90 Dodge - Gas Mileage

[sudani]

I have a 90 Dodge with a 318 motor. It has 122,000 miles on it. It was getting around 9mph. I recently put a flowmaster exhaust system on it and had to replace the catylic converter. I'm getting about 11 now. Seems to run better. I would like to get better mileage. Some people have said to
Replace the rear end with a smaller one

Any idea how much this would improve the mileage? Are there any other ideas? (ie. Tornado etc ).

Is there any other options to improve mileage. Any device that holley or would headers help.

thanks for any comments or help

[Le Gimp]

Should be about 220hp and 300f-lb torque.

ohv V8 5.2 / 318 220hp 300f-lb 5-speed manual: 14/19

4-speed automatic: 13/17

5-speed manual: --

4-speed automatic: 14.4

LG

[sudani]

The mileage isn't that good. The truck is a 3 speed automatic with no overdrive. Any ideas on how to improve the mileage?

TP

[Le Gimp]

Just speculation since I am not familiar with that year and engine. My Suburban has a 95 engine in it and still has a distributor, so I know they used them at least that late.

You already cleaned up the exhaust. How about the air intake?

Plugs and wires (you should have done them first).

Does it have a distributor or coilpack.

If Distributor, I'd look at either rebuilding it or replacing it. The bushings will wear causing timing problems that will reduce your efficency.

Check your vaccum advance if you have a distributor. Same for timing.

If coilpack, see if there is any way to test it to make sure you don't have a coil that is weak.

Synthetic oil all the way around.

If you change the rear end ratio to improve your gas mileage, keep in mind that it will reduce your load/towing ability.

Good luck.

LG

[BleedDodge]

New Dodge trucks still use distributors, yep. I totally agree with refurbishing or replacing that. Plugs and wires for sure.

Clean the throttle body and change your air filter for good measure. That Tornado thing you mentioned is useless, I don't suggest using it.

What gears do you have in the rear end? It will say on the sticker under the hood, if it hasn't been ripped off...

[Le Gimp]

My 2002 (4.7L) uses a Coil per Plug system. The coils actually mount on top of the plugs with a wiring harness connecting them to the computer. No distributor, not high voltage plug wires.

It is a bitch to get them out to replace the plugs, which Dodge still recommends changing every 30K miles. Stupid plugs.

[BleedDodge]

That's bad. I've seen the Ford ones and they don't look very friendly to work on either...

[bawana]

If that a 2 wheel drive it must have some kick azz gears in the rear end to be getting milage that bad.I have a 89 four wheel drive ramcharger with the three speed auto(no overdrive) and with 11.5x32 inch tires I still get like 10--14 mpg and I thought that was a pig.

[praisethelowered]

My 87 w/ a 360, 4 spd., and 3.42 gears is epa rated 11/13. I was getting about 9, buit recently removed a clogged cat. I haven't had a chance to check the milage since then, but it seems better. I have 148,000 miles and a carburator, so your experience may differ some from mine.

[fanworks]

I have a 1990 D-150 3speed automatic with 318 (5.2L) V8 (Automatic currently suffering some weird problems, getting diagnosed). It also has the 3.21 rear end, smallest they made. She had 83k miles on her when I bought it, and on a really good day with lots of downhills on a freeway she'll get 15mpg. Factory mileage is 14mpg, which is pretty close to what mine gets (Like 13.973333). Switch to autolite platinum/double platinum plugs, they help alot. Also get rid of stock spark plug cables, Dodge's cables wear out to easily, get a set of Bosch Nascar Low Impedence spark plug cables to replace them with. Also check points and cap, mine is still stock and running, but probably will need some replacing in the future.

Also, don't go above 70mph max, you're all RPM over about 35-40mph. Stay around 60-65 and your gas mileage goes way up, drops the engine RPM a fair amount.

[fredjacksonsan]

Dad's got the 318, 4spd manual(w/creeper gear so no o/d), and 3.55 gears in his, gets 13 or 14 on the highway and 10 or just under in town.