Increased mileage by nut at the wheel in 3/4 ton Suburban...

[101Volts]

Vehicle: 1999 Chevrolet Suburban K2500 Turbo Diesel

Mods: Cold Air Intake, 80 PSI in front tires, roof rack delete, air dam, use of block heater to start at 116 fWT at crank-over*, 0w40 Shell T6 oil, Amsoil Severe Gear 75w90 in Differentials, Scangauge II.

The SGII isn't calibrated correctly and is optimistic but since the first time I drove on the same roads** I've increased the average rating from higher 20s and a touch above 30 to 37.x by the time I turned the vehicle off. A little adjustment to my mentality of this made a difference: I was often driving slow, making sure the MPGs read higher then I considered normal and traffic was light or non-existent this time. I reached above 30 AVG before I turned on the 4 mile stretch where I got up to 40 but then had a stop sign and right turn. Somehow I didn't think making the instant meter read high more frequently made this much of a difference but it does and quick accelerating from 30 MPH to 40 in the 2k-2.5k RPM range in Overdrive doesn't effect the average MPG rating a lot.

As for the actual MPGs I got they're probably closer to higher 20s or 30 than 37.x by the time I turned off the engine. I haven't tracked from fillup to fillup but the actual F.E. did seem to be getting around 20 when judging by the needle while the SGII read 25-27 AVG.

Edit -

* on this particular trip. The actual starting temperature varies depending on the ambient temperature and in my experience the block heater is good for around 50 degrees above ambient temperature, give or take a few degrees.

** "The same roads" meaning that I was going the same exact trip from my house to one particular destination; 6 to 7 miles down the road from me then on a side road for 4 miles then under 1 mile to the stop point. This does not speak for all the roads I drive on although I've learned something significant from this one trip!

[elhigh]

It's funny how accelerating more briskly than you might think is most effective, is more effective. I think it's because you spend more time cruising in the butter zone once you get past the acceleration stage.

Any aero mods in the cards for your Burb? They're aerodynamically disastrous, there's LOTS of low hanging fruit to be had, and any improvements you make will pay off in a big way if you use the truck a lot.

[slowmover]

Aero only good for sustained highway, in general. Trip planning means most when the vehicle has huge penalties in acceleration and braking (I.e., the shortest route is often not the best route).

OP needs to keep records. All miles and all gallons. Nothing else matters, especially not tank to tank variations. It's the average mpg that matters.

And bring the tires down to something sensible. My 8,000-lb pickup is at 55-psi F/R. Almost on top of recommendation. Braking and handling are better. As a result (and my tires go over 100k before replacement) my tires stay in better contact with the road, AND with a larger contact patch. A high center of gravity vehicle needs some sidewall "give". It also reduces the likelihood of punctures.

. Take it to a CAT Scale and weigh all four corners with full fuel, driver plus gear always present. Pretty much any LR-E Load & Pressure Table will suffice, but tire manufacturer brand and model spec is best. That number plus 5-psi is about right. Heaviest load at either axle end determines pressure for that axle.

Best shocks and new body plus suspension bushings/ ball joints are important. As is elimination of steering slop. There's more money to be had in attending this approach.

Fewer starts, fewer stop & go over a given set of destinations, and fewer steering corrections (is pretty much the recipe for a heavy personal vehicle).

All else is downhill from that (in effectiveness).

With this exception on a diesel truck: maintenance of coolant temp in cold weather. Good to see use of block heater, but an exterior mount grill cover, and an interior "winter front" which covers the heat exchangers for sub-40F temps covers all air temps down to cold. I go from two grill cover pieces to four as temps get below the need for A/C use (and overnight temps), to their removal and use of WF when temps no longer get above 40F.

I have my doubts about cold air intake for diesels in pickups (except in highest temps and under a load), but leave that to the DD/GM crowd to figure out.

[101Volts]

Originally Posted by elhigh

It's funny how accelerating more briskly than you might think is most effective, is more effective. I think it's because you spend more time cruising in the butter zone once you get past the acceleration stage.

Any aero mods in the cards for your Burb? They're aerodynamically disastrous, there's LOTS of low hanging fruit to be had, and any improvements you make will pay off in a big way if you use the truck a lot.

It's either staying in the 35-90 MPG on the instant meter or briskly accelerating, not lowering the average much and then having 200+, 400+, 600+ and even 1000+ MPG on the instant meter depending on the road.

When reading the SG2 I find using a (Top left, top right, bottom right) configuration of GPH-MPG then AVG works best for me. I don't use the bottom left for much, I alternate between fWT and intake air temperature. I was using LOD instead of GPH but that doesn't get as detailed as I'd like to read.

As for aero mods I thought of going all out (smooth hubcaps, partial kammback, higher hood, lower an inch or two, 'air dam' on the sides, etc) but haven't been going after it a whole lot. I had duct tape serving as wheel arch covers (full in rear and partial in front) but my Mother didn't like it so there it went. Something less "rednecky" would suffice however.

Originally Posted by slowmover

Aero only good for sustained highway, in general. Trip planning means most when the vehicle has huge penalties in acceleration and braking (I.e., the shortest route is often not the best route).

It's generally driven at speeds higher than 40, sees HWY travel fairly frequently and generally drives least 15 miles before getting to the first destination and sitting so it does usually get to operating temperature. It's not a short-trip (under 5 miles) vehicle.

Originally Posted by slowmover

OP needs to keep records. All miles and all gallons. Nothing else matters, especially not tank to tank variations. It's the average mpg that matters.

I was but then found the fuel tank leaked. I may have fixed it but am not sure if it's a fix which will last a while, the tank hasn't been filled up since before it leaked.

Originally Posted by slowmover

And bring the tires down to something sensible. My 8,000-lb pickup is at 55-psi F/R. Almost on top of recommendation. Braking and handling are better. As a result (and my tires go over 100k before replacement) my tires stay in better contact with the road, AND with a larger contact patch. A high center of gravity vehicle needs some sidewall "give". It also reduces the likelihood of punctures.

How's that? The rear tires call for 80 PSI on the doorjamb and 55 on the front. I can understand inflating to an appropriate amount of air to prevent abnormal treadwear, blowouts and have good traction though I initially thought the 55 figure was just for comfort in the front and the tires said "80 PSI Max" so I pumped them to 80 too.

Originally Posted by slowmover

. Take it to a CAT Scale and weigh all four corners with full fuel, driver plus gear always present. Pretty much any LR-E Load & Pressure Table will suffice, but tire manufacturer brand and model spec is best. That number plus 5-psi is about right. Heaviest load at either axle end determines pressure for that axle.

I'm clueless and don't yet know what this is for. Are you suggesting a way to find the optimal pressure and tire combination? I understand a CAT Scale is for weighing.

Originally Posted by slowmover

Best shocks and new body plus suspension bushings/ ball joints are important. As is elimination of steering slop. There's more money to be had in attending this approach.

The shocks are about 20.5 months old now with approx. 8.5k miles on them. I'm not sure the brand as the previous owner put them on shortly before I purchased the vehicle and the stickers came off but I do have what may be steering slop, when I brake hard the vehicle pulls to a side. It happened today even though I put the transmission in 2nd.

Originally Posted by slowmover

Fewer starts, fewer stop & go over a given set of destinations, and fewer steering corrections (is pretty much the recipe for a heavy personal vehicle).

More time with the vehicle at peak operating temperature and more time cruising in low fuel/high instant MPG readout, sure. I understand this. Reiterating; the vehicle usually gets to operating temperature before I shut it off again. I do let it idle a few minutes before shutting off to cool the turbocharger but I'm not sure if that's necessary or is something which only applied to other turbocharger vehicles.

Originally Posted by slowmover

All else is downhill from that (in effectiveness).

With this exception on a diesel truck: maintenance of coolant temp in cold weather. Good to see use of block heater, but an exterior mount grill cover, and an interior "winter front" which covers the heat exchangers for sub-40F temps covers all air temps down to cold. I go from two grill cover pieces to four as temps get below the need for A/C use (and overnight temps), to their removal and use of WF when temps no longer get above 40F.

I forgot to mention I do have a partial "grille" cover out of tape. However it's on the bumper and only covers one of the two holes. Still, thanks for the mention of the grille block considering winter's coming.

Originally Posted by slowmover

I have my doubts about cold air intake for diesels in pickups (except in highest temps and under a load), but leave that to the DD/GM crowd to figure out.

I don't know much about them either save for that it makes warmup time longer and that's part of why I use the block heater. It's limited though, it does help but won't get me to full operating temperature. I'd need something aftermarket for that.

[slowmover]

Basically, anything under 75-miles is a short trip. Takes that long for internal tire temps, axle oil and probably suspension grease to "warm up" to op temp. Found this to be true on my pickup as well as in Class 8 with dual axle temp gauges. Then, from there, another good number of miles are needed to fully cook off condensation related acids, etc, in lube oils.

Fixing or replacing fuel tank will be a feeling of relief.

As to tires. The reason to weigh the vehicle is to help determine proper air pressure versus individual wheel load. If the door sticker shows 55-psi front, then I'd use it all around. Actually, for handling, more air in front is better. 55/45 is worthwhile.

I run mine at 55-psi all around as it is still above minimum (my truck weighs 7,940-lbs; within 40-lbs at all four corners; Dodge says never less than fifty even though that's above what table allows), but truck does not hop or skip on rough roads as it does with higher pressures without a higher load. Any FE gain above that means worse braking and handling. Not to mention more likely to be punctured. Etc.

Finding lower limit (where tire pressure rise from cold is no more than 7% after 90-minute steady state driving) is the hard part. Not much above that is the FE compromise. In my case that might be up to 60-psi. But, now I've roughened the ride for a minute "gain". On a long trip it means that NVH tires driver eroding fine motor skills. Etc.

Pulls to one side when braking means ball joints are shot. Assume same for steering tie rod end links. Take to a shop for an evaluation (alignment). Best shocks are Bilstein brand for price versus never wears out performance.

Don't need to idle before shutdown unless heavily loaded and coming off high speed Interstate. Even a quarter mile from big road to fuel station is sufficient time. I've almost never done it in mine. Turbo failure on a stock Diesel is rare, but, again, ck with DD/GM guys.

A winter front mounts over heat exchangers underhood. Covers radiator and that support. Has an opening in front of coolant radiator with adjustable flaps. A grille cover is not the same. One adjusts the flaps to keep coolant temp just below thermostat opening temp (remove cover above 40F).

Google "MOPAR winter front Cummins" for images with truck hood open. My search only showed exterior covers for early Maxipad engines.

Back around 1992 had a neighbor who was the son of a retired GM executive. He used to make the run back and forth from Michigan to Dallas with his early 6.2L 4WD Suburban claiming 27-mpg. Had a good friend with one of the first year 6.2L and he got 20+ mpg for the 12-yrs/400K he owned it. Both used narrow tread highway style tires.

I posted more detail on a recent Dodge Cummins thread that may also apply here.
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