Isuzu 42

[Timx]

Hi, I have had problems with my alarm sounding, as you start engine it rarely alarms. But I keep an eye on gauges, so not too bothered, although temp gauge, is temperamental and I need to tap it a few times to get a true reading. Anyway today after about a three hour journey, just before last lock of the day, a buzzing alarm type noise started from the control panel. I have never heard that in eight years of ownership. As I turned the engine off the normal alarm worked before I shut it down. I tried it on and off a few times, still same pattern with this loud buzzing alarm. So after 15 minutes I tried it again, and all was fine, then after five minutes it started again, so I moored up for the night. Any ideas what this is, I am approaching the Severn so don’t want to go on there without sorting it. The gauges were fine, the coolant has been changed a couple of years ago and is right level. The control panel top seemed hotter than surrounding area to touch. Any ideas what is wrong ?

[Tracy D'arth]

Could be a temperature alarm if it comes back on so soon after a warm start.

[Timx]

Thanks temp seemed ok although dodgy meter, so a temp alarm within the control.?  Can’t understand if coolant levels are ok. Don’t know what to do.

[Tracy D'arth]

4 minutes ago, Timx said:

Thanks temp seemed ok although dodgy meter, so a temp alarm within the control.?  Can’t understand if coolant levels are ok. Don’t know what to do.

Water pump belt correctly tensioned?  Is it skin tank cooled or raw water with a heat exchanger?

[Timx]

Skin tank, and belts fine, it’s just a weird buzzing alarm.

[Steve56]

5 hours ago, Timx said:

Thanks temp seemed ok although dodgy meter, so a temp alarm within the control.?  Can’t understand if coolant levels are ok. Don’t know what to do.

From memory I think that this engine has a temperature switch which operates the warning light and alarm. Then a separate sender for the guage. Both are by the thermostat housing. When the alarm goes off you could try pulling the wire off the switch to see if it stops. If it does you then have to decide if the engine is really overheating or if there is a fault with the switch or wiring.

[Timx]

Thanks

[Tony Brooks]

I think I would be looking at the oil pressure gauge/switch wiring (if you have either) and the same for the temperature sender/switch. I would not be surprised from the symptoms if a sender wire was not chaffing and intermittently shorting to something metal.

[Timx]

Thank you, I am going to get someone to look at it, I looked at oil level , belts and coolant today before taking off for a short cruise, all fine.

my major concern is that I have been planning on going down the Severn and then up the Avon. Not sure wether  to give that up as too risky given circumstances.

I am also confused by these alarms, the usual one on starting, would I presume, indicate broken belts, no charging, oil or temp, or is that wrong as I have never heard this buzzing alarm, what does that signify?

The temp gauge is dodgy, but usually a couple of knocks on the screen knocks it back to what you would expect, which I did whilst this buzzer was sounding and it went back to just over starting point as usual. 
But after engine cooled for ten minutes it did stay off for ten minutes whilst engine was running before buzzing again, so would that indicate a temperature sensor somewhere else.

I did have the coolant completely changed a couple of years ago, and the level is consistent.

if I get someone out to look at it, what could they tell if there is no problem at the time.?

The usual alarm is inconsistent and I did get a mechanic to look at it, and just by checking the connections it worked straight away till next day.

should I ask them to replace everything?

[Tony Brooks]

If you ask them to replace everything I can almost guarantee they will not replace the wiring so if my thoughts are correct it will not cure the fault. (I am in no way saying it is). It will also cost you a lot of money.

 

This is a classic case of where the boater could get a faster and cheaper solution if they knew a bit about their engine and carried out some simple checks.

 

It is almost certain that you only have one buzzer/sounder that uses diodes to allow it to monitor alternator charge, oil pressure, and engine temperature so the different sound you hear is unlikely to be a different buzzer but the same buzzer operating on  a lower or intermittent voltage. This is why I suggested an intermittent short circuit between a cable and some metal part of the engine and boat. It might also be a problem in the large  multi-plug that many boats have in their main engine wiring harness.

 

The alarm on starting indicates the following, no charge and no oil pressure, as the engine is cold it does not indicate an overheat at that time.

 

However, having spent time explaining about a possible short circuit one has to recognize that the oil pressure and temperature switch/senders are arguably the least reliable part of the engine electrics. This is why you have been advised to disconnect them in turn, so when the buzzing stops you know that you have found a faulty item. Remember that you have been told that you might have a separate temperature switch (for a warning lamp and buzzer) and sender to the gauge. The same could apply for oil pressure.

 

Just to complicate things a faulty alternator could produce the same symptom, so we also need to know what the charging current and voltage does when this problem occurs. If you end up disconnecting the wires on all the senders and engine switches and checking their cables for short-circuiting, but the sounder is still sounding then that only leaves the alternator as the potentially faulty component.

 

If it were not for the potential cost I would suggest checking for shorts and the multi-plug and if no problem is found  simply change the senders/switches, but that will probably cost a lot of money, hence the advice to disconnect each sender in turn plus monitor the charging voltage and current.

[Timx]

Thanks for the information.

[Timx]

So far,a great guy has checked everything, (great boat mechanic)and all looks ok. So last possible problem was actual alarm being faulty, so have ordered another one. But apparently it’s more likely to be with the hot weather and newish solar panels, as this can set the alarm off, with too much power going in, and I need to turn the solar panels off when travelling. All makes sense, hard to diagnose with so many possibilities, but I feel secure it’s not a boat engine problem , but a diagnostic problem.