yamaha overheating

[iisinc]

Long story, short! 115Hp 1992 yamaha. good water pump flow (pee hole strong). new thermostats, poppit valve checked (OK). 120-130 PSI all 4 cylinders. Saltaway used several times. Never had impeller break apart. My next move will be to remove heads and water passages and clean. Any other ideas before I do all this?? Any help will be deeply appreciated.<br /><br />Thanks,<br /><br />Steve R.

 

[jim dozier]

Re: yamaha overheating

Before you start disassembling the motor verify that the engine is in fact overheating. You don't say what led you to believe it was overheating. For about $50 you can get a point and read infrared thermometer at Radio Shack to check cylinder head temps.<br /><br />At what engine speed and under what conditions is it overheating? Is the engine running well otherwise. If in fact it is overheating, I would replace the impeller (unless you have already done so) even if it looks OK before I pulled the head. They can loose their elasticity and can take a permanent set that may reduce their effectiveness. While you have the lower unit off I would clamp a garden hose on the pickup tube and check the flow through the engine.

 

[iisinc]

Re: yamaha overheating

Originally posted by jimd:<br /> Before you start disassembling the motor verify that the engine is in fact overheating. You don't say what led you to believe it was overheating. For about $50 you can get a point and read infrared thermometer at Radio Shack to check cylinder head temps.<br /><br />At what engine speed and under what conditions is it overheating? Is the engine running well otherwise. If in fact it is overheating, I would replace the impeller (unless you have already done so) even if it looks OK before I pulled the head. They can loose their elasticity and can take a permanent set that may reduce their effectiveness. While you have the lower unit off I would clamp a garden hose on the pickup tube and check the flow through the engine.

 

[iisinc]

Re: yamaha overheating

Originally posted by iisinc:<br />

Originally posted by jimd:<br /> Before you start disassembling the motor verify that the engine is in fact overheating. You don't say what led you to believe it was overheating. For about $50 you can get a point and read infrared thermometer at Radio Shack to check cylinder head temps.<br /><br />At what engine speed and under what conditions is it overheating? Is the engine running well otherwise. If in fact it is overheating, I would replace the impeller (unless you have already done so) even if it looks OK before I pulled the head. They can loose their elasticity and can take a permanent set that may reduce their effectiveness. While you have the lower unit off I would clamp a garden hose on the pickup tube and check the flow through the engine.

 

[iisinc]

Re: yamaha overheating

JIMD,<br />Thanks for your reply. I did check temp with IR thermometer, and it is getting warm, but only on the starboard head. I switched senders and still got a buzzer from the starboard side. Impeller has been changed. Also, The engine starts missing when it gets hot. Is there an RPM limiter on the 1992 115HP yamahas? I think I am going to have to remove heads to inspect cylinders and water jackets. Any more advice will be received gratiously.<br /><br />Thanks Again,<br /><br />Steve R.

 

[jim dozier]

Re: yamaha overheating

How do the spark plugs look on the starboard cylinders compared to the port cylinders. Are any of the spark plugs especially clean or lean burning? Clean plugs (cleaner than the others) might be indicative of a water leak into that cylinder, possibly a head gasket. Leaking head gaskets tend to overheat at higher rpms. Cylinders running too lean might run hotter than normal, are your carbs clean?

 

[iisinc]

Re: yamaha overheating

Thanks for the reply,<br />The plugs all look dark and wet (with gas). So, looks like the heads will be coming off.<br /><br />Thanks Again,<br /><br />Steve R.