CHECK ENGINE BUZZER

[buckstopper]

I have a Yanmar 4BY180 engine in my 2008 North Pacific 36 trawler. Every time I start her up, the check engine buzzer continues buzzing until the coolant temperature reaches around 125F, at which time I restart and everything is (seems) normal. Temperature and Oil Pressure show normal when running and there are no other issues.
Engine mechanics have been unable to figure it out, and I have been putting up with it for about four years. I have been unable to find a Yanmar engine mechanic with the appropriate diagnostic equipment, so that would be my next step.
Anyone have any thoughts about this?

[SailingHarmonie]

This ought to be a really simple problem for anybody with access to the engine, a multimeter and the wiring diagram.

In the absence of a multimeter, has anybody tried just changing the temperature switch? or maybe the oil pressure switch? Those would be the obvious first guesses.

[capt jgw]

Just a WAG, but I believe that engine uses the same buzzer for temperature and oil pressure, right? Maybe the OP sender has a fault that's taking that long to clear. Check the wire connections on the oil pressure sender. Might not be temperature at all.

[buckstopper]

Thank you capt jgw and SailingHarmonie,
I have a replacement oil pressure sending unit on order and will report back after installation. if that does not work I will check the temperature sending unit wiring and buy a replacement for that as well, if necessary.
It is simple to replace the oil pressure sensor, but to replace the temperature sensor the coolant has to be drained and the intake manifold removed.

[parkstone bay]

For what it's worth, I back the the suggestion that Oil Pressure might be the issue, rather than temp. On my 12 year old Bukh DV24, the oil pressure regularly takes up to 3, maybe 4 seconds (but no more) to build up, as evidenced by the OP gauge. During these few moments - which seem like forever! - the alarm buzzer, correctly, sounds.
(Incidentally, I only found out by accident that Oil Pressure senders work on 2 different protocols world wide: USA and Rest of world. If the sender is mismatched to the gauge the unit displays backwards - which is a PITA)

[GordMay]

You might be interested in this old thread:
“Basic Engine Gauge Theory and Testing”
➥ https://www.cruisersforum.com/forums....html#post2597

[SailingHarmonie]

I am not familiar in detail with wiring of this engine, but on every other engine I have worked on, the alarm is a separate sensor than the sender to the gauge. Changing the sender to the gauge will do nothing to fix the problem. That's why looking at a wiring diagram and actually understanding the issue is important.

On most engines the alarm is activated by a switch that closes when the temperature gets too high, or a different switch when the oil pressure is too low. That switch closure makes a connection to the engine block ground, which allows current to flow through the buzzer, which then makes noise.

I don't have any reason to suspect one switch over the other, both could have a fault that would behave like this. Unless you have an idiot light that is coming on and telling you which alarm is active?

A simple test with a multimeter would answer the question and save the money of replacing a good switch.

I find it hard to wrap my head around idea of multiple professional mechanics who were stumped by this problem.

[GordMay]

As noted, in my previously linked post, Alarm Switches are "On-Off" devices, either Normally-Open or Normally-Closed; which switch 'On' or 'Off' in response to a pre-set condition. Switches are utilized to operate Warning Lights and/or Buzzers.

In order to test a ‘Normally Closed” oil pressure alarm switch, you can connect your multimeter, set to measure resistance [or continuity], between the pin and the sender’s body. You should find the switch is closed, showing zero Ohms [Cont.], while the engine is at rest. When the engine is running, the switch should open, showing infinite Ohms.

The opposite is true for a normally open oil pressure switch. While testing this switch with the engine not running; the switch contacts should be open. The meter should display infinite Ohms [Open]. When the engine is running the oil pressure increases beyond the preset value, and the contacts should close; the meter should now display zero Ohms [Cont.].

[capt jgw]

Originally Posted by GordMay

As noted, in my previously linked post, Alarm Switches are "On-Off" devices, either Normally-Open or Normally-Closed; which switch 'On' or 'Off' in response to a pre-set condition. Switches are utilized to operate Warning Lights and/or Buzzers.

In order to test a ‘Normally Closed” oil pressure alarm switch, you can connect your multimeter, set to measure resistance [or continuity], between the pin and the sender’s body. You should find the switch is closed, showing zero Ohms [Cont.], while the engine is at rest. When the engine is running, the switch should open, showing infinite Ohms.

The opposite is true for a normally open oil pressure switch. While testing this switch with the engine not running; the switch contacts should be open. The meter should display infinite Ohms [Open]. When the engine is running the oil pressure increases beyond the preset value, and the contacts should close; the meter should now display zero Ohms [Cont.].

If the pressure switch is meant to only operate an idiot light, it's likely "normally closed". With no pressure the switch is closed and the light is on. When pressure rises the switch opens and turns off the light. It's a lot simpler to wire it that way so it's most likely what they would do. A buzzer can be wired in parallel with the light and would work the same. I added one to one of my engines that didn't come with one.