Yamaha F80TLRB alarm goes off

[2bigreds]

Hi everybody I'm new at this so please help. Took the boat out and engine shut down, open the cover and there was fire melt down at the terminal cover. Towed the boat home, open the cover and found rectifier burn caused CDI, wire and air intake to melt too. After replacing all of these thing, ran the motor, water came out pretty hard, so no problem. On the last trip, after about 5 minutes of idle the overheat/oil alarm goes off. Turn off the motor and the engine block felt warm to touch, so turn on the motor again, pee hole has strong water flow, no alarm sound. In about 5 minutes, alarm goes off again even at low rpm, but if at high rpm, the alarm would go off quicker (2 to 3 minutes). What should I do next, any suggestions, Please help. Thanks

[99yam40]

It would help if you told us what kind of preventative maintenance you have performed on this motor in the past.

I would say replace water pump, stat, and PRV.
Inspect and clean passages if needed.

[2bigreds]

Yamaha F80TLRB alarm goes off

I just bought this boat and the only thing I did before taking it out was new oil change. You suggest that to change: impeller, thermostat and pressure release valve (where is this valve located). Thanks

[2bigreds]

Eventhough the water out the pee hole is strong, I should change impeller anyway? Thanks

[99yam40]

If you do not know when it was changed last then replace all the things that Yamaha recommends as regular preventative maintenance. Indicator stream is just that an indicator that water is flowing , not that it is enough.

You can pull and test the stats and temp switch or sensor to make sure they function properly and replace if needed.
Look for corrosion in the passages to see if you will need to pull motor apart to clean cooling passages.

You will need to look at parts breakdown to see if it has one and where the PRV is located. This valve will cause a low speed overheat if it sticks open normally, but it is a regular maintenance item.

Can you tell if you are getting a low oil pressure alarm and not a overheat?
You should have gauges that would indicate which.

Was that a water cooled rectifier that melted?

[LakeLanierTom]

I had similar alarm on F100TLRB

After a customer repeatedly ran the motor until the overheat alarm went off, I serviced the waterpump and flushed the impeller pieces out the thermostat cover (ran briefly without t-stat or cover installed). The engine would then set off the oil alarm after a few minutes run time. I checked oil pressure by screwing in an analog gauge where the sensor was installed and verified oil pressure was fine, then replaced the oil pressure switch with a new one and the oil alarm quick going off... Apparently they can fail, too. Best to verify oil pressure before you just replace the switch.

I have also had an oil pressure switch rubber boot fill with water and set off a false oil pressure alarm.

Tom

[2bigreds]

Thanks 99yam40 and LakeLanierTom, I will do all those things and let you guys know what happen. Hope that would solve the problem. Thanks again. PS anyother suggestion just keep me posted.

[2bigreds]

Thanks 99yam40 and LakeLanierTom, I will do all those things and let you guys know what happen. Hope that would solve the problem. Oh when alarm goes off both lights (overheat/oil) come on. How do you determine if it's one or the other. Thanks again. PS anyother suggestion just keep me posted.

[2bigreds]

Hey guys, I did all that was suggested (PREVENTIVE MAINTAINANCE) and the alarm DID NOT go off when hook up to water hose. After ran for about 15 to 20 minutes, shut down and felt rectifier regulator (where the problem first started) it is VERY HOT. Does the rectifier regulator suppose to get hot? I'm affraid if it gets any hotter it would burn again. Any idea or suggestions? Thanks

[99yam40]

What all did you do and did you find anything that looked like it would have caused a overheat and oil problem?

If this is not a water cooled rectifier then I would look at the current out put to see if it is putting out max amps for some reason when it is heating up. But it should be able to put out max without overheating.
Maybe not at idle though

Make sure it is mounted properly to the block so that it can transfer heat,
and make sure nothing is interfering with air flow around the heat sink of rectifier

[2bigreds]

I changed thermerstat, all anode, prv and impeller. The thermerstat is slightly corroded, so that might be it. When testing motor, left the motor cover and terminal cover (where rectifier locates) off. By the way, what's the purpose of rectifier regulator and cause of it to overheat and burn? Thanks