Universal M25XPB, water temp gauge OR alarm faulty

[jtg]

I have just serviced the engine (Hx cleaned & test, cleaned strainer, new raw impeller, manifold cover, tested thermostat, oil & filter, & fuel filters).
On the last two or three outings, motoring at 1500-2000 rpm, after 30-40 minutes, water temp gauge shows ~165F, alarm buzzer starts an intermittent and periodic crackle. On the last outing, after about 40 minutes, water temp alarm sounded, water temp gauge still shows ~165F.
I ran through the CatalinaDirect, test/confirm gauge (substituting BRN with YEL wire according to my boat and universal documentation) through step 3. Step 4 suggests sending unit may be defective.
I am left wondering, has my sender (to gauge) gone bad, has my switch (to alarm) gone bad, and/or do I have an un-invited switch to buzzer ground.
On my next outing, given crackle or water temp alarm I will remove the wire connection to the switch hoping to confirm/discover that after 40 minutes running there is an un-invited ground with the brown wire.

Any other ideas, tests, or suggestions?
TIA
jtg

 

[JoeWhite]

Does the alarm sound stop if you increase or decrease the RPM? If so then it is the alternator arm bracket that hits against the engine. Increase the clearance by placing a thick washer behind the bolt
Also check if the alternator bracket that is mounted to the engine is cracked or broken.
MORE INFO ADDED:
The high temperature alarm sensor is a plug. Inside the plug is a bimetal strip. As the engine vibrates at some resonant frequency the bimetal strip oscillates violently inside it's housing and grounding causing the buzzing sound at certain RPM.
Changing the engine RPM stops the resonant frequency.
The engine shakes more than normal as a result of broken alternator bracket.

 

[Ralph Johnstone]

Welcome to the site.

alarm buzzer starts an intermittent and periodic crackle.

Check the following:

1. With the buzzer coming on as a crackle, I would suspect a ground fault. The temperature switch is an ON or OFF switch which SHOULD produce a full audible sound or nothing.​

2. Check the block temperature with an IR gun.​

3. I would think the switch rating is higher than 165 deg. See if you can find a temp. stamped on it.​

​

If nothing else makes sense, replace the temp. switch as they're not expensive.

 

[Benny17441]

Have you inspected the wiring harness from the engine to the control panel? Usually a visual inspection will show if the insulation has chaffed in its path against a sharp fiberglass corner. I suspect you may be looking for an intermittent electrical short and since the alarm wires run through this harness it is a most logical place to find a problem.

 

[jtg]

Does the alarm sound stop of you increase or decrease the RPM? If so then it is the alternator arm bracket that hits against the engine. Increase the clearance by placing a thick washer behind the bolt
Also check if the alternator bracket that is mounted to the engine is cracked or broken.

Joe,
Confused again.
Before installing washers on the arm bracket, tried to simulate a test. With the engine running I grounded the alternator bracket. Nothing. No crackle, no alarm.
I could not simulate, nor remember, the particular RPM that was most popular with either crackle or alarm.
I have yet to check the alternator mounting bracket for cracked or broken.
Jerry

 

[jtg]

Have you inspected the wiring harness from the engine to the control panel? Usually a visual inspection will show if the insulation has chaffed in its path against a sharp fiberglass corner. I suspect you may be looking for an intermittent electrical short and since the alarm wires run through this harness it is a most logical place to find a problem.

Benny,
Concur. I like simpler. I have traced out the better part of the path of the BRN (alarm) wire. Nothing jumped out as worn to support a short.
My next 'sea trials' will follow this line of thought. If it continues to crackle and then alarm, I intend to remove the BRN wire from the thermostat and alarm and run a jumper connection. If the crackle and alarm go away, it is an electrical short. If the crackle and alarm continue, it is the switch.
Jerry

 

[captcoho]

If you had the coolant system empty for service, did you fully purge all the air out the system? If you have coolant lines going to the water heater there are many places to trap air, and that may cause the temperature to rise. My dock neighbor battled this issue for a whole season until he managed to "burp" all the air out. He checked the stat twice, searched all the wiring. removed and reinstalled the Hx, replaced the pressure cap, changed all the hoses and clamps, opened and closed the bleeder. Until he somehow got trapped air out.

 

[peter_ms]

You will likely find the the connector/wire on the oil pressure sender behind the oilr filter is broken or come off making intermittent contact.
the temp and oil pressure alarm are the same buzzer as I recall.165 is normal for the M25XPC

 

[JoeWhite]

Jerry, read my post #2 above, I have added detailed info to further explain.
The oil and high temp alarms are two independant circuits. They are connected to 2 different posts on the soanalert sharing one ground. The soanalert produces pulses for oil and steady sound for water temp.
I suppose to confirm which circuit is producing this buzzing sound, each wire can be disconnected separately from soanalert to find out which one is causing the problem.
Wires can not be disconnected from oil pressure switch as it provides power to fuel pump. You can short the 2 terminal wires to bypass the swich.
This test can be conducted at the slip with docklines tied and in gear rev up during high tide and listen for buzzing.
When in gear the engine works harder and shakes more than idle.

 

[LeslieTroyer]

To test if wire or sensor,
take wire off sensor. - no alarm
Ground sensor wire - should alarm Fully
If above works it’s the sensor. If not it’s something else.

 

[jtg]

Hi Guys,

My apologies, I have still trying to figure out this forum.

Despite tagging this thread to follow, after the first three responses, I was not notified of any subsequent posting.
Following any one conversation (line of investigation) is proving confusing.
Any hinters or pointers appreciated.

I will try to address each facet of this "investigation" in following individual replies.

SPOILER ALERT: I have ordered a new water temp alarm switch.

TIA
Jerry

Ss

 

[jtg]

RE: alternator grounding/resonant vibration.

With the additional detail provided, this makes a little more sense.

I have added washers to the swing bracket and inspected the pivot mounting bracket. The issue remains.

I am further puzzling over why the alarm does not sound immediately but rather only after a varying period of time. Perhaps this is related tension differences?

Testing this will prove difficult because each time I tension the belt I am likely to be defining a different RPM for the resonant vibration.

I assume this will continue with a new switch. :-(

Jerry

 

[jtg]

RE: ground fault

The behavior is: warm up then "crackling" for a short time then "alarming".

I have taken the BRN cable out of the loop jumpering from the switch to the alarm.

Further, my (new) IR temp gauge indicates the temps at various points on the engine seem to be in line with proper operations.

The alarming remains.

Switch ordered.

Jerry

 

[jtg]

RE: burping and/or water heater circuit

This was the issue when the water gauge AND the alarm were firing. I believe this has been addressed with successful bleeding before this current problem: gauge shows good and alarm indicates bad.

Additional details...

I discovered both the water heater circuit AND the reservoir circuit earlier when replacing the old coolant. I initially drained the old (yellow) and replaced with new (pink). While bleeding/burping the coolant was not coming out pink. I immediately drained again, pumped out water heater and reservoir circuits and replaced again with fresh new and bled/burped the system.

Temp measuring posts suggest the engine is not a full operating temp until the coolant to the water heater is the same as the temp from the water heater, thereby potentially providing an additional heat exchanger cooling function. My testing thus far has not yet achieved this coolant temp to/from water heater equality.

I am taking the water heater out of the loop until the gauge and alarm agree.

Jerry

 

[jtg]

RE: oil/water signals crossed.

I am discounting this for the time being as it is the water light that comes on with the alarm. Sorry for not mentioning this earlier.

Jerry

 

[LeslieTroyer]

Another question on setup. Do you have the small circuit board at the instrument panel that is then connected to the alarm and temp gauge? They did this for a short time and it is problematic

 

[jtg]

Another question on setup. Do you have the small circuit board at the instrument panel that is then connected to the alarm and temp gauge? They did this for a short time and it is problematic

Les,

No, no circuit board. The wire bundle comes into the console and the wires are broken out on a conncetion bar to make local connections to either the meters, alarm, or lights. I can provide a picture if you are interested.
jtg

 

[LeslieTroyer]

No that’s ok. When Seaward Introduced the temp alarm they used a small board to piggyback on the analogue temp sensor, and output an alarm signal if current got too “high” indicating over temp. These circuits were crap. Just making sure that’s not your problem.