Author Topic: Low oil pressure shut off  (Read 582 times)

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Offline Sonny

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Low oil pressure shut off
« on: March 27, 2020, 04:32:33 pm »
I'm an idiot and did a whole bunch of somewhat spirited driving on a lake. Heard some nasty noises and while limping home, rods escaped. Thinking the oil in the pan was flung to the outside and the pickup sucked air. Since I was having such a fun time in the bright sun, if the low oil pressure light was on, I did not see it.

Swapping in my new engine had me thinking. In my job, we have shutdowns for everything, why not Subaru?

Idea: use the n/c to ground "low oil pressure" switch to interrupt one or both of the ignition and fuel components in an attempt to stop the engine before it makes a window. Not really here to argue if it would stop it fast enough to prevent damage. Just looking for opinions on what would be best to interrupt, fuel or spark or both.

Fuel = a potentially lean condition for a moment.
Spark, could see a washed cylinder.

Interrupting the key switch will kill both, which is my front runner. Any opinions on if that could potentially cause damage? I've never just "turned the car off"  while driving under load. 

I would have a momentary override switch for starting, as obviously there's no oil pressure before the engine starts turning. (Bonus antitheft?)


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Offline Ambystom01

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Re: Low oil pressure shut off
« Reply #1 on: March 27, 2020, 05:15:04 pm »
I think you're better off getting a baffled oil pan rather than install a switch that cuts power when low oil pressure is detected, which will also mean no power steering or power brakes.
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Offline Mason

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Re: Low oil pressure shut off
« Reply #2 on: March 27, 2020, 05:30:05 pm »
Get an oil pressure guage. Defi have an alarm you can set that beep when it is below the limit

Offline Sonny

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Re: Low oil pressure shut off
« Reply #3 on: March 27, 2020, 09:36:02 pm »
Hmm, I have definitely looked at the baffled pan. big $$ though, I have read even just installing a pan and pickup from a newer generation can help. This idea though, I could do with stuff I already have. Like the idea for the noisy guage. Not too down on having a pod in the interior.

Adding a bright assay light to the dim "low oil light"  circuit did cross my mind, which pretty much lead to " why not shut it down instead" train.
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Offline firebane

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Re: Low oil pressure shut off
« Reply #4 on: March 27, 2020, 10:08:16 pm »
Hmm, I have definitely looked at the baffled pan. big $$ though, I have read even just installing a pan and pickup from a newer generation can help. This idea though, I could do with stuff I already have. Like the idea for the noisy guage. Not too down on having a pod in the interior.

Adding a bright assay light to the dim "low oil light"  circuit did cross my mind, which pretty much lead to " why not shut it down instead" train.

Oil pressure light comes on at a level that is considered "too late"

My car runs around 30psi or so at idle and upwards of 110psi when cold. If I noticed and substantial drop in pressure I know I'm in trouble.

When you are driving spirited the oil ends up at one side of the or the other and cause starvation issues. Some vehicles handle this better than others, unfortunately subarus do not

Offline funk32

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Re: Low oil pressure shut off
« Reply #5 on: March 28, 2020, 05:10:06 pm »
The big reason you don't see low oil p cut off is because it is dangerous for cars that are driven on public roads by people who barely know how to drive on the highway.  Cut the engine, you loose power steering, abs, traction control and what ever else.

Offline funk32

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Re: Low oil pressure shut off
« Reply #6 on: March 28, 2020, 05:10:44 pm »
I think you're better off getting a baffled oil pan rather than install a switch that cuts power when low oil pressure is detected, which will also mean no power steering or power brakes.

This lol i missed this comment in my quick scan through.

Offline RockThePylon

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Re: Low oil pressure shut off
« Reply #7 on: March 28, 2020, 05:41:24 pm »
You have 0psi at startup, so you'd need a bypass for startup (works as anti-theft too?). Could also be a sketchy situation if your engine randomly cut ignition in the fast lane on Deerfoot during rush hour.
Also, the oil pressure sender clicks around 3psi . MAY leave you with something salavagable, but if your oil pressure drops that low, damage is done.

I'd rather have a gauge that provides a programmable limit with audible/visual alarm. Then you can acknowledge it and stop when safe.
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Offline jellynuts

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Re: Low oil pressure shut off
« Reply #8 on: March 28, 2020, 10:12:17 pm »
Get a skid plate too.
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Offline darthekai

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Re: Low oil pressure shut off
« Reply #9 on: March 29, 2020, 01:17:49 pm »
Just to be a Devils advocate. Is there a signal you could interrupt or otherwise tamper with that would send the car into limp mode and cut boost and drop the rpm limit to something super obvious like 3k?

Could be a stealth solution. Be nice though if the dummy light was ranged a bit higher. I say the best way is get a new pickup in there, a baffled pan if you can afford it, and a gauge with an alarm. If you really don't like to look, make sure the alarm is super loud and cram it under your dash.
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Offline Sonny

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Re: Low oil pressure shut off
« Reply #10 on: March 29, 2020, 07:44:46 pm »
You have 0psi at startup, so you'd need a bypass for startup (works as anti-theft too?). Could also be a sketchy situation if your engine randomly cut ignition in the fast lane on Deerfoot during rush hour.
Also, the oil pressure sender clicks around 3psi . MAY leave you with something salavagable, but if your oil pressure drops that low, damage is done.

I'd rather have a gauge that provides a programmable limit with audible/visual alarm. Then you can acknowledge it and stop when safe.

I would have a bypass momentary jumper switch to simulate "good" oil pressure (bonus antitheft) as mentioned.

As for concerns about engine cutting out causing a dangerous driving situation, it is a manual transmission, so technically I would have power steering and brakes until almost zero kph if left in gear. Coasting to a stop at a safe spot and letting the clutch go in gear would immediately restore brakes. You usually have a couple brake pedal pushes left even with engine off anyway.

I have no traction control, abs or stability control (ahh old jdm car simple, can't beat it!)

That's good to know about the oil pressure switch being so low. I was going to bench test. I guess If I were to do it, would definitely be looking for a higher pressure switch.

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Offline diamondedge

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Re: Low oil pressure shut off
« Reply #11 on: March 29, 2020, 10:14:33 pm »
In control and safety systems, to limit damage caused by an out of control process, the last absolute thing you want is the ESD/emergency shutdown or in essence what you're trying to wire in; cut the absolute function
down of your engine prior to damage. Sure it exists, but you don't see plants that have minor issues going around shutting in every single valve and blowing down the flare.

Nah man. Design it a few layers up, a gauge with a warning light when it drops below a certain PSI is plenty good. Add in the baffle and pick up, a few more layers of safety.


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Offline tperkins

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Re: Low oil pressure shut off
« Reply #12 on: March 30, 2020, 08:51:08 am »
In control and safety systems, to limit damage caused by an out of control process, the last absolute thing you want is the ESD/emergency shutdown or in essence what you're trying to wire in; cut the absolute function
down of your engine prior to damage. Sure it exists, but you don't see plants that have minor issues going around shutting in every single valve and blowing down the flare.

Nah man. Design it a few layers up, a gauge with a warning light when it drops below a certain PSI is plenty good. Add in the baffle and pick up, a few more layers of safety.

Also, no offence to OP but don't do the thing we have all seen 10 videos and threads "doing donuts in my subaru, knock?"

The 3 is raw.  Lighter than more agile.  The 6 probably feels like a 747.  And by that contrast, my STI probably feels like the Hindenburg.  So GR's are like the International Space Station.

Offline firebane

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Re: Low oil pressure shut off
« Reply #13 on: March 30, 2020, 09:31:56 am »
Also, no offence to OP but don't do the thing we have all seen 10 videos and threads "doing donuts in my subaru, knock?"

Well to be honest that can happen to a lot of vehicles especially when people are wringing out the engine in excess of 5,000rpm. Subarus are just unfortunately more prone to do engine design.

Offline tperkins

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Re: Low oil pressure shut off
« Reply #14 on: March 30, 2020, 09:58:39 am »
Well to be honest that can happen to a lot of vehicles especially when people are wringing out the engine in excess of 5,000rpm. Subarus are just unfortunately more prone to do engine design.

Yeah, I agree. I did some skids when I had a Subaru, and even with oil pressure gauge I felt uncomfortable ever doing any really tight donuts for any extended period of time. Maybe do 1-2 and back out, just knowing the potential.
The 3 is raw.  Lighter than more agile.  The 6 probably feels like a 747.  And by that contrast, my STI probably feels like the Hindenburg.  So GR's are like the International Space Station.