Alternatives to mineral oil for in-hull transducer?

[Jim Sullivan]

Have a Uniden QT-206 depthfinder with an in-hull, adjustable transducer. I know a number of Cape Dory owners have the same setup that I do. Initially used propylene glycol (R/V anti-freeze) in which to place the transducer. After about two seasons of use, I started getting erratic readings which appears due to the loss of some of the anti-freeze although I could not see any signs of leakage. I've checked the Archives on this Board and found that many use mineral oil. I've tried the mineral oil and it seems to work good (stable and reasonable readings) although it is tricky to add just enough oil but not too much. The Owner's Manual indicated 71 ml (2.4 fl.oz.) which I found was not enough to fully wet the bottom of the transducer. I've seen elsewhere where some have placed the transducer in soft wax (ex. toilet bowl wax ring) or silicone Type II caulking against the inside hull and had good results. Was wondering if regular bearing grease would be a good alternative to mineral oil. It could be packed into the base for the adjustable transducer such as to eliminate any air pockets between the hull and the transducer. I don't think there would be any leakage with grease unlike mineral oil and other liquids. Comments?

Thanks,

Jim