Overheat at Idle

[I_squared_r]

271 hours. I went up to Lake George this past weekend and the overheat alarm would sound if I idled too long. Water temp was 77F in some areas so it's a bit warmer than my home port. The pump strainer and thermostat look good. Good flow through the pissers. So I pulled the pump and found a little rope there. I'm wondering if this has been causing cavitation the past year. The boat cavitates a bit with 5+ people on board. Otherwise the pump looks great after 180 hours. Could this be the overheat problem? I'm taking the boat to NYC on the next trip and I'm trying to avoid an issue. I'm thinking the next step is to flush it with salt-away and hope for the best.

 

[I_squared_r]

Following up on this thread for anyone else going down this path..

I took out the rope and put 5200 in the intake tunnel. There's a little less cavitation and my top speed improved. Pump is in great condition. I also flushed the motor 2x with salt-away. Water flow out pissers is good.

But its still happening. I was idling for 25 minutes while filling paddleboards and no alarm. Then later in the day it went off after a few minutes of idling. I'm suspecting it's a bad temp sensor so I'm going to bring a laser thermometer to check the motor temps.

If the sensor is OK, my other theory is that the water temps are above average this year and causing it to overheat. My mechanic friend said that some of his customers have this same problem when the water is hot. Riva sells a thermostat delete. The thermostat's function is for the engine to warm up faster so without the thermostat it's important not to start the engine and immediately beat on it. Maybe I'll try this delete..

RIVA Yamaha 1.8L Thermostat Delete Kit

RIVA Yamaha 1.8L Thermostat Delete kit allows Yamaha SVHO, SHO & HO engines to run cooler by replacing the thermostat with a specialized restrictor. Ideal for modified watercraft operating in high air & water temperatures.

rivaracing.com

 

[Cobra Jet Steering LLC]

That is a known issue with that year I had the same thing and had one of the sensors replaced no more issues.

 

[212s]

But its still happening. I was idling for 25 minutes while filling paddleboards and no alarm. Then later in the day it went off after a few minutes of idling. I'm suspecting it's a bad temp sensor so I'm going to bring a laser thermometer to check the motor temps.

Check the water flow out the bypass under the swim platform when the engine is warmed up - you should get a steady stream of hot water. Water out the pilot holes indicates good flow through the oil cooler and intercooler, or a blockage at the pump, but that's it. If there's a salt or calcium build up in the water jackets, the pilot holes will still stream fine yet the engine will run hot.

If the sensor is OK, my other theory is that the water temps are above average this year and causing it to overheat.

Water temp is well below the operating temp of the engine (160F) so cooling should not be an issue unless you have a blockage or bad sensor. We have 80+F water temps here during the summer and no heat issues.

Riva sells a thermostat delete. The thermostat's function is for the engine to warm up faster so without the thermostat it's important not to start the engine and immediately beat on it. Maybe I'll try this delete..

I don't recommend it - that delete is for racing purposes. The thermostat's function is two fold - to help warm up the engine faster, but to also maintain the engine temp at 160F for proper combustion temp during use - the engines will run best at optimal operating temp of 160F. Removing the thermostat will make the engine run too cool and rich, wasting fuel and fouling your plugs. When racing, the engines are going WOT 99% of the time so the plugs don't foul.

 

[Cobra Jet Steering LLC]

my sensor did the same thing very inconsistent changed out the sensor in the front of the engine under warranty and it never happened again. also the non contact thermometer insisted nothing was hot on the engine.

 

[I_squared_r]

Thanks for the suggestions. I was just reading the service manual and doing research. I'm going to put the boat in the water and see if there's a steady stream of water coming from under the swim platform like @212s said. And if it appears fine, then I'll remove the sensors and check the resistance values while I warm up water.

According to the manual the thermoswitch has continuity when temperature greater than 201F. I don't think I can suspect any 1 of the 3 sensors by reading this chart. Probably I have to remove all 3 and test them.

 

[I_squared_r]

I ran it on the hose and took a video. Probably isn't a good test, but it looks like very little flow? Maybe i'll water test it later today

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[Judge]

I ran it on the hose and took a video. Probably isn't a good test, but it looks like very little flow? Maybe i'll water test it later today

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Did you clamp off the hose at the pump intake? If not, you will lose water out the pump so minimal water out the pissers is normal in that case. When the hose is clamped off, the pissers will have better flow.

 

[I_squared_r]

Did you clamp off the hose at the pump intake? If not, you will lose water out the pump so minimal water out the pissers is normal in that case. When the hose is clamped off, the pissers will have better flow.

Here is the new video with the line from the pump pinched. Not much difference of flow coming from the engine, but the flow from intercoolers improved a lot.

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[I_squared_r]

I took out the thermostat and pinched the cooling line from the pump. It looks like plenty of flow through the engine's cooling passages. I'm going to check the thermostat again versus yamaha's measurements and then test the sensors

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[tdonoughue]

Hard to tell, but that looks about like what I see when mine is on the hose.

Do you have an IR thermometer or camera? Try shooting the area on the engine near the sensor when it goes off. If it is +200F, it ain't the sensor and you have to start considering the water jackets. If it is normal, then the sensor is a contender.

Someone once pulled the sensor and saw that there was a bunch of buildup in the hole where the sensor sat (thus indicating, even if flow was good, that buildup in the water jackets was affecting flow through the engine).

 

[I_squared_r]

Hard to tell, but that looks about like what I see when mine is on the hose.

Do you have an IR thermometer or camera? Try shooting the area on the engine near the sensor when it goes off. If it is +200F, it ain't the sensor and you have to start considering the water jackets. If it is normal, then the sensor is a contender.

Someone once pulled the sensor and saw that there was a bunch of buildup in the hole where the sensor sat (thus indicating, even if flow was good, that buildup in the water jackets was affecting flow through the engine).

While the thermostat was out, I checked it according to the service manual and I got 4.6mm
I'm going to pull the sensors this week and see if there's build up and check the resistance values with a multimeter. I'm thinking that I can flush the motor with the sensors out in an attempt to clean the cooling passages. But right now I'm not thinking clogged cooling passages are a problem.
I also have a IR thermometer somewhere that I'll leave on the boat.

 

[I_squared_r]

I pulled 2 of the 3 sensors and tested them according to the yamaha service manual. The engine temperature sensor and the exhaust temperature sensors are easy to access. The thermoswitch isn't and looks like the intake manifold needs to be removed.

Exhaust Temperature Sensor
@32F is 28.1kΩ and is good in the range of 24.0-37.1kΩ
@212F is 1.03kΩ and is good in the range of 0.87-1.18kΩ

Engine Temperature Sensor
@68F is 48kΩ and is bad in the range of 54.2-69.0kΩ
@212F is 3.45kΩ and is good in the range of 3.12-3.48kΩ

Also the engine temperature sensor has some rust on the outside. I've read other people having issues with this. It's a little weird that the data for the engine temperature sensor is good at 212F but not at 68F. I think it's difficult for me to measure the temperature because room temperature can vary. 212F is easy because that is boiling water.

I think the move is to order the engine temperature sensor and see if it helps. If not then pull the intake manifold and check the 3rd sensor.

 

[tdonoughue]

Oh, I would probably be replacing that pictured sensor no matter what the test showed. And the fact that it showed out of spec just cinches it.

Yep. Replace and then see if the problem is solved.

 

[Judge]

I pulled 2 of the 3 sensors and tested them according to the yamaha service manual. The engine temperature sensor and the exhaust temperature sensors are easy to access. The thermoswitch isn't and looks like the intake manifold needs to be removed.

Exhaust Temperature Sensor
@32F is 28.1kΩ and is good in the range of 24.0-37.1kΩ
@212F is 1.03kΩ and is good in the range of 0.87-1.18kΩ

Engine Temperature Sensor
@68F is 48kΩ and is bad in the range of 54.2-69.0kΩ
@212F is 3.45kΩ and is good in the range of 3.12-3.48kΩ

Also the engine temperature sensor has some rust on the outside. I've read other people having issues with this. It's a little weird that the data for the engine temperature sensor is good at 212F but not at 68F. I think it's difficult for me to measure the temperature because room temperature can vary. 212F is easy because that is boiling water.

I think the move is to order the engine temperature sensor and see if it helps. If not then pull the intake manifold and check the 3rd sensor.

View attachment 186399

That looks pretty nasty. Like TD suggested.... that one is worth replacing.

Did the exhaust sensor look better?

 

[I_squared_r]

That looks pretty nasty. Like TD suggested.... that one is worth replacing.

Did the exhaust sensor look better?

Yeah exhaust sensor looks perfect. And from I can see, the thermoswitch looks perfect too. These engine temperature sensors aren't really intended for marine use because the rest of my engine compartment looks perfect. Except for those steel hose clamps yamaha puts everywhere... I've been slowly replacing those.

I ordered 1 from pennsylvania and should arrive quickly. I'm hoping to water test thursday night. weather looks great.

 

[FSH 210 Sport]

Check the water flow out the bypass under the swim platform when the engine is warmed up - you should get a steady stream of hot water. Water out the pilot holes indicates good flow through the oil cooler and intercooler, or a blockage at the pump, but that's it. If there's a salt or calcium build up in the water jackets, the pilot holes will still stream fine yet the engine will run hot.

Water temp is well below the operating temp of the engine (160F) so cooling should not be an issue unless you have a blockage or bad sensor. We have 80+F water temps here during the summer and no heat issues.

I don't recommend it - that delete is for racing purposes. The thermostat's function is two fold - to help warm up the engine faster, but to also maintain the engine temp at 160F for proper combustion temp during use - the engines will run best at optimal operating temp of 160F. Removing the thermostat will make the engine run too cool and rich, wasting fuel and fouling your plugs. When racing, the engines are going WOT 99% of the time so the plugs don't foul.

Seconding @212s post here especially the part about thermostats… I would add that proper ring sealing is dependent on the proper heat on the water jacket around the cylinders as well as maintaining proper clearances between the piston and the cylinder. The ECM is looking for water temperature within a certain range, as well as IAT intake air temp and MAP manifold absolute pressure to place the fuel delivery at the proper place within the engine mapping.

When I checked back today I saw you had tested the thermostat which is excellent.

The videos you took show ample water flows while on the hose so your issue has to be a sensor.

 

[I_squared_r]

No issues in the past 2 outings. I'm going to wait longer before declaring it fixed. Then I'll put a new thermostat in for preventative maintenance.. Almost 300 hours in salt water so it's a good idea to change it.