Replacing an engine coalescing (CCV) filter

This is Steve’s post detailing some maintenance he did recently on the coach.  His mechanically-minded buddies may enjoy it, but probably nobody else.

Betsy has been intermittently displaying a fault code indicating “high crankcase pressure” for quite some time, and after a bunch of research, I learned one thing I could do to possibly resolve the problem is replace the crankcase ventilation (CCV) filter, also known as a coalescing filter.  Note that there is also a “coalescent” filter in the air brake system on large diesel RV’s, but the one I’m talking about here is on top of the engine on our 2008 Cummins ISL 400hp unit.  A bit confusing, and even the Freightliner guys weren’t familiar with this part when I ordered it.  But the filter itself had the word “coalescing” printed on it, so there’s no doubt.

Engines with closed crankcase systems use this filter to prevent crankcase oil from escaping the engine and reduce emissions, and my thought was that it might somehow be getting plugged up and throwing the codes.

Since the filter is on top of the engine, the only way to access it is to remove the engine cover inside the coach.  I wasn’t crazy about having a mechanic inside Betsy tearing our bedroom apart, and since the filter replacement itself is easy I decided to do the job myself. According to the mechanic, it would have been about two hours of labor for him to do it, so we saved a nice chunk of change too.  Win-win!

About 90% of the job involved removing and re-installing the bedroom access panels to change the filter, which was a simple 20-minute job.

We have a Sleep Number bed, so I deflated and disassembled the mattress to reduce the weight so I could prop up the bed base:

I replaced a bedchamber a few years ago, so I knew how to take the mattress apart.  Mona Liza ran over and laundered all of the mattress components while I did the work
I propped the bed base up with a piece of metal bar, backed up by a 2×4 just in case.  If this thing lands on your back, you’re toast!
Finding the screws to remove the flooring. You may be able to use a magnet to locate them, but mine weren’t magnetic so I just yanked them out and replaced them with new ones
Those black plates are the 2-piece engine covers that have several screws holding them together
That rectangular cover where my hand houses the filter. About 12 bolts attach it to the engine
CCV Filter
Here’s the new filter (left) next to the old one sitting in the cover (right) . There was a spring-loaded pressure valve in the filter that I suspect was the culprit – time will tell!

Since the fault code was very intermittent, it will take a while to confirm if I fixed the problem.

Diffuser (tailpipe) replacement

I was feeling so good about how that project went that I decided to replace Betsy’s diffuser (tailpipe) while I was all sweaty and dirty.  Freightliner somehow forgot to install a new one when I had my maintenance done and asked them to do it, so I bought the part and did it myself.  Another 1/2 hour of labor cost saved!

This is the 2nd time I’ve replaced Betsy’s diffuser.  Although it’s ceramic-coated, temperatures of over 900º give it a limited lifespan and make it impossible to keep clean.

That simply won’t do…

Since I don’t happen to carry an air hammer with a cutting chisel in the coach, I drilled a whole bunch of small holes and then cut between them with a hammer and chisel to remove the old piece:


Now that’s more like it!

All in all a good day for Betsy!



  1. Great pictures of this you guys. Glad we don’t have to do that maintenance one at least. With our gasser, we have storage rather than an engine under our bed. Getting under there for anything more than taking out the toilet paper isn’t something I’d want to do.

  2. It’s quite a tight space to replace that filter in the Phaeton … while the mattress props up, the bed frame remains in place. Mui was issuing a few choice words the first time he replaced the filter.

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