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Author Topic:   Yamaha Outboard Motor 200-HP Overheat at Idle and Low RPM
Riptide23WA posted 06-28-2007 05:02 PM ET (US)   Profile for Riptide23WA   Send Email to Riptide23WA  
I have a pair of 1992 Yamaha outboard motors that overheat at very low RPM, typically at or near idle. Usually, it happens as I'm approaching my marina slip, idling just in gear as I enter the approach. I have good water flow out of the telltale at low RPM, as far as I can tell, without the use of a pressure gauge.

The engines have water pumps only two years old, and my slip is pretty far up a freshwater river, so it gets a decent flush on each ride back. The odd thing is, both engines alarm at almost exactly the same time. When the alarm comes in, the rev limiter kicks in. One old salt said to rev the engines up against the rev limiter until the thermostats pop open. And that does seem to work, and the alarms clear.

But that method does not make one very popular at the dock when you are returning back late from a night of fishing, with alarms blaring and engines bouncing off a rev limiter.

Another mechanic said the new thermostats need to be "broken in", wearing in the poppet shaft a bit. I have never heard of that, and have owned new engines in the past that did not exhibit this behavior. Further, I cannot explain would could be happening in both engines almost simultaneously that causes this condition.

Any thoughts anyone?

Sal DiMercurio posted 06-28-2007 05:15 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Oh man, I don't believe I'm reading this.
Up against the rev limiter while in neutral,.....
You "NEVER" ever run your engine over 2000 rpms, while in neutral; on a 2 stroke engine, no matter what the reason or who told you so.
It sounds like your water passages are clogged up with either mud, silt, or salt.
Riptide23WA posted 06-28-2007 08:58 PM ET (US)     Profile for Riptide23WA  Send Email to Riptide23WA     
Hi Sal, they weren't in neutral while bumping against the rev limiter. They were in gear. And I thought about the clog thing, except that to have both engines alarm at the same time just seems odd...

But I will pursue that avenue a bit more.


Sal DiMercurio posted 06-28-2007 09:01 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Sorry Pat, I thought you just went though a no wake zone & reved them at the dock while in neutral.
Chuck Tribolet posted 06-28-2007 11:39 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
When the rev limiter kicks in, are you at high (> 5000 RPM)
revs? Some engine management systems (OMC fer sure) will drop
the rev limit when things overheat (OMC to 2000 RPM IIRC).


Sal DiMercurio posted 06-29-2007 12:04 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Chuck, I doubt his engine is reving high enough to even hit the rev limiter if it's in gear.
The engin [ s ] are probably going into slow mode from over heating, but alarms should be blowing him out of his mind if the engines really are getting to hot
If he's able to get those engines to rev so high as to actually hit the rev limiter, he's swinging way to small of props.
My guess on the limiter for those engines is 6100 - 6200 rpms.
By any chance, [ riptide ], do you leave the engines in the down position when storing the boat?
I ask that because if you do, there's most likely growth in the water passages.
Let us know what you find.
Riptide23WA posted 06-29-2007 07:29 AM ET (US)     Profile for Riptide23WA  Send Email to Riptide23WA     
"Slow" mode is probably a better term, as I think the engines go into a protective mode in a high temperature condition, and limit rpm to around 2000. After a few seconds of the engines bouncing against this limit, something pops open, suddenly the alarms clear, and the rev limit is lifted, and everything runs seemingly fine.

The engines are tilted up when not in use, and frankly, don't really get much use... I was thinking that if it was clogging of some sort, it would be more apparent at high load/high rpm, not low load/low rpm.


seahorse posted 06-29-2007 08:22 AM ET (US)     Profile for seahorse  Send Email to seahorse     
If you have V6 Yamahas, perhaps the pressure relief valve, also known as the poppet valve, is sticking open a bit and not allowing the block to completely fill with water at idle. It is very common problem in salt water and in muddy or sandy waters.

It is located on the back exhaust cover in the bottom aft of the motor.

Yamaha recently redesigned the valve itself to cut down on sticking so it is best to get a new gasket, valve, and grommet for best results.

By the way, I have never heard the excuse about "thermostats breakin in".

Sal DiMercurio posted 06-29-2007 12:38 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Do the over heat alarms go off?
Sal DiMercurio posted 06-29-2007 12:48 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Sorry, just noticed you said they [ alarms ] do.
Your engines are not hitting the rev limiter.
The rev limiter only comes on if you over rev those engines to approx 500 rpms over maximum recommended factory rpms.
Riptide23WA posted 06-29-2007 05:05 PM ET (US)     Profile for Riptide23WA  Send Email to Riptide23WA     
Seahorse, that sounds logical. Will pull on that thread some more...

Sal, one guy came over and said " You haven't cut the wire to that alarm yet? Everyone else does..." Maybe seahorse is right: it IS a common problem with these engines.


Sal DiMercurio posted 06-29-2007 05:25 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
I would take Sea-Horses advise over anyone elses, as he is the certified tech.
He's the guy I turn to when I'm stumped.
And by the way Sea-horse, thanks for your friendship & your 100% of the time being right when solving my engine problems.
We have known each other for 10 years & you are truely a friend.

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