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1999 Mule 2500 Oil Pressure Questions

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1. What does the pressure switch  (see pic) with one wire going to it do? I don't see an oil pressure idiot light so it must supply ground when seeing no oil pressure to either the fuel pump or the ignition. Does anyone know which system it interrupts? My fuel pump is bad so I am converting to a vacuum fuel pump but don't want to loose the no oil pressure warning feature. I could wire this pressure switch to the over temp light on the dash since I replaced this with a digital temp guage so the over temp dash light is unused at the moment.


2. Inside the crankcase, under the oil pump cover, sits a spring over a steel ball. See pics. This must regulate oil pump pressure. It seems odd to me that there is a gap between the spring and the oil pump cover. Does this gap seem correct? I guess that it could be to insure some zero pressure flow before it gets reduced by the spring???? I don't recall ever seeing another set up with a gap though.


Many thanks, Mike





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My 550 has the same setup with the pump.

that spring and ball is a relief valve. If the oil pressure gets too high it will shoot oil Back into the crankcase.

And I'm 99% sure that it's a low oil cutoff, and most generally cut off ignition


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1.  There are two types of oil pressure "switches".  One is  an actual switch.  When oil pressure is low, the switch closes providing a ground to an oil pressure warning light.  The other type is a variable resistor that operates an analog gauge. Although possilbe, I don't know of any ATV/UTV engines that have a low oil cut-off switch.  The sloshing around of oil in the crankcase during rough rides can cause the engine to shut off.

2.  The spring valve is an over pressure relief valve that dumps excess pressured oil back to the crankcase.  A rudimentary pressure regulator of sorts.  If the oil filter gets plugged, there's a separate bypass valve that allows unfiltered oil to continue lubricating the engine.  It's a different spring loaded valve than the one in your picture.

If anyone knows how to increase idle oil pressure in the Chery engines, let me know.  Seems like these engines have 10 psi oil pressure at idle.  I prefer 20 psi.  50 weight oil helps, but not enough.

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