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Poor gas mileage

My aunt has a retired 1994 GMC moving van that she bought from the UHAUL store. She owned a shop in louisiana and she buys inventory in Houston but recently she stopes using it because it gets 3 mpg and she almost spent a grand on her last trip on gas. And lots of water comes out of the tailpipe. I think it’s the carb but my uncle thinks it needs an engine overhaul what might be the problem?

I wished your aunt hadn’t bought the van from a moving company. ESPECIALLY from U-HAUL. This company has a past history of not maintaining their vehicles.

Your uncle is probably right, the engine needs an overhaul.

I suspect there is a more pressing issue than a fuel guzzling problem.

Is there also an overheating fault? If so, head gaskets and intake manifold gaskets are possibly leaking.

If she wants to keep it, it may be a good idea to have pressure test done to verify and locate any leaks.

Fifteen years old, used and abused by countless U-Haulers over the years, it could be almost anything. A number of years ago I drove a U-Haul truck from my old house to my new house (about six miles) with the parking brake on the entire way. Didn’t realize it until I got close to the new place and saw the rear wheels smoking. Never even felt like it was lagging, but I’m sure it didn’t help the gas mileage.

Does this thing actually have a carb or is it fuel injected? How many miles?

It has a carb and it has 160000 miles on it

Okay. I’m siding with RR here; I too have heard bad things about U-Haul trucks not being maintained very well. You might get lucky and all it needs is a carb adjustment/rebuild, but I suspect it could use that and a whole lot of other things.

How is it with oil and coolant? Any funny colors, smells, leaks, abnormal fluid loss, low fluid level, anything like that?

No the only fluid is from the tail pipe

TBI fuel injection frequently gets mistaken for a carb,they look a lot alike if you don’t look close. 1994 is a prime TBI year.

Has ANY routine maintenance been done, like spark plugs and wires, air filter, fuel filter? Some one may have taken the thermostat out, or the cooling fans may run continuously, or the engine coolant temperature sensor may lead the engine computer to inject too much fuel, all the time. The engine may be misfiring …which you WON’T realize if the misfirings are singular events on different cylinders.
Tune-up and check for engine codes.

You are correct old school. TBI engines were standard across the board for Chevy G series from around circa 1990 until the LT-1-derived engines showed up in 1996.

A 1994 with a carb? I doubt it. Rocketman