80HP Yamaha 2-Stroke Overheating Issue

[fishfun83]

Took the boat out a couple of days ago and the engine ran great while idling. After 15 minutes or so, I increased the speed to approximately 3/4 throttle and the boat ran good for about 2 miles. After 2 miles, the motor started running rough and the warning buzzer went off. Shut the motor off for about 20 minutes before restarting. Idled around fishing for about 2 hours with no more issues. The pump impeller was replaced about a year ago and there is an excellent pee stream. Any ideas on the problem will be greatly appreciated.

[99yam40]

thermostat would be one thing to check.

inspecting the water pump would be another just to make sure all of the vanes are still there and no melting has happened.

maybe you just had something plug off the pick up screen while running if it only did that once

[fishfun83]

Thanks for the response. The alarm went off about a year ago while I was going about 3/4 throttle. At that time, I thought perhaps the warning buzzer was faulty because the engine never ran bad while the buzzer was going off. This time, the engine sounded like it was missing so I do not think it is a bad warning buzzer. I will replace the thermostat and check the water pump as you suggested. Question: If there is a good pee stream, does that mean I am getting circulation of water on the engine head?

[yamaha80]

No, I have a 80 HP 1997 Yamaha and I had the same issue last year. I took the exhaust cover off and I had a lot of salt build up in there. There is a passageway from the exhaust up to the cavity where the thermostat is and that was blocked with salt also. A quick way to determine that is when you remove the thermostat hook up the water and see if you have water reaching where the thermostat sits. If water is getting there and your thermostat is good you may be looking at the passages around the head being blocked. Hope this helps

[TownsendsFJR1300]

Plus 1 ^^^ re salt build up around the cylinders and head if used in salt water.

What year is the engine / hours?

Is the engine used in salt water and if so flushed with fresh water?


*When running at higher RPM's, if there's NO COOLANT FLOW, (due to salt build up/CLOGGED, in the head / cylinder), no water flow makes the cylinder/head over heat.

Cylinder head removal is usually needed to physically remove the salt (which will be significant).

[99yam40]

I have stopped =my brothers C60 from overheating at high RPM by dropping the lower unit, pulling the statcover and stat, hooked up a water hose directly to the water tube heading to power head, turning water wide open letting it flow out everywhere it can, and then shooting compressed air into the water hose off and on .( I just poked a hole in the hose with my small nossel on my air gun, but maybe set up a tee and some valves would work)
lots of stuff came out.
the air and water helps move things around and out.

We ran it up and down the river for 30 minutes with no overheating.

Something to try if you do not want to take it apart right away

[fishfun83]

The engine is a 1997 80hp Yamaha and it is used in salt water. Have no idea what the engine hours are. I keep the boat in the water at a boat slip and it would be difficult for me to flush the engine each time I use the boat without falling overboard. Last night I took the boat out and idled around for about 30 minutes. The pee stream was strong and the temperature of the stream was cool. Put my hand on the outer exhaust cover and it was pretty hot. Hot enough that I couldn' t leave my hand on it but the engine buzzer never went off. Don't think it was hot enough for that to happen.

Question: If I determine my problem is salt built up in the cooling passages, is the Outer Exhaust Cover the only part of the engine that I need to remove and clean or are there cooling passages around the cylinder head also?

[99yam40]

the more fuel you burn the more heat is produced.
so more cooling is needed at higher RPM

cooling water flows all around the cylinders and the heads also

[TownsendsFJR1300]

The engine is a 1997 80hp Yamaha and it is used in salt water. Have no idea what the engine hours are. I keep the boat in the water at a boat slip and it would be difficult for me to flush the engine each time I use the boat without falling overboard. Last night I took the boat out and idled around for about 30 minutes. The pee stream was strong and the temperature of the stream was cool. Put my hand on the outer exhaust cover and it was pretty hot. Hot enough that I couldn' t leave my hand on it but the engine buzzer never went off. Don't think it was hot enough for that to happen.

Question: If I determine my problem is salt built up in the cooling passages, is the Outer Exhaust Cover the only part of the engine that I need to remove and clean or are there cooling passages around the cylinder head also?

The cylinder head and around block/cylinder passages will be caked up bad/ clogged with salt. The head has to come off...

You'll be surprised how much salt is in there and it still ran that good.

Once all that's scrapped out, she'll run full throttle all day long.

Might want to check / replace anodes while your there...

[fishfun83]

Looking at the diagram for the C80TLRV, if I need to clean salt deposits from the cylinder head and the exhaust cover, I only need gaskets items 31,36, 48 and 49. Would someone check me on this. Also, the only anode I know of is on the bottom of the lower unit. Is there another one somewhere?

[99yam40]

do not forget about the stat and PRV and gaskets
#25 is an anode, but not sure I would replace that looking at all of the older motors that still had them in them.

I would try blowing and washing it out as best you can before risking breaking bolts
but that is just me

[TownsendsFJR1300]

Looking at the diagram for the C80TLRV, if I need to clean salt deposits from the cylinder head and the exhaust cover, I only need gaskets items 31,36, 48 and 49. Would someone check me on this. Also, the only anode I know of is on the bottom of the lower unit. Is there another one somewhere?

As 99Yam posted, try cleaning out before doing a tear down, might luck out. Last one I did was a Yammy, 200 V6 which was really caked bad shut..



https://www.boats.net/catalog/yamaha...nder-crankcase

Part 25 is TWO anodes (which looking at the diagram) are accessible with head on.

Parts 48 & 49 are correct for the exhaust stack.

Part #44 is the thermostat and Pressure Control Valve casket (I'd likely replace both if original)


Lastly, should you disassemble, any bolts that don't want to loosen, STOP, spray lubricant, use some heat (even a heat gun), maybe some smacking of the bolt to loosen corrosion, etc. Forcing a stuck bolt will just end up with more work pick out broken threads later. We lucked out and didn't have any broken bolts

[TownsendsFJR1300]

Parts 31 and 36 ARE both needed as well..

[fishfun83]

I am a little confused I think because I am not sure where the pee stream is getting its source of water. I drove the boat at idle around for about an hour without any issues. The pee stream was cool. Does that tell me that even though there could be restrictions in the engine cooling system, there is enough flow to keep the engine cool at idle but maybe not at full throttle? If the engine passages are clogged, would the pee stream be hot at full throttle but perhaps cool at idle speed if not fully closed?

[TownsendsFJR1300]

I am a little confused I think because I am not sure where the pee stream is getting its source of water. I drove the boat at idle around for about an hour without any issues. The pee stream was cool. Does that tell me that even though there could be restrictions in the engine cooling system, there is enough flow to keep the engine cool at idle but maybe not at full throttle? If the engine passages are clogged, would the pee stream be hot at full throttle but perhaps cool at idle speed if not fully closed?

The pee stream shows the WP is working and your getting water to the power head (as it should).

Water IS getting to the powerhead, BUT IS BLOCKED OFF BY SALT BUILD UP IN the block, around the cylinder and head..

At higher RPM's the engine is making more heat. With the passages clogged, NOT enough water IS NOT GETTING around the cylinder and head to cool it down.
Lower RPM's, the engine is staying cool enough to run AT LOWER RPMs, less heat..