Fluctuating Temperature Gauge

[Searay87]

re: 1987 Merc 3.0L w/Alpha One Drive, Faria Gauge

I reported in another thread that my temperature gauge was reading very low, just under 100F. It's been reading this way all summer. I bought a new T-stat and gasket but have not replaced it. Today while running the boat on the lake the gauge would intermittently fluctuate between 175F and 100F with a period of about 3-4 seconds at each reading. The fluctuation between the two temperatures is instantaneous.



I've checked some of the other threads and it sounds like I could possibly have a bad sending unit. Does this sound rignt? Does anyone have any other ideas? I'd love to have a wiring diagram and some idea of where to find the sending unit? Can anyone offer a trouble shooting procedure? Do I have a bad connection or a bad ground? How do I check the gauge?

Thanks,

Bob

 

[dubs283]

Re: Fluctuating Temperature Gauge

you can check the guage by removing the sender wire at the sender on the engine

with the key in the "run" position, strike the end of the sender wire to ground

the guage should spike in one direction

you can also apply 12 volts (+) to the end of the wire and it should spike the other direction

this will tell you if the guage is working properly, if so the problem is in the sender unit in the engine