Disappointing mileage

[Vaughn MacKenzie]

I'm posting on behalf of a friend, but he's only getting 15-17mpg with his '84 Blazer on the highway at 65-70mph. It's Auto but I don't know what gear ratio. It seems wound up more on the highway than mine so I think it has lower gearing.

He's changed the fuel filter and we disconnected the vacuum hose to the center diaphragm in the intake to close the EGR. Was that a bad thing to do?

He hasn't had it that long and MPG is about the same, best he is gotten is almost 18 driving conservatively.

I am wondering what realistic expectations are and what can be done to improve mileage. His engine is much healthier than my Blazer, at least his has nowhere near the blowby mine does.

Thanks all,

Vaughn

[john8662]

What size tires? anything bigger than the 31's they come with affect the mileage, or what your reading as accurate. Also, does this blazer have the 700R4 overdrive transmission. Almost every used 6.2 I look at seems to have some TH350 trans shoved underneath, because someone didn't like the 700R4. So not having the overdrive would eat the fuel. Just something to check for.

[cschneider]

I believe there were more 6.2L shipped with the TH400 than any other automatic but I'm not completely sure. With a TH400 and 3.73s this is about right. Larger diameter tires can actually improve your mileage but since most are heavier that doesn't usually translate in practice. I think 15-17 is a respectable mileage but could be improved by gearing and the like.

[Ratau]

Vaughn

The mileage on my Blazer is around 7 km/l converted to US gallon it is close to 16.5 mpg. If the TC don

[G. Gearloose]

Hmmm, I don't subscribe to the tires thing.
I get 20-21 with 35" mud terrains, 4.10 full floater, 700r4, Banks, and my experience with my earlier trucks says its not the Banks giving the good milage...I think its

Good air pressure in tires
Crisp timing
easy foot
700r4

Oh yah, I think the only thing synthetic in it is the seats and rug.

[john8662]

Originally posted by G. Gearloose:
Hmmm, I don't subscribe to the tires thing.
I get 20-21 with 35" mud terrains, 4.10 full floater, 700r4, Banks Well, I just said the 31's being stock size, and installing bigger tires resulting in worse fuel mileage because of most stock configurations. Your truck ain't exactly stock, bigger tires, but compensating with 4.10 gear ratio, and more power from a turbo. I just argue tires because if you install 35's with say the 3.08 or 3.42 gears they come with stock, you're gonna take a big hit, lugging the engine plus inaccurate speedo.

Like my truck, 86 C10 6.2 N/A. It had 235-75 R15's stock, I installed 30.9 R15, I used to see 24mpg, now 21 (before pump messed up - 17).

[G. Gearloose]

Ah yes, I see..

[Peter J. Bierman]

Average of 15 mile/gallon on 33 tires.
cruising at 70 MPH and some serious hills.
TH400 3.73 gears

this is Twin Turbo configuration with 300Hp pump.

Peter

[Vaughn MacKenzie]

His Blazer is a 4-speed OD (is that the 700R4?). He does have 31" tires on there now and MPG is corrected for speedo error.

Well sounds like it's on par then. For some reason I was thinking these things would get 18-21 pretty easily but I guess not? I know they're a brick and all and IDI engines probably are less fuel efficient than the direct injection variety.


We are fixing to set out on a long road trip to the NE and he's planning to draft off of me in hopes of better mileage. I'm driving the Ram pulling a small TT which will serve as a wind break :rolleyes:

Gearloose what is considered ideal timing? Say non-turbo basically stock? On my Ram the 12-valve Cummins is 13.5 BTDC from the factory and guys set them anywhere from 15 to 18 degrees. 16 is a good number.

Vaughn

[G. Gearloose]

Sorry, I don't know the numbers, I set it by ear...

Search these forums, you should come up with something..

But my old '83 K20 6.2 NA with 4.10, 35" mud terrains and 700R4 got 19-20 mpg average also, not just highway.

He should see 18 easy, if he doesn't drive like a kook...

[CA_Grizzly]

700r4 3.42 gears 31"tires get around 17-20 on highway but I drive at 75 and accelerate fast.