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99 suburban low gas mileage

I just replace my 94 burban with a 99.

To my astonishment it gets lower gas mileage that my 94 with 320,000 miles! It got 16 MPG while the 99 gets about 12? Same engine, no 4 wheel drive. Replaced plug wires and plugs but no improvement Any suggestions?

How are you measuring the mileage?

I wonder why anyone would want to know what their mileage was if they had a Suburban. ?

Get a different vehicle. The 99 Suburban is rated at 12mpg city, 14 combined. Remember that 99 was right in the middle of the “everyone’s gotta have the biggest freakin’ truck they can find, and they don’t care what the mpg is because gas is only like 88 cents a gallon!” craze.

My suggestion is not to throw parts at a vehicle that is running as designed. Think of all the fuel you could have bought for what those plugs and wires cost (even if the labor was free).

Readers, don’t replace plugs and wires unless there is a reason.

Go by a parts store and have them scan it. The ‘check engine’ light might be burned out or disconnected.

Different engine . The 94 had the old wheezy TBI LO5 350 and the 99 had the more powerful LT-1 derived Vortec 350. At any rate the 1994 2WD Suburban 1500 is rated at 11 MPG city and 16 highway. The 99 model is rated at 12 and 17 MPG respectively. Both figures are within the ballpark. Does the 99 have the trailer towing package? I might be mistaken, but I believe that got you 4.10 rear end, with the standard rear end gear being 3.73 or 3.42, combined with a few extra pounds that that the 99 is carrying around, that could explain some of the discrepancy.

But you are talking about one the largest vehicles on the road, you can only expect but so much.

We do get a lot of posts from people that expect to get better than advertised mpg. Is it correct to say “don’t call me until it is worse than rated”?

I believe it is correct to dismiss claims of poor mileage as long as they are not below rated mpg.

I have to agree. I was surprised to see the post title. I was assuming I’d open it up and find a report of like 4mpg or something. You bought a suburban and you’re posting about 12mpg as low gas mileage. Get a Cavalier if you want better mileage.

That said, you did just buy a used vehicle. What do you know about its maintenance history? If in doubt I’d just do a full round of maintenance - air & fuel filters included.

Tire pressure is one of the big ones.
Make sure no brakes are dragging.
Make sure the alignment is correct.
Check your coolant temp sensor and thermostat operation.

Its likely that none of this will do anything. Improved MPGs are not and have not been on the list is things auto makers seriously work on. So you get something else that is smaller and lighter with a smaller engine.