X-15 Cummins thread

Has 260 WB and a meritor driveline,I also took to Cummins and they took front plate off engine and tried adjusting around on the gear train but it did no good so maybe it does have something to do with compression .idk. They did say efficiency series is louder than performance series but I can’t imagine a manufacturer turning out an engine as loud as it is.

 

I have a new kw t680 mid roof pulling flatbed with the efficiency series and I run short runs from 40 to 180 miles one way .i run empty half the time and run 63 mph in the Dallas area. I am being totally honest ,I get from 8 to 8.5 mpg and that’s running apu all night about three times per fuel up .this engine rattles loud though and Cummins can’t fix it they say just run it .they think has to do with gear train but they went into front of motor and didn’t help anything but other than that I’m pleased. Only have 10 k on truck so it may break in some more and get even better idk.

 

The air compressors are naturally aspirated and quite loud when they kick in as it echos back out the air cleaners. Previous isx were all boosted air compressors and very quiet.

 

Yeah but it’s not the compressor,I hear it when it kicks in out. This sound is much like metal on metal and is constant.it didn’t do this the first 5000 miles either so it has developed

 

I have the older cm2350 and yes it rattles. It sounds like it will blow apart at any minute. Yet it makes good smooth power and doesn't burn any oil. Someone told me you just have to get used to it, that's the way they are. So far...so good.

 

Does the rattling happen at certain RPMs? Or all times.

 

I only notice it when accelerating, which is 1000-1500rpm. I almost never idle it, it is smooth(er) at 700 or with cruise idle on at 900. When cruising at 1400 or 1500 under maybe 30-40% load it is barely noticeable. Only time I hear it loud and think that can't be good is under hard acceleration window down driving beside 4' cement wall. Like I do every time I am released from us customs. It has always been like this, and isn't getting any worse.

It did used to have a hard shudder when under heavy load in the 1200-1250 rpm range. Which it doesn't do anymore. I have read a lot on that, people have similar issue, and find it is the clutch springs. Which makes no sense why mine hasn't done that in probably 200,000 km. It is at about 425,000 km today. I have no idea. But it's consistent in fuel mpg, slowly getting better actually, consistently in the 6.5 range now, up from 5.5 range. When I say hard acceleration I don't mean climbing higher than about 1500 maybe 1600 rpm. Max boost though.

 

No doubt it's crazy! When I went to Denton on factory tour to see my truck go down the line they were talking about adding a third shift. I didn't order any stripes but did get it painted legendary brown with matching brown frame. The push for higher production may come at lower quality. My CB coax wasn't plugged together at sleeper boot,took some work finding it but all is good now. Also driveshafts were not true and vibrated pretty bad. Not Peterbilt fault as spicer is supplier but you would think they would have found it on Dyno at factory. They put new shafts in it and all is good now.