1995 yamaha 115 tlrt model 6e5

[optitackle]

Out a couple weeks ago and hit bottom. Took part of the lower unit off.
Replaced the lower unit and everything was going good during break in until i hit the 3200 rpm range of break in when the overheat alarm goes off.
Dropped the lower unit to make sure everything was together correctly. Impeller in correct. Everything hooked up properly.
Changed the t-stats and pressure relief valve.
Back out again and alarm goes off at 3200rpm.
Waterflow is great out of telltale.
Checked the temperature of the heads with a temp gun and get a reading of 162.
Confused as to what might be going on.
Boat has always been well maintained and only ever run in freshwater.
Does anyone have any ideas as where i should go next?
Thanks.

 

[scoflaw]

Not sure what you hit, possible you plugged up some water jackets with mud /sand ? Backflush from t-stats downward. How's the fit from tube to rubber grommet on water pump ?

 

[optitackle]

Hit a submerged rock. Fit from the water tube to the water pump is right on.
Wondering if i should remove the water jackets on the back of the cylinders and see what kind of shape the internals are in. Quite possible i sucked up a small piece of crap as i ran the motor on the trailer at the ramp after i installed the new lower unit.
Will keep this thread going until i get to the bottom of this.

 

[racerone]

A factory lower unit or something else ?-----Perhaps install your old water pump as a test.

 

[optitackle]

Just pulled the water jackets and not a single drop of crud in there.
Possibly a bed sensor as i am getting a reading of 162 with a temp gun?
The lower unit i installed is an aftermarket from SEI.
I have been wondering about getting a Yamaha impeller and see if that makes a difference.
Thank you for all of the replies.

 

[rejesterd]

I would guess your impeller is fine if it's peeing strong.

Seems like your thermoswitch might be bad. Basically, the test for that is to take it out and suspend it in a pan of cool water. Make sure it's not touching the bottom of the pan. Also suspend a thermometer in there. Then hook up a multimeter to the wires on the switch. Put the multimeter on the continuity setting. Then heat the pan, and see at what temperature you start to see continuity in the switch. You should first see continuity around 160-180 F. Then wait until it starts losing continuity and check your thermometer again. It should lose continuity anywhere from about 145-170 F.

Or you can just replace it for $40 or so.

 

[optitackle]

Did the water in the pot test. Both switches got continuity at 190. Not sure how accurate a meat thermometer is in water.
Not sure where to go from here.
Pulled the lower unit again and double checked everything.
HELP!!!!!!!

 

[rejesterd]

Yeah, the meat thermometer should be pretty close. I would say it's out of spec and needs to be replaced.

 

[optitackle]

Rejested the only thing that concerns me is that both switches gave continuity at 190. Do they both go at the same time?
I am really starting to lean towards the water pump.
Just seems strange that the only thing that has changed is the lower unit.
Going to drop the lower unit and run the garden hose up through the water intake pipe and see if water comes down through the exhaust.
Will keep you posted.
Thanks for all the suggestions guys.

 

[rejesterd]

I actually thought there was only one thermoswitch for this engine. I don't have your exact manual, but it should be pretty close to the specs I mentioned. You can also try the same heat test, only measure the resistance.

at 5 ˚C (41 ˚F): 4.62 kΩ
at 20 ˚C (68 ˚F): 2.44 kΩ
at100 ˚C (212 ˚F): 0.19 kΩ

That's probably a more accurate test. Some manuals say test continuity and others say resistance.

 

[optitackle]

Put anew yamaha water pump in and problem solved. No more overheating issue. Removed cowling and heads were warm but the way they should be. I could hold my habd on rhem for 20 seconds and didnt feel hot just warm.
I would like to thank everyone for all their advice. Great board to figure stuff out on.
Back to fishing once again.

 

[Texasmark]

Out a couple weeks ago and hit bottom. Took part of the lower unit off.
Replaced the lower unit and everything was going good during break in until i hit the 3200 rpm range of break in when the overheat alarm goes off.
Dropped the lower unit to make sure everything was together correctly. Impeller in correct. Everything hooked up properly.
Changed the t-stats and pressure relief valve.
Back out again and alarm goes off at 3200rpm.
Waterflow is great out of telltale.
Checked the temperature of the heads with a temp gun and get a reading of 162.
Confused as to what might be going on.
Boat has always been well maintained and only ever run in freshwater.
Does anyone have any ideas as where i should go next?
Thanks.

Going to assume that engines are pretty much identical in the following regards as they are the same type and made from the same components operating under the same conditions.

Mercury 90 looper, 2004 2 stroke, per the service manual:

T stat starts opening at 143F with small tolerance. Your 162 is a good number on crankcase temperature running WOT or anything around there. At idle on a hot day it should stay around the Tstat opening temp pretty much. Over temp alarm is set at 192F. Obviously you have a long way to go before you are in trouble with an OTemp. Cooling is controlled by the Tstat below 2500 RPMs....your number must be 3200 for a Yammie. Above that speed, water pressure pushes the pop-off bypass valve off it's seat and allows full flow regardless of the position of the Tstat. Now you know the particulars, just find which one isn't doing it's job.

HTH