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I read a few days (*cough cough*) ago that it was good to oil the sponge air filter on a lawn mower (read "Briggs & Stratton 3.5 hp") with motor oil. I tried this once or twice and the air filter clogged pretty quickly. I brought one filter in to a shop (yeah, days and days ago ago) to get a replacment and they LTAO at me (I think that's how the kids say it). But this very year I encountered a filter from a 2005 engine that was partly permeated with oil - from the top, so it was deliberate.

Is there any legit reason to oil a sponge air filter?

The manual says to on carb on tank models - 09xxxx and 10xxxx. I've wondered about it.
1. Does the oil trap tiny debris? The sponge is pretty dense.
2. Do carbs on tank need a misting of oil?
I do it cuz manual says to. I get 10-15 hours of dusty mowing before foam above big holes in AF housing get dark brown.

Engine manufactures recommend oiling the sponge type filters. It helps to trap dirt in the filter . Just think if it didn't get all cruddy like that all the dirt would get ingested by your engine.

How i oil air filters:
I use SAE30 oil... i use the cheap Countyline SAE30 from TSC for air filters.coat the top of the filter in oil and wring it and rub it around. blot the filter with a shop paper towel to get rid of any excess oil..

As with Scrubby, I dip the pinkie in engine oil then wipe the top of the filter and blot off the excess on some paper towel.
If the entire filter is oiled the intake holes on the bottom choke with dust which can not be cleaned
This allows the filter to work progressively with the unoiled bottom section taking out the coarse stuff & the oiled top pulling out the fines .

Anyone ever try bar and chain oil it is tackier and would trap more dirt? Just a thought.

hlw49 said:

Anyone ever try bar and chain oil it is tackier and would trap more dirt? Just a thought.

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If it was better Briggs would say to use it.

SAE30 works perfect in foam filters. You want the filter to get dirty. It's doing its job.

I do as Briggs says. Saturate in oil, wring out excess oil in a shop rag. Yes the oil helps catch grit and junk.

dougand3 said:

1. Does the oil trap tiny debris? The sponge is pretty dense.

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Yes

dougand3 said:

2. Do carbs on tank need a misting of oil?

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No they need a full saturation of oil then squeezed out in a shop rag.

dougand3 said:

I get 10-15 hours of dusty mowing before foam above big holes in AF housing get dark brown.

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Don't worry about the color. Run the filter till the mower starts to run rich or not start.

Briggs says NOT to, say every day, remove the filter and clean it. Once a year or till you have running issues. Course you could be mowing dirt and clog it in one day too. Reason Briggs says to leave it alone is about the sealing area being opened up allowing grit into the engine more often, not good.

I run a bead of grease around the sealing areas of all filters. Those square Briggs Quantum types never seal 100% just to name one. Rubber gets hard and doesn't seal anymore. Don't rely on a rubber seal. You will see grit all around the grease area when you remove the filter that would of gone into your engine.

Richard Milhous said:

I read a few days (*cough cough*) ago that it was good to oil the sponge air filter on a lawn mower (read "Briggs & Stratton 3.5 hp") with motor oil. I tried this once or twice and the air filter clogged pretty quickly. I brought one filter in to a shop (yeah, days and days ago ago) to get a replacment and they LTAO at me (I think that's how the kids say it). But this very year I encountered a filter from a 2005 engine that was partly permeated with oil - from the top, so it was deliberate.

Is there any legit reason to oil a sponge air filter?

Click to expand...

The oil catches small particles that could pass through the foam.

I put the clean filter in a plastic bag, dribble a little oil into the bag, and give it a few squeezes to distribute the oil. Doesn't take much oil, keeps your hands clean.

Those push mower foam filters don't take much oil, Too much and it will drip out and too little will allow dirt to get past the filter