Dirty Air Filter

I've looked at my air filter a couple times in the last 3 months, and I thought it looked really clean. Decided to change it the other day since it has been a year. When I placed it beside the new one, I realized just how dirty it was.

The sunlight was basically the same on both, but the clean one is reflecting so much more light because it is so much whiter/cleaner. I don't recall ever being on anything but paved roads. I think the moral of this story is don't try to determine how dirty the filter is by just looking at it, but change it routinely for best protection and performance.

Dale,

Does your air filter have a gauge that shows yellow when it is clean and turns red when the filter needs changing? Mine has that indicator, and I have been having the coach for 3 years and it still shows yellow (o.k.) Do you think I should change it before the red indicator flips up?

Tuga, three years? Change the filter. You are not going to believe how much crap you will find when you pull the cover. Have a vacuum cleaner handy to clean up real good before you install the new filter.
One of our old Foretravels had the filter indicator and after a couple of years of showing green (good) I had a look and the filter was real bad.

Its either once a year or every 12000 miles for me. They get real dirty. The last time I pulled the old one out, fter one year, there was dirt laying in the canister. I wouldn't trust those pressure guages.

Back in the 60's when working at my father's service station, we would hold the trouble light inside the filter and if you could see light through the filter it was ok; no light, replace. Fram even had a device that you could place the filter around a light bulb, cover the top of the filter and press the light switch. MY father would not buy this since it cost money and took up work bench space.

He also thought I lost my mind when I bought my first motor home....he was probably correct.

Tuga, I don't have the gage on the bus, but I hav one on my Dodge truck. The filter on it gets dirty long before the gage changes to red, so I don't know that I trust them.

I agree with Gary about the 12,000 or once a year. It doesn't take long for a dirty filter to eat up the cost of a new one in increased fuel consumption. More importantly is the accumulation of damage to the engine.

Denny, I've used the light test many times on cars/trucks. I'm not sure it would be effective on the bus filter, since it is so thick.

If a dirty filter causes the loss of 1 mpg, it costs $54 extra every 1,000 miles when diesel is $2.25 per gallon. Doesn't take long to pay for a new air filter.

Can these filters just be picked up at any NAPA? I have such trouble getting items shipped since I am never in one place for very long.

Thanks,

Adam

The bus is not like a car. At least not like the old cars with carbs.

The computer controls the fuel delivery based on turbo boost which is a result of air flow. As the filter gets dirty it actually is a more efficient filter at the expense of air flow. My point however is a dirty air filter on our buses will not cause black smoke and unburned fuel. It will just impact the horsepower output of the coach. If it performs well there is no harm.

I'm with Tuga.

I have several years on my air filter also. If anyone wants to disprove what I am saying bring a new filter to OKC along with a stopwatch. We can do a timed acceleration run with my old (current) filter in place. Then we will repeat the accelration run with the new one in place.

If the run times are the same I keep the filter for free. If not, I will pay for it. Any takers?

Jon, That is surprising to me! From some of the other posts I've seen in the last couple years and from what little I know about autos in general, I thought a dirty air filter would impact the fuel mileage and allow more debris to enter the engine regardless of the type fuel sytem.

If what you are saying is 100% correct, then that is good news. I had just as soon change my filter every three years as I had every year, but I'm still a little skeptical about this subject. Why is the DD system any different than any other vehicle that has electronic injection? Are you saying that when the system senses less air flow, it just reduces the fuel flow to match?

The filter minder is good for the trucks and I have seen them turn to red, but we were putting 120K a year on them at the time and 200K plus for teams.

On the bus, I just blow them out at oil change time and 3 years sounds reasonable to me. Besides, for most, after 3 years your only looking at about 36,000 miles. I just changed mine out because the old one looked real dirty and what's 55 bucks every few years or so.

Well, this is one place I can reduce my maintenance cost a little.

I told myself when this thread started, here is one I wont be chiming in on because if I do these folks will think I'm nuts.

As many of you are aware Deb and I operated a tractor trailer in a local quarry for 12 years. Arguably a much dustier environment that we will ever experience in the bus.

Our truck had a Cat and when we sold it last year it had right at 1 million miles and without major engine repair of any type. I did a valve adjustment and new injectors at 550000 and that's it. When we got rid of it it would be around 1 gal of oil down at 10000 miles but I believe 90% of that was leaking.

The truck had an air filter restriction gauge with a red line at 25 inches of vacuum. Not only would I run them till, under full throttle and load, that gauge would hit the red line but then I would pull it and blow it out and reinstall it for a second go around. When I did pull it it was definitely noticeably HEAVIER than its new replacement and a couple of times I gathered up as much of the dirt i could and could easily fill a 2 pound coffee can with the silt I got out of it by banging and turning it on the concrete and blowing it out with air.

When reinstalled the gauge would barley move and the filter would then give me another half life compared to how long it took to get into the red initially.

I can't believe I have told this story but it needed to be said and there you have it.

The biggest difference I noticed when dirty is the turbo would not whistle as loudly as it would when clean but my manifold pressure would still be 24 at full throttle and I could not feel any lesser power.

The air filter in the bus is the one that was in there when we bought it. I blew it out and reinstalled it and I will get back to you when I replace it:o

There are a couple of different types of restriction gauges. One is on the canister itself and another is installed in the dash. Ours was in the dash and I do not know how or if I would have been able to safely exercise my technique without it.

On my 93 Newell I noticed low boost pressure when traveling thru Durango, CO (climbing hills). I located a new replacement air filter in Farmington, NM, installed it, and it made all the difference when climbing. The filter was really dirty. If I remember correctly the 8V92 didn't have an air fitler guage. My point here is - your engine will tell you when it is time to change the filter.

I have noticed, that it says "Do not blow out the bus air filter with and air gun". Maybe that is because they want you to buy a new one!

I had found a test document regarding air filters on large diesel engines a while back on the internet. It may have been a SAE study. On the sample engines where the filter was replaced early with relatively low mileage the oil samples showed significantly more silica (basically sand) and the cylinder walls showed more visible wear. They also tested the cotton cleanable filters (like a K&N that are coated with oil) and they let much more abrasives through, especially when new. Many of us tend to over service our busses, but I believe the air filter is one thing that works better when it is a little dirty. I take mine out @ each oil change and inspect it with a light as someone else had mentioned. We have been replacing ours at about 25-30K miles. I do not drive on any dirt or gravel roads, which would have a significant impact on the life of the filter.

Steve,
From what you have said, it makes it appear that smaller particles can go through the clean filter easier than through a dirty one. I wish I could go to the dump and get my old one back. At least, I know I shouldn't have to change this any time soon.

So does this mean nobody wants to take me up on my challenge at OKC?

BTW, if you do take yours out and find a bunch of dust and dirt in the bottom of the air cleaner housing it is dust and dirt that did not pass through the filter, but was blocked. When you shut the engine off the negative pressure downstream of the filter went to zero and the dirt was no longer held in place against the filter and fell from it.