Engine RPM and gearing
 

I have a 99 international 9200 daycab with a cat C12 and 10 speed with 3:73 gears. I dont know what the operating range is for the cat c12. Im at about 1700 rpms at 65 mph. Is that good? And I'm getting about 6-6.5 mpg. I feel like it's geared too high. There is this hose that comes down under the engine that almost touches the ground, and it has some smoke that comes from it when I drive long distances at highway speeds. What should I do? Am I burning the oil up at such a high RPM?

Not much will change with the burning oil. How much oil do you have to add?

Try slowing down. That truck should run great at 60 mph. 1700 rpms is too high for a c12.

something does not sound right. :shock: I have a c12 4.10 gears 22.5 tires and my runs 1650 at 65 mph. my cat owners manual does not mention any problems running these rpm's. but I will add my mpg sucks :cry: :cry:

What about the hose? Is there supposed to be smoke coming from it? Is there anything else I can do to get rid of this thing? Its kind of annoying. Thanks guys!!

No, your engine is wore out.

Wait, what kind of smoke is it? If it's white, you could have bigger problems. Maybe theres coolant getting into your oil. Does your coolant steadily go down?

Get your oil tested ASAP.

Well its grey smoke. Hopefully nothing is wrong!! Where can I get it tested at? Whats normal gas mileage?

Also, when I bought the truck the guy told me that the oil looked fine and to dont worry about changing it. But I think I'm going to change it this weekend, but I have no clue how much oil to put in. Can anyone help me on this? Thanks guys!!

The "hose" is the crankcase breather.

Any compression or combustion gases that get past the piston rings into the crankcase are vented to the atmosphere thru that pipe or hose.

The grey smoke that you see coming out of there is called "blow by".

If there is a large amount of blow by, that means the piston rings are worn out or broken and the engine needs an overhaul.

I have also seen blow by caused by worn exhaust valve guides allowing exhaust gases to flow past the exhaust valve stems.

In any case, if you have an extreme amount of smoke or vapors coming from the crankcase breather tube, then the engine has problems.

White smoke from antifreeze entering the combustion chambers would also be seen coming from the exhaust, not just the crankcase breather.

How so?

The C12's we have where I work are governed @ 2100 RPM's

IMHO, it's better to run an engine at a higher RPM, than to lug it at a lower RPM and cause high EGT, torsional vibrations thru the driveline, etc.

Correction:

1700 rpms is too high of a cruise RPM to try to get decent fuel mileage.