Intermittent Overheat

[22Angler]

I have an intermittent overheat issue on my 1993 Yamaha 200. The motor runs great but every once in a while (once or twice per outing) the engine temp will rise causing the engine to go into SLOW mode. I power down and let it run at idle for 1-2 minutes and the temp goes back down. After that I can run it hard at any RPM it it may not overheat the rest of the day. The first time this happened I thought that maybe I had debris caught around the water intake but it has now happened several times. Could I have a T-stat which sticks? Any thoughts wouldld help

 

[rodbolt]

Re: Intermittent Overheat

are you POSITIVE its temp?
doesnt sound like it,sounds more like slow transfer on the oil side.
usually once the block gets hot enough to trigger the temp switchs it takes more than 1 to 2 minutes to cool that much aluminium back down.
is this a saltwater application?

 

[22Angler]

Re: Intermittent Overheat

Yes I believe its the temp. The Buzzer goes off, The motor goes in SLOW mode and the temp guage shows that the engine is hot. The temp guage quickly goes back down once I let it Idle. Maybe it is more than 1-2 minutes but certainly less than 5.

 

[22Angler]

Re: Intermittent Overheat

Yes it is a Salt Water application

 

[rodbolt]

Re: Intermittent Overheat

over heat switch closes about 183 and opens about 165.the same buzzer is used for low engine oil tank level.
same buzzer same tone same RPM reduction the tach visuals indicate if its oil or temp.
however if your sure its not oil then most likly scale is clogging the blind passage under the head where the switchs sit.

 

[22Angler]

Re: Intermittent Overheat

Rodbolt - I have never heard of this before. How does this get corrected?

 

[22Angler]

Re: Intermittent Overheat

Anyone have any thoughts on this?

 

[Fl_Richard]

Re: Intermittent Overheat

Pull the heads clean the scale and re-assemble.

 

[Mr_engineer]

Re: Intermittent Overheat

I had the same issue on my 1998 C150 last year. I had to pull the head covers and heads, mechanically clean the water jackets and reassemble. The problem was solved. It took my engine 12 years to develop the problem eventhough it was always flushed after each use. I run mine in Galveston Bay which is salt and silt.

 

[22Angler]

Re: Intermittent Overheat

Mr_engineer, "I had the same issue on my 1998 C150 last year." Was your motor actually overheating or was it a false reading from the sender/switch? I am asking because mine is getting hot (per the temp guage) but quickly cools off.

 

[99yam40]

Re: Intermittent Overheat

Test the switch in a pot of water as you heat it if you want to know if it is working properly.