Another Temperature issue

clerihew82

Seaman
Joined
Jul 10, 2007
Messages
57
I have a 1998 5.7 mercruiser. I got the boat a few months ago and got it on the water and has been running a little hot. I installed a new SEI 116 outdrive so i know the impeller is brand new. It was running a little over 180 degrees so i decided to change the thermostat since i didnt know when the last time it was changed. The old one looked like it had 180 degrees stamped on it and i replaced it with a 160 degree sierra thermostat. I didnt have the correct gasket on the housing when i put it pack together so i put some gasket maker on there but from the engine block to the housing and the threads on the sender there is 0 ohms so i know it is getting a good ground. The new thermostat is running a hotter than the old one. I was out last night and it was running about 190 at idle. I am wondering if the gauge and or the sender is faulty?? I found online(cause i dont have a manual) that the ohm readings at the sender should be about: 176 degrees 332 ohms and 212 degrees 177 ohms at the sender. I went a minute ago and tested it and it was at 160 degrees 183 ohms and 180 degrees 151 ohms.. Is that correct? At running temp which the gauge shows to be about 190 i can put my hand on the thermostat housing and hold it there and it is just a little warm. Also the risers are cool to the touch also when at running temp. boat thermostat.jpg
 

searay3

Senior Chief Petty Officer
Joined
Apr 7, 2005
Messages
655
Re: Another Temperature issue

Borrow or buy a temp gun. Sears has them for around 70 bucks. Aim it at the thermostat housing and on the risers. Doesn't sound like it's overheating by your description. By the resistance readings, it does sound like the senders bad. If you put up some serial numbers, someone will be along to get you a link to a proper manual.
 

clerihew82

Seaman
Joined
Jul 10, 2007
Messages
57
Re: Another Temperature issue

engine serial # mercruiser 5.7 OL029850
new SEI 116 outdrive
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: Another Temperature issue

Is that drive a plain Alpha one clone, or does it replace the gen 2? Reason I ask is the earlier alpha's are known to cool poorly at idle. Pick up the revs to 1100 or 1400 on my boat & it cools down to 140. Then running along it will go back to 160. I have to turn my idle back up, it's down to 550.
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: Another Temperature issue

Then you don't have my issue. I believe the Gen 2's are better than the earlier Alpha Ones.
 
Top