Temp sensor bypass or test.

[Thompsoncustom]

Well found out today that the temp sensor in my head (1990 johnson 20hp) is forcing the motor into slow mode. Water coming out of the tale tell does not appear to be hot and I find 45 bucks to replace this sensor extremely high for what it is. Since this is a new to me motor I'm gonna put a impeller in it and see if that fixes it even tho it's pumping water.

I was thinking about bypassing the sensor completely, my old motor doesn't have it so it's a nice future but it might be causing me more headaches than it's worth. Is there a method of testing the sensor to see if it's bad?

My old motor has the thermostat stuck completely open all the time so if I do bypass the temp sensor I'll probably mod the thermostat to stay open all the time so it stays cooler but not to cool. Anyone see a problem with this?

 

[racerone]

?????------If you think $ 45 is high then what about the cost of a tank of fuel ???---------Cheaper to buy fish at the supermarket I believe.

 

[oldboat1]

Replace the t.stat along with the impeller. Surface temp at top of the head should be around 140, no more than 160. If a saltwater motor, need to thoroughly fresh water flush, and probably open/clean cooling passages.

 

[Thompsoncustom]

Paid 200 for the motor so that's 25% of the cost of the whole thing.

Fresh water motor but the rivers around here are all brown and muddy so it's possible it's got something in it as well. I figured when I get the head cover off I'll get in there and clean it all out.

Would be nice if there was a way to test the heat sensor.

 

[racerone]

What you paid for the motor has nothing to do with the cost of replacement parts.----------Manufacturing parts , then packaging / identifying / storing / retrieving / shipping those parts is very expensive.--------I see more and more parts for even newer motors as listed NLA.

 

[schematic]

easy to test sensor. Just ask....

Before wasting the effort, check the engine to see if its actually overheating....

 

[oldboat1]

one test is to get it running at proper temp, and see if the sensor behaves itself:happy:. Think the cost analysis there needs some rethinking. Easily takes $800 to $1000 at a shop to get a motor up and running, if basically in good shape. That's maybe $130 - $140 in parts if DIY. Think you could probably get $350 for your motor in good running condition..... (1990, 25hp....$$$)

Check the intake screens. Good to run it in a barrel of clean water after replacing impeller, t.stat.

 

[Thompsoncustom]

What do you guys suggest for testing the sensor and if its really over heating in the first place. I just assumed it wasn't since the tell tale wasn't very hot.

 

[racerone]

The tell tale may come off the motor before the water circulates through the block.----So it is not a good indicator of cooling , not at all.-----Shops used to use wax material with different melting points.----Today of course you can pick up an infra red meter for not too much money ( not too much being a relative term ) for some folks I guess.

 

[schematic]

measure the head temp. Telltail does not give engine temp indication on all outboards.

 

[oldboat1]

That infrared temp gun that Racerone mentions is useful for all kinds of things, and very useful for head temps. (also can be used to find electrical shorts [heat], but that's another story). An old time way to test is to put the heel of your hand on the top of the head -- if can hold it there for a few seconds, it's probably about the right running temp. If too hot to touch, shut it down.

 

[racerone]

I used to lecture to people about installing a new pump impeller when they pick up a used outboard.----------Now I chuckle and wait till I read about the $$$$ it cost them when they fry the motor !!!

 

[Thompsoncustom]

Thanks for the info on the tell tale, It looked like the hose was connected to the head so I just assumed that would be a good place to get a idea of the water temp.

Took the boat back out and ran it full throttle till it was put into slow mode than put my hand on the head, I could keep my palm on the head for 2 to 3 secs before it was to hot. unplugged the heat sensor and ran it some more stopping every min to check the head temp with my hand and it always seemed the same. Might have to get a infrared gun just to be sure, wouldn't be bad to have one around anyways.

 

[oldboat1]

Be careful running WOT with a motor that may be running hot. It sounds like it is not smoking', but may be hot enough to trigger the warning system (probably 160+). If it were mine, I would just do the impeller -- probably the t.stat and impeller -- then try it some. If you have the coin, an infrared gun would be a better way of testing (obviously more accurate -- also safer when reaching around.) But I wouldn't wait for further testing. An impeller and t.stat is routine maintenance, and a "rule" with a motor that is new to you.

 

[Thompsoncustom]

Got some parts coming including a Impeller, thermostat, and infrared temp gun. So I'll get some reads off the motor before and after the part replacement.

 

[N2Boating]

Did this problem ever get solved?

 

[GA_Boater]

Did this problem ever get solved?

Wrong motor, so off topic, old thread hijack.

Closed.