Hard to believe

[mcgall83001]

I'm on my way home from purchasing a 1995 Chevy Suburban 6.5 diesel

Ran the first half tank at 70mph and got 11.5 mpg

Filled up

Ran the second 1/2 tank at 60mph for a whopping 20.5 mpg

That's a 9 mpg ( almost double) increase for a 10mph reduction in speed. Seems like a lot to me.

I'll try again at 70 and 60 mph to insure I got correct readings.

 

[W0lfpack91]

I'm on my way home from purchasing a 1995 Chevy Suburban 6.5 diesel

Ran the first half tank at 70mph and got 11.5 mpg

Filled up

Ran the second 1/2 tank at 60mph for a whopping 20.5 mpg

That's a 9 mpg ( almost double) increase for a 10mph reduction in speed. Seems like a lot to me.

I'll try again at 70 and 60 mph to insure I got correct readings.

Less speed less RPM. Diesel does not use air flow to determine engine speed it uses fuel. Less RPM =less fuel. If you can gear it to run the same RPM at 70mph as it does now at 60 you can expect similar MPG at 70.

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[ttengineer]

I'm on my way home from purchasing a 1995 Chevy Suburban 6.5 diesel

Ran the first half tank at 70mph and got 11.5 mpg

Filled up

Ran the second 1/2 tank at 60mph for a whopping 20.5 mpg

That's a 9 mpg ( almost double) increase for a 10mph reduction in speed. Seems like a lot to me.

I'll try again at 70 and 60 mph to insure I got correct readings.

Less speed less RPM. Diesel does not use air flow to determine engine speed it uses fuel. Less RPM =less fuel. If you can gear it to run the same RPM at 70mph as it does now at 60 you can expect similar MPG at 70.

Sent from my SM-G955U using Tapatalk

That’s not exactly correct.

Diesels run more efficiently at higher RPMs, to a point. Lots of factors to consider as well, like turbo, ambient temp, etc.

In my 6.7 the sweet spot is 5th gear at 2000 RPM.


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[W0lfpack91]

I'm on my way home from purchasing a 1995 Chevy Suburban 6.5 diesel

Ran the first half tank at 70mph and got 11.5 mpg

Filled up

Ran the second 1/2 tank at 60mph for a whopping 20.5 mpg

That's a 9 mpg ( almost double) increase for a 10mph reduction in speed. Seems like a lot to me.

I'll try again at 70 and 60 mph to insure I got correct readings.

Less speed less RPM. Diesel does not use air flow to determine engine speed it uses fuel. Less RPM =less fuel. If you can gear it to run the same RPM at 70mph as it does now at 60 you can expect similar MPG at 70.

Sent from my SM-G955U using Tapatalk

That’s not exactly correct.

Diesels run more efficiently at higher RPMs, to a point. Lots of factors to consider as well, like turbo, ambient temp, etc.

In my 6.7 the sweet spot is 5th gear at 2000 RPM.


Sent from my iPad using Tapatalk

The point of a turbo is to get a more complete burn off existing fuel by increasing the air content. The opperating concept behind the turbo in a gas burner vs a diesel is diffrent, gas burners use turbos to force more air to be able to burn more fuel increasing power. They get their economy by producing more power in half the physical displacement. A diesel however has a constant fuel delivery run directly off throttle pressure, the harder you press the more fuel is delivered to the engine, a turbo induces air to ramp burn percentage making the vehicle more effecient with the constant fuel delivery. If tuned correctly yes a turbo can increase MPG but thats by being able to cut back the fuel delivery to a lower variable at the same power output throughout the RPM curve vs an NA diesel. Also the idea of cooler denser air vs hot air is also true but those are variables that cant be counted on in the real world as easily as on a spreadsheet. From a basic operation standpoint the principles of a diesel engine opperation dictate less RPM = Less fuel.

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[twodollars]

Let's see some pics and specs! My 94 2500 burb with 6.5 averages 17 on highway at 75.