Low oil pressure alarm for 617.952 - PeachParts Mercedes-Benz Forum

Diesel911 · #1 02-22-2008, 12:57 AM

Not a new idea but this is the way I did mine.
My instalation of a low oil pressure alarm
Tools needed: 1/8 inch pipe tap. 7/16 drill bit, 1 oil pressure sensor (for the “idiot light“ dash type low oil pressure warning light) I got from the junk yard off of a Chevy Monte Carlo of unknown year, about 4 feet of thin wire (I used telephone wire like you would use inside your house for a phone extension wire),and 12VDC Single Tone Pieso Buzzer 3-28VDC 5mA buzzer from Radio Shack part #273-060 cost less than $5. 1 female spade connector and some double stick foam tape.
I removed the top cover from my oil filter and drilled a 7/16 hole between the cast reinforcing webs (located on the inside of the cover). I used the 1/8 inch pipe tap and threaded the hole from the out side of the cap. Cleaned it off with brake cleaner and re-installed in on the oil filter housing.
Put pipe tape on the threads of the oil pressure sending unit and screwed in into the oil filter top cover (do not tighten too much as the you could split the cover and if it leaks a little it is easy to tighten more later).
I needed a source of positive 12V that would only be on after the engine was started and turn off when the engine is turned off. I decided to tap into the + Heater Monovalve connector with the red wire. I attached the female spade connector to the black wire and slide it over the oil pressure sending unit spade connector (it is grounded through the oil filter/engine block).

I found an open hole in the fire wall rubber grommet over by the Power Brake Booster to run the wire through. And connected the black wire to the black Buzzer wire and the red wire to the red Buzzer wire.
I put some double stick foam tape on the back of the Buzzer and stuck it on the upper frame of the parking brake.
It works fine.

Carson357 · #2 02-22-2008, 01:16 AM

why? do you have issues with low oil pressure? no offense meant, but it looks really bad. just my opinion, no disrespect intended.

pawoSD · #3 02-22-2008, 01:25 AM

The idea is so that if a line blew or the engine puked its oil and lost pressure, or if the oil pump dies.....you would know right away from the buzzer going off instead of just a light or watching the gauge all the time. This simple little setup could be the deciding factor if your engine lives in the event of oil pressure loss. It doesn't look bad, you can't even see that its there!

Clever place to mount the sensor, though it makes removing the cover more annoying as you have to unplug wires.

Good write-up!

Edit: BIG flaw in the choice for 12V power. The monovalve wire has 0 volts on it when the heat is on, and it switches on and off rapidly to maintain temperature. The only time it has constant 12V is when the climate control is set to cool the air. I'd find another 12V source. Such as the cig-outlet circuit. Also, adding power draw to the climate control is not a good idea either....

#4 02-22-2008, 01:38 AM

Overboost protection circuit. The valve has a constant +12V to the valve when the key is on.

Diesel911 · #5 02-22-2008, 01:46 AM

Quote:

Originally Posted by pawoSD

The idea is so that if a line blew or the engine puked its oil and lost pressure, or if the oil pump dies.....you would know right away from the buzzer going off instead of just a light or watching the gauge all the time. This simple little setup could be the deciding factor if your engine lives in the event of oil pressure loss. It doesn't look bad, you can't even see that its there!

Clever place to mount the sensor, though it makes removing the cover more annoying as you have to unplug wires.

Good write-up!

Edit: BIG flaw in the choice for 12V power. The monovalve wire has 0 volts on it when the heat is on, and it switches on and off rapidly to maintain temperature. The only time it has constant 12V is when the climate control is set to cool the air. I'd find another 12V source. Such as the cig-outlet circuit. Also, adding power draw to the climate control is not a good idea either....

I will check that out. May be something is not right with my monovalve system as I did not have the heat on and I get electricity there when the engine is on. But to be sure I will look for a better place to put the + wire.
Thanks for the tip.
Right now as soon as you turn the key the buzzer sounds until the engine starts until the oil pressure shuts it off. It is noisy sitting there through the glow plug cycle also. Is there some place where I can tap into to get + current when the key is in the run position that will not cause it to buzz during the pre-glow cycle.
If not I am thinking to put in a push button disconnect switch that I can hold down durnig the glow plug cycle so there will be no noise.
I am later want to add a high temp sensor wired to the same buzzer but that is a project for another time.

Diesel911 · #6 02-22-2008, 01:49 AM

Quote:

Originally Posted by ForcedInduction

Overboost protection circuit. The valve has a constant +12V to the valve when the key is on.

Thanks alot I will check that out!

Carson357 · #7 02-22-2008, 01:50 AM

possibly re think the location of the sensor, and route the wires a bit differently, would be nice if you could create something to have entire unit behind cluster,

Diesel911 · #8 02-22-2008, 01:57 AM

Quote:

Originally Posted by Carson357

why? do you have issues with low oil pressure? no offense meant, but it looks really bad. just my opinion, no disrespect intended.

Not a problem I do not agree with all the threads and posts I have seen either. There are better alarm systems available (often for marine use) but they cost alot.
I look at my instruments some times but I bet my Wife seldom looks at them (and it is her car). If she hears the alarm she might do the right thing and get the car off the road and shut it down.

#9 02-22-2008, 02:04 AM

Quote:

Originally Posted by Diesel911

Is there some place where I can tap into to get + current when the key is in the run position that will not cause it to buzz during the pre-glow cycle.
If not I am thinking to put in a push button disconnect switch that I can hold down durnig the glow plug cycle so there will be no noise.

Use a normally closed relay that is wired to break the circuit (energize) when there is voltage in the glowplug circuit.

Dusty-NZ · #10 09-18-2008, 04:32 AM

This is a really old thread , but I wanted to post my experience .

My '72 220D had a fairly fresh engine (20k) I left home one morning , got straight onto the open road we live on , drove up to 80kmph , that took maybe a minute and a half, I looked at the dash to spot the oil gage dropping the pressure right off.
I IMMEDIATELY took it out of gear , and the engine stopped dead>

After the inevitable engine dismantle , it was discovered that the oil pump drive was sheared off.
In the time it took me to notice (seconds) and react, the #1 rod welded itself to the crank journal .

STUFFED it completely. cost $2400 to repair the engine.

I just mentioned this 'cause the fact that I saw the oil pressure gage drop was a fluke , an alarm MIGHT have saved my engine , maybe , it all happened so fast.

I think the ounce of prevention offered by the original poster is a reasonable addition if you could stand the darn buzzer at startup time.

kerry · #11 09-18-2008, 09:10 AM

Barry was working on a kit for a low oil pressure alarm. I wonder what happened with that?

thedjjack · #12 05-18-2009, 03:42 AM

Old thread but now linked to a newer thread...

here is my 2 cents...why not add a t-fitting off the back of the oil filter where the gauge comes off for the alarm? (I have an aftermarket oil pressure gauge as I have the OM617 engine in my Jeep) Saves taping, proper seal, neater, do not have to take out with filter changes.

Cheers

#13 05-18-2009, 07:26 AM

I'd probably drill the turbo's banjo fitting instead.

funola · #14 05-18-2009, 08:03 AM

Why not have the low oil pressure alarm automatically shut the engine off upon low oil pressure?

pawoSD · #15 05-18-2009, 10:09 AM

Quote:

Originally Posted by funola

Why not have the low oil pressure alarm automatically shut the engine off upon low oil pressure?

That would add a whole new level of complexity because the car shutoff is mechanical/vacuum and the sensor system would be electronic....so it would have to trigger a mechanical vacuum switch or something.

Its possible, but more complicated.