Oil Pressure Indicator [and Temperature Circuit Board]

[Bumbugo13]

When we bought our 1986 Ericson 32-3, there was an oil indicator toggle switch with adjacent space for a light on the ignition/instrument panel. I quickly figured out that the toggle wasn't actually connected to anything. No wires, no actual switch, no light bulb. There is a single unconnected wire hanging free on the back side of the panel. Does anybody know what kind of switch is supposed to there? Or does anyone have an operable oil indicator that they can take a picture of?

I am assuming that there is a sensor somewhere around the engine. But haven't located it yet. The boat is powered by a Universal M-25.

Any constructive input is most welcome! Thank you!

 

[Kenneth K]

The switch is for the optional exhaust blower in the cowl vent line. Some boats had them, some didn't, others have since had them removed.

For a humorous read: https://ericsonyachts.org/ie/ubs/universal-m25-engine-wiring-upgrade-part-1-cockpit-gauges.162/

The little red lamp above the switch is the engine's low oil pressure light. Since you don't have an oil pressure gauge, you need to have this light working. It should come on when the key is turned ON at the engine panel, and go out once the engine is running. Many owners install a buzzer in parallel with the light. The oil pressure sensor is screwed into the aft port side of the engine (M25) and uses a single light blue wire to connect to the light. This light blue wire is the ground (the pressure switch closes at low pressure to complete the ground). Positive power for the light is taken from any + source on the engine panel.

You'll likely want to get around to removing that ammeter from the engine panel if it's still hooked up. The small gauge wires connected to the alternator are thought to be a fire hazard. Use caution especially if you have an upgraded, high output alternator.

More on removing the ammeter: https://ericsonyachts.org/ie/threads/universal-diesel-wiring-modifications-how-to.12178/#post-83793

More on installing an oil pressure gauge: https://ericsonyachts.org/ie/ubs/adding-an-oil-pressure-manifold-and-gauge.763/

 

[Christian Williams]

I am soooo glad to have company in this confusion....

 

[Loren Beach]

Perhaps I am better off having our engine compartment exhaust fan (now, with the recent engine changeout) wired into the "on" position on the switch panel. One less decision to make!

 

[Bumbugo13]

Thanks Kenneth K. That's really good information. You reminded me about the blower. Most appreciated!

 

[Christian Williams]

I'm hoping Kenneth can understand this, or anybody else:

My oil pressure buzzer/warning light stopped working , and I've hit the wall.

I replaced the existing Cole Hersee cockpit panel unit, which kept buzzing under 1500 rpms--an annoyance.

Now it won't work at all.

I figured it connects to the oil pressure switch on the engine block. That switch merely reports, by a diaphragm, whether there is oil pressure or not. When ignition is on, buzzer buzzes (no oil pressure yet) . When engine starts, buzzer stops. (Mine kept going off intermittently while motoring.)

However, my engine also has an oil pressure sender, which shares wiring with the buzzer.

...

There's an ancient circuit board on the cockpit panel water temperature gauge. That gauge goes to the temperature sender on the thermostat housing.



The circuit board--they're now discontinued--was wired to the old buzzer, where it shared a pole with the oil switch sender wire. Apparently the idea was to set the buzzer off in the case not only "no oil pressure" but also in the case of "low oil pressure." [No,
high temperature. See Jerry's correction in next post]

Well, come on! What's the question?

I just want the oil pressure switch. But I can';t seem to simplify the wiring to get the buzzer to go off when ignition turns on, and off when the engine starts).

Can't I just disconnect the oil pressure sender and the circuit board? And rely on the oil pressure switch wired directly to the buzzer?

This ought to be simple, but I can't get it to work (the oil pressure switch worked yesterday and so does the new buzzer--it must be my wiring).

 

[Jerry VB]

However, my engine also has an oil pressure sender, which shares wiring with the buzzer.

There's an ancient circuit board on the cockpit panel water temperature gauge. That gauge goes to the temperature sender on the thermostat housing.

The circuit board--they're now discontinued--was wired to the old buzzer, where it shared a pole with the oil switch sender wire. Apparently the idea was to set the buzzer off in the case not only "no oil pressure" but also in the case of "low oil pressure."

I expect the circuit board would buzz the buzzer for high temperature, not low oil pressure, given that it is attached to the temperature gauge. It has a comparator (black eight-legged IC) and a potentiometer (variable resistor - dial thing on the right) to set the threshold. It should ground the output wire connected to the buzzer when the temperature exceeds the threshold.

Well, come on! What's the question?

Well, golly, I just want the oil pressure switch. But I can't seem to simplify the wiring to get the buzzer to go off when ignition turns on, and off when the engine starts).

Can't I just disconnect the oil pressure sender and the circuit board? And rely on the oil pressure switch wired directly to the buzzer?

This ought to be simple, but I can't get it to work (the oil pressure switch worked yesterday and so does the new buzzer--it must be my wiring).

You should be able to simply abandon in place the circuit board and disconnect the wire(s) between it and the oil pressure buzzer. I only see three wires and two go to the meter, so I'm deducing the buzzer connection is the black wire in the middle of the board.

For the simplified buzzer circuit, attach +12v to the one side ("+" side) of the buzzer and the oil pressure switch to the low side of the buzzer and it should Just Work[tm]. The buzzer probably is polarity sensitive so you need to get the right wires connected to the +12v supply and oil pressure switch. You can verify this by connecting the buzzer to its +12v supply and ground the other side - buzzing is success. This also will verify you have power to the "+" side of the buzzer.

For debugging the oil pressure switch, you can connect an ohmmeter (multimeter) set to lowest resistance setting - 100 or 1000 ohms - to the oil pressure switch lead at the panel and verify it is zero(ish) ohms to ground with the engine off and infinite(ish) ohms with the engine running. If it ain't, there is something wrong in the wire (likely) or oil pressure switch. Repeating the ohmmeter test at the engine would identify if it is the wire or the switch.

P.S. The above assumes the oil pressure switch has one terminal and shorts that terminal to ground when the oil pressure is low. If it has two terminals, it supplies +12v when the oil pressure is low. For a two terminal switch, one terminal needs to go to +12v, the other terminal needs to go to the "+" buzzer terminal, and the "-" buzzer terminal goes to ground.

 

[G Kiba]

The circuit for wiring the buzzer and oil pressure light is simple on my boat. Purple wire is 12V off the key-on side of the ignition switch. Blue connects to the sender completing the ground when there is oil pressure at the sender.

 

[Christian Williams]

I will apply these lessons today.

 

[Kenneth K]

Can't I just disconnect the oil pressure sender and the circuit board? And rely on the oil pressure switch wired directly to the buzzer?

Well, I kind of get it. I think.

First there's the nomenclature issue--we call these things switches and senders interchangeably when really a switch is just an on/off device while a sender creates variable resistances (ohms) that need to be interpreted by a gauge. Below, #1 and #3 are pressure switches (they connect to separate light/buzzer combinations); #2 is a pressure sender (it connects to an oil pressure gauge--there would be no reason to have a pressure sender without a corresponding pressure gauge).


Seems I've read that most of the pressure switches are set at either 7 or 11 psi. They can't discriminate between low or zero pressure, only whether the pressure is above or below the set threshold psi.

Secondly, the device by the red arrow in your second photo looks more like a block temperature warning switch than a pressure sender. Here is Aqualarm's (the middle device):
Having one of these would explain why you have a circuit board--likely, both your oil pressure switch and your block temp switch were part of a panel like the one above. The circuitry allows both switches to share a single buzzer and mute button, and allows a triggered switch/alarm to be silenced while the other switch/alarm is still armed.

Third, note in my first photo above that there are two types of pressure switches; double pole (#1), and single-pole (#2).

The single-pole switch can only be used in the negative side of the circuit. The second "pole" is the switch body itself, which screws into and, thus, grounds itself to the engine block. This is what Ericson typically used to ground the oil pressure idiot light (which pulled its positive power from a wire off of the engine panel). See "A" below:

In a double-pole switch, the two poles at the top are insulated from the metal body itself, so this switch can be used in the positive side of a circuit. A double pole switch, installed in the positive side of a circuit, would be typical in a circuit-board type alarm setup because this is what provides power to the circuit board. See "B" below:

So, to finally answer your question, "Can't I just disconnect the oil pressure sender and the circuit board? And rely on the oil pressure switch wired directly to the buzzer?" Yes, it should be that easy. If it's not, my guess is that you are trying to build circuit A, below, (the Ericson OEM setup) using a double-pole switch, which would leave the circuit ungrounded. Try grounding one of the poles to your ground bus bar (as in C, below). Or, try using a single-pole pressure switch.


Finally, if your buzzer/light kept coming on below 1500 rpm, hopefully, it was just a bad pressure switch. If not, it could be that you actually have low oil pressure below 1500 rpm. When starting my engine cold, I read near 40 psi. When warmed up to 185 deg, pressure drops to about 30+/- psi. But, I do remember when I was running 10W-30 oil, in a hot engine, at low idle speeds (say below 800 rpm), I was surprised the needle would go well below 20psi. After switching to 15W-40 oil, the pressure stays a little higher at low rpm.

Also, if you have a block temperature switch installed (looks like there's one on your exhaust manifold tank), you can still keep it hooked up even if you rip out the circuit board. It's just a temperature switch--it closes above (usually) about 200F to complete a circuit. Hook it up to a separate buzzer/light combination and you'll have over-temp warnings as well. It can operate completely independent of the water temperature sender & gauge circuitry.

 

[Christian Williams]

So this is a block temperature switch. (I guessed "oil pressure sender" based only on the engine diagram shown above).



I traced the black and white 10 gauge wires of that device to the cockpit instrument panel. Black is the ground. The white wire joins the blue wire arriving from the oil pressure switch on the engine (at the funky Y connector marked "A") and goes to the buzzer.



So: the buzzer was connected at one pole to a single wire combining the block temperature switch and also the oil pressure switch. That same pole also connected to a separate blue wire, 22 gauge, from the circuit board. (The other pole of the buzzer is power.)

Does that make sense?

I will put an ohm meter on the oil pressure switch and report.

Thanks for the careful explanation. There's not much written about these obsolete circuit boards and this may subtract from the confusion.

 

[Kenneth K]

Yeah, and I think the block temp alarm is worth keeping. If you're motoring at 180-185F and shed an impeller vane, it likely wouldn't take long to hit 200F. The block temp switch might catch it before you notice it on the gauge.

The circuit board just complicates the wiring and troubleshooting, mostly for the benefit of two alarms sharing a buzzer. I'd buy a second, chirping alarm from eBay and hook it up to the temp switch. You'd be able to tell, aurally, which alarm is going off.

 

[Kenneth K]

So this is a block temperature switch. (I guessed "oil temperature sender" based only on the engine diagram shown above).

Yes.

I traced the black and white 10 gauge wires of that device to the cockpit instrument panel. Black is the ground.
View attachment 44951

Despite the colors of the wires, both sides make up the ground circuit. This ground is only completed when the switch closes (above ~200F). They should have used the same color wire on both sides of the switch.

The white wire joins the blue wire arriving from the oil pressure switch on the engine (at the funky Y connector marked "A") and goes to the buzzer.
So: the buzzer was connected at one pole to a single wire combining the block temperature switch and also the oil pressure switch.

Yeah, that makes sense. Either the white wire from the Temp switch or the blue wire from the Press switch (both are grounds) can complete the ground to the buzzer (who's hotwired positive lead comes off the engine panel).

That same pole also connected to a separate blue wire, 22 gauge, from the circuit board. (The other pole of the buzzer is power.) Does that make sense?

This part doesn't make sense to me. While I get that the circuit board would need ground circuits from the switches, I would think it would require independent grounds from each switch. That way, the circuit board can decide how to process one warning versus the other. If, instead, a common ground from either switch just completes a circuit to ring a buzzer, then the circuit board is providing no additional function.

Here, I'd have to guess that, at one point, things were wired differently. Perhaps the circuit board quit working and a PO just combined the grounds to get the buzzer to function again.

 

[Christian Williams]

Here are my findings in the case of the oil pressure switch buzzer not buzzing.

The buzzer itself works. Buzzes when grounded.

With "Ohms" selected on the multimeter, connecting one probe to the cockpit panel pressure switch lead and the other probe to a panel ground, the reading is OL. The reading is the same whether engine is running or not. No ohms numbers at all. I did move the decimal point around on the Mastech multimeter.

To bypass any wire issue, I also was able to put the probe directly on the switch itself (it's a one-lead switch), and the other probe on the engine as ground. OL with engine off or on, no numbers.

I hope this means something unambiguous, and not just that I don't know how to use a multimeter.

I think this is the switch I have:

 

[Jerry VB]

To bypass any wire issue, I also was able to put the probe directly on the switch itself (it's a one-lead switch), and the other probe on the engine as ground. OL with engine off or on, no numbers.

Sounds like a bad switch to me. It should be closed (grounded / ~0 ohm) with the engine off. In terms of boat stuff, it should be reasonably inexpensive and easy to replace.

 

[Christian Williams]

I guess a new switch is my next move. I want to be confident in the diagnosis since on my model the oil pressure switch is really hard to reach. I'll have to remove the water lift muffler and hoses and maybe even the exhaust elbow.

 

[Kenneth K]

OL means open line. It's the same reading you should get when the probes aren't touching anything....sounds like a bad switch.

I also was able to put the probe directly on the switch itself (it's a one-lead switch).

Before you remove the switch, remove the single lead from the top of the switch and touch it anywhere on the block. The buzzer should buzz, and this would prove it's a bad switch.

 

[Christian Williams]

I ordered "OP22891 Oil Switch - Set at 15 P.S.I" from WM, because the 5432 tech manual says "If the oil pressure falls below 14 psi. (1.0 kgf /cm2 ) the oil warning lamp· will light on the dash panel." [note: I returned this part]

I also ordered from Fridayparts.com [This part fit]
Oil Pressure Switch for Kubota V1500 V1501 V1702 V1902 DH1101 D1100 D1302 D1301 D1402 Z482 Engine

Yeah but: The Kubota part doesn't say the psi setting, and besides, Kubota is metric. The WM part is NPT--whereas the correct switch is said by others to be British Standard. But did Westerbeke drill the hole? Some say they did.

We'll see what fits. This certainly is giving me fits.

 

[Kenneth K]

A brake shop made a braided stainless/rubber oil line for me for about $10-15. I moved the switch to where I could access it and add a pressure sender.

The brass adapter between the block and hose is a BSP-NPT adapter...another $10 or so from eBay.

 

[Nick J]

Does anyone make a combo switch and pressure sensor unit? I would like to add a pressure gauge and thought that would be easier than plumbing up additional ports. The remote oil filter kit I'm installing has two additional ports I can use to install a sender, so it may not be an issue for me anymore, but could help others. I have the same question for the water temp switch.