I have a 2000 Grand Cherokee 4.0 n I'm looking for better gas miliage


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I have a 2000 Grand Cherokee 4.0 n I'm looking for better gas mileage. I'm not a mechanic by any means so my knowledge is limited. I thought of changing the plugs, maybe a cold air intake but the milage is hurting after my previous 30mpg ride. Any advice is much appreciated.

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What mpg are you getting?

There is little to be done to improve mpg. 16&18 mpg city & highway new.

Cold air intakes get relearned by the PCM and you get about 500 mi of 1more mpg then it goes back.

However there are things to get you back to normal.
Proper speedo gear for the tire size and rear gears.
Plugs, clean injectors, check fuel pressure, clean intake, TB and IAC, clean valves and combustion chamber (steam or sea foam) clean battery cables and opposite ground ends. Load test battery. Validate alternator output to loads specifically extra non stock loads (amps radios lights...)
Check for codes. O2 sensors or bad cats rob mpg.

Bigger wider tires kill mpg-increased rolling resistance. Lift kits kill mpg- pushing a bigger brick through the air.
External lights add wing resistance.
Same with roof racks.
Lighten loads - heavy bumpers, spare tire, tools trunk stuff... Loose weight.
Proper tire pressure reduces rolling resistance.

Lay off the skinny pedal, slow to PULL OUT, brake easy...

Highway at 65mpg actually gets the best mpg.


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I get 19mpg on average, which is much more than I expected (2020 JGC V6). I drive 70% highway, the rest city, usually 60-70mph on the highway, and don't have a heavy foot. The sticker on the JGC says 19mpg in the city, I get that on average gas tank with mixed driving, which the sticker claims should get 21mpg. I don't get 21mpg even on pure highway driving unless it's straight and 60mph exactly for a long period, then I get about 23mpg, which is still less than the claimed 24mpg highway that the sticker claims.

And I do use ESS.

I gave up trying, I just drive without looking at that damned addictive gauge with the green showing me when I'm under average, argh, that this is hard to turn off, but now it's only on when wife drives me around (she's learning to drive) that way she sees if she's driving properly, and she wants to save gas too lol, or the Jeep, I think.

EDIT: Sorry, I misread, thought you had a 2020, not 2000, and was about to ask what kind of 4.0 is that in a 2020. Seems to me that's great mileage for a 2000 big 6, as it's just a bit worse than a brand new Pentastar.

I would recommend you to read this article as I find it really helpful in improving the mileage of my cars at home.

20 Useful Tips to Improve Your Gas Mileage - Carbibles

They are ok to good suggestions. Not all are Jeep related.

I challenge the gas at night theory. Id like to see that proven scientifically.
These tanks are far underground where the temp is constant. Id expect no temp change underground at these depths. However if the line from the tank is long (1000ft) and above ground. That may heat up enough to change volume significantly.

Electric fans do make 1-2 mpg gains highway only. Stop and go may be about the same. Crawling may be loss.

Above 35 mph the fan will unlikely kick on due to the air being forced through the radiator. So savings is loosing the hp stealing drag on the engine from the mechanical fan.

Octane is not as important as % ethanol. Ethanol does not have the same energy per volume as gas. Lower % better mpg

Last one is cruse control. Proved this on a avg 35mpg honda. Using cruse on a 130 mi highway 55-70mph keeping at no higher than max or 65mph. The mpg averaged 5-7mpg less than free pedaling it in the economy zone calculated by the ecu. Got 49mpg best avg 47.

Inthe jeep best was 20.5mpg avg over several 585 mile trips all highway. Keeping the 6th gear and app 2250-2500 rpm and letting mph go below 65.

Never look down on anyone unless you are helping them up - Jesse Jackson
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