I just got an 81 300sd and I was wondering if there is any kind of aftermarket low oil pressure light or buzzer I can put in it? My dad toasted his sd after he broke oil line and now I'm all paranoid about it. I spend half my time driving looking at my oil pressure.

You should be able to pull off the electric oil pressure sensor and replace it with a T-fitting so you can also attach a warning light sensor from something like a VW Diesel. There are a couple of blank warning light positions in an SD gauge cluster. Hook up an audible warning as well.

Sixto
87 300SDL

It shouldn't be that hard if you don't mind cutting a hole somewhere for a warning light.
I'm sure newer MB's have low oil pressure indicators, and the sender for one of those could likely be used, or else one from most any other manufacturer. You would just need a brass 'T' fitting to put inbetween the factory line for the pressure gauge and the block. Finding fittings with the correct threading will be the only difficulty here. Also, ensure that the fittings will be able to seal with the factory ports.
Once the low pressure sender is in, all the ones I have seen work very simply. They just use a single terminal and serve as a switched ground for a wire from the warning light, so you supply +12V to the light, and run the other wire for the light to the sender. When oil pressure falls, the sender will ground the wire, and complete the circuit.

edit: I wouldn't use an audible warning - it would also be on whenever the key is in the run position but the engine is off. Like when you are preglowing, or waiting in the car and listening to the radio. Could be really annoying.

__________________
1971 220D/4-speed ~250K mi. Family owned (dads side) through three generations since <5K miles.
1992 Chrysler LeBaron, 3.0V6 125K. Family owned (moms side) through three generations since new.
1977 Chevy Camaro Continual hotrod project
1970 Cadillac Sedan DeVille 472ci and nearly 19' long
1974 Fiat Spider Still needs work

thanks, I'll hit the junkyard tomorrow to try to find that vw part

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.
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__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

thanks for the help, I'll go hunt down those fittings.

jbaj, does it buzz while you're waiting for the glow light to go out as the author expected?

Sixto
87 300SDL

Late reply, sorry.

Yes, it buzzes quite annoyingly at glow time, or any time oil pressure isn't up.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Oil cooler lines don't just blow, they leak for a very long time before they actually give way. If you just inspected them once in awhile and changed them when you see them starting to leak you won't have a problem.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

the line itself did not break or leak, it was apperantly shook loose from the metal fitting.

__________________
"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

http://www.wecrash.com/pics/ddda_banner.gif

Perhaps bad motor mounts resulting in excessive vibrations transmitted to the car that caused it?

__________________
1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

The mounts weren't too bad, but I think a previous owner might have cheaped out and had a hydraulic shop make him a new line with the same fittings instead of buying the OEM lines.

__________________
"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

http://www.wecrash.com/pics/ddda_banner.gif

Oh... that's bad. Indeed, the OEM lines aren't very cheap, but I guess people shouldn't expect parts from a Benz to be cheap as these weren't cheap cars when new. I too share your fear/concern for toasting my engine and would also like to see if I can get a low oil pressure warning of some sort.

__________________
1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver

Yeah well if fixed properly the oil cooler lines should never blow. Neglect them or cheap out and well, roll the dice.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200