Air Filter Change Indicator

[Neil Womack]

I know most OEMs suggest changing air filters based operating conditions and or mileage/hours. But in reality we should change the filter when it restricts air flow at a given point.

My John Deere has a little pill bottle size devise (Donaldson Mfg) that measures inches of mercury on the intake side of the air filter.

Would such a devise work on a gas engine and how would we determine the air filter change point?

I think diesel engines differ on the intake side by not having a throttle plate to restrict air flow. As opening the throttle on a diesel is just rotating the injector pump plunger to deliver more fuel to the cylinder injector.

 

[Ken2]

Lots of filter makers sell these indicators. They work well on diesels with constant governor settings, like tractors, or constant speed diesels, like generators. The operator has time to look at the indicator. The diesel, of course, doesn't have a throttle...its induction is wide open and the amount of air being drawn in is determined by the rpm and amount of turbo boost.

On a gasoline engine, there's only enough air flow through the throttle plate and filter to begin to activate the indicator at full throttle and high rpm. At full throttle and high rpm, who's got time to look at that little plastic thingy?


Ken

 

[S2000driver]

Air filters in tractors, lawn mowers, etc get dirty very quickly without much warning, depending how dusty the conditions are. In this case, it's very convenient to look at an indicator compared to opening a box over and over.

I think the dirt accumulation in an automotive filter is slow enough that pulling it out once a year to check it is sufficient.

 

[rpn453]

The indicator is held at its highest vacuum setting until reset, so you just check when you open the hood and reset when you install a new filter.

 

[rpn453]

I agree that they'd be useful, and it would work on gas as well. I've seen one on a '96 Chev half-ton (350). I think it was stock.

The point at which the filter should be changed could be determined by either:
1. An arbitrarily chosen value based on performance loss.
2. An economic feasibility study for when filter replacement should occur based on losses in fuel economy.
Hopefully the manufacturer would do #2 for us, but let us choose what is acceptable if based on #1.

[ February 09, 2003, 12:51 PM: Message edited by: rpn453 ]

 

[Ken4]

I think most newer cars already have the air filter restriction sensor. The CEL/MIL simply lights up when it's blocked.