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Author Topic:   Mercury Oil Tank Level Sensor
bill705 posted 10-19-2006 08:34 PM ET (US)   Profile for bill705   Send Email to bill705  
I replaced the under-cowling oil reservoir tank on my 1991 100-HP Mercury. I cut the old one out to look at it. Here are a few pictures of it

The ring magnet came loose from the float. Bill

jimh posted 10-19-2006 11:39 PM ET (US)     Profile for jimh  Send Email to jimh     
Bill--Thanks for those great pictures. It took me a minute to figure out what your caption meant: The magnet has separated from the float. Therefore, the magnet does not rise with the float as the oil level rises. It must have been giving you a LOW-OIL alarm all the time.

As I mentioned earlier, I think that Mercury had a good idea by using a magnetic float and a magnetically operated reed relay that was kept out of the oil reservoir interior.

bill705 posted 10-20-2006 02:36 PM ET (US)     Profile for bill705  Send Email to bill705     
As it turned out, all three parts involved were bad. It never really gave the "beep beep beep" like it should have but it started to sort of chirp and tic or come on steady at half the volume or come on steady at full volume for ten or fifteen seconds and then clear up. I put the water temp sensor in a pan of water with a thermometer and it checked out ok and the oil sensor seemed to be ok. When I would short the leads for the oil sensor it would just beep once and quit, not the "beep beep beep" like it should have so that meant the module was defective and I replaced it and had the correct "beep beep beep" when I would short the leads. Next time out it did the same thing so I got a new reed switch and as soon as I replaced it I had the "beep beep beep" constantly as if it was out of oil so I drained the tank and could see the loose magnet.
The original reed switch had a high resistance when it should have been making continuity and that's why it acted so wierd.
The new tank was somewhat different as it had some internal braces that the old one didn't.

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