Low oil pressure alarm. - Page 14 - PeachParts Mercedes-Benz Forum

jbaj007 · #**196** 07-05-2010, 04:54 PM

Here's an old, old post on my system. May give some ideas. Seems like there are a lot of better thoughts here now. Back then it was "innovative" (like 8-track stereo

) Still working well, though.

http://www.peachparts.com/shopforum/showthread.php?t=55188&highlight=low+oil+pressure+switch)

Post #7

Jeremy5848 · #**197** 07-05-2010, 10:14 PM

Quote:

Originally Posted by jbaj007

Here's an old, old post on my system. May give some ideas. Seems like there are a lot of better thoughts here now. Back then it was "innovative" (like 8-track stereo

) Still working well, though.
Post #7

I tried this on my 124 but access is difficult and I'm not sure the added hardware would clear the chassis under all conditions. Good to hear your invention is still working. It would be preferable for those who don't want anything to show from the top of the engine bay. That's the one objection to tapping into the oil filter cover.

whunter · #**198** 01-03-2013, 08:27 AM

I used an ice cube relay and spare horn.
Be careful where you mount the horn or it will blast your ears.

.

ah-kay · #**199** 01-03-2013, 11:48 AM

1) Where is the oil pressure switch for the 60x and 61x engine which gives a contact closure for no/low oil pressure. 61x engine is non electrical, I think.
2) Would it sound during start up? It would during start up and shut off, right.
3) I am also thinking about adding in a vacuum relay to tie in with the shut off valve to cut off the engine fuel supply. If I do this then I need to delay the activation during start up.

Any info is appreciated.

Jeremy5848 · #**200** 01-03-2013, 07:43 PM

Quote:

Originally Posted by ah-kay

1) Where is the oil pressure switch for the 60x and 61x engine which gives a contact closure for no/low oil pressure. 61x engine is non electrical, I think.
2) Would it sound during start up? It would during start up and shut off, right.
3) I am also thinking about adding in a vacuum relay to tie in with the shut off valve to cut off the engine fuel supply. If I do this then I need to delay the activation during start up.

Any info is appreciated.

My low oil pressure alarm is a blinking red LED, not a horn or buzzer. It's easily visible in daylight and impossible to ignore at night. It blinks when the ignition is turned on and the engine started, then stops blinking when the oil pressure comes up. That means the alarm does a self-test every time you start the engine (wouldn't want to do that with a horn).

Neither 60x or 61x engines have a low oil pressure switch -- you have to add your own. I recommend one from a VW diesel -- same thread as the Mercedes sender and you can get one that trips at about 1.0 bar (15 PSI). That's high enough that the engine will still be OK, giving you a second or more to get the engine shut down safely. (A 5 PSI switch is too low, you want to be informed sooner.) The LED may blink a couple of times when the engine returns to idle after being driven and the oil is hot. Any foreign car parts place will have the VW switch, it's part #068919081A when I bought mine, also part #P4030-28194 in other catalogs, about US$10 to 25 depending on the source.

In the diagram above, the two resistors are about 300 Ohms each (value is not critical). I used two 1 Watt resistors to handle the current and not get hot. The LED draws very little but the wiring diagram I used is a for a switch that closes when there is oil pressure -- that's what the VWs use. The LED blinks (it's from Radio Shack, #276-312) until the oil pressure comes up, then the switch shorts out the LED and it stops blinking. The resistors continue to draw a little current, that's normal. You can also use a relay but this is simpler.

The switch can be mounted in place of the sender (at the base of the oil filter canister) but then your oil pressure gauge won't work. I drilled and tapped a hole in the oil filter cover for my switch.

The alarm LED was installed in the instrument cluster.

Jeremy

whunter · #**201** 03-15-2013, 03:55 AM

for new members

barry12345 · #**202** 03-15-2013, 11:11 AM

It cannot get much cheaper than the led setup in the later post. Especially if you gather up an oil presure switch from a volkswagon wreck. I wonder if the gentleman might mention how he handled his coolant overheating indicator as well.

The oil pressure gauge is just not good enough as it is imposible to observe it continually. You want to know almost instantly when the oil pressure sags on 123s anyways. A minute later is probably almost a minute too long.

We have a case here where an engine saved on occasion has got to be worth a couple of dollars and some time. The horn system can be economical as posted by Hunter as well.

Although I found a slight delay getting by a very loud horn type blast in a car with an audiable system. I nearly left my seat I remember but at the same time you could not miss it.

Blinking leds may be available in different wattages as well. Perhaps the brighter the better within reason. Anyways that installation of the leds near the cluster gauges almost looks factory.

The option and it is not really nearly as adaquate is to keep your oil lines in decent condition. I think why almost all oil line failures occur on the highway is simply that is when the circulation thermostat is open for the oil cooler.

A combination of good oil hoses with some form of low oil pressure warning device better than just the oil pressure gauge is almost mandatory. Cheap decent replacement engines may soon become harder to find. Plus who really wants to landup changing an engine because the hoses are neglected and spending a few dollars on a warning system could have prevented it.

There have been enough people lose their engines this way. That it is not an over reaction to do something that lessens the chance of you becoming another one of them.

Jeremy5848 · #**203** 03-15-2013, 11:32 AM

Here's an additional note on the oil pressure switch.

Mercedes and VW use senders with 10x1mm threads. If you drill and tap a 10x1mm hole in the oil filter cover, you will find that the switch does not bottom out correctly because the cover is not completely flat -- the first picture in my post above shows this. Use multiple copper o-rings to allow a little stand-off.

Another option is to use a 1/8-27 NPT tap (taper pipe thread). This size is close to 10x1mm metric but not exact, so the threads of the oil pressure switch will jam in the hole part way and the switch body won't hit the cover. Don't run the tap all the way into the cover or the fit will be too loose. Tap a few threads, then stop and try the switch for fit. Tap deeper only if necessary. Use Teflon tape on the threads to prevent leaking.

Jeremy

Jeremy5848 · #**204** 03-15-2013, 11:51 AM

The coolant over-temp indicator is even easier. It uses the existing switch that turns on the auxiliary electric fan in high speed. (Low speed is usually triggered by the a/c system.) This high-speed switch is in different places in different engines and the trigger point depends on the switch. Most trigger around 105°C. At this point the coolant is getting pretty hot but it's not yet a disaster. I used a yellow flashing LED to tell me that the aux fan had come on (you can't always hear it) and that it was time for me to pay attention to the temperature gauge.

Notes:
(1) The LED may start to blink even though the gauge doesn't show 105°C. This is because the gauge and its sender won't be perfectly calibrated with the switch.
(2) If your car always runs over 105°C you may find this alarm to be an annoyance. OTOH, maybe you have a cooling problem.

In the schematic diagram below, the reference (6) for +12 Volts is for pin 6 of the 15-pin round connector on the instrument cluster in a 1987 300D Turbo. Some cars may use different pins, please make sure which pin is "hot" in your car.

Jeremy

Quote:

Originally Posted by barry12345

I wonder if the gentleman might mention how he handled his coolant overheating indicator as well.

funola · #**205** 03-15-2013, 12:12 PM

Jeremy5848, how would you compare your oil pressure alarm to the VW factory dynamic oil pressure alarm? This is a timely subject since I just pulled the oil pressure alarm board from a VW cluster. Is it worthwhile to try and integrate it into my 300DT or just use your design? To use the VW board, I'd need:

- add 2 pressure switches
- bring out the W terminal from the alternator
- trace out the board connections and wire it up

It may not even work depending if the board gets the W signal directly from the alternator or from the tach.

Jeremy5848 · #**206** 03-15-2013, 12:56 PM

I'm not familiar with the VW design although I've read about it. It's actually quite sophisticated and looks at engine RPM as well as oil pressure. To make the VW design work you'd need to get it to accept the Mercedes tach signal and modify the RPM limits as necessary. Not easy but possible. Let us know if you make it work and in the meantime, try my design.

Jeremy

Orv · #**207** 03-15-2013, 02:05 PM

I'd note, based on my experience with the VW system, that the alert doesn't have to be particularly loud...it just has to be different from any other sound the car makes. VW's system just silently flashes the oil light when the pressure is low at idle, and other conditions (e.g., key in, door open) make a beeping sound, but the high-RPM oil pressure alert is a raspy sounding buzzer. It's instantly attention-grabbing because it's a "new" sound in the in-car environment.

For the Mercedes, given the headlight warning buzzer sound as a "normal" part of the environment, I'd suggest a piezo buzzer...the high-pitched, pure-tone "EEEEE" will stand out from the car's normal noises.

funola · #**208** 03-15-2013, 02:37 PM

Quote:

Originally Posted by Orv

I'd note, based on my experience with the VW system, that the alert doesn't have to be particularly loud...it just has to be different from any other sound the car makes. VW's system just silently flashes the oil light when the pressure is low at idle, and other conditions (e.g., key in, door open) make a beeping sound, but the high-RPM oil pressure alert is a raspy sounding buzzer. It's instantly attention-grabbing because it's a "new" sound in the in-car environment.

For the Mercedes, given the headlight warning buzzer sound as a "normal" part of the environment, I'd suggest a piezo buzzer...the high-pitched, pure-tone "EEEEE" will stand out from the car's normal noises.

That raspy buzzer is a mechanical buzzer, the relay looking thing the pic- 1930's technology lol. It was not very loud when I tested it at idle. I would want something louder.

Orv · #**209** 03-15-2013, 02:42 PM

BTW, tapping the oil filter cover is genius -- wouldn't have thought of that. I wonder if this'd also be a good place for an oil temp sensor? VWs used to put them in the oil filter mount.

Orv · #**210** 03-15-2013, 02:44 PM

Quote:

Originally Posted by funola

That raspy buzzer is a mechanical buzzer, the relay looking thing the pic- 1930's technology lol. It was not very loud when I tested it at idle. I would want something louder.

Wouldn't hurt, although it DEFINITELY grabbed my attention when my VW blew an oil cooler O-ring at 45 mph.