Oil Pressure Warning Alarm - Page 2 - PeachParts Mercedes-Benz Forum

compress ignite · #16 07-31-2012, 03:40 PM

Easy marker for self(Future)

Thanks!

oldiesel · #17 07-31-2012, 10:26 PM

Cat p/n is 7N5946 the switch has both NO & NC terminals, 1/8 npt thread.
I have used these in my boat for over 20yrs the engine never drops below 35psi at idle and the generator never idles so they work fine in that application.
Im pleased to see that just as i thought we have people in this group smart enough to solve the below 25psi idle problem and hopefully some one will come up with a good solution that most of us can DIY.

Jeremy5848 · #18 08-01-2012, 01:19 AM

Quote:

Originally Posted by oldiesel

Cat p/n is 7N5946 the switch has both NO & NC terminals, 1/8 npt thread.
I have used these in my boat for over 20yrs the engine never drops below 35psi at idle and the generator never idles so they work fine in that application.
Im pleased to see that just as i thought we have people in this group smart enough to solve the below 25psi idle problem and hopefully some one will come up with a good solution that most of us can DIY.

Price:
Vendor #1 $66.84
Vendor #2 $64.00
Vendor #3 $34.52 tracparts.com "Caterpillar Aftermarket Replacement Parts"

7N5946 Switch
Circuit 1 normally closed
Circuit 2 normally open
With an increase in pressure, circuit 1 opens
and circuit 2 closes at ................... 145 kPa (21 psi) max.
With a decrease in pressure, circuit 2 opens
and circuit 1 closes at ................ 75 + 20 kPa (11 ± 3 psi)

That sounds like exactly what we need!

Jeremy

gsxr · #19 08-01-2012, 11:54 AM

Just curious. Has anyone ever seen an issue where there was a sudden reduction in oil pressure at speed, but where the pressure still remained above ~1 bar? I'm thinking that all the hand-wringing about having extra protection above idle pressures might be kinda useless. All I care about is if the oil pressure goes below ~0.3 bar when the engine is running.

How does the W140 low oil pressure light work?

kerry · #20 08-01-2012, 12:10 PM

I haven't seen any data on how long a person has to react once the oil pressure drops before engine damage occurs. If it's a catastrophic failure like a broken cooler line or a failed oil pump chain and you're driving 80mph, it seems even a short hesitation in shutting down the engine wont stop engine damage. Any opinions out there? Seems to me like 5 seconds is a long time without oil if the engine is turning 3k.

gsxr · #21 08-01-2012, 12:25 PM

Quote:

Originally Posted by kerry

I haven't seen any data on how long a person has to react once the oil pressure drops before engine damage occurs. If it's a catastrophic failure like a broken cooler line or a failed oil pump chain and you're driving 80mph, it seems even a short hesitation in shutting down the engine wont stop engine damage. Any opinions out there? Seems to me like 5 seconds is a long time without oil if the engine is turning 3k.

Which is another reason I prefer Group V (ester) synthetics like Red Line for the "clinging" properties of the oil... might provide a few more seconds of protection, which could be all that's needed to prevent a motor from becoming a doorstop!

Jeremy5848 · #22 08-01-2012, 01:23 PM

Dave may have a point - we are primarily guarding against catastrophic oil pressure failures, the kind that result from a mechanical failure that either dumps all the oil on the road or disables the oil pump so that there is oil but no pressure. (Note that the first failure should illuminate the 'low oil' warning light while the engine still has good oil pressure; this happened to me once when I left the oil cap off of the engine.)

In either case, pressure could quickly drop to near-zero so an alarm at, say 3000 RPM and 1.5 bar really won't do much good -- you might gain a second or two at most, maybe not even that. OTOH, an alarm at 1.0 bar will be just as helpful at highway speed while in most engines not becoming a nuisance at idle.

My '87 300D would blink the alarm LED once or twice on a hot day when the engine came down from 3000 RPM to idle (perhaps due to a lag in the operation of the ELR circuit) but the '95 E300 with the same alarm has never done that. Both engines idle at about 20 psi as shown by the same VDO mechanical oil pressure gauge.

So maybe we should apply the KISS method here and not try to invent something requiring a 47-inch LCD-flatscreen-1070dpi TrueColor® TV set.

Jeremy

funola · #23 08-01-2012, 01:34 PM

I think it should not be too difficult to get a signal out from the tach to logically control the oil pressure alarm.

in addition to the oil pressure alarm I think an oil level alarm is also needed. any ideas for an add on oil level sensor?

Keep up the good work.

gsxr · #24 08-01-2012, 01:35 PM

Quote:

Originally Posted by funola

I think it should not be too difficult to get a signal out from the tach to logically control the oil pressure alarm.

in addition to the oil pressure alarm I think an oil level alarm is also needed. any ideas for an add on oil level sensor?

W124's already have an oil level sensor from the factory, complete with timing circuitry. No need to mess with the OE setup, it works quite well.

funola · #25 08-01-2012, 01:42 PM

Quote:

Originally Posted by gsxr

W124's already have an oil level sensor from the factory, complete with timing circuitry. No need to mess with the OE setup, it works quite well.

I was not aware w124 have oil level sensors. I was talking about w123 which is more common. can the w124 oil level sensor be easily adapted to the w123?

gsxr · #26 08-01-2012, 01:47 PM

Quote:

Originally Posted by funola

I was not aware w124 have oil level sensors. I was talking about w123 which is more common. can the w124 oil level sensor be easily adapted to the w123?

More specifically... the OM60x diesels and M102/M103/M104/M119/M120 engines all have oil level sensors. They are built into the oil pan and no, it would not be easy to retrofit into an older engine. The sender is located on the left side of the engine and when turning left, the contacts close. The factory setup has a 60-second timer built into the instrument cluster, so the dash light doesn't go on until the sender has been sensing low oil for 1 minute. This prevents nuisance flickering during cornering. Otherwise, the sensor works pretty well, and on most engines will turn the dash light on when the level is at the "MIN" mark on the dipstick. But it's no help to save a motor from sudden oil loss - still need the pressure warning for that.

funola · #27 08-01-2012, 01:58 PM

Quote:

Originally Posted by gsxr

More specifically... the OM60x diesels and M102/M103/M104/M119/M120 engines all have oil level sensors. They are built into the oil pan and no, it would not be easy to retrofit into an older engine. The sender is located on the left side of the engine and when turning left, the contacts close. The factory setup has a 60-second timer built into the instrument cluster, so the dash light doesn't go on until the sender has been sensing low oil for 1 minute. This prevents nuisance flickering during cornering. Otherwise, the sensor works pretty well, and on most engines will turn the dash light on when the level is at the "MIN" mark on the dipstick. But it's no help to save a motor from sudden oil loss - still need the pressure warning for that.

thanks for the w124 description. I think an oil level sensor to let you know before you lose all of your oil is a good thing to have. for the w123, maybe an oil level sensor via the dipstick tube is easiest spot to add one?

I agree to KISS. I would prefer a loud buzzer and a flashing red light over a fancy LCD display.

oldiesel · #28 08-01-2012, 02:24 PM

I am disapointed to see that circuit 1 closes on dropping pressure at 11psi,i never looked up the specs as it is printed 25psi on the body of the switch. My thinking of course was that if the warning came on at 24psi that gave an extra second or two to get it shut down.
Yep Cat parts are all a bit on the high dollar side but generally they are of good quality.

sixto · #29 08-01-2012, 02:27 PM

While we're splitting hairs, how about wiring the low pressure sensor to the overboost solenoid to reduce engine power? Won't work on post-91's and ALDA-less engines. Another option is to fit a pre-oiler system to buy more time but that's too easy. Going further off-track, I read about a late model Ford or GM Diesel that incrementally reduced top speed when the urea tank ran dry. At some point it was limited to 35 mph which forced the reviewer to fill the tank... which wasn't empty! It had a faulty level sensor.

Sixto
87 300D^2

Jeremy5848 · #30 08-01-2012, 02:33 PM

I'll rewrite and post my circuit, which should be adaptable to any engine that has an available oil pressure line or tapped access point. Easy to DIY, three parts are required (minimum). Also, the VW oil pressure sensor is available in a number of flavors and one could even adapt the VW diesel alarm circuit although that is straying from the KISS principle.

Jeremy