Bought a showroom clean condition ’88 GMC K2500 pickup with the 350 engine, fully loaded ready to tow.
My first refill and it ‘pears I’m getting less than 10 mpg – and I go REAAAL easy on the gas anyway.
I never had a 350 before, and I’m just thinking this thing has a problem, but she runs gray out of the tailpipe: it has the EFI throttle body system, but has anyone else had one of these and can guide me.
I know the first thing people say is the driver, but a stock 1100cc Volkswagen Beatle will pull away faster than I will (I have a hopped up Harley if I want to go fast).
Quality repairs for your home.
AaronR Construction
Vancouver, Canada
Replies
Just for comparison I have an 06 with a 6,0 (I believe that is like 377 cu in.) and it gets 11-12 on the highway. I am not gentle on the throttle nor do I drive slow so it might creep up to 14 with you driving it. So my thought is you might have it checked out at a shop you feel compfortable with. DanT
I understand you have a Harley. How do you like it?
I've got a 96 K1500 that gets about 12 in normal use (mostly city, seldom fully loaded, occasionally towing a dump trailer), but will get 16-17 on the highway. Prior to that I had a C2500 ext cab with a utility bed. It got around 10-11 & 15, IIRC, but it carried lots of tools and a crew.
Your 2500 is a heavier vehicle and may have a lower rear end than my 1500. How much weight do you have in the bed? Your number sounds a little low, but not completely unreasonable.
copper p0rn
I had an 87 Ford F250 with a carburated 351.
Low double digits for MPG. Didn't matter if it was empty or full... stompimg on it brought the gas needle down faster. Extension ladders hanging in the breeze would bring the MPG into single digit territory.
It got better mileage with the aluminum heads and RV cam than stock, though.... :)
If you haven't tuned up that truck, then do so. Use OEM parts- not the cheap junk from the discount auto parts store. Check the timing. Replace the O2 sensor (again, use OE parts).
What is the gear ratio? If you are spinning over 2k rpm at 60 mph, you will have great pulling for towing at the expense of MPG.
Throttle body EFI is just a glorified carb. You get better cold starts and driveability, but you are still squirting fuel all the time.
You won't get mileage improvements unless you buy something newer with sequential fire injectors... but you are still feeding 5.7L of displacement, so you might get 15-19MPG. An RV profile cam might help.... but I wouldn't expect more than a 1 or 2 mpg improvement.
If you want MPG, you should have bought something with a V or inline 6. The same vintage Chevy W/T series trucks with the V6 would easily get 20 MPG. The Fords with the 5.0 also got good MPG.
If you want towing capacity, a heavy duty chassis and decent MPG, then you should have bought a diesel.
Compared to the newer GM engines with approximately equal displacement, the old 350s were thirsty. We had an 87 Suburban with the 350 & 3.73 gears. The best we got out of it was about 12 mpg. Our current 94 Suburban doesn't do any better. Both 4x4s. You've probably got 4.10 gears in the 2500, so I'd think your mileage is about normal.
The newer GM engines do a lot better -- except for the 8.1 L in my truck. 11mpg when my wife drives it, 9.5 mpg when I drive it.
Same eng in my 96 3500 van. I get 11 average. 1/2 hiway , half backroads and city. Best ever was empty hiway, I got 13.
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Here's another vehicle for comparison. '98 Ford E250 with a 5.4 liter engine (330 cubic inches#. It gets between 10 and 12 mpg. Usually closer to 10 and worse in the winter #I think the gas formula changes#
It doesn't seem to matter too much what kind of driving I do. Around town, it needs to constantly accelerate a lot of weight #almost 7,000 lbs loaded) and on the highway, it's like pushing a barn door through the air.
I suspect the best gas mileage would be achieved at a steady 50 mph or so, but I never do that kind of driving. It's stop/start and the occasional 30 minutes at 65-70 mph.
Oh, I forgot to mention, it has 225,000 miles on it and the engine runs like a top so I'm not complaining.
I had an '86 Jimmy "Camper Special(K2500, 4 speed manual) and got about the same mileage.
Those rigs weren't built for fuel economy - they were built to haul and pull big loads. I used mine quite a bit to haul horses and cattle in the mountain back country (lots of off road driving) and it would do it all day - but it took lots of gas!!
In '92, I drove it from San Jose, CA to Wilmington, NC and back. I didn't track the mileage 'cause I didn't really want to know. - lol
2003 F250 4x4 with 5.4, gets 10 full or empty.
I had a 3/4 ton Chevy with a 350, same thing. 10MPG was it.
Joe H
I don't think you'll do much better than 10mpg in the 1988 truck.
I bought an 08 chevy crewcab 4x4 with the 4.8L v8 and it gets around 12mpg around town and 17mpg highway. I was expecting a little better but oh well. Trucks have always had bad fuel economy and probably always will.
I read an article a few months back about the government considering taxing truck buyers even more because they use so much gas. I know they have gas guzzler tax for cars like lamborghinis and vipers so I guess it'd make sense to whack the truck buyers also.
My 88 C2500 5.7L got about 10-11 mpg around town, close to 20mpg on the highway - back when it had a camper shell.Rebeccah
Does sound pretty typical of that vintage truck. My '03 F150 4x2 gets about 15mpg doing the kind of country road driving I do, and that's with a thousand pounds of toolboxes and lumber rack on it. It always annoys me when one of my friends with a late model 1-ton diesel tells me he's getting well over 20mpg.
alot ofit is rear end gear ratio
Considering that a 1988 GMC Suburban
- 350 was expected to get 13 mpg
And given what I heard for years from neighbor with IIRC, same truck as you just bought, you're likely stuck right with the MPG you're finding you're getting.
Hope you own stock in exxon-mobile?
"I'm a work in progress; still learning every day!"
Wow. If I got 13 it would be a victoryQuality repairs for your home.
AaronR ConstructionVancouver, Canada
well many things never live up to "expectations"...and your truck seems to be one of those
;-)
"I'm a work in progress; still learning every day!"
I had a 86 4wd with a carb and a 350,
I got around 10 maybe 12 at the best.
My 89 dodge with a 318 throttle body gets the same..
96 ford van with v6 and 95 ford Explorer with v6 both get around 17.
I was told the Ford v6 did pretty well and its true.
78 chevy one ton dump with 4wd gets around 8.
Sounds a little low to me but not by much. With the big block you'd be right in the ballpark imho. Used to drive a 2wd version of your truck some years ago; iirc used to get around 12 mpg in town and you could eke out 16 or so on the open road. Unfortunately I think you've discovered why diesels became so popular in 3/4 and 1 ton trucks.
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I have an '85 one ton 4x2 automatic Chevy dually with a 350 carbed , it gets about 10mpg or so, loaded or not, driving fast or not, city or highway..same result.
I wish the dually I drove back then (these were all company trucks) did as well as yours- F-350 4x2 with a 460. Pulled like a locomotive but it was hard passing a gas station- 6 to 8 mpg.
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I have a 2001 3500 Chevy van with a 350. Here in Colorado Springs in the city I get 13.5-14.25 mpg. I have gotten 18 on the freeway. That's loaded pretty heavily with shelving, tools, and a three rung ladder rack.
I know that seems hard to believe, but it's been very consistent.
Back in Michigan I was lucky to get 12 and 14, respectively. I'm chalking it up to thicker air.
I do drive like I have an egg under the gas pedal.
Edited 11/8/2009 8:15 pm by True North
As far as getting better gas mileage...
1. Have that TBI checked out for best calibration, etc.
2. Dual exhaust. And headers, instead of the standard exhaust manifolds. Large pipe, and mufflers that allow a lot of flow.
3. Maybe the best thing you can do: Get rid of the turbo 350 trans, and put in one of the first 750-r4 transmissions.
One with overdrive and tc lockup.
The later ones get into too much electronic gadgetry. It is easier to get the earlier ones set up.
If the truck has cruise control, you already have the only switch you really need, for the torque convertor lockup.
Part of it is the 3/4 ton part.. that's a heavy truck. I assume crew cab or extended cab which adds even more weight..
It's not the 350! I have one in my 1997 1/2 Ton chevy and with 300,000 miles on it I get 19 MPG average.. 17 in town and as high as 21 on the freeway..
However I'm careful about maintinance and watch my tuneup like a hawk..Write your mileage down at each tankful.. I have a pocket calculator handy so I can figure the mileage as I fill up..
Any steady decline and I look for a reason why..
Tire pressure is way more important than most people realize to mileage..
I run my tires near the max pressure.
Driving technique is also critical..
I can't teach you what decades of racing has taught me about energy conservation. If you are serious about wanting better mileage start reading about the technique of cornering.. It's called a line and where the apex of that line determines your use of energy..
Learning to drive properly (not as they teach you in drivers ed classes) will make a serious differance in mileage..
Realize too that the longer you spend in lower gears the more fuel you use for a given speed.
i've had a lot of trucks and a lot of 350's10-12 MPG about average on a 350. Have done 14 in very careful driving
I've had a ford 360 and 390 both in 3/4 tons. I was able to get them up[ to 14-16 MPG with economizer carbs.
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When did the GM 350 go to EFI? My 85s have been carburetor fuel systems
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I'm not sure.. My guess would be right around that period.. Cadillac had FI in the 70's Corvette got it's FI in 84 and it follows that once those two had proven to be reliable and better mileage the trucks would follow. 85,86?
the normal is high end like corvette gets upgrades first, then normal sedans, then economy cars and trucks.Had to be 86 or later on the trucks.I know there are aftermarket computer chips available for either performance or for mileage....
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Corvette got it's FI in 84
Frenchy, You must not be a Corvette enthusiast! The first Corvette to have fuel injection in a stock car was in 1957.
It was the mechanical Rochester "Ram Jet" fuel injection system. Not exactly hi-tech by today's standards, but a step up from a carb in those days.
I owned a 1965 "fuelie" I believe it was rated at 375 HP
You sold it??
Yes, When I left for Vietnam. Figured I'd get killed and wouldn't need it! Wrong on both counts.
My F.I.L. owns several Chevy dealerships, so I have replaced it many times, but that was my favorite car of all.
BTW, he had a '53 and sold it with no miles on it. Worth about 2 million today.
Of course, however we were speaking about electronic not mechanical.. By the way I may be the last person in America that has the proper factory tune up guage for the older mechanical FI.
I did my last tune up of mechanical FI sometime in the 1970's (it doesn't work on Hilborn style or The Lucas feul injection in D type Jaguars)
I know that you knew that.....just throwing out some Corvette info!
You two greasers can quit polishing your nuts now!;)
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Please look down below for my answerQuality repairs for your home.
AaronR ConstructionVancouver, Canada
Aaron,
I talked to the neighbor who has the two 3/4 ton chevy full size trucks.
Gets 18mpg on the two wheel drive that he got from me. (It was only getting about 3mpg, when I gave it to him.)
And 21 to 23 on the 4x4.
I asked him for his reccomendation.
He said the first thing he'd do is to replace the throttle body injection with a Holley brand aftermarket unit.
The second thing he'd do is to replace the ignition components.
The cap. rotor, wires, all should be 'performance' quality. That includes the wires that are not just carbon core, but have the actual wire wound like a spring, around the core. (I have those. You have to be careful, and inspect inside the boot with something like a very thin penknife, to make sure they actually HAVE the wire in there. I inspected 6 different sets that were all supposed to be performance wires, and 4 of the sets said right on the box they had the wire... Only one set actually -had- the wire.)
New plugs, of course. The platinums are hype, and foul up pretty quickly. The ones that have a split tip on the side electrode, do make a difference. The ones with a groove, instead of actually splitting the electrode, not so much. Good for a while, then that groove fills up. Gap at 40. (I made my own split tip plugs, using a dremel cutoff wheel, a bench vise, and a chisel... And it actually worked. Did just as well as the ones that come already split.)
Next, a high performance coil. I had a yellow colored monster coil once. It did work as advertised. There is a red colored one, MSD or something like that. That company actually makes complete sets for the ignition. (And it was their wires that actually lived up to the hype on the box, when I was looking.)
After that, he reccomends the bigger exhaust, and the headers.
He said that all that... Should get you to 18mpg, easily.
The trans with overdrive and locking torque converter would just be icing on the cake.
I don't doubt his numbers, because I have driven the trucks.
And, of course, once he has all those components in there, he knows how to tune it just right.
The real point is, as I said before, just because everyone who has kept everything stock, has had the dealer do their service for them, or has serviced it themselves, but kept everything 'stock and by the book'... says it can't be done... That doesn't mean it can't be done.
Another thing.. He has locking hubs on the front of the 4x4. The kind you have to get out of the truck and spin both of them, to lock or unlock.
I believe he installed the front end with those hubs, on purpose. Swapped it for the one that had been on there.
Reason being, when he unlocks those, the front is completely disengaged. Better mileage.
And the trucks are by no means wimpy. They are both monsters. Mine always was. I just couldn't afford to keep it running. Now, he gets 18MPG, and it is still the same old monster.
They will haul big loads with no problem. And will get off the line fast.
Get them that way, then keep your foot out of it, except when absolutely needed, and you'll get good mileage.
The 4x4 probably carries an average of a ton to a ton and a half of tools every day, and still gets the good mileage.
Thanks, Luka.
I've had the same mechanic looking after my vehicles since 1986. I'll be speaking to him tomorrow with the suggestions you made.
This vehicle could be badly in need of a TBI rebuild, I'll bet it has not run 500 mi in 2 years.
I'll keep in touch with you.Quality repairs for your home.
AaronR ConstructionVancouver, Canada
This is my thinking whether to question a purchase, even though you are asking for like comprisions. I only state this because of the age of the vehicle means you must have gotten a good price.
well figure you get another 100k miles(dont know km's)
at 15 mpg that would be 6667 gals at $4.00 gal= $26,667
at 10 mpg that would be 10,000gals at $4.00 gal= $40,000
difference= $13,333
how much do you save in gas vs additional vehicle cost? over how many years?
plus figure that much additional out of pocket, plus the interest you you would pay for the loan, say over 5 years.
worth it to question how much?
And Luka etc.
Well, of course I could sell this thing but aside from the 4.3 Silverado, I don't see what I like that's affordable. I agree, buying a new truck is an option, but I have a huge disability.....I want everything paid for. Besides, I just replaced the radio (anyone remember the terrible GM '80s radios?).
So, here is what I did (first steps)... I took the machine to my mechanic, and he replaced the thermostat with a new 195 deg unit. The old one was stuck open.
Then, to get the truck running right he replaced the idle motor, since it was not working right, the truck idled at 35 kph/25 mph.
Third thing replaced was the computer's temperature sensor.
I'll get the thing back tomorrow morning and fill it up, and run through a tank.
Next step may be a new throttle body assembly and the heavy duty ignition parts Luka was talking about.
Quality repairs for your home.
AaronR ConstructionVancouver, Canada
I would try all new OEM ignition parts first. Jacobs was one of the few sources of aftermarket ignition stuff that claimed MPG increases. The OEM stuff is considerably less money and requires no changes.
Make sure the fuel pump is supplying the proper pressure- without the pressure, the fuel will not be atomized properly, and you will have lower MPG.
You may be able to buy blueprinted or pop tested injector units. Might be worthwhile looking into that.
The GM pellet style catalytic converter is quite restrictve compared to the honeycomb style.