Audible low oil pressure warning?
 

I'm finally getting around to hard wiring my low oil pressure sensor. I was going to just tap an existing warning light on my factory SPF dash (i.e. bad alternator), as I wasn't really wanting to start drilling holes into it.

Then I thought about the location of that particular light and how my left hand typically blocks it when I have it at the 9-10 o-clock position on the wheel. I also started to question why I would want a light to get my attention, especially if in the middle of a bright afternoon when it sometimes requires a squint to see the needles on the gauges? A loud SOUND would be better.

So I'm going to go with an audible warning instead. Found some 12v piezo buzzers at Radio Shack, one being a high-low siren that pumps out over 102db. I figure that even at WOT I should be able to hear that.

Mounting will also be custom, as I'm going to affix an on/off toggle ahead of the power connection and mount it so that you have to barely reach under the lower edge of the dash to flick it. That way when I'm at the local drive-in, Cars & Coffee meets or gas station and start it up to leave, I won't have this glaring siren going off. Once the car gets above 20psi, then flick the switch and the low oil pressure warning system is "armed."

Thoughts before I begin?

-Dean

Make it more automatic. Some sort of time delay before it turns itself on. Therefore eliminating the need for a switch. My two cents.

I'd go with something automatic, as you're going to scare the pi$$ out of yourself a hundred times when you forget to manually disarm the thing. I put one version of a delay/latch circuit in my gallery; if there's interest I can work it out more thoroughly so that anyone can build a copy.

Good idea. I'll look into that.

Thanks,

-Dean

Yeah, how does one source something like this off-the-shelf? I see a lot of delay switches for commercial apps but not a whole lot for 12v automotive apps. The toggle and siren have me set back all of $11-12. What will this cost me to "switch" (pun intended) to full auto?

-Dean

It's about $10 worth of parts. They can be assembled as a block unit with no PC board - I'd encapsulate the assembly in a small tube with something like RTV, with three wires coming out (in, out, ground).

I don't know of any off-the-shelf equivalent. I just sketch and build stuff myself. :)

I used to help a guy with a Can Am car. He had very low mounted SBC in a Gurney Eagle chassis that had very high compression with mechanical fuel injection and used a starter on a shaft with a couple of U- Joints, it was a very unusual setup. It would infrequently resist starting and break the U joints. We finally put a small pushbutton switch that killed (grounded) the primary side of the ignition until the engine cranking speed was relatively high and had oil pressure at which time the button was released, ignition activated and the engine would take off without damaging the starter shaft and U joints. Problem solved.
You could do the same with a pressure swith AND a pushbutton, if the pressure dropped below a predetermined point while running it would stop, or it would have no ignition until the switch was released while cranking.

It sounds like you are setting yours up just like I did mine. I have the switch just under the dash so when I work on the car with the key on I can shut the buzzer off. I used a delay on make timer from Amperite 12D2-20SST1A. It was about $30 and I had them throw in three resistors that were a dollar each for an option of a 2, 3 or 4 second delay. The resistors were .25 watt, 100K, 150K and 200K. So normally when I get in and start it I will not hear the buzzer. The resistor just plugs between two terminals on the timer to change the delay. I have the 2 second resistor in now. You can add an adjustable resistor if you want.

I have a regular oil sender for my gauge and also an idiot light sender that grounds with less than I believe 8 lbs. of pressure. I also added an oil warning red light. I put it next to the oil gauge. It just uses the Acc. power with the key on and ties to the same wire that goes to the sender for ground.
Gunner is right you can do it cheaper if you build your own timer, but it wasn't worth it for me. To much other work to do and not enough experience with that.

Wayne

Low Oil Pressure Buzzer and Delay Timer
 

Dean,
mmmmmmmm. if you have access to a db meter you might want to check your actual cockpit sound pressure level at WOT. I expect it may be well over 110dbc. Depends somewhat on what sidepipes you have on your car as well.
I think you may well find a 102 db warning buzzer is completely obscured when you're standing on the throttle.

I would tend to think that an automated motor shutdown device with low oil pressure signal would be more of a fail-safe device than a simple buzzer. It would automatically shutting down the engine thus minimizing internal damage.

I think I've opened up a can of worms. :LOL:

ANY warning device is sort of like using a radar detector. For instant-on and some lazer, you are pretty much toast the moment you hear a tone.

An auto-shut down (as Blas is suggesting) is great if you can discern that it was low oil pressure that triggered the event and not a short circuit to the ignition (been there, done that...flat bed tow home just to learn I had a loose ground wire on my MSD box). I still grade myself as "suck" when it comes down to electrical trouble-shooting (but I can hang with spinning a wrench with most of you).

I'm trying to keep this simple. The toggle switch method with a $6 buzzer is K.I.S.S, light weight and easy to mount/hide. Adding a on-delay relay adds some minor costs and is more a task of just sourcing the right component (Would Fry's carry something like the Amperite 12D2-20SST1A that was suggested?). I can also handle a soldering gun and planned to do that with all connectors anyway. Auto-shutdown would involve wiring some sort of ignition kill device and that's out of my comfort zone. And I don't outsource most of my work...I'm a lean Cobra owner. :D

I do have quick access to a local Radio Shack and weekend access to either Fry's or another really good local place in Fullerton that is an electrical supply house called Orvac's. So those that "build" these things, please school me on what I need to acquire. It's becoming a good winter project while we get more waves of rain. :CRY:

Thanks,

-Dean

That's eactly what I was thinking. It's a time proven system too.

We keep having this conversation. I think the next line in the script is to point out that any sudden cutoff of the engine is likely to startle the driver, and if it's a time when an oil pressure failure would be most catastrophic, it's likely at a time the mill is wound up pretty tight and thus the driver may not WANT to be distracted.

Such systems can also fail - meaning a sudden cutoff when it's completely unexpected. Automatic cutoffs are more for stationary motors (like generators) and marine use (where the loss of go-power is not so immediately distracting or likely to cause loss of control).

Cutting off the engine also doesn't stop its rotation if the clutch is still engaged, so it's likely to spin quite a few more revs before the driver can react.

I cast a permanent vote for a warning intended to get the driver to react as quickly as possible, without actual operator interference.

An inline oil pressure switch is a stock item at "Summit" or "Jegs" and I believe its pressure setting shut-off setpoint also has a few choices. Route your ignition thru it and shutdown is automated with loss of oil pressure. Don't use your electric fuel pump because the car will continue to run until fuel pressure is dissipated. The switch connects to the tap on the block used for the oil pressure line to the oil pressure gauge.
Regarding the "Bag of worms"...
Now you need an impact switch and a rollover switch....

There area lot of good suggestions here. I ran a low oil pressure activated automatic switch that shut off my electric fuel pump and also lit a light on the dash for several years with no problem. But I also had the pressure set higher than many of the switches set it. Also had a manual fuel pump cut off switch which caused me some embarrassment a couple of times. If I had it off for working on the car with the switch on, once in a while I would forget to turn it back on. The big carb held enough gas to get me about a half block.

Ron :)

Wayne, e-mail was sent. :)

Thanks,

-Dean