10 Miles Per Gallon

My 1974 CJ5 has a stock standard 232 CID 6 cylinder engine with a Carter YF 6431 carburator and NO modifications. I checked to gas mileage over the last 3 tanks of gas and I am getting just over 10 miles per gallon. I took it my mechanic and he said i"t is running fine". Now I just drive them, I don't fixes them but I know 10 miles per gallon is LOUSY mileage. Any ideas?

 

That sounds low to me, most everyone else gets 18-19 a gallon in theirs.


A tuneup, new plugs wires and all that might help if its been a while.

 

not enough info....
how do you drive, what gears do you have (what RPM are you cruising at), ect.

Sounds a little low to me also, but then again I would be happy with double digit MPG (I have a 360 and a heavy right foot )

 

what size tires?

 

Had it tuned up middle of March and the mechanic was suppose to have put in, and I paid for and it looks like new plugs and wires and points and condenser. It has the 4-Speed manual transmission and gears that came on that model in 1974. I have been driving it back and forth to work (about 15 mile one way) (10 of those miles on the Interstate at 55 -65 MPH in fourth gear) for the last 3 tanks of gas. It is riding on B. F. Goodrich All-Terrain T/A's LT 235/75R15. My Land Rover D90 gets 15-16 MPG around town I would think a 232 six cylinder should at least get that. Just need some direction to stazrt looking for why it is running so lousy.

 

Jets, accelerator pump, float setting, brakes dragging, that's off the top of my head. Maybe set the timing ahead a degree or two. Idle mixture? Air cleaner restricted? Low tire pressure? I get about 17 or so from my Fhead in my Sixty, but I rarely run over 50 mph, either.

 

What are your axle gears? With the 232 and 4-speed you might have 4:27 gears, which are pretty low, and you have relatively small tires, which means 55-65mph is humming right along. My stock 74 with 258 and Carter YF, running 3:73 gears and 31" tires would get 14mpg consistently under almost all conditions.

 

with the original setup on my '75 (258, 3-speed, 3.73's, 31's, carter yf) i used to average 14-15 mpg. now, with the 258, a 4-speed, 3.73's, weber k550-14, and 34's, i average about 11 mpg.

 

My '75, all stock except 31" tires, was getting around 16 with 75% of driving being highway at 65mph. It only has 52,000 miles on it so the engine was in pretty good shape.

 

I would also check the mechanical and vacuume advance in the distributor, my mostly stock 72 CJ5 258 ,carter YF,T14 with 3.73 gears on 30x9.50 BFG MTs gets between 14-16 on the highway if I limit my speed to about 60mph.

 

I would start with the idle mixture and put a new air filter on (these are simple and in expensive places to start). lean it out then recheck mpg. then i would look at vaccum lines. another thought,
if the choke is not working properly it could be dumping fuel/air into the engine.

 

Driving habits are also very important. If you have the throttle floored all the time and wind it out to keep up with stop-and-go traffic, mileage will suffer. You should be able to shift at maybe 10 and 20-25 mph, and drive all over town in third. You don't need 1st at all unless you come to a complete stop. Also, your speed on the highway will make a huge difference - slower means much better mileage.

That said, I'd think you should be able to get mid-teens, but not much higher. Use a light foot, keep your speed down below 60, and see what happens.

 

:iagree: Adjust driving habits to the machines strong points first, Make sure air filter is clean, Then double check timing, Then double check carb calibration................this would include the pcv ( and egr if so equipped ).

 

Your gas mileage could stink just because your commute is short. While the jeep is warming up and the choke is on.. it uses up more gas. And since you don't drive very far, the cycle repeats so often and that makes your MPG look bad.

You could get one of those mileage gauges - it is just a vacuum gauge, and in theory the higher vacuum, the better mileage you will get.

 

Don't forget he's in Colorado Springs. The altitude is gonna cut down the power & mileage by at least 10% right there.

Bump the timing up a bit just shy of the point of detonation, put the tires to 28psi, make sure you've got a vacuum advance on the distributor, clean air filter,etc. Really I'd think 12 mpg would be where you're gonna wind up. It's still a relatively large engine that's trying to push an aerodynamic brick.

The 232 in my J2000 with 33s and 4.27s turned in about 14mpg.

 

The easiest way to see what is happening is simple:

Install a vacuum gauge, using the plugged port on the intake manifold.

Idle should show 19 to 20 on the gauge.

Acceleration can drop the needle to the bottom (zero). Steady speed on the level should show somehwere between 14 and 17, on the downstroke up to 25.

You can analyze the condition of the engine and also see how deep you have to put your foot into it to keep it going. The lower the number at cruise, the lower the MPG. A low number at idle shows a need to dig into things a little deeper. I have had extensive run-time with 258 and 304 CJ5's. The 258's will go about 17, the 304 will do better because one does not have to use as much throttle to maintain the same road speed, therefore a higher reading on the vacuum gauge on the 304.

The 304 in stock mode will go up to 19MPG on level driving back East. Back in the 70's I used to travel with a 13 foot travel trailer that weighed 2,300 pounds. On a coast to coast the worst mileage I got was around 13, the best around 15.5.

Check out DVAMO website. Page down until you see a 1974 Renegade. Sort of brings tears to my eyes.

Happy Jeeping.

 

I have a vacuum gauge on my 76 CJ 5 and over the years I have adjusted my driving style from watching the gauge and can easily get 16 to 18 MPG's now. I do have a fiberglass tub so my CJ may be a little lighter.

 

Wish I had 3:73's in my 74 CJ5 258 c.i. 4 spd gas guzzler! I am running 33" tires, 4:27 gears and can easily take off in 3rd gear from a dead stop. No speeedometer so unsure of exact mileage but I would venture to say it is well below 10 mpg................. When I bought it I went out the next day and bought a 360 to put in for more power, then fuel prices started to climb so I left the 6 in, after all it is completely manufactured with less than 5,000 miles on it topped off with a 1 bbl. carb. Now I am beginning to wonder if the 360 may actually get better mileage after all?? Guess I should figure out how high I need to lift it to be able to run the new set of 35" tires I've had in the garage now for the last year? Maybe that would help the mileage by changing the gear ratio? It is so bad I have driven it a total of 67 miles in the last 2 months!!

 

Could be your tire size is too large for your gearing, and you have to open the throttle more just to turn those big beasties over.

 

I understand you can really tell a lot about the internals of the Jeep using a vacuum gauge. I want to put one on mine. MPG is just the start. Do you know of anyplace that has a good writeup on how to read a vacuum gauge?

And as I remember, you want to keep the vacuum high for the best MPG's. Is this correct?