yamaha 140hp V4 2 stroke temperature alarm activation

[yamaha140]

Dear friends,

I am writing this thread due the fact that Im a bit worried and confused about my Yamaha 140 V4 2 stroke 1998/9 model.

About a year ago I decided to check both heads thermostats and found out that the original ones were both stuck open due to long term salt water corrosion.
I decided to change them both but instead of buying the original ones I bought two brand new CALTHERM USA branded thermostats from a local dealer and installed them both with new related gaskets.

In the mean time I always started the engine and flushed it with fresh water and ran it for a bout 5 minutes everytime for a whole year.

Last weak i put the boat to sea and left the port on 1500/2000 rpm then as soon as i went up to 3000 rpm the temperature alarm system started buzzing.
I also noticed that good water stream was coming out with pressure from the circulating pilot hole of the outboard. I let the engine cool down and as soon as the alarms stoped I tried it for the second time and same at 3000 rpm the alarm triggered once again.

Now I removed both thermostats and started the engine and water came out with good pressure from the thermostat housing water jackets and thus confirminf that no blockage is present in cylinder heads water jackets and also decided to try to run the engine at sea without thermostats to see if the alarm will trigger once again.

Can anyone pls tell me what might be the cause of the problem??


Thanks all for the patience and help,

Regards,

Johann.

[paintman]

Thermostats not opening at the right temp?
Are they identical in all respects to the genuine ones? (Reason I ask that is that I am aware of pattern stats on at least two car engines that are incorrect) TBH I'm not a big fan of using non-genuine parts in critical applications, just adds too many potential problems.
Correctly fitted - as in don't need to be fitted a certain way to allow any bleed holes to work properly?
Do you still have the old stats to refit & see if the fault is still present?

[diver12]

I would suspect that the problem is corroded up waterways. Adding the thermostats is just pushing it over the edge. Worth feeling the heads once the alarms go off. You may find one head is running hotter than the other.
The flow of water from the stat housings may be good but the blockage may be further down causing the flow to back up. Also the restriction may not be a complete blockage.
If thats the problem you will need to pull the heads off. Exhaust cover too Be prepared to get some heat into the head bolts if you do. Corroded and snapped head bolts aren't funny.

[yamaha140]

thanks guys for your opinions. i am gonna try again at sea without thermostats and see what happens and take it from there.

[Connie]

Hi , I have the same problem with my 1996 motor. Everytime I reach 3000 revs the alarm siren. did you manage to correct the problem?

Many thanks
Connie

[Nightfisher]

I'm wondering if there might be a special anti-corrosive product added to a water-barrel that will dissolve salt water corrosion build-up throughout the cooling system?

[Connie]

I have read in other forums about salt-away and some other products , i say worth the try.

[Searider]

Rydlyme Marine Descaler

[Nightfisher]

Originally Posted by Connie

I have read in other forums about salt-away and some other products , i say worth the try.

Hi, would also check to ensure max engine RPM has not been exceeded possibly due to incorrect Prop Pitch. Meaning the water flow pressure is not enough to cool due to exceeded RPM. I take it both flow pressure and engine temperature gauges are both are working to spec. Good luck.

My understanding is Yamaha outboards are extremely dependable provided they are maintained and serviced on a regular basis. Unfortunately, my experience with all or most all Outboards, Inboard Inboard/Outboards as well as diesel in pleasure boats are from a fresh-water perspective.