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Jason
Jason, Marine Mechanic
Category: Marine Electronics
Satisfied Customers: 14603
Experience:  Degree in Marine Technology, Also Certified with Mercury Marine, MCM, MIE, VP, Yamaha, Honda, Suzuki
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I am having an overheating issue with a Yamaha 150

Customer Question

I am having an overheating issue with a Yamaha 150 fourstroke. Have changed the water pump and housing, the thermostat, and pressure relief valve. Engine is still running at around 180 degrees
Submitted: 10 months ago.
Category: Marine Electronics
Expert:  Jason replied 10 months ago.

Hello my name is ***** ***** am I speaking with?

Is that 180 when read on the boats gauge? Or is that 180 using an infra red temp gun and scanning the cylinder heads manually?

Customer: replied 10 months ago.
This is Chris,It is 180-185 when read with an infrared temp gun and via computer hooked up
Customer: replied 10 months ago.
Also worth noting that the water coming out of the tell tail is cool to the touch
Expert:  Jason replied 10 months ago.

Hi Chris,

Is that 180 at idle or full throttle?

Customer: replied 10 months ago.
it runs warmer than normal at all times, @2500 RPM it runs at 160, above 300 rpm it goes up to 180
Expert:  Jason replied 10 months ago.

Are you running it on a garden hose, or with the boat in the water?

Customer: replied 10 months ago.
We are running it in the water
Customer: replied 10 months ago.
under load
Expert:  Jason replied 10 months ago.

Is there a story to this problem? What kind of history does the engine have? When did it last run cool? Did it ever overheat?

Customer: replied 10 months ago.
Boat ran well a few weeks ago, then started running really rough making a bunch of noise. Found a bad spark plug on cylinder 3, replaced that also noticed a weak stream so we did the water pump. After putting everything together we noticed it was running warm than it shoudl. Don't think that it ever overheated, at least we can't see signs of it. It is not setting an alarm off, but is running warm
Expert:  Jason replied 10 months ago.

I hate to ask but is the water pump impeller installed correctly, with all Orings in the correct spot, and none of the orings damaged or torn?

Customer: replied 10 months ago.
everything is in place based on the schematic for the engine and all orings are in good shape
Expert:  Jason replied 10 months ago.

What is the model number on this engine?

Customer: replied 10 months ago.
It is an F150TXR
Expert:  Jason replied 10 months ago.

Got it.

On the side of the engine block, where the thermostat and pressure control valve are located, is the exhaust cover. Is the exhaust cover running hotter, colder, or about the same as the cylinder head?

Customer: replied 10 months ago.
I will go take it for a run and see. Will let you know
Expert:  Jason replied 10 months ago.

Okay

Customer: replied 10 months ago.
Just checked with my dad who ran the boat. Exhaust cover was cooler than the engine, by about 20 degrees. Thermostat and control valve were cooler than engine also. Heads were running around 160, but in the engine it was around 180
Expert:  Jason replied 10 months ago.

Do you have a hand held volt ohm meter, and can you take resistance measurements?

Customer: replied 10 months ago.
I can, what should I be checking and what should I look for
Expert:  Jason replied 10 months ago.
I'm thinking your temp sensor might not be accurate. Pull the temp sensor out and stick it in a pot of room temp water and measure the resistance of the sensor. Pull the sensor out, bring the pot of water to a light boil, throw it back in and check it again. I'm attaching 2 pictures. One shows the sensors location, the other shows what the resistance values should be. Do the test and let me know what you get for a result.
Customer: replied 10 months ago.
I will do that. Will let you know what happens
Expert:  Jason replied 10 months ago.

Sounds good, let me know what happens.

Expert:  Jason replied 10 months ago.

Hi Chris, just checking in, did you have a chance to measure the resistance on the temp sensor?

Expert:  Jason replied 10 months ago.

Hi Chris,

It looks like you read my answer without replying back or leaving a rating for my service. Please keep in mind the website does charge you to speak with me. But they will hold your money and not credit me for helping you until you select a rating for me.

Thanks again,

Jason

Customer: replied 9 months ago.
Sorry to take so long getting back to you. Just had a chance to test the sensor. I had the following readings:38.8 ohms @ 68 degrees
3.38 ohms @ 212 degreesRoom temperature is a little out of the range, but it is spot on at boiling point.
Customer: replied 9 months ago.
Anything?
Customer: replied 9 months ago.
Hi, just checking in. Any suggestions about where to go with this?

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