Would intercooler improve mileage on a 99 GM turbo diesel?
Would intercooler improve mileage on a 99 GM turbo diesel?
(OP)
I've done considerable tinkering with a 99 GM 6.5 turbo diesel automatic suburban trying to improve mileage. The starting mileage was 18.5 to 19 mpg at 70 miles per hour with the air cond. on. I keep the tires at 55 lbs. The best I can get with some changes is 22.5 mpg. Would an intercooler be worth the trouble? The intake manifold runs about the same temp. as the thermostat - 195 F. The boost at 70 mph is about 3.5 lbs. and the engine is turning 1900 rpms. Has someone tried this?
I installed a rig so that I could eliminate ideas faster by having an accurate gauge of intantanous fuel mileage. I installed a digital volt meter across one section of the accelerator pedal resistance pot (drive by wire) that feeds the engine management processor. The higher the number (0 to 5 volts), the less fuel is being used. Small changes like drafting another vehicle or turning off the air gives a noticable change. Prior to the "rig", I had been led to several wrong conclusions of a theory under test because of measurement errors caused by fuel density changes.
I installed a rig so that I could eliminate ideas faster by having an accurate gauge of intantanous fuel mileage. I installed a digital volt meter across one section of the accelerator pedal resistance pot (drive by wire) that feeds the engine management processor. The higher the number (0 to 5 volts), the less fuel is being used. Small changes like drafting another vehicle or turning off the air gives a noticable change. Prior to the "rig", I had been led to several wrong conclusions of a theory under test because of measurement errors caused by fuel density changes.





RE: Would intercooler improve mileage on a 99 GM turbo diesel?
Oh. Back to your question. If I understand this stuff correctly, and I'm usually a little off the mark, you can get more torque with intercooling, which would allow you to run a taller axle, which would allow you to run the engine at a lower rpm at the same vehicle speed, which would give you better mileage. .... and would make it more difficult to tow and accelerate, so you really need to add a gear to the transmission, or a selectable overdrive. Which gets expensive pretty fast.
I suppose you could evaluate if a taller gear would help by borrowing a set of larger tires. I don't honestly know if the intercooler would help all by itself. Fogging some water into the air filter might tell you that.
Mike Halloran
Pembroke Pines, FL, USA
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
The need for an intercooler is linked to the need for a turbo. If the turbo is working hard the intercooler will be getting a lot done too. If you have the vehicle stricly for cruising and mileage experiments, they may both be a wash.
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
Fabrico: I have another GM diesel with nearly the same gearing and weight but without turbo. The non turbo one clearly runs out of air (black smoke) during most speed changes. The mileage on the non turbo isn't much less but it can't get out of it's own way in many situations where a little more power is needed. So, the turbo without an intercooler was a definite improvement. Thanks
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
Thanks everyone for your input.
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
However, with an intercooler one could also consider to increase compression ratio (less boost but same mass flow). With an increased compression ratio the engine would be more efficient at cruising and therefore increase mileage. (Of course the mileage gain would never be worth the extra costs.)
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
In theory, you would get better fuel mileage. Practically speaking, would you ever recover your investment....well that's another calculation.
They cool off the air charge. The turbo working at any boost level adds heat to the air that it pumps. A cooler air charge means more air gets injected into the cylinder. Since air is the working fluid in this thermodynamic cycle, the more that there is for the burning fuel to heat up, the more efficient your engine is. The more efficient your engine is, the less fuel it takes to produce the amount of work necessary to go the speed you want to go. End of story.
rmw
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
A turbo and intercooler are not neutral/advantageous, they are disadvantageous/neutral/advantageous. mrwizz' pickup is more in the lower range, an 18 wheeler more in the upper.
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
More air mass=more fuel burned?
Less air intake=less fuel burned?
et al.
Where do I start?
rmw
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
Adding bigger wheels and tires will make it necessary to produce more torque per moment time in acceleration. You will have a reduction in city milage for a gain in highway milage. I personally don't feel this is a beneficial solution unless the vehicle is rarely used for city driving or towing.
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
RE: Would intercooler improve mileage on a 99 GM turbo diesel?
So, bottom line, your post above is that it will increase his fuel mileage, notwithstanding all the other factors to be considered, right?
rmw