Skip to main content ↑ ↓
Topic: Air intake design (Read 819 times) previous topic - next topic

Air intake design

Hello all,
This is my 1st post here, but I've been visiting for awhile. I recently purchased a 98 U295 36ft, but had owned a 98 U270 34ft. As I was doing an initial cleaning, I found an unusual amount of dust in the cabinet above the bed, especially around the service door for the back-up camera. Until last week, I had always been curious as to what purpose those vents surrounding the back-up camera served.  It never occurred to me that's where the air intake was for the engine. Now, and I mean no disrespect, but what moron could have possible thought that was a good place for the engine to get air? I suppose it's like breathing underwater through a straw: it can work as long as you stay very still and calm, but probably not so much if you're moving around. I'm not an engineer, nor do I play one on TV either, but it seems like a poor design and even if a slight drag/vacuum is created while in moving forward, it could cause the engine work harder for air. Not only that, but driving on dusty roads, any dust would be sucked into that cavity and eventually the bedroom. So, unless there's a logical explanation for my simple mind, I plan to add a second intake source for air. 

Re: Air intake design

Reply #1 –
Next,

Here is a link to what John H has done on this problem.  Read over his various post on this subject.  Here is a link to get you started. Air Filter - Engine   

Pamela & Mike

Re: Air intake design

Reply #2 –
Thanks, I did read through that post, but it's more about the filter and not really the location of the intake. I do agree about the intake being up near the top, just not where FT put it. I have a idea and I'll post pictures once I'm done. This coach came with a few projects that need done. One was a small residential refrigerator that just didn't look or fit right, so I replaced it with a SS Dometic 4 door - but that's a different topic.

Re: Air intake design

Reply #3 –
It sounds like your upper cabinets may be missing the piece of wood that seals off the backup camera area. I drove mine while I had it off when I was replacing the camera, and DW let me know that was a NO-NO. If it *is* installed, then you would benefit from some kind of gasket or seal around that cover. We do not get dust if it is in place.
 
Trent

Re: Air intake design

Reply #4 –
Rear Air Deflector
I think this was the link that should have been attached. It works as designed and in all the years I have had mine on I never really needed to change filter, but did just once as I had a spare anyway.
You can make one easily or get one made. I use to make them to order (around 50 ) or so for Forum people but "closed the factory- so to speak"
JohnH

Re: Air intake design

Reply #5 –
I think Next hit the nail on the head.  This is a poor location for the air intake, the low pressure zone feeds dust into the intake.  I suspect the intake area around camera is well undersized for efficiency as well, being a few slots milled into alloy plate. 

Side intake would be better methinks. 

Welcome to the forum, NextForetravel. 

Re: Air intake design

Reply #6 –
Quote from: Chuck Pearson –
I think Next hit the nail on the head.  This is a poor location for the air intake, the low pressure zone feeds dust into the intake.  I suspect the intake area around camera is well undersized for efficiency as well, being a few slots milled into alloy plate. 

Side intake would be better methinks. 
 

I have posted better photos on the forum of this mod.
If I can find them .........

Re: Air intake design

Reply #7 –
Quote from: Chuck Pearson –
Side intake would be better methinks. 

Chuck,

That is where at least some of the Nimbus air intake is located.(just below the upper clearance light) It has been reported that in some cases that location causes the air filter to fill with water when the coach is driven in the rain.  In some of the GVs of the early 90s they had the air intake low behind the rear tire which caused much the same problem with dust/trash.

Pamela & Mike

Re: Air intake design

Reply #8 –
Quote from: FourTravelers –
I have posted better photos on the forum of this mod.
If I can find them .........

Again my concern would be driving in a rain storm, that scoop could be overwhelmed by water sheeting down the side of the coach.

A soaked and consequently perforated air filter media and dusted engine would be a high price to pay.

Re: Air intake design

Reply #9 –
Lets face it - on a diesel pusher, finding a good location for engine air intake is difficult.  Any place aft of the rear wheels is gonna be a very "dirty" environment, both in terms of trash ingestion and in terms of air flow.  To me (a non-engineer), optimum placement of the air intake would require two things.  First, to minimize exposure to dirt and trash, locate the intake as high above the ground as possible.  Second, locate the intake where it will see the smoothest, least "disturbed" flow of air.  I have provided a couple sample photos of air scoops below.  One of these, mounted on the roof of the coach, in a spot that is not "blocked" by the A/C unit, would meet both of my requirements.  Other than the occasional ingested bird, the air entering at that point should be pretty clean!

A coarse filter screen could catch the unfortunate birds, and a water trap could divert any rain or snow that entered the scoop.

I offer this idea FREE to all Forum members.  No need to send money...but cheap wine is always appreciated.    :thumbsup:

Re: Air intake design

Reply #10 –
Use of the better filtering, More performance, bluetech Donaldson upgrade foam air filter element would eliminate the engine damage from water injestion damaging the paper element and double the hours between filter changes needed

Re: Air intake design

Reply #11 –
Quote from: wolfe10 –
Again my concern would be driving in a rain storm, that scoop could be overwhelmed by water sheeting down the side of the coach.

A soaked and consequently perforated air filter media and dusted engine would be a high price to pay.

The inlet inside the housing behind the scoop doesnt allow water down the intake, it is elevated, water runs out and down. Filter stays dry.

Re: Air intake design

Reply #12 –
Quote from: FourTravelers –
The inlet inside the housing behind the scoop doesnt allow water down the intake, it is elevated, water runs out and down. Filter stays dry.

Thanks, for the clarification.  That is a critical part of the modification.

Re: Air intake design

Reply #13 –
The main reason I came up with my design was after driving between Yuma and S Diego a bunch of years ago thru heavy rain and sleet.After the high pass I started to notice some rough running of engine and by the time we arrived at destination I could hardly climb a short steep incline to park. I checked the air filter and it was soaking wet then looked for a cause. Took me minutes to figure out what caused it- the intake and location. I took the filter out and layed it under coach for night hoping the engine heat would dry it out. It did and I replaced it as it looked fine and no breaking of paper etc. All was good again so I decided to make the style of Deflector shown in previous post. This has worked flawlessly ever since and does not look ugly or obtrusive. I have driven in lots of rain and snow since and no water gets in. I have removed the end cylinder cap to look at filter and it stays clean and dry and my engine temps have not changed 1 degree since install. I did extend the overhang another 2" to better help keeping the camera clean and dry.
Foretravel Tech looked at it when we were there a few years ago and thought it great idea as he mentioned they see LOTS of crap etc in there when servicing.
JohnH

Re: Air intake design

Reply #14 –
Quote from: wolfe10 –
Thanks, for the clarification.  That is a critical part of the modification.
If I can find the photos........ ::)  I'll post them again, it;s easier than trying to describe it.

But I understand the concern, I was troubled by it too, I have checked for water intrusion a couple of times and all looks good.

Re: Air intake design

Reply #16 –
Yes, or one very similar to it. It is a Donaldson vertical separator just ahead of the horizontal air filter.

I will post some pics in another thread..... IF I can find them, (recently changed laptops) trying to get organized. :-[
 

Re: Air intake design

Reply #17 –
A P.O. of our coach made a modification to the original intake system. He added this stainless steel scoop over a hole cut into the air box where the lower and upper intake tubes meet. The tubes are offset, upper tube located in the very corner of the coach and the lower tube is offset inward to allow for the taillight assembly.

I did not like the fact that the PO relied on the water separator to keep water out of the filter canister.
As Brett mentioned in his post...... not a good idea.

I modified the PO's modification by adding a PVC sleeve inside the air intake and sealing around it to prevent water from just running down into the cyclone air separator. Air must enter from the upper part of the box a few inches above the bottom of the air box.
I also added a screen to prevent larger bugs and debris from entering the box. 

I like the idea of cleaner air entering from the side verses the rear "back draft" area.

 Would I have done this mod? Probably not...... I would have left it as FT had it. But I decided to leave it and improve on it.