2002 Journey Cat 330hp mileage reduction.

[CharlesMoore]

Question: I have a 2002 Journey 36DL 330 hp CAT engine with 6 speed Allison transmission. For many years our mpg was approximately 8.5 towing at 60 - 62 mph. This 2022-23 season this is dropping to 7 mpg ±. In the summer I had the airfilter changed and the yellow air flow gauge reset. Our first big trip on the way south netted about 7.5 and is now 7mpg. Anyone have any ideas why this might be happening? Nothing else has changed.

[Ray,IN]

Did you replace the fuel filters? That is the most common cause of mileage reduction.

[CharlesMoore]

No, I did not personally but Stoops Freightliner in Fremont, IN was supposed to have done this. Maybe I picked up some water and it is choking off the fuel supply? I will check the service invoice - thanks for the comment.

[Ray,IN]

Something I've done for many years is use a marker and write the date on each fuel and oil filter when it was installed. That is a reminder for me and prevents missing one when they are supposed to be replaced.
Depending on many factors, a fuel filter can maintain full flow for a few years to only a few days. This is interesting reading: https://criticalfueltech.com/faq.html

[tim myers]

Over time the valve lash can also get a little sloppy, I don't know what Cat recommends but Cummins recommends having the lifters adjusted every 5 years or 60,000 miles. Lifters out of adjustment can also affect fuel mileage.

[CharlesMoore]

Thanks for the comments. I am taking the RV into Foley RV Repair on 23 Feb 2023 to have the filter changed and an air input check. I'll ask about the lifters too since it has been more than 5 years. The coach has only 66K miles but maybe they will recommend checking them. Since we live in the coach I do not want it out of commission too long.

[Ray,IN]

Originally Posted by tim myers

Over time the valve lash can also get a little sloppy, I don't know what Cat recommends but Cummins recommends having the lifters adjusted every 5 years or 60,000 miles. Lifters out of adjustment can also affect fuel mileage.

Cummins states for the 24 valve ISC, a valve adjustment at 150,000 miles, no time interval.
reference: https://www.rvtechlibrary.com/engine/ISC_maint.pdf

[tim myers]

Well Ray, you are correct regarding the 150,000 miles, but after double checking my engine manual following are the recommendations for Valve Lash Adjustment.
150,000 miles, 5000 hours, or 4 years. I have the 5.9 ISB, I am sure others have different requirements.



Like I said, I have no idea what the Valve Lash check/adjust intervals are for the Cat Engines. I do have a friend with a Cat 3126/C7, that had a 1.5 - 2 GPM increase after he did a valve lash adjustment. I am not sure if he is following the Dash indicating or running a calculation, but knowing him it is likely a true calculation at fill up.

[Jim_HiTek]

I owned a 5.9 ISB for 12 years and I had the lash adjustment done while an exhaust gasket was being changed at around 95,000 miles and the tech said there wasn't any adjustment needed and he'd seldom done a lash adjustment. Then I asked around at different truck shops (I never go to a dealer or engine factory shop or chassis shop) and they all agreed that a lash adjustment was a waste of time and money unless you're already in there fixing something.

I would suspect though that it's a personal choice with knowledge of how long you plan on keeping the RV. What worries me about doing it is the old adage, "If it ain't broke, don't fix it".

I agree that the loss of mileage is probably due to the shop forgetting to change the fuel filter.

BTW, OP, we have the exact same RV and you might find some interesting articles at my ad free Travel & RV Repair blog, link below.

[CharlesMoore]

Thanks Jim_HiTek & howdy, I subscribe to Jim's blog and if you have a Journey, you should too. Always detailed & thoughtful posts on what he does to his Journey. A peanut gallery comment from Charlie

[Jim_HiTek]

Thanks, Charlie. I'll send you that bribe soon. Snort.