Fuel economy: 1999 Tahoe

[Edahall]

Vehicle: 1999 Chevy Tahoe, 4 door, 2 wheel drive, P235/75/15 tires, 3.42 rear axle, Vortec 350, stock height

I bought this vehicle with a bad engine. If I keep the same engine, what kind of highway fuel economy could I expect out of it? This is assuming I drive no faster than 65 mph on level highway with a steady pedal.

I'm trying to decide whether to keep the Vortec 350 or put the good 6.2L engine and drivetrain out of my 1982 Suburban into it. The Suburban gets 28-30 mpg on a long highway drive but on the other hand diesel is 70 cents more per gallon right now.

 

[Chris]

It would be more expensive and you wouldn't get any benefit over a remanufactured 5.7L. In other words, stupid.

In stock form a Tahoe will see 18-20mpg on the highway.

 

[Edahall]

It would be more expensive and you wouldn't get any benefit over a remanufactured 5.7L. In other words, stupid.

In stock form a Tahoe will see 18-20mpg on the highway.

To put in the 6.2L diesel from my 1982 Suburban, I would need a set of big block engine mounts, a serpentine setup from a 6.5L diesel and a hydroboost setup. All of this is not expensive used. The 6.2L diesel get's 28-30 mpg.

Also, the transmission in the Tahoe has 180k miles so it's probably at the end of its life. The transmission out of the Suburban is a newly rebuilt unit out of a 1989 truck.

 

[DRAGGIN95]

I have owned 2 burb's that were this body style both 2wd, they were both driven easy, and we alway's got 16 MPG out of both of them, no ,matter city or highway driving. So I could a Tahoe or Yukon 2wd getting slightly better but it won't be much.

 

[Edahall]

I have owned 2 burb's that were this body style both 2wd, they were both driven easy, and we alway's got 16 MPG out of both of them, no ,matter city or highway driving. So I could a Tahoe or Yukon 2wd getting slightly better but it won't be much.

Thanks,
The 75% better fuel economy out of a 6.2L diesel definitely tips the the scale towards the diesel conversion.

 

[Chris]

To put in the 6.2L diesel from my 1982 Suburban, I would need a set of big block engine mounts, a serpentine setup from a 6.5L diesel and a hydroboost setup. All of this is not expensive used. The 6.2L diesel get's 28-30 mpg.

Also, the transmission in the Tahoe has 180k miles so it's probably at the end of its life. The transmission out of the Suburban is a newly rebuilt unit out of a 1989 truck.

You're full of **** if you think you're getting that economy out of a N/A 6.2L diesel, let alone in a Suburban. A Cummins 4BT in a RCSB dually will only net around 25mpg tops.

You're also vastly underestimating the amount of work involved. There would be many more diesel conversions if it was easy. Off the top of my head:

New fuel tank/fuel delivery system
Engine mounts
Transmission crossmember
Driveshaft
Some method to control basic functions via the BCM (yes 98+ have those) since there will be no ignition or engine input
Some method to control your gauges which are controlled via the PCM, which is incompatible with the ancient diesel
You will need to double your budget for unexpected crap
You will probably give up and decide it's not worth it to have an unreliable, rigged up piece of ****

The way to do this properly is to source the 6.5TD from a late 90s 3/4-ton vehicle, along with the 4L80E and fuel system and it'd be a near direct swap with infinitely better reliability and road manners. What you're trying to do is just plain stupid.

 

[Tempted]

I'd guess you will get around 15-16mpgs from the 350. I'd guess you'll never get the 6.2 running in the 99. I'd guess it'd be sold for parts about 2 years down the road.

 

[Edahall]

You're full of **** if you think you're getting that economy out of a N/A 6.2L diesel, let alone in a Suburban. A Cummins 4BT in a RCSB dually will only net around 25mpg tops.

I can understand the skepticism, but this is what I get out of it. This is one of the chief reasons I may go this route since this vehicle is going to be used for commuting to school which is 125 miles each way. Other than that, my 1982 6.2L is very under-powered (135 hp), noisy and stinky. However, it does extremely well on fuel economy. Driving a smaller a car is not an option.

You're also vastly underestimating the amount of work involved. There would be many more diesel conversions if it was easy. Off the top of my head:

New fuel tank/fuel delivery system

I'll use the assembly off the 1982 Suburban or maybe just put the whole tank in if it fits.

Engine mounts

Engine mounts from a BBC should work

Transmission crossmember

The 700R4 from the 1982 Suburban is physically the same as what's in the Tahoe.

Driveshaft

Yes, looks like it'll need a different yoke to fit into the 700R4

Some method to control basic functions via the BCM (yes 98+ have those) since there will be no ignition or engine input
Some method to control your gauges which are controlled via the PCM, which is incompatible with the ancient diesel

I don't know what I'll do here. I may just use a GPS for speed. Or perhaps, the 6.2L won't go any faster than 65 mph so I'll never have to worry about speed.

The way to do this properly is to source the 6.5TD from a late 90s 3/4-ton vehicle, along with the 4L80E and fuel system and it'd be a near direct swap with infinitely better reliability and road manners. What you're trying to do is just plain stupid.

I don't need the power but need the fuel economy which I understand the 6.5TD is not so good at. I think it had something to do with the large precombustion chambers in the heads.

 

[JonZ71]

we got a 97 running stock everything 265/7017 tires and get 18mpg easy.

 

[Chris]

I can understand the skepticism, but this is what I get out of it. This is one of the chief reasons I may go this route since this vehicle is going to be used for commuting to school which is 125 miles each way. Other than that, my 1982 6.2L is very under-powered (135 hp), noisy and stinky. However, it does extremely well on fuel economy. Driving a smaller a car is not an option.


I'll use the assembly off the 1982 Suburban or maybe just put the whole tank in if it fits.


Engine mounts from a BBC should work


The 700R4 from the 1982 Suburban is physically the same as what's in the Tahoe.


Yes, looks like it'll need a different yoke to fit into the 700R4




I don't know what I'll do here. I may just use a GPS for speed. Or perhaps, the 6.2L won't go any faster than 65 mph so I'll never have to worry about speed.




I don't need the power but need the fuel economy which I understand the 6.5TD is not so good at. I think it had something to do with the large precombustion chambers in the heads.

The tank won't fit.
A 700R4 either has a mechanical or electronic speed sensor. If it's mechanical, you're SOL. If it's electronic you'd need to find some way to make the signal work with your gauge cluster. It probably won't in the end because of the pulse rate.

Listen to what you're saying. You're going to wind up with an unreliable jalopy that I wouldn't trust to drive 5 miles for a gallon of milk. Either do it right or don't even attempt it. With a fresh 5.7L in that Tahoe and a tune, 20mpg on the highway is perfectly reasonable. If my 5.7L rcsb can pull 23+, it can be done with a heavier SUV. It all boils down to the fact you aren't going to get even CLOSE to your mileage number in the end.

Other option: scrap both vehicles and buy a fuel efficient car. They'll still pull an apartment worth of stuff if you're concerned about moving. People in Europe do it all the time.