Bad Thermosensor = Intermittent overheat

[4x15mph]

@Cobra Jet Steering LLC , agree on the 2 stroke corrosion problem. Is the cooling completely different or are there water "holes" that cool through the exhaust? That is the part that I am saying would have the same problem especially if it is used in salt water and not flushed.

 

[buckbuck]

Cranky, since you are going to such lengths to flush the passages why not disconnect the exhaust at the water box and flush overnight with the engines not running. You would probably have to remove the t-stat also. That way you can recirculate while sleeping or at work.

 

[Cobra Jet Steering LLC]

He says his water boxes are just fine , he thinks the engine water jackets are messed up .

 

[buckbuck]

I guess I said that wrong. I meant flush the passages overnight. The only place that water can get back into the engine is at that point right before the water box so disconnecting there will eliminate water from being able to back up the exhaust.

 

[CrankyGypsy]

Do you rinse off your engines with fresh water after each use? Or just flush them out?

generally just a flush. sometimes i will rinse the bay and the bottom of the engines off after salt water, but i stay clear of the airbox and wiring.

...could you be cavitating slightly at speed and causing your intake to suck in air?

that's a possibility i hadn't considered. though i've been monitoring the pee holes on plane during the WOT runs and they stay solid with no sputtering.
the water was kind of rough that last day, but i was sitting very smooth on plane.

i think i should elaborate on the loudness/bogginess: it only occurs when the thermosensor (not the two thermoswitches, which i am guessing actually trip the 3000RPM limited Limp Mode) reaches 266*F. it doesn't get loud/boggy until the instant that the thermosensor trips, so i believe the overheat signal is causing the bog (and not the other way around) - could the thermosensor signal be causing the ECM to retard ignition or dump fuel to protect itself? if i throttle down (which SHOULD allow any cavitation to resolve), the loudness/bogginess doesn't subside. a reset will immediately solve the loud/bog issue. i see what you are saying @Murf'n'surf , so i may need to figure out a way to rule this possibility out.

why not disconnect the exhaust at the water box and flush overnight with the engines not running.

i'd like to do a setup like that, but won't that run the risk of drowning the head?

 

[CrankyGypsy]

@buckbuck okay, i understand what you are saying. that's a good idea!

edit: not sure i'd be able to wedge a catch bin in anywhere below the waterline, though.

 

[Cobra Jet Steering LLC]

First try to get a look inside the water passages of the engine where the thermostat is, this should give you a pretty good idea of the rest of it. I really doubt you have a blockage in the water jackets I still think you have an electrical issue, if you vacuum out the block at the thermostat using a wet vac you could pour in some C L R and let it sit a day or so to clean out the passages .

 

[CrankyGypsy]

@Cobra Jet Steering LLC i'll try to pull the 'stat housings and their cooling hoses on Wednesday. i saw the inside of those hoses last winter - they were dusty/whitish, but at the time it didn't look thick enough to be a concern. the 'stat housing had some crust in it that i already cleaned out when i replaced them.

just a heads-up: the makers of CLR advise against using it on aluminum.

 

[Cobra Jet Steering LLC]

ok then pour what ever you think is good in the block and let it sit a day or two. I use stuff that would really scare you, phosphoric acid but I rinse it out fairly quickly.

 

[Gym]

@Cobra Jet Steering LLC i'll try to pull the 'stat housings and their cooling hoses on Wednesday. i saw the inside of those hoses last winter - they were dusty/whitish, but at the time it didn't look thick enough to be a concern. the 'stat housing had some crust in it that i already cleaned out when i replaced them.

just a heads-up: the makers of CLR advise against using it on aluminum.

That advice is generally reserved for plumbing fixtures which are much lighter gauge than our engine blocks. That being said I wouldn't let it sit too long. I have flushed my engines with CLR mixed with hose water.

 

[Gus Julia]

I bet you have a bad heat sensor I had the same problem and learned it is a common issue, had it fixed under warranty and no more issues.

Having problems w

I bet you have a bad heat sensor I had the same problem and learned it is a common issue, had it fixed under warranty and no more issues.

Is changing the heat sensors a simple procedure? I am having problems with my 2007 SX210 overheating.

 

[Gus Julia]

(SX 210 2007) Still having problems with engine temperature light coming on and engines going into safety mode. Changed thermostat in both engines but still have same problem. Looking at changing temperature sensors. Per Yamaha diagram, there are three temperature sensors. Temperature Analog Sensor, On-off temperature switch near cylinder and On-off switch near the exhaust pipe. Question: Which of the three activates the engine safety mode? Tend to believe is the Temperature Analog sensor. Any help would be appreciated. Thanks

 

[tdonoughue]

I would actually be surprised if all three will not trigger the safety mode, etc. Do you have a YDS system? Or access to it? I think it should tell you why it is going into safety mode (e.g. which sensor), no?

 

[RAM7a33]

Cranky, have you checked the cooling lines and the plastic fittings? The oil cooler fitting and the exhaust manifold both have substantial restrictions in them. The Y-fittings also may have plastic flash in them from the factory due to improper manufacturing.
A couple years ago OperationROL had some overheat issues that were resolved by flushing. This was during a Shelbyville trip.

Where are these fittings located if you have any pics?

 

[Kriss]

(SX 210 2007) Still having problems with engine temperature light coming on and engines going into safety mode. Changed thermostat in both engines but still have same problem. Looking at changing temperature sensors. Per Yamaha diagram, there are three temperature sensors. Temperature Analog Sensor, On-off temperature switch near cylinder and On-off switch near the exhaust pipe. Question: Which of the three activates the engine safety mode? Tend to believe is the Temperature Analog sensor. Any help would be appreciated. Thanks

I have the same issue with my 2006 SX210 Yamaha. When i disconnect the thermoswitch on the engine block below cylinder 1 the temp light disappear?
Did you solve the problem?

 

[darrickhatch]

i replaced the thermosensor today with a used one. since it's an HO, i was able to pull the two water hoses under the manifold between piston #4 & #3 for access to the sensor - otherwise, the Pressure Control Valve might need removed by non-HO owners. then i was able to blindly get a 17mm open box wrench onto the sensor and break it free, swap in the new one, snug it up, and re-attach the hoses. done. water test next week.

the old one was definitely not looking good:
View attachment 31948
when i did the manifold replacements, i noticed the rubber that fills/protects the back of the sensor had broken out (i actually thought this particular sensor was on the other engine). i cleaned it really well and then sealed it with a few coats of Corroseal - a rust converter that i requested a free sample of. i had hoped it would convert the rust and seal any new water out. well, obviously that stuff did not do a very good job at all.

Thanks for posting this!
I'm fairly new to the forum, and have a 2005 SX230 with a newly rebuilt Starboard Engine from SBT in January (don't know if this was a good idea but the technician I hired in Orlando said it was alright) that started overheating intermittently. I just replaced this Thermosensor (great advice... had to get the pressure control valve out of the way) and the muffler thermoswitch, but that didn't solve it. I've got great flow coming out the pee holes, and it seems to be happening only at lower rpms.

I also pulled the y-fitting (no blockage) and the hose joint (hose header) to ensure there were no restrictions as well, and the only part I have left to replace is the thermoswitch under the exhaust manifold. Don't want to have to do that one as it seems impossible without taking everything above it off... I have the new part and plugged the new one into the harness, fired up the engine on the hose and got the overheating light 30 seconds later... guessing I might need YDS to further troubleshoot.

Thoughts?

 

[Jordan72G]

Thanks for posting this!
I'm fairly new to the forum, and have a 2005 SX230 with a newly rebuilt Starboard Engine from SBT in January (don't know if this was a good idea but the technician I hired in Orlando said it was alright) that started overheating intermittently. I just replaced this Thermosensor (great advice... had to get the pressure control valve out of the way) and the muffler thermoswitch, but that didn't solve it. I've got great flow coming out the pee holes, and it seems to be happening only at lower rpms.

I also pulled the y-fitting (no blockage) and the hose joint (hose header) to ensure there were no restrictions as well, and the only part I have left to replace is the thermoswitch under the exhaust manifold. Don't want to have to do that one as it seems impossible without taking everything above it off... I have the new part and plugged the new one into the harness, fired up the engine on the hose and got the overheating light 30 seconds later... guessing I might need YDS to further troubleshoot.

Thoughts?

Did you figure out your problems? I am having similar problems except mine kicks on at higher RPM’s. Thanks

 

[darrickhatch]

Did you figure out your problems? I am having similar problems except mine kicks on at higher RPM’s. Thanks

After replacing the two "more easily" accessible sensors (exhaust thermoswitch and block thermosenor assembly), problem went away. I had a light pop on again but realized shortly after that it was my oil pressure switch... it was overdue for an oil change.

 

[wajetter]

Attached are some numbers I had on my engines. Also attached is the latest YDS down load when I put it to bed this past season.
I think you are going to find that your temps will come up while underway and when you drop to idle they continue to climb because there is not enough flow to remove the heat. Somewhere you have a restriction.
Is this a California boat? Does it have catalytic convertors?

@buckbuck it seems the spreadsheets you shared don't have comparison of temperature between engines.
I'm chasing an overheat that caused the oil frothed and a rod knock spun bearing last summer on my port engine.
This happened around 10K RPM after a couple minutes. Prior to that, a lot of idling at the ramp and no issue.
When I touched a few areas around the engine for temperature:
- Oil tank: very hot (and oil steaming and frothed)
- Block: very hot
- Exhaust pipes - normal
These same areas areas on the starboard engine were normal temperature.
Unfortunately, the temp sensors didn't do their job. All i noticed was a drop in RPM to 7K, then back up to 10, then back to 6 and it died. When restarted, the knock was already there.

 

[Murf'n'surf]

@buckbuck it seems the spreadsheets you shared don't have comparison of temperature between engines.
I'm chasing an overheat that caused the oil frothed and a rod knock spun bearing last summer on my port engine.
This happened around 10K RPM after a couple minutes. Prior to that, a lot of idling at the ramp and no issue.
When I touched a few areas around the engine for temperature:
- Oil tank: very hot (and oil steaming and frothed)
- Block: very hot
- Exhaust pipes - normal
These same areas areas on the starboard engine were normal temperature.
Unfortunately, the temp sensors didn't do their job. All i noticed was a drop in RPM to 7K, then back up to 10, then back to 6 and it died. When restarted, the knock was already there.

What does this "frothed" oil look like? White milky oil? If so, you are looking at cooling water in your oil.