So after reading for the umpteenth time the go to solution for seemingly every problem "change the fuel and air filters" I got to thinking, when are the filters really bad? Most heavy trucks and machines come with a "Filter Minder" a simple vacuum diaphragm with a calibrated spring for measuring filter restriction. A quick search of Napa online reveals item 4801, and at about $20 its around the same price as a new filter.

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1991 300d 2.5 Turbo OM602

So simple install, remove the filter housing, drill a hole and squeeze the provided grommet into the hole. Push the minder in, reassemble, and done!

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1991 300d 2.5 Turbo OM602

How would this work with a turbo? I don't think you'll be switching filters less often.

You're right about changing oil and filters being the ritual. But personally, I prefer to slaughter a sheep and make a burnt offering of the entrails.

Turns out my filter was just fine after all, and as a bonus no opening the housing to look and guess, pardon the bad image my camera is being ornery

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1991 300d 2.5 Turbo OM602

Ha right? Yep totally kosher for turbo these mount suction side so turbo or not doesn't matter. Its a simple vacuum gauge that locks at the highest restriction it sees. As the filter plugs the yellow bar gets pulled down farther and farther. I'm working on a solution for the fuel filters as well. The air filter I didn't replace this time paid for the minder so any saved filters from here out=Gravy money!

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1991 300d 2.5 Turbo OM602

And this exercise represents an advantage over simply replacing your air filter every spring, in what way?

Technical note: you need to slaughter a goat, not a sheep. Longhair preferable. Don't ask how I know that.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

In the long run it saves Money and a little time not having to replace the Air Filter before you need to. Depending on the cost of an Air Filter it might take several years to pay for itself.

It also has a minor use in trouble shooting. If you are having an issue and you see it is tripped you have a place to start from.

I think it also depends on where you live.
Where I am there is a Freeway not even 1/4 of a Mile away choked with Truck Traffic going to the Port of Long Beach and it is windy and a lot of My area boarders and industrial area that has empty grass free land.
More dust then you would guess here and other particulates.

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84 300D, 82 Volvo 244Gl Diesel

Vaild point clean city driving; none other than an easy eye diagnosis without popping the filter cover. But I commute down one gravel road and live on another and NC spring pollen falls almost thicker than snow. The thought spurred out of the fact my filters are usually quite ugly but turns out are so oversized for the small 2.5 motor it wasnt affecting anything, the current filter is still working fine despite being a couple years old. Plus and most importantly its a shiny new gauge to play with. Off to source goats to cure an injector nailing problem!

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1991 300d 2.5 Turbo OM602

Yes real fast payback on the air filters if you tend to keep your vehicles a few years, and replace air filters by mileage or time frame. But you have hit the nail on the head in regards to the one for fuel checking fuel filter indicator. I would much rather change that in my drive when showing signs of clogging than on the side of the road, on the way home after a twelve hour shift. Ask me how I know.

My Dodge Ram has a filter minder. It is basically worthless because I check the filter to make sure the minder is working. The filter was pretty dirty and the minder hasn't moved. I'll change it when I go to the store.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

The filter minder is very useful, especially in vehicles or equipment that operate in adverse conditions. Every time you touch an air filter, there is the hazard that something can go wrong; accidental dust ingestion, filter damage, or improper installation. It's less important in our cars which operate in a relatively clean environment and the filter is relatively cheap.

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'83 300D, 126K miles.

Thats part of my point exactly. Ugly dirty filter doesn't equal restricted filter. There is a big misconception about filters stopping working when they look dirty vs actually being plugged. No not as big a deal on a $20 car filter as it is on a $50 or $100 tractor filter but i like having an actual measurement vs eyeballing it. I'm putting together a version for fuel filters something similar to what i have on my aftermarket Racor Ill post pics when i get home.

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1991 300d 2.5 Turbo OM602

X2 on the Cali version 300D >$75.00 part. I wouldn't want to toss that until needed. OOps sorry PParts.

For those who do not remove the filter often it is an interesting idea.

It would be more difficult to install on 1985 and earlier air induction systems.

.

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ASE Master Mechanic
https://whunter.carrd.co/

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
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Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
2003 Volvo V70

https://www.boldegoist.com/

Yep! As a filter collect debris, it actually filters out smaller particles more efficiently. Changing a filter too early is actually not as good for your engine. That's the beauty of a filter minder, it tells you when to change the filter and gives you plenty of warning when to do so (if you pay attention to the gauge).

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked