First Results of Mile Per Gallon Tests for 1998 Suburban LT (350)

Fill the tank. Note the exact gallon count. Drive till Empty. Divide the number of miles driven until empty, by the exact gallon count.

Charles

Everything sounds dead on...except you should be the one filling it up. That will take out a large variance of how full it is. If the pump is running max flow and shuts off, it will not be as full as if it was running second, or even first notch. If your a 'clicker', then you can get gas all the way up to the top of the filler if you work at it.

Its not unheard of to get at least a little more MPG then it says on the sticker. When I finally got my carb tuned in on my '85 4x4 1/2T Suburban, I was getting 17-18mpg on the Freeway running 80mph. That was more than a point or two above what comparable NEW Suburbans were rated at, at the time. I was getting 12-14MPG for in-town driving. I also had enough power to light up both rear tires on dry roads from a stand still too. Not to mention enough power to tow an 8000lb skid-loader on a 2000lb trailer...

My brother in law was always disgusted with the mileage of his 2wd truck when he found out that a coworker got 2mpg better with the EXACT same truck but with 4wd.

To try to pull a little more out of your 'Burban, try varying your speed a bit each way per tank. Try running different octane gas, also

Per Walter Welle:

Go to Staples or some other outlet and get a little ledger book.

Every time you fill up, note the miles and number of gallons.

Over time, you can add up all the gallons and divide by the sum of miles - which will reduce any errors from individual fillups.

Don't "top off" your tank on any fuel injected vehicle.

There's a hose near the top of the filler tube - it indirectly heads off to your charcoal canister. Topping off lets raw fuel down that line (normally only meant for vapors). This will cause your canister to wear out sooner than expected (well, the contents of it!), and can make for a gassy stink near the front of your truck.

Just let it run wide open until the first "click" then stop fuelling. Let that be your basis point. I always try to fuel up at the same station too, so variances in gas quality doesn't become an issue (mostly just when you're doing testing).

I have topped of my 89 burb since it was new and I have never had any problems with it and it is TBI. I do it regularly with all of my FI cars.

... and it's still a bad idea. Don't confuse "getting lucky" with "doing it right". If you flood your charcoal cannister you are in for quite a few issues, and a bad gas smell in your engine compartment is by far the least serious. There's a reason why the cannister is there, just as there's a reason why they tell you not to top off your tank and it's not some dark, political agenda. Despite what you might think, they tell us this not to deliberately annoy just you.

Cheers - Jonathan

I think you are making more of this than there is because fuel could slush up filler nexk in right conditions and flood it if it was that easy to do. I question the basis of your theory, not that you have one.

I am with SnoMan on this one. The hose near the top of the filler does NOT go any where near the charcoal canister! It is to allow the air from the tank to escape while the filler tube has gas rushing down it.

The lines going to the charcoal canister are fuel vapor lines whose purpose is to hinder evaporation of gas in the tank. Its basic design has changed over the years, but its purpose remains the same.

Getting EVERY drop of gas that is Humanly possible(i.e. filling to the top of the filler) could eventually make its way to the vapor canister only because there is less expansion room in the tank and the liquid gas has a chance to push up the vapor line.

Greetings,

I did not state that the vent line to the fill neck went to the charcoal cannister, but now that I went back and re-read the previous posts I can see where it could be implied. My bad.

However...

The basic fact remains that "topping off" your tank can cause problems with the charcoal cannister (which can lead to other issues), it is warned against both in owners' manuals (and even on the pumps where I live, although probably for other albeit similar reasons), and it's still not good practice to try to force as much fuel into your tank and up into the filler neck as humanly possible. Therefore, my basic statement still stands.

Cheers - Jonathan

I have accumulated millions of miles of driving gas powered passenger vehicles and never had any problems with any vapor canisters and I have always topped off. I had nearly 600,000 miles on my Cutlass alone...always topped off and NEVER any problems with the vapor canister.

Now, if when you say 'topping off' you are referring to filling gas all the way to the top of the filler, then I agree, to a point. If that is the form of topping off you are referring to then you are the only person in my life that I have ever come across that thinks that is the only meaning of topping off.

Enough said about the topping off subject I think. Its time I unflag this topic because it has drifted far enough away from what the OP needed, and he obviously already got what he wanted from the initial replies.

This is a good idea. My grandfather has always been insanely meticulous when it comes to keeping vehicle records. For instance, when he sold his 1974 Caprice Classic in 1988, he had logged every single fill up, the cost per gallon, the number of gallons required to fill, and the mileage.

He does this with every single car he's ever owned, as well as kept every receipt for every oil change, repair, tire rotation, etc... NOTHING goes undocumented. He's got a good system though, and at 85 years old, I think he knows what works by now.

Doing it this way will also let you see long term changes in performance. For example that over the course of a few years the mileage may decrease slightly as the vehicle ages.

Plus having the documention will look great if you ever decide to sell it.

~jp

The Reason the EPA Mandates those labels has nothing to do with vehicle emissions.

It has to do with Vapor Recovery during refueling. If you attempt to top off some vehicles with the vapor boot sealed to the filler neck. What happens is a over pressure situation, and can cause the vehicles fuel tank to spit out vapors and raw fuel.

Now it is possible on Some vehicles to flood the Charcoal Canister during a fill up. 84 to 86 C-4 Corvettes come to mind.

On my F-I vehicles if I let the pump stop at the first click, I usually do not get a full tank, closer to 3/4's really. That's OK for in town, but when Im going on a long distance trip, it's very annoying not to have a full tank. I don't know about you, Im good for 300 to 450 miles between rest stops. Charles

This is a good idea. My grandfather has always been insanely meticulous when it comes to keeping vehicle records. For instance, when he sold his 1974 Caprice Classic in 1988, he had logged every single fill up, the cost per gallon, the number of gallons required to fill, and the mileage.

He does this with every single car he's ever owned, as well as kept every receipt for every oil change, repair, tire rotation, etc... NOTHING goes undocumented. He's got a good system though, and at 85 years old, I think he knows what works by now.

Doing it this way will also let you see long term changes in performance. For example that over the course of a few years the mileage may decrease slightly as the vehicle ages.

Plus having the documention will look great if you ever decide to sell it.

~jp

yeah, all 97 boxes of it. old john

Hello, Jon! You wrote on 8 Jan 2006 02:53:57 -0800:

JP> He does this with every single car he's ever owned, as well as kept JP> every receipt for every oil change, repair, tire rotation, etc... JP> NOTHING goes undocumented. He's got a good system though, and at 85 JP> years old, I think he knows what works by now.

JP> Doing it this way will also let you see long term changes in JP> performance. For example that over the course of a few years the JP> mileage may decrease slightly as the vehicle ages.

JP> Plus having the documention will look great if you ever decide to sell JP> it.

With best regards, snipped-for-privacy@comcast.net. E-mail: snipped-for-privacy@comcast.net

I keep telling myself that someday I'm going to start on that system. I've yet to do it, but I did find a little portable file case (lost in the mess in the back of my K5 no less) that'd be ideal for keeping my vehicle records in. I think once I get back on the road I may go through the few dozen receipts and invoices in the console and try to organize them in some way.

When I was delivering pizza I kept very detailed gas and mileage records. I think I may start doing that at the very least.

~jp