My jeep is getting worse and worse gas mileage

4x4Jesus

4x4Jesus

Caught the Bug
Is it normal to get 10 1/2 to 11 1/2 miles per gallon on the street. I was getting about 14 on the street, and it seems like ever since I switched to synthetic oil my gas mileage is drastically reduced.

Would changing the oil from normal to synthetic cause my gas mileage to drop.?

Could it be the tire wear? New tires vs slightly worn tires?

3.8 L automatic ,5.13 gears. 35 inch nitto trail grappler
 
I've never heard of that kind of gas mileage loss linked to changing oil types. Combustion if often the issue with mpg loss soooo...I would replace the spark plugs(especially if they are the original anyway) and possibly the plug wires to see if that helps. :idontknow:
 
4x4Jesus said:
Is it normal to get 10 1/2 to 11 1/2 miles per gallon on the street. I was getting about 14 on the street, and it seems like ever since I switched to synthetic oil my gas mileage is drastically reduced.

Would changing the oil from normal to synthetic cause my gas mileage to drop.?

Could it be the tire wear? New tires vs slightly worn tires?

3.8 L automatic ,5.13 gears. 35 inch nitto trail grappler
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when did you change the gears and tires?
 
StrizzyChris said:
I've never heard of that kind of gas mileage loss linked to changing oil types. Combustion if often the issue with mpg loss soooo...I would replace the spark plugs(especially if they are the original anyway) and possibly the plug wires to see if that helps. :idontknow:
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I might give that a try since they are all original 73k miles. At what mileage are you suppose to replace them?

jeeeep said:
when did you change the gears and tires?
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Gears and tires are not new.
 
agree on plugs and wires, also check your air filter, carburetor throttle body (take it off to clean it, it's easy - don't tighten too much when you put it back on, the plastic will crack)
 
jeeeep said:
agree on plugs and wires, also check your air filter, carburetor throttle body (take it off to clean it, it's easy - don't tighten too much when you put it back on, the plastic will crack)
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Maybe that's why he has such bad mileage. Jeep stopped using carbs a long time ago. He must have gotten an old one. :eek:
 
4x4Jesus said:
I might give that a try since they are all original 73k miles. At what mileage are you suppose to replace them?
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I dont know what Chrysler states, but I have always replaced my plugs every 50K miles and plug wires with them if they look damaged/cracked/etc. OR any time I'm having performance issues. I agree with above to clean/replace your engine air filter as well. Also while your at it, you might as well replace the cabin air filter. All of these can be bought on eBay for cheap. I would recommend against K&N unless you are prepared to maintain it.
 
I know cleaning the throttle body got one of my buddy's about a 3-4 mpg rise. Easy to do. There are all sorts of videos on YT on how to do it. Should do it every 12000 miles.
 
I was having a problem with very low mileage as well. I had the fuel injectors cleaned and I got approximately 3-4 miles per gallon back. Doesn't sound like much but it made a difference to me...mentally!


2010 MANGO TANGO SPORT JKU🇺🇸
 
I was getting around 10-11 mpg's a few months back too. I changed my spark plugs, wires, and replaced my filthy K&N CAI cone and I'm back to a steady 13-14 mpg's again.

Nothing amazing, but pretty solid for a 2008 3.8L JK that is an oil-aholic.
 
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