Skip to main content ↑ ↓
Topic: Should I see air in my Racor prefilter? (Read 858 times) previous topic - next topic

Should I see air in my Racor prefilter?

I have recently changed the S3230P element and 300200 pre-filter on my '99 M-11. I have gone through the purge procedure and the engine is running normally. But, the pre-filter is always about half filled with air with the engine at idle. I was wondering if this is normal, or a possible indication of a small air leak somewhere between the tank and pump that may become a problem when the engine is under load?

Thanks!
Chris

Re: Should I see air in my Racor prefilter?

Reply #1 –
Chris, are you talking of a clear cylinder that you can see the fuel running through at idle?  If so, at low idle, mine on the M11 engine would be a foamy fuel, kinda frothy I guess.  If I increased to a faster idle, that froth went away and just a steady stream of fuel without froth ran through the cylinder.  And that gave me some appreciation of how much fuel would burn going down the road, quite a flow.  Hope that helps.  Let me know if this answered this for you, please.

(We did change out our fuel system though to put in a system that does not have that cylinder)  Mike
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches

Re: Should I see air in my Racor prefilter?

Reply #2 –
Quote from: Michael & Jackie –
If I increased to a faster idle, that froth went away and just a steady stream of fuel without froth ran through the cylinder.  And that gave me some appreciation of how much fuel would burn going down the road, quite a flow.
Michael,

My understanding is that most of the fuel you see going through that filter is not burned during its pass through the fuel system. Part is burned to provide energy, but most is returned to the fuel tank. The excess fuel provides cooling and lubrication to the fuel system.

Our "old" 1997 coach doesn't have the Racor filter system with a purge button. We have a simple filter with a plastic bowl that attaches to the bottom of the filter. I have never seen air in the plastic bowl. Fortunately, I've never seen water there either.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: Should I see air in my Racor prefilter?

Reply #3 –
Chris,
If the prefilter will not fill completely you probably have a air leak at the "o" ring. This arrangement is problematic and has been replaced by many of us with a Racor 790R30.
The selected media item is not currently available.Bob & Faith Rozek
1997 U320 40'
Xtreme Remodel
2010 Scion XD

Re: Should I see air in my Racor prefilter?

Reply #4 –
We got rid of that filter, as well. They use a fuel assist pump that is part of the whole assembly and is powered by the little black box at the top of the engine compartment that also has the "purge" button. Our little box died, and the assist pump was not getting any power.  If the engine was under load (going up a mountain !!) it coughed and bucked because it was fuel starved.  A very smart mechanic in Santa Fe (Hal Burns Truck Repair) discovered the cause of the problem and also Cummins' procedure to remedy same. Toss the glass Winn/2020 filter and replace with a new, simple armature and a standard water separating filter.  Bingo ... running like a top ever since. Very inexpensive fix, once you diagnose.
Carol & Jeff Savournin
Usta have a '93 U225 36', Usta have a '95 U320 40', Usta have a '02 U320 40'
Usta have a 2006 Born Free, Usta have a 2011 Phoenix Cruiser
Usta have a 2012 Jeep Wrangler Unlimited 4dr
"Your time is limited, so don't waste it living someone else's life."  Steve Jobs

Re: Should I see air in my Racor prefilter?

Reply #5 –
Thanks everyone for the feedback. Yes we are seeing air in the clear cylinder but that sounds normal according to Mike. I had a previous leak at the "o" ring which led me to replace the cylinder and rings last month (and you have to get two of the "o" rings separately). But on the last trip, the engine was coughing going up a hill so I changed both fuel filters at the campground. It may be that the fuel assist pump / black box may be having problems and I should consider the fix from Carol and flite2010. Something more bulletproof than the current setup. Thanks again!

Chris

Re: Should I see air in my Racor prefilter?

Reply #6 –
Chris,
I considered going with a replacement filter only, but after changing the primary and secondary filters without an operating priming pump, I decided it was well worth the extra cost. Pre-filling the filters with diesel and installing was a real PITA!!!!!!
The selected media item is not currently available.Bob & Faith Rozek
1997 U320 40'
Xtreme Remodel
2010 Scion XD

Re: Should I see air in my Racor prefilter?

Reply #7 –
Chris (cburpee).  Thanks for the PM.  I told you that I would send you a link to a document that might help with the "new to you" 1999 and it is below.  I have two friends who also just bought those years and have given them this link....that is available to anyone in the ForeFourm....to perhaps given them some help, thinking points.  When I began this I had hopes that all with these models would chime in, add helping and interesting facts, tips, that those of us with these could gain some experience, help each other.  As time has gone along since the April posting, I see that some of this applies to other similar year engines, like the 1998's.  Other information may go to any FT, and good.  But I really was seeking something to help those of us new to these coaches.  Respond here or PM if I can help in any way.  This is the link in the Forum.  Your additions here or directly to the list would be appreciated.

http://www.foreforums.com/index.php?topic=15108.msg90504#msg90504

Cheers and Travel Mercies, Mike
Mike
2001 U320 4010 Build 5878 (Gus)
Wrangle Unlimited Toad
Nacogdoches
 

Re: Should I see air in my Racor prefilter?

Reply #8 –
A competent diesel mechanic can check the vacuum pressure on the fuel lines and tell quickly that there is a problem.  There may also be a "fuel heater" included in that whole Winn/2020 setup ... and unless you are doing "Ice Road Trucking" there is no need for a fuel heater, according to the mechanic at Hal Burns.  It is just a lot of fanciness that you can do away with.
Carol & Jeff Savournin
Usta have a '93 U225 36', Usta have a '95 U320 40', Usta have a '02 U320 40'
Usta have a 2006 Born Free, Usta have a 2011 Phoenix Cruiser
Usta have a 2012 Jeep Wrangler Unlimited 4dr
"Your time is limited, so don't waste it living someone else's life."  Steve Jobs