Where is Engine Audible Alarm Oil Switch ?

[Julian]

I have a 2400 SCR and get alarms every now and again.

Its a 5.00 Merc with Carb and Alpha 1 leg. closed cooling. Year 2,000

New leg water pump and thermostat installed

Oil Pressure and temperature appear to be ok 165f / 40psi

I cleaned out the Leg oil bottle, it still alarmed.
I disconnected the Leg oil bottle, it still alarmed.

I replaced the temperature switch for the alarm, it still alarmed

I decided to change the oil switch out and believe the part is 87-805605A1

The problem I have is I cant seem to find the audible alarm oil switch. I called Mercruiser and asked where it was located and they did not know ?
They told me there should be 3 oil switches/senders. I found the cone shaped fuel pump cut off oil switch.
T'd into the same fitting is the oil gauge sender unit , however I looked down both sides of the engine and the front of the engine.

Can anyone please tell me if there is in another oil switch and where on the engine it is located, I have seen wiring diagrams showing the switch but cant locate it on the actual engine.

I am new to boating and any help from anyone who knows the location of the switch it would certainly be appreciated.
Thanks

[mmwjr]

Welcome aboard

The gauge sendor which is bell shaped is next to the distributor.

The fuel pump oil pressure switch and alarm switch are just above the blocks oil filter location on the port rear down low by the oil pan interface.

The alarm switch will have only one wire on it, tan.

[Julian]

Hi Mike,
Here are pictures of the 2 sensors on the side of the engine are you saying the one with one terminal is the engine oil audible alarm switch, if the gauge sender is located on top of the engine, is it plumbed into the head ?? I know the 2 terminal model is the fuel pump switch
Thanks

[mmwjr]

Nope the first one is the gauge sendor and should be mounted on top of the engine near the distributor.

The alarm sendor is small.

Take a look at the merc engine manual located under the documents tab of this site.

[Julian]

Hi Mike,
These are the 2 on the side of the engine teed together next to the oil filter at this time I cant look around the distributor. Here is the picture of the alarm sensor the dealer has ordered. however there is nothing like this on the side of the engine next to the oil filter, just the 2 i previously posted
Does the manual actually show a picture with its location or just a wiring diagram ?
Thank you

[mmwjr]

Ok what mentioned is the typical set up.

Yes this last on is it. There is another oil port on the top of the engine back on the port side next to the distributor.

Tan/blue wire.

The manual does not show the location but does have the wiring diagram.

[mmwjr]

mercruiser oil pressure switch


mercruiser oil pressure switch

Link to diagram

Sorry having trouble posting link from iPad

[Julian]

Thanks, I will have a look tomorrow for this last sensor next to the distributor on the Port side, you say it is still in the block and not close to the inlet manifold or head ?
Thank you for your help

[mmwjr]

Originally Posted by Julian

Thanks, I will have a look tomorrow for this last sensor next to the distributor on the Port side, you say it is still in the block and not close to the inlet manifold or head ?
Thank you for your help

Yes on the block but the intake manifold rear gasket is next to it.

[Julian]

Thanks Ill check, its not easy for a big Boy

[Julian]

Thanks , Found it covered in black paint from when the engine was painted new. Hard to see as it blended in.
I hope this fixes the alarms if not I am not sure where to look
Once again thanks for the help

[Julian]

Well, changed oil pressure switch,
Still alarms when running engine under load at 3,000 RPM on plane. only seems to come on for a few seconds and as soon as you back off the throttle it stops the alarm. Disconnected the temp alarm switch and the alarms seem to stop, however the alarm is intermittent so who knows

Disconnected new oil switch, disconnected leg oil bottle, connected temp alarm switch & still alarms.
Temp gauge never moves from 175 however using laser temp the intercooler reads 165 on the outside.
Does anyone know what temp the water temp alarm switch triggers at. (this is a new switch)
I wonder if its air pockets, (enclosed system )engine water pump, short circuit
The intercooler always seems a bit low but when I top it up the level of the overflow bottle increases. It appears that the overflow system bottle only acts as an overflow bottle as there is a top hole in the bottle so its not a sealed system sucking coolant in and out like a car overflow
Any help appreciated
Thanks

[mmwjr]

So the new temp switch still causes an alarm?

Yet temp sender and helm gauge as well as IR say its good?

Sounds like either the new switch is faulty or damaged.

[gmc60]

wow what kind of boat came with that girl ?

[Julian]

Originally Posted by mmwjr

So the new temp switch still causes an alarm?

Yet temp sender and helm gauge as well as IR say its good?

Sounds like either the new switch is faulty or damaged.

Thanks Mike. I somehow dont think it is however at this point I am not totally sure. The Engine has an enclosed San Juan Fresh water cooling system, which I notice in their instructions that they say it might take some time to get the air out of the system.
I have just installed an additional temp gauge on the temp alarm sensor location, and confirmed its accuracy with a laser temp, however I havent been able to take the boat out. Running at unloaded RPM and idle the temp seems great 150-156f, the more you rev it out of gear the more the temp decreases.
Can anyone contribute to this idea, that when the boat is on plane (usually when the alarm sounds) the brass sensor housing is probably at one of the highest points on the engine and there could possibly be air in the system which enters the brass alarm sensor location and triggers the alarm due to cavitation. I automatically back off as soon as the alarm occurs, then the alarm clears.

Any suggestions appreciated

Thanks

[Julian]

Does anyone know at what temperature the hot engine alarm sensor triggers on a 2400 SCR, the sensor is part number WT3000 or old number WT3000P thanks

[mmwjr]

Between 180 and 200. This is to hot for an open cooling system. Try using an IR temp gun to get actual temps from different points.

[jparsons121]

Two comments for consideration..

1) The switches complete the circuit by providing a ground to the buzzer when tripped. So inspect the wiring to be sure that the intermittent issue isn't caused by one of the sensor wires grounding out against the block, etc.

2) Air is a poor heat conductor, so if an air pocket was making it's way thru the system to the t-stat housing/sensor you would see a drop in temp. At least that's my experience when I lost cooling and overheated. Temp went up and up, then dropped to nothing when the water boiled off in the system..