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#2191704 - 03/07/11 10:32 AM How do low oil sensors work?
callbay Offline

Registered: 05/29/05
Posts: 610
Loc: Ozark Mountains
I have had a couple experiences lately with low oil sensors not stopping the small engine even though there was hardly any oil in the engine. In the last case I drained out only 16 ozs of oil and the manual says it holds 1 1/2 qts. and the dipstick says 2 qts. The wires were attached to the sensor so is something just malfunctioning? It was a 20 HP Kohler 2 cyl (see my recent post on no oil on the dipstick)

Seems like the sensors should stop way sooner or we should not counrt on them to do their job.

#2191726 - 03/07/11 10:53 AM Re: How do low oil sensors work? [Re: callbay]
suspiciousmind Offline

Registered: 12/11/09
Posts: 357
Loc: NC/SC
We should not count on them to do their job.

They're looking for a low pressure situation which occurs when there's not enough oil in the sump to keep the galleries's actually too late then....damage has likely been done.

Keep an eye on the oil level by checking it frequently.

Edited by suspiciousmind (03/07/11 10:57 AM)
1990 miata 5 speed
1992 Accord 5 speed
1996 Accord auto
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2002 4runner 3.4 4wd auto
M1 0w/30 in everything

#2191736 - 03/07/11 11:02 AM Re: How do low oil sensors work? [Re: callbay]
punisher Offline

Registered: 09/11/04
Posts: 1923
Loc: snowblind in TX
Most sensors on small engines are a float type with a magnet located inside the float. When the float level (oil level) reaches a certain point the magnet gets near enough to a reed switch and closes it grounding out the coil. More expensive small engines, with a pressurized system) do have a pressure sensor that performs the same function.

The level sensors work for the most part and stop engines when the actual level falls. Pressure type sensors can let an engine run really low on oil as long as the oil pickup can get enough oil to keep the system pressurized. It is normal operation to not have the system stop with low oil levels, as long as there is enough oil to keep pressure up.

#2191738 - 03/07/11 11:04 AM Re: How do low oil sensors work? [Re: callbay]
Texan4Life Offline

Registered: 01/28/10
Posts: 2135
Loc: Texas
Thats a good question. If it is pressure lubed, then it is suppose to alarm at a specific psi setting. Even though it was critically low it could have still maintained oil pressure. ie. the oil pump pickup was still submerged in oil.

On splash lubed engines I'm not sure exactly. I always thought it was a sensor of some kind that could tell when it was submerged or being touched by oil. But when I took apart my gx160 cone it had some doo-dad that I haven't see before. It sits in the bottom of the sump with a tube that goes up to the wires on the side of the block.
2005 Dodge Ram 1500, 5.7L
[Current Fill: PP 0w-20][Baldwin B2-HPG]

#2193831 - 03/09/11 08:23 AM Re: How do low oil sensors work? [Re: callbay]
eljefino Offline

Registered: 06/15/03
Posts: 24000
Loc: ME
How would a pressure sensor allow spark during cranking? Any override? Or do you just have to get it going fast enough to fling some oil around and make it catch?

#2195405 - 03/10/11 12:53 PM Re: How do low oil sensors work? [Re: eljefino]
wolfc70 Offline

Registered: 04/13/07
Posts: 360
Loc: Wisconsin
Originally Posted By: eljefino
How would a pressure sensor allow spark during cranking? Any override? Or do you just have to get it going fast enough to fling some oil around and make it catch?

Most have a 15-30 second override to allow the engine to start. On my splash lubed OHV Briggs generator the manual states that the low oil shutdown activates after 20 seconds. It lists that in the trouble shooting section for when the engine starts then shuts off shortly.

Once it is up and running, the low oil cutoff seems to work instantly. I was running my generator (mainly to just run some fuel through it) to power a grinder while I was fixing my laundry lines. The soft ground sank under one wheel causing the gen set to list to one side. I have no idea how long it was like that, I did not notice it until it shut off. I moved it, restarted the engine and it started sinking again. While I was moving it again, I must have lifted the front too high, as it shut off again. I then check the oil level and it was close to full. It is a nice feature, but I could see how on a job site if you do not have perfectly level ground, it could be a big PITA.
2011 Honda Accord EX Saloon, Manual, K24Z3, Toyota Synthetic 0w-20, Napa Gold 7356
2008 Pontiac Vibe 1ZZFE, PP 5w-20, Federated LF410F