01 200 ox overheats

[Fl_Richard]

My buddies engine is overheating. We replaced the thermostats and PRV. He claims the impeller was replaced a few months ago. New stats helped but motor still overheats at about 3800 rpm consistently. Pees a good stream, stream is cool while alarm sounds can hold my hand for two seconds on head at the thermostat location. (feels hot -youch) Splashing water on them was never hot enough to boil. The Yamaha LCD gauge flashes a bar above the over temp icon.

The motors never entered any limp mode or power drop when the alarm sounded. After a shut down of both motors the alarm would silence. The port motor would alarm temperature for a minute or two them be perfectly happy buzzing around at 3600 RPM's. Any more RPM and the alarm would eventually start again. Any clues? On a Johnson I'd be looking at water tube alignment and impeller/pump housing.

The thermostats had corrosion on them and their seats and passages received a good clean out when we replaced them. The water passages themselves were surprisingly small. I could stick my pinky in the PRV hole it felt clean. I was told that Yamaha's scale up in the heads causing this water circulation problem and overheating.

Thanks for the help.

 

[Fl_Richard]

Re: 01 200 ox overheats

^^^ Added info and bump

 

[99yam40]

Re: 01 200 ox overheats

You can test the temp switches/sensors to be sure they are working properly, but my guess is the scaling build up in the cooling passages

 

[Fl_Richard]

Re: 01 200 ox overheats

The parts diagrams look like the water jackets are removable from the heads without removing the heads. Do you think if I removed these and cleaned them up it will solve the overheat issue?

I talked to the owner today, he says he's sure the impellers were installed correctly and the watertubes are aligned properly.

 

[99yam40]

Re: 01 200 ox overheats

like a I said test the temp switches/sensors to be sure they are working properly. if they are then you are getting a true high temp. I have seen a impeller loose pieces if started without water in the pump in just a few seconds.

 

[rodbolt]

Re: 01 200 ox overheats

if its an overheat and its above 2000 RPM it will go into RPM reduction. what indicates are you getting on the tach?

 

[Fl_Richard]

Re: 01 200 ox overheats

Flashing LCD "Block" above the water temperature icon on the tach. Does the power drop occur at the exact same time as the alarm sounds? I shut it down as soon as the alarm sounded, is it possible I shut it down (one hand on the throttles one on the wheel) before the system did?

 

[rodbolt]

Re: 01 200 ox overheats

it pretty much happens at the same time.
if the cooling system is known good then most likly scale has built up under the head blocking the blind pasage that leads to the switch location. usually means pulling the covers and the head to manually descale it.
aint saltwater wonderful .

 

[Fl_Richard]

Re: 01 200 ox overheats

My salty Johnsons dont scale up They seem to have water passages five times larger than these Yammies... but thats another thread.

I'd rather not pull the heads to descale. I can, but for the favor factor I'd rather keep it as non intrusive as possible. Can I do a reasonably good job of descaling by just removing the head water covers?

Thank you!!

 

[rodbolt]

Re: 01 200 ox overheats

nope
head covers are on the discharge water side.

 

[Fl_Richard]

Re: 01 200 ox overheats

Well alright but it's gonna cost him some good beer. Nothing in a can

Thank you, why is it never easy?

 

[rodbolt]

Re: 01 200 ox overheats

dunno.
but chivas or glen levit works.

 

[krisnowicki]

Re: 01 200 ox overheats

I had a merc outboard and put it in a barrel with vinegar and water mixed and pump it through all day, if the water in the barrel got to hot shut it off or add ice. I let it idle and cicle all day and you would see the bits coming to the top. Scale is nasty.

 

[Fl_Richard]

Re: 01 200 ox overheats

Wish it could be so easy. I thought about running some CLR through it with a auto soap dispenser in the rinse line..... I'm going to test the sensors just because. Then I'm sure I'll be pulling the heads to do a proper job.

It's never easy...

 

[rodbolt]

Re: 01 200 ox overheats

salt water is wonderful.
jonnyrudes scale up,mercs scale up.
saltwater is an equal oppertunity nasty.

 

[Fl_Richard]

Re: 01 200 ox overheats

Well I pulled the twin Yammy heads and water covers.. they didnt look to bad. Pressure cleaned them to blast of the scale and re-assembeled.

Sunday we took her out 22 miles, it would run WOT without over heating for the first time since I've been on the boat.

We worked on the scale starting at about 9:00 am until about 2:00. Thats five hours for two engines. Cost $240 in parts for both motors and they run grrrrreat!

Thanks Rodbolt! You nailed it!

 

[rodbolt]

Re: 01 200 ox overheats

glad ya gotta cadillacing.
if ya do something 30+ years ya may just get lucky once or twice .

 

[Fl_Richard]

Re: 01 200 ox overheats

Thats why it's nice to get advice from a professional. I can spin a wrench (or a wench) and do OK. But first time in it's awfully nice to know how deep the water is.

Thank you again! I truly apriciate your expertice and judgement.