the new tire diameter - worth about 4% in your case if the speedo was originally calibrated for 265's even more if it was calibrated for 235's... ...

 

[JyRO]

Good call...

Gary - That's good thinking. I think you've nailed it, and I wasn't even thinking about that until your reply. Without speedometer re-calibration, the speed will be off and the odometer would show less miles covered for any given distance. That in itself will make your fuel mileage "look" worse that what it actually is. Anyway, good call Gary.



Also, larger tires and winter fuel will reduce your fuel mileage like others have said above.



- JyRO

 

[Pit Bull]

Re: Good call...

Originally posted by JyRO

Gary - That's good thinking. I think you've nailed it, and I wasn't even thinking about that until your reply. Without speedometer re-calibration, the speed will be off and the odometer would show less miles covered for any given distance. That in itself will make your fuel mileage "look" worse that what it actually is. Anyway, good call Gary.



Also, larger tires and winter fuel will reduce your fuel mileage like others have said above.



- JyRO

JyRO, what we have here is a failure to communicate. When I said larger tires will throw off your MPG they I was talking about the odometer reading (revolutions per mile) of the larger tire. I would think the larger tires themselves would have very limited affect on fuel mileage unless they were huge. Sorry for the lack of communication and I am glad that Gary made it clear

 

[JyRO]

Pitbull -

When I said larger tires will throw off your MPG they I was talking about the odometer reading (revolutions per mile) of the larger tire.

I think I know what you're saying... you're saying neglecting speedometer error you don't think bigger tires will effect mileage a lot. And I agree. I think it will reduce fuel mileage to a small degree only. Probably 1, mabye 2 mpg at the most, unless the new tires are extremely larger than the previous.



But my reply was an agreement and compliment to Gary regarding marksmith's original topic. And as far as I know, marksmith has not said whether he has had his speedometer/odometer recalibrated for the larger tires. So the fact that his odometer might be off will skew his calculations and make it, "look," as if he was losing a lot of fuel economy. Where in reality he's probably not losing that much. That was the point of Gary's reply (I'm pretty sure), and what I complimented Gary for.



- JyRO

 

[rono]

What Gary - KJ6Q, said. When I went to the 315's I checked my speed with my GPS and after with some math found that my speed was off 13%. When taking the milage off the odometer, and adding 13% more miles than showing, then figuring my milage, I had not lost very much mpg at all, maybe 1 to 1. 5.

Ron

 

[marksmith]

sorry guys for not checking this sooner.

My speedo is not correct and I jumped from 265's to 285's. From what I can gather that is about 4% (Thanks Gary) It didn't dawn on me about winterized fuel, so that is prolly part of it and I found out last night that the last three tanks were filled at the local country store, where before I changed all the stuff I didn't get very good mileage with that diesel.



I am going to change the fuel filter anyway (13K miles) and fuel up at the CFN for a few tanks and see where I set. My GPS is in my pickup now so I can accurately track mileage and I will get back to you all.



Oh BTW I also ditched the Muffler about a week after the new tires and fuel filter. Guess if this doesn't fix it I am gonna have to buy the Comp Box and Injectors and... ... ... ... ... . that way I won't even want to worry about mileage.



Thank you for your help, I appreciate it.

Mark Smith