Onan Aux Issue

[Davey Summa]

I run valvoline 10w-40 fully synthetic in it.

[Painter]

I have seen this cause the problem. Although the fully synthetic oil does provide proper lube for the engine, by the time the low oil switch sees the pressure it doesn't like it and errs on the side of caution. I have had to do more than a few oil changes to prove this to boat owners that were trying to get better fuel economy out of their marine gensets. Easy enough to see if this may be your problem. Also a different low oil switch make like what it sees better than the one that is on it now.

[Davey Summa]

When I went to the local onan place the switch I asked for was 309-0322 even though the individual behind the counter seemed to think that another switch was the one I needed.
(She showed me that two were listed but my series should have the other)The only thing was the switch she thought I needed required a different plug end. It was also three times the price for some reason. The wiring on my unit showed no sign of ever being changed from original so I went with the one that matched my wiring end. I hate to spend more money on another switch if isn't really the problem...but I just may. I guess I could drain the brand new synthetic oil and put in 20w-50 petro based.

[Rich Biebel]

Did you install a pressure gauge in place of the switch to verify the pressure is good?

Oil weight should really not be an issue here but the pressure needs to be confirmed as good with a mechanical gauge.

The proper switch is a must......but if the pressure is low it may be your problem.

Obviously lower weight oil will have an effect on pressure as will temperature. I seriously doubt the issue is the oil your using.

The parts manual shows a single terminal switch and it is mounted in a 90 degree fitting.

Part number is 309-0319 and is also shown in the price guide as a good number and list price is $12....

Yes your machine has a run relay and a resistor that is part of this circuit. The oil pressure switch closes to ground when pressure builds up. 30lbs is the proper minimum pressure.

I cannot cut and past the page on testing this control circuity for you from the Servcice Manual and don't have a paper copy to be able to print out...Those old machines used a lot of old type circuitry....and once you verify the pressure is good you can move on to the wiring and find the relay and resistor....

If it is one wire it can only do one thing.....close the wire to ground and open it to ground. That generally means it controls something else......a relay.....since it cannot directly supply the 12+ needed for the coil......

[Davey Summa]

I will check the pressure with a gauge this week. My oil pressure switch is the correct one then. 309-0322 replaced the 309-0309 and 309-0319.

I exposed the switch panel and it looks very simple. very small board and two relays.