Yamaha C115 overheating over 2000rpms

[Jschultz]

Hello everyone! I’m new to the forum but as you can guess I’m having engine troubles. I have a Yamaha C115 TLRX outboard that has started overheating over 2000 rpms. I’ve replaced the thermostats, water pump impeller and housing, poppit valve and spring and it continues to overheat. I’ve recently pulled the heads to inspect water passages and found very little corrosion/debris around the water jackets. Am I overlooking something? I can’t think of anything else that would cause the alarm and rev limiter to go off. The engine is getting around 170 degrees when it overheats...

 

[Sea Rider]

Welcome to IBoats,

Does the motor counts with an Overheat Sensor, Is the motor used in fresh or salt water, It's a carbed, EFI model ?

Happy Boating

 

[cuenta]

premix or oil pump

 

[Jschultz]

Motor is carbureted, primarily used in saltwater. Premix oil at 50:1. Taken boat to freshwater 2 times after I bought it with the wife and kids, no problems. Every time I’ve been to saltwater it’s overheated. First time I replaced the thermostats and went to replace water pump and found bad lower unit bearings. Just replaced lower unit with new lower unit with water pump and housing included. Took it back out to saltwater, over heats again....I now have the head covers and heads off the engine. I removed the power pack to inspect the water tube passages but haven’t looked into them yet.

 

[Sea Rider]

So the motor only overheats in salt water and in fresh water doesn't ? What's the year of manufacture and precise model ?

Happy Boating

 

[Jschultz]

1999 C115 TLRX
The fresh water that it was in was kind of a fluke. It's a spring feed river so the water temp was never above 78 degrees. I haven’t been back on fresh water, I almost exclusively go to the salt flats.

 

[Sea Rider]

Have you checked the Thermo Switch condition, probably is faulty and triggers itself way before it should, it's around 40 bucks. When stripping the whole power head's water passages is that all of them needs to be inspected. That motor has a front exhaust system with covers and internal water passage that haven't been ispected, right ?, could be bit clogged and increasing the motor's working temp above the opt temp range Assume that when the motor overheats the rpm is reduced to min safe rpm, right ?

Happy Boating

 

[Jschultz]

Yes the rpm reduces like a rev limiter. Steam is apparent when I let off. I haven’t pulled the exhaust cover yet but I will check that next.

 

[Sea Rider]

Yes the rpm reduces like a rev limiter. Steam is apparent when I let off. I haven’t pulled the exhaust cover yet but I will check that next.

Prior doing that would be ideal to troubleshoot the thermo switch heat condition, the issue is that involves a precise procedure to follow that should be stated on the Yam's Service Manual. It's not as simple as heating thermos on water to check if opens/closes properly. It's more an electric than a mechanical thing.

The exhaust uses 2 gaskets that will need to be changed, old ones could be already dried, hardened, burned when removed, the cost is around 20 bucks each.. For peace of mind better order a new thermo switch and 2 exhust gaskets...

Happy Boating

 

[Jschultz]

So I removed, cleaned and installed the exhaust system with new gaskets. Water tested it today. Overheats over 2000 rpms, confirmed temp with temp gun. Removed thermostats and tried again, overheats still. Removed thermostat covers to verify water flow, lots of exhaust came out of thermostat housing when I started the engine?? Water eventually started flowing out but I didn’t think exhaust soul’s be in the water jackets? Head gaskets are good, 125 plus on all 4 cylinders...

 

[Sea Rider]

That motor needs a witch doctor LOL. Was the exhaust system internals found relatively clean, no debris, salt layers. if all was found clean what about installing a new thermo switch and soon after a proper flush with Salt Away salt remover in a barrel for at least one hour. If keeps overheating check this video : https://www.youtube.com/watch?v=xuL3rTtc-VA

Those Yam cylinder heads are usually 2 piece each and with use tend to collect obstructions in their water circuits, the only possible way to clean those to immaculate factory condition is to remove both cylinder heads and scrape the obstructions mechanicaly, install new head gaskets, torque head bolts to specs and test.

Happy Boating

 

[Faztbullet]

Sound like the poppet is stuck open....

 

[rejesterd]

Remove the water inlet screen on the lower unit, and back flush it. Or at least check for debris inside that area. Also check the pipe that connects to the water pump housing. That might be crudded up. Seems like you've replaced all the relevant parts, so my money would be on a restriction somewhere.

 

[fullthrottle52]

Just a repost from another forum. I am no expert but read this today. Hope it helps.
I've been chasing an overheat condition in my Mercruiser 4.3/Alpha power. Two new water pump impellors, risers, all new hoses, thermostats, gauge and sending unit. Above 3600 RPM the temp would start climbing up to around 190-200.

I was at the dealer picking up some parts and asked the tech if he had any suggestions. Right away he said to drop the lower unit and pull out the copper pipe that connects the water pump to the upper housing. Sure enough there was a 1/4" hole corroded through up at the top. He also said to pull out the rubber grommet that the pipe fits into and clean up any corrosion where it seats. He had seen them so corroded that it would squish the tube almost closed.

Got it all back together and it's running at 160 degrees regardless of RPM.

I've been Googling this issue and haven't seen any mention of looking at the cooling pipe.
__________________

 

[Sea Rider]

What does a 4.3 Merc inboard motor has to do with an Yamaha 115 HP outboard one, 2 different water animals, so comparison is worthless...

Happy Boating

 

[emoney]

You changed the Poppit valve? Overheat demons are just like electrical demons, ugh, so I feel for you. Definitely time to chase those water passages. Sounds like exhaust corrosion at play. Water's flowing good out the telltale? Do you get water from all the right places when using the onboard flusher (not running of course)? I have no ideas, just spitballing because we've all been at Furstration level Defcon 5 before. Hope you find it soon and it's cheap fix.