Water temp sending unit not working

[mastercylinder63]

Greetings to all who always helps me and saves me money in expensive repairs. My water temp gauge is showing zero. I took off the sending unit wire and put it to ground. The gauge pinned. I took the old sending unit to the marine parts store and told them to match it up for a 4.3 v6 mercruiser. The unit the parts guy gave me was slightly shorter, but he said it will work fine. I put some pipe tape on the threads and then installed it. I ran the engine for fifteen minutes and the temp gauge still reads zero.
What did I do wrong?? Should I have not used pipe tape on the threads or is it not working because the sending unit is a little shorter, or can it be something else?? Thanks, again !!!

 

[achris]

Re: Water temp sending unit not working

Have you changed/checked the thermostat? If so, did you put a standard gasket back on? The correct gasket has a couple of brass eyelets in it for continuity. Without them the gauge will not work.........

 

[mastercylinder63]

Re: Water temp sending unit not working

I installed the wire onto the threaded post first, then a flat washer, lock washer and final nut.

 

[achris]

Re: Water temp sending unit not working

Not referring to the sender wire, referring to the ground continuity. You can test for that by installing a temporary wire from the engine block to the body of the sender. If the gauge now works, you have a problem between the engine block and the sender. As I said in my first post... the usual thing is people replace the Merc thermostat housing gasket with a standard automotive gasket, then the gauge doesn't work....

 

[Bt Doctur]

Re: Water temp sending unit not working

teflon tape is a no-no. prevents a good ground at the sensor

 

[mastercylinder63]

Re: Water temp sending unit not working

To answer achris question, I didn't replace or check the thermostat. "The exhaust maifold does seem to be barely warm after 15-20 minutes of running the motor at idle, using a freshwater garden hose."
I removed the new temp sending unit again removing all the teflon tape. I again reinstalled it, and ran the motor for 15 - 20 minutes. Still nothing. Next, I ran a ground wire to the outside of the sending unit and conected it to ground. Still nothing. Once again I removed it and took an ohm meter to it. Cold it doesn't show continuity. I put the sending unit in very hot water, it shows full continuity. So I know the switch works. The sending unit is a Teleflex 52320S009 3/8" single station unit and the temp gauge is a Faria. SHould I just buy a real Mercruiser part instead??? Thanks Again

 

[NHGuy]

Re: Water temp sending unit not working

It sounds as if your thermostat may be stuck open. If that's the case the engine will never get warm. To check the temp of the engine get one of those laser pointer infrared thermometers. Use it to take temps when the motor is running.

 

[mastercylinder63]

Re: Water temp sending unit not working

I would think if the thermostat is in the fully open position, the engine should at least get to 120* The temp gauge starts to register @ 100*, but shows 0*, but you have a good point. I think I may run the starboard engine and check those manifolds for the hell of it. By the way, the starboard is a replacement 2007 model and the port engine is a 1997 model, so the little stuff is starting to go.

 

[achris]

Re: Water temp sending unit not working

You need to check the actual resistance of the sender. The gauge needs a 33-240 ohm sender. So when cold it should be reading around 240 ohms, at very hot it should be 33 ohms. Keep the multimeter on the sender as it cools to ensure it increases resistance.

 

[OldNBold51]

Re: Water temp sending unit not working

I just posted about this same issue on my 7.4L. I had 2 different aftermarket sending units that never registered. I broke down and bought the mercruiser sending unit, cleaned the threads real well on both unit and housing and now have a working temp gauge.

 

[mastercylinder63]

Re: Water temp sending unit not working

Thanks for all the input. I took out the thermostat and it was stuck open, so the engine was not getting to operating temperature. I swapped it out with a new unit and the tempature gauge is reading as it should once again!!