Yamaha 40 overheat issue

CDory23 · Posted: Mon Jan 04, 2016 9:28 pm Post subject: Yamaha 40 overheat issue

When I went out for the last day of rockfishing at bodega bay on New years eve I ran into some Starboard motor issues. I warmed the motors at harbor as normal and headed out. I was cruising for about 20 minutes to the fishing grounds when the starboard motor alarm came on. I immediately shut it down to problem solve. The gauge indicated it was a temperature alarm. Once allowed to cool a bit I started it up expecting to see the telltale not peeing water. It had a strong stream, it should as I just replaced the impellers around 50 hours ago. I ended up salvaging the day going to closer fishing grounds with the port motor averaging about 10mph.

Today I got around to removing the thermostat and I found quite a bit of corrosion when I removed it, but the thermostat tested fine.. Maybe the corrosion was built up so much it restricted flow? Perhaps I loosened it when I removed it and that made it test fine? So now I"m at the stage of trying to clean the corrosion as good as possible and confirming that this area was the problem issue. I decided to remove the port motor thermostat as well and the corrosion looked about the same.

Are there any tips on confirming this was the issue before I go back in the water and find out the hard way again? I was hoping there is a way to clean the whole passage way out and also test the stream post thermostat flow.

Any advice appreciated.

Thanks
Any tip

South of Heaven · Posted: Mon Jan 04, 2016 10:12 pm Post subject:

I can't give you any advice on your issue but I'm very interested in it. I have an 09 Yamy 40 (EFI). What year is yours? I'd love to know why the alarm came on but the impeller is good. Maybe you sucked in some seaweed or something? Then when you shut the motor off the "suction" stopped and the blockage was discharged?

hardee · Posted: Mon Jan 04, 2016 10:14 pm Post subject:

Did the alarm stay on after you allowed it to cool and even with the good pee stream?

tsturm · Posted: Mon Jan 04, 2016 10:49 pm Post subject:

C-Val · Posted: Mon Jan 04, 2016 11:48 pm Post subject:

I had a overheat alarm for the first time this summer. I didn't even know what was happening at first. I do know it was rough and I was lugging a bit with a heavy load, but I really think it was seaweed partially blocking my intake.

There was a lot of stuff in the water and after I stopped and made sure it was clear it never happened again.

(In my case, I am thinking of buying a lower pitch prop for heavy loads in rough water as well)

CDory23 · Posted: Mon Jan 04, 2016 11:53 pm Post subject:

I failed to mention that one of the first things I did was raise the motor to check for a blockage. There was none. Also throughout the day I started the motor up several times to see if the problem had gone away. The tell tale stream was strong every time the motor was running but it would over heat quickly. At this point I"m going to clean the corrosion as good as possible and see where that gets me.

I also may reinstall the cover with no thermostat and see if I get an overheat with just running engine on idle in driveway.

The corrosion looked as if it was in a pattern where the end of the thermostat sets and could potentially blocked flow even when open. Also with such blockage maybe I sucked something small up that could normally pass through but was trapped by the corrosion layer creating even less to no flow leaving me with the overheat issue. I'll post back with progress

T.R. Bauer · Posted: Tue Jan 05, 2016 12:22 am Post subject:

Well, nobody is going to know for sure, but I think your hypothesis is probably spot on with the corrosion - gauge reads hot, good water flow at the indicator, but little actual cooling. On some motors is is possible to remove the temp sensor (if it is even threaded) and put something you can attach a hose to in there to measure if it is flowing to the top end at all. I think it is now. If open water is close by, well it's a great excuse to get out of the house and test it.

hardee · Posted: Tue Jan 05, 2016 2:22 pm Post subject:

Might also be a faulty temp sensor, maybe.

Harvey
SleepyC Moon

CDory23 · Posted: Tue Jan 05, 2016 3:49 pm Post subject:

Are you speaking of the temp sensor that detects the oil temp?

rogerbum · Posted: Tue Jan 05, 2016 3:55 pm Post subject:

greeneyegi · Posted: Tue Jan 05, 2016 7:06 pm Post subject:

I just purchased my 2003 dory with twin yammy 50s a couple months ago.I got a great deal because the marina reported to the new owner of 1 week that he needed to repower the boat(9xx hours) because of corrosion,one motor had an alarm for hi temp alrm.

Long story short.The thermostat was corroded and had backed up the flow a-bit.There is a cover you can take off the side of the motor to see the cooling system of the motor.Mine was perfect.No corrosion whatsoever.Typically their is a bit of corrosion around where the stat sits.Block is a bit thin there.
I took my air/power washer tip i have for engine cleaning,used some special salt away and cleaned it up and its been perfect every since.
Ive got a inspection camera that fits in small holes spark plug holes etc to inspect this stuff.Very cheap cool tool that can actually plug in your smart phone.
If youre interested in this i can explain to you in more depth.What to do.Took a good three hours to dissasemble and have back together.
I wouldnt worry too much

BrentB · Posted: Tue Jan 05, 2016 7:11 pm Post subject:

how old are the thermostats?

CDory23 · Posted: Wed Jan 06, 2016 10:28 am Post subject:

The thermostats are the originals from 2003. I don't think they have ever been taken out or inspected. I will be doing so now every impeller change. I don't see a reason in replacing them since they test fine. I'm going to clean everything up as well as possible tomorrow (my day off) and put her back together and hopefully test out soon.

Anybody have any idea how large the water jacket passage is post thermostat? Is it safe to say anything that passes through the thermostat should safely pass through the entire cooling jacket? Any other areas I can easily concentrate on or clean?

Also, if I see this much corrosion around where the thermostat sets causing issues should I expect there to be more other places or is this particular area more prone to corrosion build up issues perhaps because of the different metals and obstruction in flow due to the thermostat.

Thanks

greeneyegi · Posted: Wed Jan 06, 2016 10:35 am Post subject:

while replacing thermostats,you might as well open that plate/cover on side and look inside the block.It all depends on if the motor was flushed after salt water use.

CDory23 · Posted: Sun Jan 10, 2016 11:13 am Post subject:

Took the boat out yesterday after a complete cleaning of the thermostats and the area they sit to include a 24 hour period of Corrosion x doing its work. That solved the issue. I really think thermostat inspection should be part of routine manintenance when the impeller is changed. I'm adding it to my duties.

Thanks all for the help.