Just how efficient are oil bath air cleaners? I have wondered this for years. Are they better at filtering dirty air than a paper element or oiled-cloth reusable filter or worse? Are there applications where they are still in use today such as industrial or military?
A friend of mine has one on his '53 Chevy and swears by it. BUT, when he removes it, he's VERY careful. I didn't know there was oil in them and took it off for him one day. Spilt oil took a while to clean up. Wasn't too bad though.
They are still used on machinery used in dusty environments because they will trap and hold several POUNDS of dirt without plugging up or losing efficiency. Oil bath filters are better and cheaper to use than paper filters because they last the life of the car. But the first cost is higher, and they are harder to fit under the hood which is why car makers abandoned them. They are also more restrictive. This must be taken into account when the engine, carburetor etc are designed. There is little or nothing to be gained on a stock engine if the filter was properly sized to the engine. But if you hop up your engine it will be too small. This is why the oil bath filter was thrown away on hopped up motors, not because it was too small for a stock motor but because it was too small for the hopped up motor.
Good article in Hemmings about it last May http://www.hemmings.com/hcc/stories/2012/05/01/hmn_tips1.html
Take the oil bath air filter off an old motor and inspect inside the carburetor. It will be just as clean as one with a paper filter and probably cleaner.
Oil bath filters remove more than 99% of the dust in the air and they do not become restricted as they get dirty. In fact they get more efficient when the filter material is coated with oil and dust, like a K&N filter which works on a similar principle. As I said before the advantage of the paper filter to car makers is 1) It is lighter and easier to fit in under the hood 2) they can make more money selling replacements 3) is it way cheaper to the car maker, not so much for the consumer. For the consumer the down side is you need to check it once in a while (same as any filter) and clean and oil it from time to time. These days if you drive on paved roads an oil bath filter will go for years and years before it needs service. Just check it, and if the oil bath is not full of dirt and silt you are good to go. The up side is you never have to buy a filter element which these days can cost up to $35. All you need is a quart of 50 motor oil which will last for years.
Bingo! That was my next question...What weight oil did they use? The first car I ever had was a '56 Ford with an oil bath air cleaner. I used 30 weight in it 'cause that's what I had on the shelf.
Don't wish to hijack the thread ...just add my 2 cents ... the oil bath breather and the carb it is used on was designed to work together .. without the oil bath the carb will tend to be just a little bit leaner. It has to do with the restriction pulling air through the oil ..Also cold weather will restrict the air even farther .. IE richer the mixture
Yes 50 weight is correct. My '50 Buick Shop Manual lists it in their along with the other lubes, oils, etc.
Oil baths don't pull through the oil, they rely on a 'sharp bend' of the airway to deposit particulates in the oil. My experience is that the air resistance is less with an oil bath than one of those 6" diameter paper elements. Quieter too. Had a paper element on my 54 235 w/ rochester B and the whistle drove me nutz. found an old oil bath, welded up the holes, painted it and it did great. quiet and better throttle response. just my 2 cents. build 'em to drive 'em.
bishop is right the oil bath does not have the air traveling through it just close to it the sharp bend causes the particles inertia to pull themselves out of the air stream and settle in the oil. I always wondered how well they worked.
Oil bath filters are not as good at filtering compared to the newer designs, but as was pointed out, in severe duty applications they won't clog as quickly while still doing an adequate job. When St. Helens blew up here, the WSP tried numerous things to filter the fine ash (including oil baths) and quickly found that anything less than 100% filtration (or as close as they could get) meant a dead patrol car. One thing missed here, when oil bath filters were popular, getting 100K on a set of rings was considered excellent and oil change intervals were typically at 1 or 2K miles. Yes, materials/manufacturing improvements are big part of why newer motors last longer, but you won't find oil baths anywhere anymore except where newer types are cost prohibitive.
Do not put a oil bath on a carb not designed for one,I had a 59 Olds 371 in my 53 88 and decided to put the 53 oil bath on it and it drank alot more gas so I ended up just using the lid.
There seems to be some misunderstanding about how an "oil bath" air cleaner works. By definition, air goes thru an oil bath. As can be seen in the 2 samples of air cleaners, the air is directed into the oil and the air flow carries oil up into the wire mesh and coats it. If this were not so, the dirt could not be captured and would travel thru the dry mesh and into the engine. Oil level is critical to proper function: too little and the oil bath effect and washdown of the dirt from the mesh cannot be achieved, too much and the oil can be drawn all the way into the engine carrying the dirt from the mesh with it. Oil bath air cleaners are efficient , as pointed out previously, they were not easily fit into available space on more modern designs. Look under your hood and see where you could put one on a late model. Todays attitudes and expectations are not the same as in the '50s and oil bath simply do not fit in. And for those who have done some research on the internet, don't believe everything you read, consider the context and the source. Misinformation is rampant. One man's uninformed opinion can be quoted and requoted until it seems to become legitimate. The best source for technical information should be gleaned from manufacturers' and OEM literature, not from forums. Ideally I would quote each reference work by book, volume, author etc but alas I have not! Oil bath air cleaners were designed to function within the airflow demands of the engine. I am confident that they had a CFM rating and naturally would not use one for a small 4 cyl on a large V8 or vice versa. The airflow is what made it work.
i noticed on my tractors, the oil bath filters also trap water. i always thought one of the reasons they were fazed out was for environmental reasons.
Even back in the day when oil bath air filters were being used, many didn't think that the air actually went through the oil. When it gets extremely cold, 50W oil became almost solid and the filter had to be heated or removed to start an engine. If it was changed to a lighter oil, the oil would be sucked into the engine when it got warm under the hood. Lighter oil would slosh around more too. They were used longer on heavy trucks where the filter was mounted on the outside and could be much taller and use thinner oil. As displacements got larger, the area needed for oil bath filters to be as effective got too big to allow their use.
The airflow doesn't actually percolate through the oil as one might imagine but the velocity of the airflow picks up and carries some of the oil up into the mesh. The airflow at low velocity and idle may actually cause bubbling effect, at higher flow rates the oil pool is altered and distorted so that technically the air does not flow through the oil but carries some oil up to wash down the mesh. At idle or shutdown, the oil drains off the mesh and carries some of the captured dirt with it into the pan.
The factory manual for my shoebox says to use 20 or 30 weight, as I recall. I've found that 30 works well.
Oil bath air cleaners work by capturing dust and dirt in the oil. It is done by a rapid change in direction of the air flow. When the air flow direction changes, the heavier dust and dirt particles can not make the direction change and leave the air stream, and are captured in the oil. The cleaned air continues into the carburetor. The captured particles settle to the bottom of the oil. The oil tends to stay clean because of the settling. Oil bath air cleaners are extremely efficient in removing dust and dirt particles from the air. They need to be serviced on a regular basis and it can be a messy job. The filter material is cleaned and lightly oiled during the servicing. It should not be further coated with oil during operation as this will have a choking effect on the air flow and cause the engine to run rich.
I think some of you are romanticizing about oil bath air cleaners. I find it hard to believe the OEM's stopped using them and changed to paper filters simply in order to make money off of sales of replacement filters. How many replacement air filters you think the OEM's sell anyway? I'm sure that the longer service intervals and longer service life of modern cars has nothing to do with more efficient air cleaners. Here's some actual data that might help: https://www.widman.biz/English/Analysis/Oil_bath.html Heres some more info from a manufacturer that still produces oil bath air cleaners for use on heavy equipment. Scroll down to the second page and read what they have to say about efficiency. https://www.krone-filter.de/assets/...rs/oil-bath-air-cleaners-from-mann-hummel.pdf
Looking at the paper element air filter in my OT vehicles as part of the periodic service, the amount of dirt they actually appear to capture is minimal. BUT the roads by which we travel these days, compared to say the 50's are significantly more sealed surface so the amount of dust thrown up is much less. So, paper elements are adequate these days. Farm equipment still uses oil bath because it can trap a lot more dirt without becoming clogged up than a paper filter. Same with oil filtration, when did you last see a twin stage cyclonic oil filter system on a passenger car? I think that's the main reason for the change. There's not the necessity any more.
What I can tell you is the paper filters with a safety filter on farm tractors started the engine life went way up over oil bath units..
While we are talking tractors…. Most large modern farm tractors have a centrifugal pre cleaner to get a lot of the dust, then have huge paper filters, to clean the air! Bones
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