Hi,

I'm looking for some economical ways to improve fuel efficency on a 1986 Dodge B250 van.

I just purchased the 86 Dodge B250 van to haul my race bikes up and down CA to the local tracks. Most of the hauling will be freeway usage, and we have some flexibility as to when we leave, and what speed we go. While we may hit a little stop-and-go traffic, city driving isn't a major concern.

I believe the van comes with a 3 speed automatic transmission, and I believe the 3.55:1 final drive gearing. According to the previous owner, it gets about 13MPG freeway. Engine appears to be in very good shape, based on the results of the smog test. We're typically expecting to haul less than 1000 lbs. 1500 would be the absolute maximum, including passengers.

We're looking at about 350-400 miles round trip each weekend on the van, so small improvements in fuel efficiency are going to pay off big time for us.

First place I thought to look was at the final drive gearing. It seems like the van goes in and out of 1st and 2nd gear fairly quickly, and spins the engine pretty high on the freeway in 3rd. So, lowering the gearing seems like a good place to start. What would be the tallest final drive I could safely run with this engine?

Drive slow, check tire pressures, make sure the engine is properly tuned of course. Any other tips? Looking for straightforward stuff that can be done at reasonable cost.

 

Well, since you are into racing, I would highly recommend getting a high flow CAT and high flow exhaust. Then, find a way to increase the air intake to the TB.

Even though my van is the next generation of Ram Van, there are several items there in the shown thread to really help with MPG improvements ...

https://dodgeforum.com/forum/dodge-r...rovements.html

My Ram Van is the B2500 with HD suspension (heavier weight), 8-lug wheels, 12-passenger, 3.92:1 rear gearing, with the 46RE tranny. By no means is it a fuel saver. However, I took the time to read many of those extreme mile pushers to get an idea to adjust my van. 14mpg hwy was all it could do. After a trip to FL, it did 19.7mpg hwy.

 

Okay, thanks.

One of the mitigating factors is that the van originally cost $600. Mechanically, it's in solid shape, with just a minor fluid leak. But, we don't want to put money into it that isn't going to pay off over the next year or so.

I'm not planning to race the van - just planning to race the bikes I'm hauling with the van.

 

I just ran the numbers for my van...

1986 Dodge ram van:

Tire revs per mile (235/70/15): 720.4
3rd gear ratio: 1:1

Stock Final drive ratio: 3.55
Engine Revs per mile: 2557.42
RPM @ 65mph: 2770.53

Modified Final Drive ratio: 2.76
Engine Revs per mile: 1988.304
RPM @ 65MPH: 2153.996

2770 cruising RPMs seems a little excessive, especially for such a big engine. 2.76 is about the tallest ratio I could find, and seems like it would drop the cruising RPMs to a little more reasonable, but still slightly high 2153.

I would imagine that this would put more load on the transmission and drivetrain at RPM, but it seems like it wouldn't be unreasonable given the loads we're hauling. Anyone have any thoughts?

Also, what about running a good 75w/90 gear oil in the rear diff, rather than the spec 80w140?

 

I read stev post and he did quite a bit of things to increase MPG I think what burning and I are both interested in is did you see a difference from a few critical things?

 

Grease and alignment are both great suggestions. I've heard the same from other forums. It probably makes sense to lift each tire off the ground, to spin it and make sure the brakes aren't dragging.

 

Yeah I think Im going to change out the rear Diff fluid also.... Probably due for it anyway at 80k...

 

Well, for towing, My 2000 B1500 SWB had the V6 3.9L and the 3.55:1 rear. I did tow with it in limited trips. On the flat interstate, it tugged along the loaded 4,500lbs Coachmen Travel Trailer at 60mph. When we came to an incline or hill, it dropped to 45 to 40mph. The V6 was just too under powered to pull that weight.

Now with the V8 5.2L, towing something that heavy and the 3.55 rear may be a better combination. If your dirt bikes, racing gear, and trailer are much less, then moving to the other gear combination may work well for you.

As for the 75W90, Chrysler published a TSB for our generation vans to use the 75W90 synthetic. The original spec was 80W90. If you have 80W140 in there, change that out as soon as you can for better mpg.

 

Good to hear on the gear oil. I have no idea what the maintenance history is on this van. Might very well be on the original stuff.

I took the van out for a 140 mile drive this weekend, and averaged a shade over 13mpg at 55/60, with a touch of light city driving. Would like to improve on that, but it's good to know that I'm at least in the same range as when the van was new.

Also, I'm thinking of running Rotella T 5w40 synth in the engine. Any idea if that would be a problem? I know the spec is for 10w30 weight oil, but the Rotella is great stuff for the price, and only available in that weight.

 

Actually, the heavier the oil, the less will reach the upper end of the engine. Our Magnum engines are a bit different than the LA engines. 10W30 for summer 75+ degrees and 5W30 for colder temps. Our Ram Van is getting better mpg with the 5W30 than the 10W30. If you went 5W40, chances are the mpg will be even less than what you are running now.

As for oil, I've been much of a dino user rather than synthetic. However, my boys and their Camaros have taught use some things. The oldest started using Royal Purple 5W30 synthetic in his 1991 Camaro. What a difference it made after one day of driving. That old engine of his had the "known" lifter tick noise since he got the car. The tick totally disappeared. My next oil change will be the 10W30 of Royal Purple synthetic since summer is now upon us.


As being on the oil subject, I've replaced the Fram PH16 to the much larger and better performer Purolator L30001 filter. It's doing a great job. Expect the oil pressure to rise a little, but still in the safe zone. The oil pump can move more oil keeping things much cooler and lubricated now.