Ever have an Oil Pressure Switch go bad?

[RickMorgan]

On my Westerbeke 44Cs, we’ve struggled for several seasons with sudden loss of power in either (catamaran) engine. After numerous fuel filter changes and troubleshooting efforts, I called in a mechanic. A quick look and a call to a Westerbeke factory technician, and he comes back with a $35 part. A new oil pressure switch!

He said the Westy tech told him the fuel pump is wired to the oil pressure switch, although why was not revealed. If the switch fails, the fuel pump quits, simulating a fuel starvation event.

For you technical folks, any reason I can’t (1) wire the fuel pump to some other circuit? (2), would any there be any difference if I used an auto parts switch (cost $8 vs, Westerbekes $35 part. A newer version in the Westerbeke catalog costs $95.). The switch activates an alarm if the oil pressure drops, or in my case, the switch fails.

I look forward to your responses. None from Westerbeke!

[Shenandoah52]

Originally Posted by RickMorgan

For you technical folks, any reason I can’t (1) wire the fuel pump to some other circuit? (2), would any there be any difference if I used an auto parts switch (cost $8 vs, Westerbekes $35 part. A newer version in the Westerbeke catalog costs $95.). The switch activates an alarm if the oil pressure drops, or in my case, the switch fails.

I look forward to your responses. None from Westerbeke!

(1) You could certainly wire the fuel pump to some other circuit but then in the case of inadequate oil pressure you risk losing the engine to catastrophic failure. Having the fuel pump wired via the oil pressure switch is to save your motor if the oil pump fails.

(2) That would depend on the metals used internally in the switch. Corrosion never sleeps. A gauge would be a different story as many boats use automotive gauges.

[model 10]

I've had 2 go bad. What happened was they clogged up, the orifice is super small. One way to prevent that from happening is to fill the fitting it screws into with a light oil, like trans fluid. That oil will stay in the switch and keep it free.

[Compass790]

For you technical folks, any reason I can’t (1) wire the fuel pump to some other circuit? (2), would any there be any difference if I used an auto parts switch (cost $8 vs, Westerbekes $35 part. A newer version in the Westerbeke catalog costs $95.). The switch activates an alarm if the oil pressure drops, or in my case, the switch fails.

I look forward to your responses. None from Westerbeke![/QUOTE]

I see no reason not to use an auto pressure switch, doubt they make them different for marine motors as they appear to have the same ones on sister engines that aren't marinised.
According to a grizzled old diesel mech it's common for them to fail but I've only had one failure.
I'll leave it to someone with more electrical knowledge to comment on powering off another circuit but my GUESS is you could no problem.
I'm sure an electrical expert will be along soon

[Lepke]

The switch has contacts inside that can pit. Best way for long life is use a relay to turn on the pump and the switch only handles the low amp draw of of the relay. Sometimes the total length of the wire run is too far for the size of wire. That causes the pump to draw more amps. It's becoming popular for engine makers to have relays with short runs on most auxiliary equipment.

[model 10]

Originally Posted by Compass790

For you technical folks, any reason I can’t (1) wire the fuel pump to some other circuit? (2), would any there be any difference if I used an auto parts switch (cost $8 vs, Westerbekes $35 part. A newer version in the Westerbeke catalog costs $95.).

Big difference between an AC and a DC switch. The cheap switch will be an AC switch, the expensive switch will be a DC rated switch. The AC switch only needs to handle a load 50-60 times per second. The DC switch is full time. Almost everybody cheats and uses an AC switch.

[Jammer]

In my experience the usual failure mode is that they start to leak oil.


As posted upthread they are wired to the fuel pump so that your engine will shut off if there is a loss of oil pressure.


Difference between the automotive and marine versions? Who knows, probably not, maybe the marine one has a different connector or is better sealed or more corrosion resistant, but I doubt it.

[a64pilot]

Fuel pump wired through the oil PSI switch is an automotive safety thing to ensure in the event of an accident that the fuel pump is cut off.
Imagine having a wreck where the fuel line is broken and the pump pumps its max output of fuel all over the hot engine, and continues to do so.
I have a story about that on a farm truck we had, almost lost the house.
Mazda and others use Oil PSI. GM reads engine RPM. If you get into a GM car leave the radio off and listen carefully, when you turn the key on you will hear a buzz for a few seconds that then stops, that’s the fuel pump pressurizing the fuel system, then when the car starts the ECU reads RPM and turns the pump back on.
Most Mazda cars don’t start instantly because the fuel pump isn’t enabled until there is oil pressure. Or at least older Miata’s anyway.

No reason at all to not use an automotive switch, the switch has a tiny orifice so that if the switch gets physically busted, only a small oil leak will occur and not damage the engine.

You can also of course wire the pump to the ignition circuit, but I’d just carry a spare automotive switch or two myself.

[model 10]

[QUOTE=a64pilot;
the switch has a tiny orifice so that if the switch gets physically busted, only a small oil leak will occur and not damage the engine.


Remember the AD that had everybody put an orifice at the engine fitting too? That's why it was good to fill the oil psi line with 5606.

[Shenandoah52]

Originally Posted by a64pilot

Fuel pump wired through the oil PSI switch is an automotive safety thing to ensure in the event of an accident that the fuel pump is cut off.
Imagine having a wreck where the fuel line is broken and the pump pumps its max output of fuel all over the hot engine, and continues to do so.

For autos they also make a switch specifically to shut the fuel pump off in case of an accident that is basically a funnel-like base with a ball bearing in it that will jump out of the funnel and shut off the power (breaks the circuit) to the high pressure electric fuel pump in the case of an accident. It's G-force triggered as well as gravity triggered in case of a roll-over.

I put one on my hot rod for the very reason you stated above. Having a high pressure fuel pump continue to pump fuel at 55 psi especially thru a broken fuel line that may atomize it is a nightmare scenario to be sure. I also use it as a theft deterrent by manually putting it in the 'off' position. It's well hidden but easily accessible to me.

Many car accidents will not necessarily kill the motor, hence stop oil pressure, so that extra layer of protection is well worth the slight cost of the safety switch. Don't think I'd recommends it for boats that can jump wakes, however.

[StoneCrab]

Do you have an oil pressure gauge that you can see? It would be interesting to see at what pressure the oil pressure switch is cutting out.

An alternate solution, if you have fuel starvation situations or just want your diesel to be self priming, having an electric fuel pump in the fuel line is the answer. It has many benefits.

Every diesel that I've owned has had a fuel return line. The older engines had cam driven mechanical diaphragm pumps on the side of the engine. This is the device with the lever that you need to pump when priming the engine after you service it. It always seems to be mounted on the side of the engine that is opposite to the injection pump, making bleeding a two man operation if you don't add an electric pump.

Adding an electric pump in-line with the mechanical one makes life sooo much easier. No more manual priming, cleaner fuel and much quicker start ups. Due to the use of check valves in both systems, the fuel can freely flow through either pump when the pump is not being used, so you can have the electric pump tied to the ignition for an always on state or on a separate circuit where you just use it on startup.

The electric fuel pump can run with the motor stopped. The extra fuel just cycles back through the filters to the fuel return system. The fuel to the engine is cut off at the injection pump.

To expand this one more level, the added electric pump can also be used to "polish" the fuel by running the fuel through the filters and then back to the tank. Run it at anchor after filling up. A few ball valves and a second set of filters provides a great way of making sure that the fuel in your tank is as clean as possible.

Unlike a car, your boat is unlikely to suffer a catastrophic crash requiring the fuel cut off to prevent an inferno. I see the thinking on wiring the fuel pump through the pressure switch, but in my opinion, I'd prefer to run that circuit to an alarm and leave the fuel pump on the ignition circuit.

If I am approaching a harbor entrance or motoring away from the rocks, I'd prefer to have the choice to motor on with the low oil pressure alarm blaring, than to have the pressure switch make that decision for me.

[Boatyarddog]

Originally Posted by RickMorgan

On my Westerbeke 44Cs, we’ve struggled for several seasons with sudden loss of power in either (catamaran) engine. After numerous fuel filter changes and troubleshooting efforts, I called in a mechanic. A quick look and a call to a Westerbeke factory technician, and he comes back with a $35 part. A new oil pressure switch!

He said the Westy tech told him the fuel pump is wired to the oil pressure switch, although why was not revealed. If the switch fails, the fuel pump quits, simulating a fuel starvation event.

For you technical folks, any reason I can’t (1) wire the fuel pump to some other circuit? (2), would any there be any difference if I used an auto parts switch (cost $8 vs, Westerbekes $35 part. A newer version in the Westerbeke catalog costs $95.). The switch activates an alarm if the oil pressure drops, or in my case, the switch fails.

I look forward to your responses. None from Westerbeke!

You got away cheap, could have cost you a $12000 engine refit.
Be happy, and leave it as it is.
SV Cloud Duster

[Squanderbucks]

The OP is asking why not disconnect the Low pop pressure switch from the run circuit. On generators where the engines are rarely watched for water temp, oil
pressure, and exhaust temp with dedicated gauges these engines are built to be on “auto pilot” and self protect themselves with any of the usual engine killers such as water pump failure ( over heat) loss of oil pressure (the switch in question) or faI lure of the exhaust elbow.
These are wired together on safely circuit if any of the fail.
IMO it would be a mistake to try and circumvent this system.
A better response would be to fix the problem causing the alarm. If it is just the switch failure the just replace it - be sure to use one that matches the original one. Some are normally open and other normally closed. Almost all are made in China these days so expect to replace from time to time.

[Cadence]

Originally Posted by Ecos

Big difference between an AC and a DC switch. The cheap switch will be an AC switch, the expensive switch will be a DC rated switch. The AC switch only needs to handle a load 50-60 times per second. The DC switch is full time. Almost everybody cheats and uses an AC switch.

The big difference is the ability of the contacts to suppress and arc. AC is self quenching DC is not. It's the opening of the contacts that arcs and pits them or in some cases welds them. The crown on the contacts is different causing the rating to also be different.

[SwellGuy]

Originally Posted by RickMorgan

He said the Westy tech told him the fuel pump is wired to the oil pressure switch, although why was not revealed. If the switch fails, the fuel pump quits, simulating a fuel starvation event.

Cmon guy, put your thinking cap on. You can’t think of why they might want to stop the engine if low oil pressure is indicated?

I think the solution is in finding a more reliable oil pressure sensor, not in undoing a beneficial interlock that helps prevent your engine from killing itself if there’s no oil pressure.