Running hot

[Father's Day]

Hello Everyone
Went out today and noticed that when I'm running in the no wake zone the engine temp gage climbs all the way to hot side. If I goose up the throttle she starts to come down, if I put her in idle comes down to middle. When I run all out she stays in the middle. Any thoughts
150 Merc two stroke.
Thanks

 

[PointedRose]

Your impeller might not be pushing water. When was the last time the lower unit was dropped and a fresh impeller installed? Is it pushing a stream of water through the tell tale?

 

[Father's Day]

Your impeller might not be pushing water. When was the last time the lower unit was dropped and a fresh impeller installed? Is it pushing a stream of water through the tell tale?

This is the 3rd season on the impella I'm getting a good stream out the tell tale I was thinking the same gonna have the marina pull the boat for me next week thanks

 

[Doc Stressor]

The condition you describe is typical of a poppet valve that is stuck in the open position, which is how they usually fail.

This is a pressure relief valve that is normally closed at idle speeds when water pressure is low. As water pressure increases with rpm, the valve opens and lets water escape from the cooling jacket. When it is stuck open, water drains out of the cooling jacket at low rpm which leads to the overheat condition. The overheat condition goes away at higher rpm since the valve would normally be open anyway. A stuck open poppet valve can cause the engine to run at below optimal temperature at intermediate rpm.

Replacement is usually not very difficult.

 

[Father's Day]

The condition you describe is typical of a poppet valve that is stuck in the open position, which is how they usually fail.

This is a pressure relief valve that is normally closed at idle speeds when water pressure is low. As water pressure increases with rpm, the valve opens and lets water escape from the cooling jacket. When it is stuck open, water drains out of the cooling jacket at low rpm which leads to the overheat condition. The overheat condition goes away at higher rpm since the valve would normally be open anyway. A stuck open poppet valve can cause the engine to run at below optimal temperature at intermediate rpm.

Replacement is usually not very difficult.

The condition you describe is typical of a poppet valve that is stuck in the open position, which is how they usually fail.

This is a pressure relief valve that is normally closed at idle speeds when water pressure is low. As water pressure increases with rpm, the valve opens and lets water escape from the cooling jacket. When it is stuck open, water drains out of the cooling jacket at low rpm which leads to the overheat condition. The overheat condition goes away at higher rpm since the valve would normally be open anyway. A stuck open poppet valve can cause the engine to run at below optimal temperature at intermediate rpm.

Replacement is usually not very difficult.

Ok thanks I'll try that first, looks easy to replace and I won't have to pull the boat. I'll let you know

 

[seasick]

There are threads on the poppet valve and what to watch out for. Personally, I would prefer to have the boat out of the water but to an extent, that depends on the engine model. For example on older SX motors, the popett is behind the ECU and that has to be removed along with the cables and brackets. The bolts that hold the ecu may be tough to remove.

Although your symptom is typical for a stuck open poppet valve, as mentioned, a weak pump may also be responsible. It's hard to tell since the only way to know is to judge if the pee stream at idle is normal force. If the poppet is bad, that won't affect the pee stream but a bad pump will.
To an extent, you can judge the condition of the pump by timing how long it takes for the motor to pee when first started. Some model motor can take 20 seconds or more but if yours used to take 15 seconds let say and now it takes 40 for the stream to start, the pump may need replacement

 

[Father's Day]

There are threads on the poppet valve and what to watch out for. Personally, I would prefer to have the boat out of the water but to an extent, that depends on the engine model. For example on older SX motors, the popett is behind the ECU and that has to be removed along with the cables and brackets. The bolts that hold the ecu may be tough to remove.

Although your symptom is typical for a stuck open poppet valve, as mentioned, a weak pump may also be responsible. It's hard to tell since the only way to know is to judge if the pee stream at idle is normal force. If the poppet is bad, that won't affect the pee stream but a bad pump will.
To an extent, you can judge the condition of the pump by timing how long it takes for the motor to pee when first started. Some model motor can take 20 seconds or more but if yours used to take 15 seconds let say and now it takes 40 for the stream to start, the pump may need replacement

I'm going to go down to boat now to see where the poppet is, saw a YouTube video I thought it was right in the front . The stream is fine that why I wasn't thinking impella Thanks I'll let you know

 

[seasick]

I missed you statement that the motors are 2s Mercs.
The good news is that the poppet is not behind the PCM but it is very difficult to work on without removing the lower cowling and that will can be a very difficult job in general and kind of impossible in the water. The difficulty of the job depends to a degree on the model year and specifically if the rear lower cowling has an access hole to insert a socket into to remove the rear cowling bolt (one of four bolts that need to be removed. Although you only need to remove one half of the lower cowling, the other half is likely to fall off when all bolts are removed. Without that hole ( it may have a plug in it) it is very hard to get a socket on the rear bolt and turn it. I use 1/4 tools, with several extensions and swivel joints. You may also want to tie up the harnesses and a hose to two to get a little more working space. While you are in that area, and if you have Optimax, you should remove, inspect and clean the strainer that feeds coolin water to the air compressor.

 

[Father's Day]

I missed you statement that the motors are 2s Mercs.
The good news is that the poppet is not behind the PCM but it is very difficult to work on without removing the lower cowling and that will can be a very difficult job in general and kind of impossible in the water. The difficulty of the job depends to a degree on the model year and specifically if the rear lower cowling has an access hole to insert a socket into to remove the rear cowling bolt (one of four bolts that need to be removed. Although you only need to remove one half of the lower cowling, the other half is likely to fall off when all bolts are removed. Without that hole ( it may have a plug in it) it is very hard to get a socket on the rear bolt and turn it. I use 1/4 tools, with several extensions and swivel joints. You may also want to tie up the harnesses and a hose to two to get a little more working space. While you are in that area, and if you have Optimax, you should remove, inspect and clean the strainer that feeds coolin water to the air compressor.

Yeah I couldn't find it, thought that's where it is. Gonna pay to have it pulled out of the water.
Thanks

 

[seasick]

Follow the starboard cylinder bank hose connected to the thermostat. If you have a 150 Opti, that hose (except on early model years) runs directly down the side to the poppet valve. You may need to remove a few electrical connectors and fuse holders to get to the poppet

 

[Father's Day]

Follow the starboard cylinder bank hose connected to the thermostat. If you have a 150 Opti, that hose (except on early model years) runs directly down the side to the poppet valve. You may need to remove a few electrical connectors and fuse holders to get to the poppet

Thanks I'll let you know

 

[5-Salt]

Hello Everyone
Went out today and noticed that when I'm running in the no wake zone the engine temp gage climbs all the way to hot side. If I goose up the throttle she starts to come down, if I put her in idle comes down to middle. When I run all out she stays in the middle. Any thoughts
150 Merc two stroke.
Thanks

Impeller and Thermostat(s)

 

[seasick]

As stated earlier in this thread;

Although your symptom is typical for a stuck open poppet valve, as mentioned, a weak pump may also be responsible. It's hard to tell since the only way to know is to judge if the pee stream at idle is normal force. If the poppet is bad, that won't affect the pee stream but a bad pump will.
To an extent, you can judge the condition of the pump by timing how long it takes for the motor to pee when first started. Some model motor can take 20 seconds or more but if yours used to take 15 seconds let say and now it takes 40 for the stream to start, the pump may need replacement

 

[seasick]

One more piece of info about Optis if that is the motor you have.
The pee stream comes from the cooling water feed from the pump to the air compressor. It is possible to have a good pee steam but no or reduced flow to the heads. If the poppet is stuck open, the heads will get hot ( starboard bank more than port bank) at lower revs . you may also see more water coming out of the dump port, the water outlet next to the flush port.

 

[Father's Day]

One more piece of info about Optis if that is the motor you have.
The pee stream comes from the cooling water feed from the pump to the air compressor. It is possible to have a good pee steam but no or reduced flow to the heads. If the poppet is stuck open, the heads will get hot ( starboard bank more than port bank) at lower revs . you may also see more water coming out of the dump port, the water outlet next to the flush port.

Ok so I called my mechanic he changed out the poppet value and all is good now. The lower cowl had to be removed, and I didn't trust myself not the drop everything into the drink. Thanks everyone for all your advice.