1996 Johnson 88 spl overheat warning

[cdcoates43]

How do you test the temp sensors?
How do you remove them?

On my spl at start up the engine self test system runs and my overheat light stays on with a 30 second (roughly) alarm and then it goes quiet but the light remains lit. The overheat alarm never comes back on but on every restart I get the same thing. The motor has been run hot before but I have had the whole cooling system revamped (new t-stat, water channels cleaned, water pump re-built) and the heads never get too hot to touch. I think I might have a bad temp sensor (there is no change if I start the motor up with one or both of the temp sensors disconnected) but I don't know how to test them or remove them. They look like a rubber grommet pressed into the head but they are counter sunk and the only thing to grab and pull on is the tan wire. Thanks!

 

[emdsapmgr]

Re: 1996 Johnson 88 spl overheat warning

Usually on an overheat situation, you will get a constant, loud horn. It is always possible that one/both of the overheat switches are bad. It is a valid test to disconnect them and see what happens. (there is a bullet connector under the rubber sleeve on the wire right by both sensors.) They are pretty usually reliable, but nothing lasts forever. The overheat sensor/switches are removed by pulling the head cover (not the head itself) off an then installing a new one, then reinstalling the cover-and new cover gasket. Once you get the head cover off, inspect the water passaged under to cover. It's possible to have a restriction inside that cover, blocking waterflow thru the head passages. The overheat switches go to ground at 212 degrees and sound the horn. The switch will open when the powerhead gets back down to 175, which is still pretty hot. Normal idle head temps would be between 143 and 155. (Lower when on plane.)

 

[boobie]

Re: 1996 Johnson 88 spl overheat warning

If you have a system check tach on it, it may be bad. OMC had problems with them back in those days.

 

[cdcoates43]

Re: 1996 Johnson 88 spl overheat warning

Thanks for the input. I'll double check my heat sensors individually. Is there anyway to check the system check in my old tach.

 

[boobie]

Re: 1996 Johnson 88 spl overheat warning

The only way I know is to substitute a known good one and try it. Know anybody that will loan you one ??

 

[kjdunne]

Re: 1996 Johnson 88 spl overheat warning

You state that there is no change with both temp sensors disconnected. Points to a bad tach or a problem in the wiring between the engine and tach.

 

[cdcoates43]

Re: 1996 Johnson 88 spl overheat warning

SO the long story is I replaced the tach a while back with an after market that didn't have the system check in it because I didn't know what I was doing. When great people of iBoats Forums got me headed in the right direction I just plugged the connector back into the old tach and stowed it under my center console where I could check it easily if I needed to. So now I've ordered an inexpensive, stand alone gauge to replace the old worn out tach. I think it is the original so judging by what you guys have said and from a few other posts I have read, it seems highly likely the old tach was worn out in more ways than one. Hopefully the new gauge solves my problem. It will be here soon so I'll be back then with an update.

Thanks for all the help so far!

 

[cdcoates43]

Re: 1996 Johnson 88 spl overheat warning

New gauge solved the problem ... Man, I wish I had done this 5 years ago! Thanks for the advice!