Low oil pressure alarm. - Page 11 - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 06-27-2010, 07:22 PM

Quote:

Originally Posted by Diesel911

I can only speak in general that the Gauges that come on regular cars from the Factory are not as accurate as add on Gauges or when you connect up a test Gauge. . .

Agreed. I just completed testing both the electric oil pressure sender and the gauge on my '87. The sender (relatively new - installed a year or so ago) measured resistance values close to what the FSM said it should for various pressures, using my Fluke 8800 DVM.

The oil pressure gauge (meter movement), however, (originally out of an '88 gasser -- I wanted the vacuum gauge) reads about 1 bar high across most of its range, based on a comparison with my new VDO mechanical gauge. This is confirmed with the VW oil pressure switch, which switches at 1.4 bar when the electric gauge reads about 2.5 bar.

All of this assumes that my Fluke and VDO are accurate, of course, but you've got to start somewhere. Even the possibility that the gauge reads high makes me want to have something else watching the oil pressure.

The alarm design is pretty much done. I want to have a working version in my car before publishing it to the forum. It uses three parts from Radio Shack and the VW switch. Total cost about $15.

I'm also working on a coolant high-temperature alarm that will use only two components at a cost of about $3. Sixto, among others, feels that it's even more important than a low oil pressure alarm, at least for the 603 engine.

Jeremy

samboyellowsub · #2 06-30-2010, 12:02 AM

has anyone tried wiring the low oil pressure alarm up to the factory buzzer that is behind the dash? it seams like it could be easier than installing a new one from Radioshack (that would probably be made in china). Any thoughts on this?

Jeremy5848 · #3 06-30-2010, 02:46 AM

Quote:

Originally Posted by samboyellowsub

has anyone tried wiring the low oil pressure alarm up to the factory buzzer that is behind the dash? it seams like it could be easier than installing a new one from Radioshack (that would probably be made in china). Any thoughts on this?

An interesting idea but the people who flew Apollo 13 would not agree with you. Having one alarm for several functions leaves you wondering which problem is being announced. It also leaves you with the risk of having the alarm on for one problem and then another problem occurs. You don't know about the second problem because it is trying to use a buzzer that's already buzzing. Better to have a separate alarm or at least have an alarm buzzer coupled with a set of lights to tell you which problem is causing the alarm.

In any case, the alarms that I am about to publish here use bright flashing LEDs; they should be bright enough even in daylight, especially as they blink about 2X per second, that you shouldn't miss them. A buzzer can be added but I'm trying initially to keep the circuit as simple as possible for the non-electronic types in the forum.

The factory buzzer behind the instrument cluster already has several functions (key in ignition, lights left on, seat belt). Although anything is possible, it would be a complicated job to add another function. If you really have to use a Mercedes part, get a spare "N2/4 Warning Module" from a junkyard car and use its buzzer.

Jeremy

samboyellowsub · #4 06-30-2010, 09:04 AM

if after hooking an alarm up to the factory buzzer, I just can't imagine riding down the highway, hearing the alarm, and thinking, "oh crap! did my seat belt come undone or did my oil cooler hose break!?!" What I'd probably do actually, is use the terminal for the seat belt alarm! I really don't need a machine to tell me my seat belt is on or off.

is that warning module another buzzer from a mercedes? the same part that I'm talking about, maybe?

Jeremy5848 · #5 07-04-2010, 10:49 PM

I've just posted the design of my low oil pressure alarm here.

jbaj007 · #6 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.

heat gauage 300sd)

Post #7

Jeremy5848 · #7 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.

ah-kay · #8 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 · #9 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 · #10 03-15-2013, 03:55 AM

for new members

barry12345 · #11 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 · #12 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.

Jeremy5848 · #13 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 · #14 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 · #15 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.