This from an earlier thread:

Here's from an old post. I did this a while back and it still works fine. May help some or at least give you some ideas.

"NO/LOW oil pressure warning system on 300SD 1984. This is what I did, you may have another way.

Usual cleanliness, safety warnings apply.
If you do this wrong, your oil WILL run out of your engine and ruin your day!!!! Check all joints and connections on the bench FIRST!!!
Obviously, YOU need to verify ALL before proceeding. I hope this helps, but I can't be responsible. (yada, yada yada, lawyer, yada, atty., yada, yada).

Parts:
Radio Shack 12v. buzzer (cheap)
Radio Shack red LED (with built in resistor)
12mm X 1.5 male X 1/8" NPT female adapter (steel)
1/8" NPT street "T" (has a male with two females)(brass)
1/8" male X 1/4" female adapter(brass)
mid '80's Audi or VW (water cooled) oil pressure sender for idiot light) (~6 psi. ?) (cheap)
Tools:
1/8" NPT tap
1/8" NPT die
12mm.X1.5 tap

Try here for fittings http://www.fittingsandadapters.com/

If you have access to machining tools or can find other appropriate METRIC fittings (I looked everywhere for other metric fittigs and found nothing that fit this purpose) you can do this much more easily. A metric street "T" would make this nice, but it eluded me. Maybe someone has a source?

1. Remove the oil pressure sending unit from your car with a pan underneath. You will drip out ~ 1/2 pint of oil, then it will stop.

2. Braze (I soldered with a torch and plumber's solder) into the threads (small thickness of braze or solder) of the female side of the 1/8 male X 1/4 female adapter. Now retap that side with the 12mm. X 1.5 tap. You'll be surprised how close they were already. This is where your original Mercedes oil sender will eventually go, so be attentive.

3. Tap and die all 1/8" NPT threads in the "T" and adapters with the 1/8" NPT tap and/or die to clean them up and deepen the amount of "bite" for security. You'll see what I mean when you dry fit them.

4. The Audi/VW sender has a 10mm thread. Take your 1/8" die and run it over that. Yes,... rethread the 10mm. on the Audi sender and make it 1/8" NPT. They are SOOO close to start, after you run the 1/8" NPT die over it, they match quite well.

5. Assembly:
a. 12mm. X 1.5 male X 1/8 NPT female adapter goes into the oil filter housing (use an aluminum crush washer)
b. male of the street "T" goes into female of that adapter.
c. Audi/VW sender (rethreaded to 1/8" NPT) goes into the side branch of the "T".
d. 1/8" male X 1/4" female (brazed and retapped to 12mm. X 1.5 thread pitch) adapter goes into end of the "T"
e. Original Mercedes sender goes into the retapped end of that adapter (use an aluminum crush washer). Reconnect original wire.
f. Put a new wire (with spade connector) to the connector on the VW sender and run it to the buzzer. Connect other side of buzzer to a "start/on" hot lead. Connect the LED in parallel with the buzzer and place buzzer and LED where you want to.

I have all of the hardware done on my car and am running around to check and recheck stability and for any leaks. I have not hooked up the buzzer yet, since I have a few things to do at the same time to my instrument cluster. (my modified gas engine inst. panel with economy gauge as a boost gauge for the turbodiesel needs calibrating). The buzzer may get annoying since I expect it to buzz whenever the key is on without the engine running(oil pressure less than 6 psi). We will see if I go with only the light long term. Since 6psi is the same as zero, as far as I'm concerned, it should work to warn of a pesky ruptured oil cooler hose, broken filter canister bolt, road rage bullet through oil cooler (this is SoCal after all) or what not.

FWIW that's what I've done.

Edit: Hooked it all up with 0.3 bar VW switch and it works perfectly. LED right in between gauges and buzzer is unmistakeable.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Here's a low oil pressure/high coolant temperature kit. Do people think it could be adapted to our engines?

http://www.moyermarine.com/cgi-bin/shopper.cgi?search=action&category=KTAS&keywords=all&template=Templates/B000_storebuilder.html

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Surely we can find a 12 volt buzzer which does not require a relay.
A timer is just another thing to fail.

If you are referring to my post about the switches I was talking about two switches... the oil pressure switch is on with no oil pressure... but is hooked in line with a switch at the operator station who presses a normally ON switch to OFF to keep the buzzer from buzzing until the engine provides enough oil pressure for the oil pressure switch itself to take away electricity from the buzzer... this is the simplest system I know of which causes the operator to either hear or act to not hear the buzzer each time they start the car... a fail safe system as far as causing the operator to test AND fail safe as far as the switch configuration.

Indeed a buzzer can be had, some had posted however that they didn't like buzzers. It's a matter of preference.

I see your line of thinking with your setup, it seems failsafe, but the circuit still relies on the integrity of it to conduct and the contacts to make for it to sound the alarm, so what happens if it works @ startup, and 2 miles down the road you hit that little road crack, where that frayed to one or two last strands wire fails completely? Fail safe means it alarms or halts a machine with a loss of power to a holding circuit or PLC input (safety circuit would fail into a safety mode), so if the circuit failed it would falsely alarm, but would never fail to warn you in a time of need. There's really several ways to do this, pending what you want to spend and what your preferences are, I was just simply putting in my views to add to the idea pool.

__________________
Chris
64 190D R.I.P.
80 240D W/617 engine -for sale
82 240D -for sale

Fail-Safe (didn't someone write a book in the '60s???)
It is certainly true that designing a completely fail-safe system that also is simple and affordable and installable by an owner (rather than designed-in by the factory) is not easy.

Then there is the question: what is the risk? How often does this happen? Is the effort better directed to performing preventive maintenance such as changing oil cooler hoses, etc?

The combination of those two items may explain why Mercedes chose to not put them on their cars.

Practical concerns
It's possible to install a low-pressure warning without putting switches and wiring at risk in the engine compartment. It can all be done in the dash.

In the case of W123 cars and others using a mechanical oil pressure gauge, the low oil pressure switch (tee'd into the plastic oil line) and all of its wiring can be behind the instrument cluster where it will be safe.

Cars with electric oil pressure senders (W124 and similar) will need a different circuit, an FET input switch, for example, that turns on a light when the resistance of the sender gets too high or low (I don't know which way it works). Using an FET will minimize the load on the oil pressure gauge circuit. This can also be safely mounted behind the instrument cluster.

Buzzers
For a gasser, the buzzer at startup would be a momentary thing -- just until the engine fires and the oil pressure builds up. For a diesel, having a buzzer sounding continuously during pre-glow will quickly get old, I think. If the buzzer is loud enough to be heard over road noise, stereo, etc, it will be really annoying in the driveway with the engine not running. How about a flashing red LED? Some pretty bright ones are now available.

An interesting discussion. Keep it up!

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

If there is anything I don't want in my circuit it is a field effect transistor ! LOL. You would then need something to protect it ...like backwards mounted Zener diodes... etc... just more things to fail.... LOL

That is why I suggested the button to keep the noise off during that time...

I don't know what the ' field of study' is... lets call it ' ergonomic attention span for Mercedesapians. But any light is less effective for speed of grabbing attention to an serious mechanical fault than an auditory BUUUUUZZZZEEEERRRRR.... I suppose if being precise...as I always am... auditory is redundant in that sentence.
LOL

There are warning systems available for trucks and boats. Perhaps some of the components can be looke into for use on Mercedes.

__________________
84 300D, 82 Volvo 244Gl Diesel

First, there are chimes or beeper alarms used in cars today that are more pleasant than the raucous buzzers that most carmakers dispensed with many years ago.
Perhaps one of these newer noisemakers could be adapted to this low-pressure warning system and simplify the circuit, while retaining an automatic-check function whenever the ignition is turned on.

Second - A buddy that competes in vintage sportscar racing installed a large low oil-pressure warning light on his steering column to supplement the guage. I think he found his low-pressure warning kit through a racing supplier. With the prevailing engine noise during a race, and with a helmet on, a buzzer would have been worthless. Downside of this setup is you would be have to mount an obtrusive light housing on the dash or steering column, however, as someone else mentioned, there are spots in the cluster where an extra warning light could be added.

Third - I'm not crazy about having the warning triggered only by low oil level, as there can be situations where low oil-pressure wouldn't be automatically accompanied by low oil level.
The solution would be to fit a suitable tee to the oil-filter pressure port - tricky but probably the best arrangement as I certainly wouldn't want an oil switch dangling from a makeshift splice in a plastic oil line or fastened at the cluster where it might dribble black goo on my pants or carpet someday.

Happy Motoring, Mark

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DrDKW

Many years ago some cars had low pressure oil senders which disabled the ignition circuit.
I think Pinto was one of them...

Generators typically have them. The Perkins 108 in my Wanderlodge has both a high temperature and low oil pressure automatic shut off.

As a truly failsafe system, it'd be designed to pull a vacuum on the shut-off when low pressure activated it but then it would need to be disabled during starting.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I will be having a custom turbo oil supply line made for my new turbo, I will see about having an extra T for an oil pressure sender added.

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

It was nice that you assumed that we might be able to design and execute an oil level sender.... high praise...

What about just modifying one of the ones like the SDL uses and drilling/tapping it into the side of the oil pan? Are the pans shaped similarly enough to provide a good place to measure?

I mean, we were ready to risk the car shutting itself down to save itself on a busy interstate, so surely the possibility of a hole in the oil pan starting to leak/pour won't scare anybody... after all, the sensor will tell you if the installation of the sensor failed

EDIT: we replaced my oil pan six months ago and I don't remember the specifics of the sender. But... it's a thought.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Sorry if I'm gonna confuse things
So I really like the concept we are talking about. We are trying to prevent a low oil pressure situation and this is sortta related:
There are a few guys selling 'pre-lube kits out there. The idea being that you can electrically pump up your oil pressure before you start the engine.
Here are two I've found there are I am sure lots more:
http://www.prelube.com/
http://www.varnaproducts.com/EPPump.php
One of those has a built in oil changer option... cool.
What I would like to see is an inexpensive little electric oil pump that will kick in at say1 or 2 bar (be nice if I could adjust that) ANYTIME the pressure drops.
-it would kick in when you are about to start.
-it would kick in when your very worn engine is pretty darn hot and you are at a red light and the pressure drops below...whatever and help keep your bottom end together for a few more miles.
-and I hadn't thought of the built in tap for changing my oil but put it on the list too.
Perhaps a light when it runs and a buzzer to warn of oil pressure below that..
Comments?

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

Alberta, This has been discussed a lot in the archives... I am all for it... but plumbing routing in our engines is not easy to figure and execute.