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Continuous Alarm before Startup

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cham

Contributing Member
I’ve got a 1995 Chaparral 1930SS with a 5.0L V8 Mercruiser engine. Specifically it’s a 350 Mag Alpha/Bravo.

Went to start it up this spring and before I could, a continuous alarm sounds in the ignition on (run) position. Never actually tried to start it. Based on my research and calling Mercury Marine, this can only be a few things.

1. Low oil pressure, which will only go off continuously if the engine is running and meets a few other parameters if I’m correct. This makes me think even if the sensor is bad, the engine has to meet those parameters before it can sound the alarm.

2. Excessive water temps; haven’t started it so obviously it’s not overheating but it could still be the sender/switch being faulty.

3. Lastly it could be low stern drive oil level or bad oil level sensor.

Let me know if I missed anything but this is what I was told by Mercury Marine.

So for the temperature sensor sender and temperature switch, I unplugged the wires for both, turned the key, alarm continued to sound. This is the correct way to test right? The switch doesn’t make continuity to ground until engine temp is above the overheat threshold?

I have checked the gear oil reservoir level and it is full. I’ve heard the float can stick but it’s in a tough to reach location so moving a pencil around in the reservoir made no difference. I cannot remove it unless I cut the oil level sensor wires either. Can I cut one of its wires to see if that fixes the alarm as that would prevent any continuity to ground?

Will low battery voltage sound a continuous alarm before startup? It does have a two battery system.
 
The oil pressure switch is if the ignition is on, doesn’t have to be running

That is normal, every time you start it goes off until the engine has been running a few seconds and gets oil pressure high enough. The switch opens at 4 psi and interrupts the ground side of the buzzer. Yes you are correct taking the wire of these switches should eliminate the alarm if one of the switches is at fault, but try starting it, should shut off after a few seconds of running.
 
That’s interesting, I’ve read an heard both opinions. I gave the Mercury Marine tech rep the Serial No. and like I said, he claimed the system knows the engine is not running and said it can’t alarm for low oil pressure until at least 5 seconds of the engine running. But I’ve also read online people echoing exactly what you said.

As far as it being normal, I’ll have to ask my grandfather again what it used to do in past seasons, its his boat. It is very possible it has always done this and for whatever reason this season made him think differently. I’m used to 2 stroke Outboards so I’m a little out of my depth lol.
 
sandkicker said:
Carbed or injected.... Carbed engines alarm soon ignition sw is on... injected engines are smarter.
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Yes it is carbed. In my experience with Outboards, the systems would do alarm checks when you turn ignition on which would just be a beep or two confirming the different alarms are working. Are you sure the continuous alarm is normal?
 
cham said:
Yes it is carbed. In my experience with Outboards, the systems would do alarm checks when you turn ignition on which would just be a beep or two confirming the different alarms are working. Are you sure the continuous alarm is normal?
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Yes 100% normal turn the ignition on and without the oil pressure switch being electrically open due to oil pressure being above 4 or 7 psi it will sound. You have outlined the three switches that will make it stay on after it is running. Do you have a working oil pressure gauge? If you are worried watch the oil pressure gauge or hook up a cheap mechanical gauge
 
Okay I hear you. So I’m guessing in that case the ECM-555 or triple nickel ECM doesn’t apply to my engine, only adjacent models? This seems to have more reasons for continuous alarms like fault with sea pump (water pump), engine over speed, etc.

I’m still wondering if the alarm can sound if one of my batteries is low voltage. I’ve charged the main battery but the backup is likely dead.
 
cham said:
Okay I hear you. So I’m guessing in that case the ECM-555 or triple nickel ECM doesn’t apply to my engine, only adjacent models? This seems to have more reasons for continuous alarms like fault with sea pump (water pump), engine over speed, etc.

I’m still wondering if the alarm can sound if one of my batteries is low voltage. I’ve charged the main battery but the backup is likely dead.
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You say yours is carbed ? in post 1 you mention two different engines- you say it is a 5.0L and then also say it is a 350 Mag. It can't be both as they are two different size engines. The 5.0l is a 5.0l/305 CID V8 , the 350 mag is a 350 CID /5.7 V8

do you have an engine photo or serial number

Yes the carbed engines really have only those 3 faults, while the Fuel injected and MPI engines have a control unit with more capacity for fault generation and storing.
 
Dieter said:
You say yours is carbed ? in post 1 you mention two different engines- you say it is a 5.0L and then also say it is a 350 Mag. It can't be both as they are two different size engines. The 5.0l is a 5.0l/305 CID V8 , the 350 mag is a 350 CID /5.7 V8

do you have an engine photo or serial number

Yes the carbed engines really have only those 3 faults, while the Fuel injected and MPI engines have a control unit with more capacity for fault generation and storing.
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Oh sorry I was going off what Marine Engine spits out when you input the Serial No. From Marine engine:

Mercruiser (200 / 5.0l / Lx 260 / 5.7l 350 Mag Alpha / Bravo) Engine Components​

I now see the 350 refers to 5.7L.

It is a 5.0L and I see the 305 CID for the displacement on the engine arrestor cover plate. Photo below
 
It’s not allowing me to post a photo of the engine cover but I assure you it’s the MCM 5.0L V8 305 CID. Serial No: 0F429743. It is definitely carbureted.
 
So after another phone call with Mercury Marine and them telling me it’s not normal and should not be sounding a continuous alarm before startup, I asked for them to send over the engine Owners manual.

Low and behold this is what I found:
IMG_2431.jpeg


I even asked the tech rep to look at the manual to confirm it can only be those three variables causing the alarm to go off. He must have not seen the “NOTE” just below.
 
The water temp switch and the low gear oil resevior sensor will NOT cause an alarm with ignition key in the on position as long at the temp is below switch set point and gear oil level is above sensor level.

The oil pressure switch see Zero pressure when engine is not running and that triggers the alarm.

As Dieter said once engine is spinning/running and oil pressure gets above ~4-7 psi, the oil pressure switch opens and alarm goes away
 
kghost said:
The water temp switch and the low gear oil resevior sensor will NOT cause an alarm with ignition key in the on position as long at the temp is below switch set point and gear oil level is above sensor level.
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Yes I know. That is as long as those sensors and switches are not faulty and grounding out.

Regardless the constant tone before startup is normal and all is well as long as it goes out after the engine is turning (oil pressure builds).

Thanks guys for lending me your insight. I appreciate y’all bearing with me 🤙!
 
cham said:
Yes I know. That is as long as those sensors and switches are not faulty and grounding out.

Regardless the constant tone before startup is normal and all is well as long as it goes out after the engine is turning (oil pressure builds).

Thanks guys for lending me your insight. I appreciate y’all bearing with me 🤙!
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Know you know and get used to where your gauges should be. Normally it doesn’t start to over heat overnight. On my old boat I saw the idle temp creep up 10-15 degrees as the impeller wore over a period of years… then next time I used it temp pegged as vane busted off the impeller. In retrospect could ve seen that coming
 
Thanks @Dieter , turns out its never as simple as one would hope. So fired her up today and the alarm stayed on while running for about 10-15 seconds. The first I have heard about this, but the oil pressure gauge was pinned at max last year so he had the mechanic look at it when it got winterized. Turns out sender was not plugged in and the gauge was faulty per the old invoice. So the shop then replaced the sender and gauge.

Curious now because the shop took it out on the water to perform other tests as per the invoice, so I would have assumed they would catch an alarm going off with the engine running. Can't imagine it'd develop while it was sitting over the winter. Is there a separate sensor-switch for the oil pressure sender that is connected to the alarm buzzer system? The overheat temperature system had two probes where the thermostat was, it seems one was for the gauge, and the other was for the alarm.
 
If you track down all tan with blue striped wires you should find one leads to gear oil resevoir, one to temp switch and one to oil pressure switch. If your oil filter is down and to the back of the engine on passenger side of boat, it may be very close to the oil filter. if not there it may be on the intake manifold near the distributor

Again the wire color attached will determine if its part of the alarm circuit.
 
Are the gauge wires also tan and blue because both of the temperature probes for the overheating circuit had a tan with blue stripe wire.
 
Here is the schematic. Its up to you to find the devices on the engine.
If you strongly feel you have an issue you may consider going back to the shop that did the work and inquire about your issue or have them test it.

5.0 1993 alpha.jpg
 

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cham said:
Thanks @Dieter , turns out its never as simple as one would hope. So fired her up today and the alarm stayed on while running for about 10-15 seconds. The first I have heard about this, but the oil pressure gauge was pinned at max last year so he had the mechanic look at it when it got winterized. Turns out sender was not plugged in and the gauge was faulty per the old invoice. So the shop then replaced the sender and gauge.

Curious now because the shop took it out on the water to perform other tests as per the invoice, so I would have assumed they would catch an alarm going off with the engine running. Can't imagine it'd develop while it was sitting over the winter. Is there a separate sensor-switch for the oil pressure sender that is connected to the alarm buzzer system? The overheat temperature system had two probes where the thermostat was, it seems one was for the gauge, and the other was for the alarm.
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10-15 sec seems a bit long , I would unplug the oil pressure switch and see if the alarm stays off might just be the switch being a little lazy or gummed up.

Note this is completely different from the sender gauge issue mentioned, the buzzer uses a switch gauge uses a sender to vary an ohm signal for gauge. Switch is open or closed at 4-7 psi like an idiot light in an older car. Jack has given you the wiring diagram.

if it were my boat I would hook up a cheap mechanical gauge ($25 at auto parts store) look how long it takes for oil pressure to come up when starting. in all likely hood this will be fine. If that is the case I would replace the oil pressure switch see if response changes, or leave it alone and know all is well.
 
Dieter said:
Note this is completely different from the sender gauge issue mentioned, the buzzer uses a switch gauge uses a sender to vary an ohm signal for gauge. Switch is open or closed at 4-7 psi like an idiot light in an older car. Jack has given you the wiring diagram.
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My thoughts exactly. Since the oil pressure sender and gauge were faulty and replaced by the mechanic, logically the oil pressure switch wouldn’t be too far behind those components in terms of longevity and is likely faulty too.

Marine Engine does not show any “oil pressure switch” for my engine though. What it does show are two different “oil pressure senders”. One being a “dual sender”.

Based on my research it sounds like the “dual sender” can be a type of combination sensor and switch? I think that means it has its own probe just like the temperature sensor switch did. It monitors oil pressure itself before deciding to open its circuit while the “oil pressure sender” for the gauge is totally different and only monitors pressure.
 
Not sure of your engine serial number which is the best way to confirm but I believe it is #5. The dual sender is for dual helm boats where you have two sets of gauges... i believe the switch will be mounted on top of block end wall by distributor. Its either there or above the filter. I believe it has one wire on it check wires colors vs what jack sent.

MerCruiser 5.0LX (4 Barrel.) GM 305 V-8 1988-1995 Audio Warning System Parts

MerCruiser 5.0lx (4 bbl.) gm 305 v-8 1988-1995 audio warning system parts. Buy a genuine Mercury Quicksilver or aftermarket part.
www.marineengine.com www.marineengine.com
 
Dieter said:
Not sure of your engine serial number which is the best way to confirm but I believe it is #5.
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Haha you beat me to it. Alright this will be the first thing I’ll check for failure.

If that checks out, then I’ll try the stern drive gear level sensor. If that checks out I think it’s time to just have the mechanic remedy something he might have wired incorrectly. Certainly wanted to avoid this as there is no telling how many weeks out he is. I’ll report back my findings 🤙!
 
cham said:
Haha you beat me to it. Alright this will be the first thing I’ll check for failure.

If that checks out, then I’ll try the stern drive gear level sensor. If that checks out I think it’s time to just have the mechanic remedy something he might have wired incorrectly. Certainly wanted to avoid this as there is no telling how many weeks out he is. I’ll report back my findings
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It doesn't sound like the mechanic did any thing wrong so probably taking it back will be a waste of time. It really doesn't appear that there is anything wrong with your boat, just taking a little longer than normal to open the oil pressure switch. if it was gear lube it would be going of constantly and not shut off
 
Dieter said:
It doesn't sound like the mechanic did any thing wrong so probably taking it back will be a waste of time. It really doesn't appear that there is anything wrong with your boat, just taking a little longer than normal to open the oil pressure switch. if it was gear lube it would be going of constantly and not shut off
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Sorry I probably wasn’t clear enough. The alarm never shut off when we started the motor. We only ran the engine for 10-15 seconds before shutting it off to be cautious since the alarm was still sounding.

I found my answer today though. So, they didn’t actually replace the sender like the invoice says. They ended up replacing the oil pressure SWITCH with a sender (wrong part). Unplugged the tan/blue wire and viola alarm is gone. So we’ve got that part on order now.

Makes sense why he never had a startup alarm before as the invoice says the “sender” which was actually the switch, was never plugged in. My grandfather asked them to look into the oil pressure gauge since it wasn’t working so they replaced the gauge and what they thought was the sender but turned out to be the switch. Hopefully this makes sense!

It also turns out the oil pressure gauge sender is up by the distributor, and the oil pressure switch location is down towards the bottom and back of the engine port side.

Here a photo of the oil pressure switch location; you can see they used a sender instead of the switch (I wrapped electrical tape so we could launch the boat and stop the alarm):

1718416202655.jpeg



Here is what it should look like:

1718416236106.jpeg


I am curious, when we go to replace the sender with the switch, will oil begin to drain out of the block?
 
You will loose a little bit (maybe an once)...most will drain back into the pan...you can use a small foil pan to catch most of it...the drips are the worst part.
 
When ordering the Switch I noticed an extra brass fitting in the diagram. I do not have the original part to compare obviously so what do you guys imagine it is for? Is it necessary? There are two options as well, and one is three times the price of the other. I went ahead and just added the cheaper $6.66 fitting just in case I need it.

Switch Fitting.png



Are the two brass spacer/adapters different in any way?

Switch Fitting Options.png
 
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