Driving tips to help a Cat C15 to be better on fuel.

I've driven lots of cats and you're pretty much on the money when talking up to 90,000 lb GCVW.
Your best economy will occur if you can keep it around 1320 to 1400 rpm when cruising.
Over 90,000 lb you need to cruise them a little differently, around 1500 - 1550 rpm, according to Cat.
I pulled a tri axle reefer with a C-15 Acert at 105,000 lbs and 1550 rpm was where it seemed to be the happiest.
In the end it's all about proper gearing for the job.

Regardless of the type of engine, lugging for long periods can cause damage due to the higher cylinder pressures at low rpm.
It's always better to drop a gear rather than lug the engine on long pulls, try to keep it at 1500 rpm or higher, within the engines power band.
If you drop a gear and run higher rpm on a long pull or heavy wind at the same speed the engine isn't working as hard, you should notice if you have a turbo boost gauge.
Best thing to do is find the torque and horsepower curves for whatever engine is in your truck.
It doesn't matter so much if the torque drops off, as long as you're still making horsepower which is the unit of work produced.
Your best economy will occur at or below the point on the graph where the torque starts to fall off.
These modern engines, (electronic engines), most of them have a HP curve that goes flat around 1600, which gives you a useable power band of between 1100 and 1600 rpm, no benefit to running any higher because above that theres nothing left to gain.

 

100 percent agreed and when we were 99,857 (hauling milk in the winter) he shifted at around 1500 but it was a 18 so it was half steps nice n easy problem was getting stopped lmao that was one of those smell them brakes kinda days. We stayed over 90 alot and 1500 rpm to run and shift at unsure of the rears but i think they were between 3.55s and 3.75s maybe they were 3.65 but 75 mpg at 1500 to 1600 rpm and she could pull a hill d amn well then we drove the bosses 600 once hauling fertilizer load to 85 gross and ran it to maryland from south VA at 70 mph it felt like no hill no obstacle could stop that truck when she was pulling lol we had at the end of the day 6.98 mpg lol my dad was like d amn just short of 7 i basically just call it 7 lol

 

Thanks for the input guys, Im going to give some of this a shot with my E Model. I am cursing on 2 lanes (pretty flat) at 1250 in 18th if I split to 17th I jus to about 1450rpm. May just have to judge that one based on wind. When I get on a big road though 70 is 1400 and it cruises just perfect. Going to try using the the shift pattern you all suggested. Truck doesn't do bad on milage now but a little better is always nice.

What would you all say is acceptable causing EGT's. If I split on the 2 lanes I can drop by EGT's and run at 1450 rpm. At 1250 rpm at 63mph my EGT's are about 750*

 

What size pipes small pipes = bad mpg and hot as hell in july but that 750 aint bad as long as she doesnt get to or above 1000 you should be fine also around 1500 is basically major failor stop and shut the truck off. If that makes you feel uncomfortable i suggest larger pipes. Also excesive cursing on a 2 lane can lead to destraction and a head on accident be careful lmao sorry i had to make that joke. Whats your egts at the 70 mph and 1400 rpm that will be the tell all

 

And that isnt too bad in the first place ive seen worse lol if your torbo went bad should could get up over 1000. Get to a parking lot and run here up to 1400 rpm and let here sit there and wait for temps to rise then take a heat and find where the heat is could be a cac problem and the stock muffler if you have it could be plugged up lots of stuff to check. How are fuel and air filters ?

 

Most stock engines I drove, the EGT never got higher than 800º or 900º by the pyrometer, depending how far away from the turbo the sensor was.
On one of the trucks I drove the EGT sensor was in the manifold and I saw temps over 1600º on some hard pulls, but that's not a good place to put the sensor as the tip can burn off and mess up your turbo.
The lower the boost, the lower the EGT, the better your economy should be.
Something a lot of truckers overlook, or is never their first thought, is their air filters.
If the engine is starving for air it can cause higher temps and loss of power.
I had a brand new filter plug up completely in a distance of 800 miles when I drove through a dust storm one time, and one winter while driving through a snow storm I plugged the air intake, the filter canister and the plumbing all the way to the turbo, packed full of snow.
(that explained all the black smoke I saw in the mirror)
When I pulled the pipe off the turbo you could see where droplets of water had hit the turbo blades, had a bunch of little dents in them.

 

Dang yeah 1600 is way way to hot suprised she didnt blow up guess that turbo was cherry red.

 

There's a huge difference in temp from the manifold to behind the turbo where most sensors are placed, probably 600º or 700º difference, I'm guessing.
The engine was "tuned" that's why the sensor was in the manifold, more accurate reading with less delay.
If the sensor is behind the turbo the temp increase will be slower showing than the sensor in the manifold, which could be all it takes to melt the engine.

 

Change the gear ratio.

 

Another truck I drove, a nearly new at the time 1996 W900L, had a 3406E @ 550 HP with a 13 spd, 3:25 rears and low pro 22.5 tires and it ran down the road pulling a reefer all day long at 68 mph @ 1350 rpm and turned in good fuel numbers.
There were 10 KW's and 10 Petes in that fleet with identical powertrains and the fleet average was 6.7 mpg, not too shabby.
But....., the owner had software from Cat that allowed him to program limitations into the engines so his drivers wouldn't get carried away with the speed those trucks were capable of.
For passing, the trucks had a function on the cruise control that would get you up to 75 mph, but only for a short period of time, maybe 10 seconds, can't remember that far back.