350 Fuel Economy & Type

[mohosa63224]

Hi All,

I am looking to buy an 1985 GMC Suburban K2500. I was supposed to check it out last week, but life got in the way so we rescheduled for this week. Anyway, the additional time has allowed me to think about the truck, and I have a question for you experts here:

The truck comes with a carbureted 350 and a THM400 3-spd auto. What do you think the fuel economy of such a truck might be stock? Also, just to be absolutely sure - this only requires regular fuel, correct?

Thanks for the help.

 

[smartcarkiller]

I checked on fueleconomy.gov and it says you should be getting around 11 in town and 15 freeway, that seems about right if its running good. Yea it takes regular fuel. I don't think they made these big trucks to be very fuel efficient, they made them to be safe and haul a crap load.

 

[79Midnight]

with a tuneup and in town driving, I get around 8 or 9, but my truck sounds too damn good NOT to open her up every so.......take off.

the burbans may not be the best on mileage, but keep in mind, it's built the last.

My buddy has a 78 burban with an unknown amount of miles, adn it runs like it did when he got it in 1992

he's taken it all over the country, and to Canada, he'll never get rid of it.

oh, and it's got the same setup as the one your looking at, and it's still all original.

Pics please?

 

[mohosa63224]

Thanks for replying. I know they're not built with fuel economy in mind, which isn't a problem. I was just curious was people tend to get. I find fueleconomy.gov to be inaccurate sometime, especially with older models.

And as for the pics, I'll be posting some as time (and the repairs) go on. But before I can start on anything else, I first need to register and insure it just to drive it home. I bought it Wednesday, and it is currently in the driveway of a relative who lives near the seller.

 

[dhcomp]

You won't get 15mpg highway, even downhill with a tailwind.

I have a 91 3/4 ton with the 350, and with stock highway tires, and OVERDRIVE, which yours wont have, i get about 16 unloaded on the freeway.

I say you see 13 tops, cruise control set, 55 on flat ground.

What do you plan to do with this truck? If you don't need a 3/4 ton, the 1/2 ton's got an overdrive transmission.
The 3/4 ton only got an overdrive for 91, so you could look for one of those too, but way more rare.

 

[Stomis]

Part of the problem is the smog era heads, coupled with a carb, and a non OD transmission PLUS its probably gears high as hell and making the motor struggle to get that 9000lb beast moving...

I bet properly geared and a late gen injected 502/4l80e would net significant improvements for that trucks mileage.

 

[mohosa63224]

I just re-read my original post. While I did end up buying the truck, the seller made a mistake when he said K2500 TH400.

It really is a K1500 (the side badges, which aren't original, say 2500) with a 700R4.

As for what I plan on doing with this truck - I'm gonna make it into an offroader. Nothing too extreme, but something that works. I also plan on using it to carry heavy loads on occasion.

 

[dhcomp]

Well, the 700r4 will net you better mileage in stock form.

 

[Thunder]

You can see ok gas milage with a 700r4.
Tune up the engine good.
Very important to change the fluid in the trans. Fluid in a 700 should always look pink and new for long trans life.
And. If the truck does not have one, get a good aftermarket trans cooler. That is a must do and have. Espically if you are hauling loads.
Change all the fluids. Synthetic fluids/oil in the engine/ drivetrain will also help a little to boost MPG.