Maxxair Vent Fan Rattle

[Boxster1971]

I'm posting this as I would imagine many of you are experiencing an annoying rattle noise from the Maxxair vent fan if your Interstate has one. I think Airstream used them until about 2015 or so. It is a great vent fan with a very effective rain shield that allows you to leave the vent open even in heavy rain. My only complaint about this fan is the rattle when closed and driving down the road.

I finally fixed the noisy rattle thanks to a member named "OffroadHamster" on the Sprinter-Source forum. Here is link to his solution:
https://sprinter-source.com/forum/sh...5&postcount=55

It's fairly simple to install the weather stripping and zip ties once you remove the rain shield from the vent fan. You can do it without removing the fan. Start with the vent fully open. From the top of van remove the two screws that hold the rain shield to the vent cover. This allows you to drop the rain shield and get access to the lift mechanism Then pop the lifting mechanism from the cover and lift the cover up all the way so you can remove the rain shield.

My fan is now totally quiet when closed and going over the worse bumps.

[Boxster1971]

Just heard from OffroadHamster that apparently MaxxAir also has a fix (a rubber boot seal) that they will ship you for free if you call them.

[Protagonist]

I won't say that mine doesn't rattle. But I will say that I never hear it rattle. Whether that's due to me going deaf, or the vent cover not rattling, or me not closing it before driving down the road (you can drive with it open), I can't say…

[nvestysly]

Our Maxxair vent cover "bumps" and "thumps" maybe even "rattles" when driving in heavy wind conditions or when a truck passes and creates a wave of air pressure/suction.

I'll be contacting Maxxair to see if the fix is available for our 2010 Interstate.

[PSchw]

I just contacted Maxxair and they gone send me the kit.

[Titus]

What number did you call to get the anti-rattle kit? Do you need to know the model number, or is there only one kit?

When ours gets noisy we check to see if it is not quite shut - but it always is. Sounds (pun intended) like we need the kit too.

[PSchw]

I just went through there support website.

[nvestysly]

I requested a kit via a phone call to tech support. Should arrive in a week or so. No charge. The kit is supposed to come with instructions. Apparently the kit does not have a part number. I'll post details later when the item arrives.

[nvestysly]

The "kit" arrived a few days ago and I wasn't certain what to do with it. I opened the vent and removed the existing gasket and installed the new gasket. Time will tell if there are fewer thumps and rattles as we drive down the road.

The old gasket seemed to be compliant so it's difficult to imagine how replacing the gasket will change the situation.

Should I have put the new gasket in some other location?

I've attached pictures of the shipping ticket, location of gasket and cross-section of gasket.

[InterBlog]

Originally Posted by Protagonist

...you can drive with it open…

Yes you can, with a caveat: it is suspected as perhaps being a cause of, or at least a contributing factor to, cheap plastic toilets eventually breaking what flimsy air seals they have, thus allowing black tank odors into the interior of Class Bs. It might be sort of a Bernoulli thing. ClassBWarned says the following of windows, and the same might apply to that roof vent, depending on the config and operational state of the van:

"If you have all of the windows closed there’s usually not an odor problem, but once you crack any of the front windows while moving, waste odor from the bath area fills the entire coach."

[Boxster1971]

Originally Posted by nvestysly

The "kit" arrived a few days ago and I wasn't certain what to do with it. I opened the vent and removed the existing gasket and installed the new gasket. Time will tell if there are fewer thumps and rattles as we drive down the road.

The old gasket seemed to be compliant so it's difficult to imagine how replacing the gasket will change the situation.

Should I have put the new gasket in some other location?

I've attached pictures of the shipping ticket, location of gasket and cross-section of gasket....

Yes - you should put the new gasket material on the rain shield, not in the same place as the existing gasket. See the Sprinter-Source link in my first post for detailed pictures of where to install this added gasket material. The rain shield as delivered has no gasket and that is source of the rattles on many installations.

[Protagonist]

Originally Posted by InterBlog

Yes you can, with a caveat: it is suspected as perhaps being a cause of, or at least a contributing factor to, cheap plastic toilets eventually breaking what flimsy air seals they have, thus allowing black tank odors into the interior of Class Bs. It might be sort of a Bernoulli thing.

I think it's much more likely that on most Interstates— except the T1N rear bath models— the black tank vent is located too close to the MaxxFan main vent and/or the bathroom vent.

On my 2012 Interstate, I never have an odor problem driving with the MaxxFan open and turned on (mine is extract-only, not reversible). However, if I drive with the bathroom vent open, odors ARE a problem.

[InterBlog]

Originally Posted by Protagonist

I think it's much more likely that on most Interstates— except the T1N rear bath models— the black tank vent is located too close to the MaxxFan main vent and/or the bathroom vent.

On my 2012 Interstate, I never have an odor problem driving with the MaxxFan open and turned on (mine is extract-only, not reversible). However, if I drive with the bathroom vent open, odors ARE a problem.

Mechanically, do we understand exactly how that works? Because the black tank is connected to its roof vent, which is passive, and generously sized, and always open, and immediately adjacent to the wet bath (very close to the toilet). Therefore I would assume that the path of least resistance should always be through that dedicated vent (surely that's what the system designers intended).

Why would the pressure differential become such that the path of least resistance would change to the point where it's easier for the air to force its way through tiny fissures in the toilet seal and into the cabin? If anything, by virtue of Bernoulli, I'd expect air to get sucked INTO the tiny toilet fissures and out through the vent. But I'm not an engineer so it's quite likely that I'm missing something.

[Protagonist]

Originally Posted by InterBlog

Why would the pressure differential become such that the path of least resistance would change to the point where it's easier for the air to force its way through tiny fissures in the toilet seal and into the cabin?

That's not what I'm saying. I'm saying that the smells apparently comes from the top of the black tank vent, and back into the van through the bathroom vent, which has a noticeable downdraft when the van is in motion on the highway (BTW, I've burned out no less than TWO vent fan motors by accidentally letting the vent fan run while driving, and the force of the downdraft caused the fan to drive the motor in reverse— I now make sure the bathroom vent is turned off and closed before driving anywhere).

[InterBlog]

Ah, OK, I see. The predicament faced by ClassBWarned is a bit different: they crack open their cab windows at highway speed and black tank odor fills the rig. Presumably the cab windows are too far forward for any similar down-drafting effect, so there's an undisclosed mechanism in play.

Coming back from Nova Scotia this summer, I noticed that the odor got worse when I had all windows and both roof vents physically closed and the a/c on recirc. But as long as there was a steady stream of fresh air coming in through the front vents when they were set to intake air, the odor was diminished (unfortunately recirc is a requirement in the deep south in hot humid weather, so I couldn't just stop using it). There was nothing wrong with our black tank vent, which we had replaced ourselves, so it wasn't a vent-related problem.

I'm left without a clear explanation as to why either phenomenon occurred, either the ClassBWarned version or our own, which we solved at least to a large extent by changing to a Dometic toilet (thread here, blog post here). The odor is / was so strong in each case that intuitively, it doesn't seem like air was somehow exiting the black tank vent and then coming back into the coach from the outside - it seemed like it's coming directly through the toilet itself (hence the improvement upon replacement with a Dometic). We don't have a tight air seal on our old Fantastic. I don't know if that might have played a role in the corresponding set of air movements.

[Titus]

Interblog
I agree with your assessment that it is unlikely that the fumes are coming out of the topside black tank vent and being drawn back in somewhere/somehow. But if it were coming up through the toilet itself (Thetford or Dometic) I think you would see air bubbling up through the water in the bottom of the bowl. Other possibility (unlikely I would think) is that the seal between the toilet and the floor leaks. (This is the wax ring on house toilets, not sure what it is in a MH.) Maybe your toilet replacement reduced the stink because of the accompanying seal replacement and not the toilet itself? Also ... I wonder if the standpipe between the black tank and the rooftop vent has a gap/leak in it? Any such gap/leak might only cause a problem when there is negative pressure inside the van. Does the stink appear with all windows/doors closed and the fantastic fan on?