How reliable are the Afour's oil pump

[zellerj]

Those with an electric fuel pump also have a oil pressure safety switch, a switch that stops flow of fuel if the oil pressure drops below a set value. I have a few questions - not that I am having difficulty myself - just curious

• At what oil pressure does the switch activate?
• Has anyone ever had this switch activate?
• If you check the oil regularly, and have no leaks - what are the chances of the oil pressure dropping to activate this switch?
• Since these switches seem to be problematic, is there a real concern with bypassing them?

How many cases of a failed oil pump have been seen with atomic fours?
Would not the engine get real noisy if the oil pump failed, and would that noise not be sufficient alarm to shut down and investigate - OPSS or not?

My old neighbor had a 50s vintage Massey Furgeson tractor that ran nice and quiet for 20 years at 5 psig oil pressure. Similar type engine to the atomic four. At what oil pressure does the A4 start to make noise?


Best,
Jim

[romantic comedy]

I will always have an oil pressure switch and gauge.

I have to laugh about the noise. If it gets that noisy, it will shut down due to no lubrication and severe engine damage.
Gotta love the sound of metal on metal, LOL

[zellerj]

Yes but in a case of catastrophic oil pressure failure - broken pump of broken line, the engine would still run a few minutes because of the fuel in the carb, so the OPSS will not shut the engine down immediately.

Best,
Jim

[67c&ccorv]

The OPSS isn't there to shut down your engine in the event of an "oil pump" failure.

It is there to stop the flow of fuel to the carb in the event of a failure to start.

[ndutton]

I think the real risk of oil pressure loss is either a massive leak in the system (the long oil pressure sender nipple comes to mind, it's been known to fracture) or a clogged pickup screen in the crankcase. Like 67 said, the OPSS isn't there to protect against an oil pressure failure but rather to be certain there isn't any fuel pumping when the engine isn't running.

Besides regular oil changes and relocating the oil pressure sensor array to a bulkhead connected with a psi rated flexible hose your best protection is the alarm system. It monitors for low oil pressure in the background in real time and alerts you instantly in case of a fault.

[wristwister]

My understanding is that the primary purpose of that oil pressure safety switch (OPSS) is to prevent the fuel pump from running and flooding out the carb in the event that the engine stops running with the ignition switch on. I suppose a side benefit of the switch is to stop the engine in the event of oil pressure loss.

In my case, the OPSS failed while we were out motoring, shutting down the engine. A quick check with a multimeter showed the switch was bad, and a simple jumper bypassing the switch had us up and running again in minutes. I believe it was a cheap automotive switch that was on there, and I have a higher grade switch on order to replace it. In the mean time, it's still jumpered, and I just need to be carefull that the ignition is never on without the engine running.

Regarding your description of the switch "activating", I think you have it a little backward. The switch is normally open, blocking current to the fuel pump. Upon sensing oil pressure (5 psi in the case of the switch I ordered) the switch closes and power goes to the fuel pump. No pressure and the switch opens. My switch has two terminals for this function. There are also switches with three terminals, where one output will be noirmally open and the other normally closed. With this type of switch, the normally closed output could be wired to an oil pressure alarm.

[zellerj]

Thanks everyone for the clarification. Makes perfect sense. I usually think backwards from everyone else.

If you are trying to start the engine with an empty float bowl, it takes a while for the engine to start. Is the oil pressure from cranking sufficient to keep the fuel pump pumping? Is a 5 PSIG OPSS going to allow the fuel pump to work?

Best,
Jim

[ILikeRust]

Cranking to start should create plenty of oil pressure to close the OPSS and turn on your fuel pump.

[romantic comedy]

I have my pump wired to the starter. One terminal provides battery voltage when the starter is turning.

I have this connected to the fuel pump side of the OPSS, and to the coil.

This way the coil and the pump get full voltage during cranking.

[lat 64]

Thanks everyone for the clarification. Makes perfect sense. I usually think backwards from everyone else.

If you are trying to start the engine with an empty float bowl, it takes a while for the engine to start. Is the oil pressure from cranking sufficient to keep the fuel pump pumping? Is a 5 PSIG OPSS going to allow the fuel pump to work?

Best,
Jim

Yes, it works just fine that way. I think it helps to give the ol' girl a few turns before it fires to get the oil moving first anyway. Remember, the majority of the time we leave these beasties just sit a lot.

I had a scare a few years ago when my OPSS was not hooked up. The engine died while idling and the pump overwhelmed the float valve. It dumped a lot of gas in the bilge when I was distracted with sail changes in some rough weather. Not fun.

be safe,
Russ

[hanleyclifford]

A very are occurance: I was motoring thru the C&D Canal and turned into the basin at Chesapeake City to anchor for the night. The engine shut down abruptly due (as it turned out) to failed ignition circuit OPSS. In this case a manual override would have saved me a few gray hairs. Luckily I coasted to the anchor spot. I use the 7 psi model switches. If you have wide clearances and any oil pressue issues it is also possible to have difficult restarting on a hot engine.

[marthur]

Does anyone put a manual over-ride switch on their instrument panel? It could be used to prime as well as over ride. Is that allowed under coast guard regs?

[ndutton]

Two comments

1. I too had an OPSS failure but I was able to attribute it directly to an antifreeze dousing during a FWC pump replacement. There was a clear reason why mine failed but I'm paying close attention to the reports of failures for seemingly no good reason. I'm wondering if there's a reliability problem (not my experience) or if skippers are simply not connecting the cause and effect dots.

2. Mike, I have an override switch for my electric fuel pump but it won't serve as a get-home jury rig. For inboard gasoline engines the USCG requires that fuel is not pumped unless the engine is either starting or running. Mechanical pumps achieve this by their nature, driven off a rotating engine. Typical to our installations, electric pumps comply via the OPSS.

There is an obscure exception though: A pump, usually electric, is allowed to transfer fuel but the USCG requires that engine operation is defeated during transfer operations. I do it with a DPDT switch. When one pole closes to operate the pump in override the other pole opens the ignition circuit to the coil. The OPSS is open when the engine is not operating thereby preventing an electrical backfeed to the coil during override.

It works well for me. I have two tanks and can transfer fuel from one to the other with this system. The transfer goes through the filter so the fuel is polished as well. I can also cycle fuel from one tank through the filter and return it to the same tank, a real polishing system. With the override switch I can prime the carburetor if I choose and I can purge the air from a new filter.

Via the switching system the coil remains de-energized the entire time the pump is in override. All good.