High Rpms And Better Fuel Mileage

[FIREMAN]

I can't remember which topic I was reading in here about coolant push and fuel mileage, so I guess I'll start my own. Last month I started keeping 460 ASET above 1500 rpms. My coolant push quit and my fuel mileage went up between 11.5% and 12%. Who can explain this? I always thought the less rpms you turn the better your mileage would be. Pulling a tanker, I went from 4.65 to 5.22 and flat bedding from 5.18 to 5.8.

[Rob]

I can't remember which topic I was reading in here about coolant push and fuel mileage, so I guess I'll start my own. Last month I started keeping 460 ASET above 1500 rpms. My coolant push quit and my fuel mileage went up between 11.5% and 12%. Who can explain this? I always thought the less rpms you turn the better your mileage would be. Pulling a tanker, I went from 4.65 to 5.22 and flat bedding from 5.18 to 5.8.

All engine have a "sweet spot" where they will deliver the best fuel economy. If your engine torque was plotted on a graph this spot is usually just to the left, or just above maximum torque output of the engine. This "sweet spot" is not normally where the engine is operated in however as it does not offer the crisp, or instantaneous throttle response that a little higher rpm does.

Rob

[cgallamore]

I can't remember which topic I was reading in here about coolant push and fuel mileage, so I guess I'll start my own. Last month I started keeping 460 ASET above 1500 rpms. My coolant push quit and my fuel mileage went up between 11.5% and 12%. Who can explain this? I always thought the less rpms you turn the better your mileage would be. Pulling a tanker, I went from 4.65 to 5.22 and flat bedding from 5.18 to 5.8.

hi fireman, ive been running i44 some been keeping an eye out for ya.

i found i get better mpg at 70 mph than 60,when i was having coolant push trouble with my vision it uually happend in the 55 mph states.

if you are having a coolant push, contact me, i got a line on a one piece tank, brand new and cheep, it wont last long.

[bruiser]

Maybe a dumb question but whats coolant push?

[Mackpro]

Maybe a dumb question but whats coolant push?

It's where coolant is pushed out of the surge tank, mostly on 2004 and up ASET "AC" engines with EGR systems (CH, CHN, CX and CXN models). It can happen on the "AI" engines in the CV, CT, MR and LE trucks but you dont see it to often. Mack had many service bulletins for fixes for coolant push.

[bbigrig]

I have noticed the same with our 2005 CXN and 2006 CHN. both are EGR and as noted in all our engine spec sheets the sweet spot is 100 rpm higher or more in comparison to non EGR e-tech engines. One truck has an 18 the other a 13 fuller trans.. runnning in the second last gear(split) at 62mph both trucks have seen a slight fuel milage improvment when hauling full loads. (rear ends are 370's)(22.5 tires)(overdrive trans)

Both trucks have over 500 miles and smoke alot less on each shift when shifted just above 1600rpm. Turbo vane/egr valve burp issues we had when shifting have dissappeared since changing shifting patterns. both turbo's are original. The 2005 is a 355/380 the 2006 is a 460xt. The 460xt is a dog.