2009 150 4 stroke Overheat Alarm Gremlin

[Gulfstream232]

Trying to sort out an issue I’m having intermittently with both my outboards. I have 2009 twin 150 4 strokes. Routinely flushed after use and maintained through a certified Yamaha dealer by the previous owner (documented). Brought the boat up to Canada from the south at the beginning of the year, previous life as a salt boat, NC. Both motors under load will intermittently throw “overheating” on the command link gauges despite the temperature remaining dead center on the gauge. The alarm sounds, I drop off plane and restart the engine (no more alarm) engine is not hot and continue underway until the alarm sounds again (intermittently). Sometimes the port goes off and sometime the starboard, sometimes both and sometimes neither at all for multiple days on the water. I’ve changed the entire cooling system on both motors: water pumps, impellers, thermostats, thermosensors, POV valves and went to far as to remove the water jackets to confirm there is no salt deposit or anything else blocking the water from getting to the top of the heads as the engines will only throw the overheating alarm above 4000 rpm. I can ***** or idle all day on both motors no issue. Any guesses where else I can troubleshoot for gremlins? Almost seems electrical? I’m at a loss…..

[99yam40]

I would find out what sensors bring in the temp alarm, pull them out and test them or replace them with new to see if that does anything,
doing one motor to see if that stops it from alarming might be a good idea

maybe disconnecting them and reconnecting will clean up the electrical connections

Seems some motors have more that one temp sensor, so locating them and shooting that area with an infrared gun when alarm sounds might give some idea if one spot is getting hotter than the other

[boscoe99]

Trying to sort out an issue I’m having intermittently with both my outboards. I have 2009 twin 150 4 strokes. Routinely flushed after use and maintained through a certified Yamaha dealer by the previous owner (documented). Brought the boat up to Canada from the south at the beginning of the year, previous life as a salt boat, NC. Both motors under load will intermittently throw “overheating” on the command link gauges despite the temperature remaining dead center on the gauge. The alarm sounds, I drop off plane and restart the engine (no more alarm) engine is not hot and continue underway until the alarm sounds again (intermittently). Sometimes the port goes off and sometime the starboard, sometimes both and sometimes neither at all for multiple days on the water. I’ve changed the entire cooling system on both motors: water pumps, impellers, thermostats, thermosensors, POV valves and went to far as to remove the water jackets to confirm there is no salt deposit or anything else blocking the water from getting to the top of the heads as the engines will only throw the overheating alarm above 4000 rpm. I can ***** or idle all day on both motors no issue. Any guesses where else I can troubleshoot for gremlins? Almost seems electrical? I’m at a loss…..

The temperature indication shown on the Command Link gauge relates to the temperature of the block. As reported to the ECU by a thermosensor.

There is also a thermoswitch that is installed within the cylinder head. That closes if and when the cylinder head gets too hot.

I would guess that the thermoswitch is closing while the the temperature of the block is just fine.

[boscoe99]

[fairdeal]

well, the temperature sensor - which is what the gauges show -
is set into the metal of the block -so "somewhat removed"
both in proximity, and response,
to the water in the water jackets.

The overheat notification is triggered by the thermoswitch,
which is set into the thermostat cover -
so it sees the water exiting the thermostat -
and should trip for "overheat" between 84-90°C

But none of that explains why the thermoswitch is closing,
if the cooling system is working properly -
and on both motors!

You can remove the thermoswitch,
check it on the stove in a pot of water -
confirm that it does not close until it gets to at least 84°

You can also visually check the thermostats on the stove -
should start to open by about 60° C
and be fully open above 70° C


I would want to know what the jacket pressure is at ~4,000 rpm
it should be a minimum of 11 psi
and I would expect to see 15-20 with a new impeller

you can easily connect a pressure gauge to the flush port hose
with a "NPT to male garden hose" adapter

[Gulfstream232]

Thank you for your responses. I have replaced both thermoswitches on the thermostat housings as well as the thermostats themselves but I’ll test them out on the stove to confirm they are operating correctly. I’ll also have a look at the thermosensors but it doesn’t sound like they’re the culprit if the block is cool and the thermo switch is responsible for triggering that alarm. Sounds like jacket pressure test is the next step to confirm new pump and impeller is operating correctly. Just so weird that some days I can travel distance in the 5’s with no issues and others it trips 60 secs after achieving planing speed in the 4’s.

[Gulfstream232]

Also worth noting, sometimes when backing off the throttle to the neutral position the audible alarm and “overheat” message on the command link garage will go away without restarting the engine. Sometimes not every time.

[fairdeal]

l'll also have a look at the thermosensors but it doesn't sound like they're the culprit if the block is cool and the thermo switch is responsible for triggering that alarm. Sounds like jacket pressure test is the next step to confirm new pump and impeller is operating correctly.

I would not bother messing with the thermosensors -
you have the gauges showing what they are reading!

But I would def want to see jacket pressure...

A quick & dirty way to get a gauge at the helm:

[Gulfstream232]

I would not bother messing with the thermosensors -
you have the gauges showing what they are reading!

But I would def want to see jacket pressure...

A quick & dirty way to get a gauge at the helm:

Will do, thank you for this. I’m assuming the readings will be different “under load” underway vs at the dock rpms in neutral? Test better completed on the water then?

[fairdeal]

I'm assuming the readings will be different under load & underway vs at the dock rpms in neutral? Test better completed on the water then?

well, you want to know what the pressure is when the pressure is above 4000 rpm

and personally, I could not bring myself to run it up that high in neutral

but more importantly,

thinking that there may be something going on with the water pickups at speed,
(turbulence? effective motor height with the boat planing?)

the best test is to see what the jacket pressure is

- as you are approaching the point where the engines show that overheat message

- when you are actually getting the overheat message

[pstephens46]

Crappy cooling systems seem to trigger issues at idle, at least in the beginning. Water flow is tremendous at higher rpm. I think Fairwinds is onto something regarding mounting. What is this boat? A cat by chance?

[Gulfstream232]

I think you might be onto something as well. The boats a Grady White Gulfstream 232, with bracket mounted outboards. I’ve mounted (2) transom mount transducers in addition to the thru hull transducer on the boat. The (2) transom mounted transducers are fairly large and mounted below the hull line adjacent to both the port and starboard motors. Oddly enough I seem to operate without issue on a full tank of gas (140gal) is it possible that the added weight could offset the turbulence from the transducers while on plane? Could the mounting location of those transducers be starving the engines of water at higher RPM on plane with less weight? I’m going to pressure check regardless as recommended but maybe I should also change the location of the transducers? I honestly didn’t think they displaced enough water to starve the pick ups while underway. Is that even possible??