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Mercury Outboards

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During the mellenium and just prior to it, all the big businesses were into building the outboard power system of the future which culminated in the "FORCE" outboard. Mercury was extremely determined, and built some real bone headed machines from the 70's to the 90's.

On most of their outboards, from 25hp up to 100 and of course the infamous "BlackMax" which was a 6 cylinder engine, mounted vertically in a monster drive that came with a warning to "not use it on a boat smaller than 40' long", weighing over a specific amount of pounds.

On the top of these outboards (which is the end of the crank case if it was horizontal but its' not)... there is a special sensor port for something that is 3/4" in diameter and must be less than 1/2" tall and fastens on the case with a dual ear plate. It must not be taller than this 1/2" because the frame that holds the cover on will not permit anything taller to fit. (see configuration)

I think its a port for an air temp sensor, that is supposed to trigger an alarm at a certain temp, because there isn't enough room in there for a traditional thermostat. On the simple side, If I don't know the difference between a air port and a water port, it might be an analog thermometer on a wire that sends increased signal when it heats up... and that in turn fires an alarm at a specific temp, or is hooked up, straight to, a temperature guage....

If I can't get the one that goes in there, I will have to build one, and I need to find a 12v analog temp sender that is 3/4" around, less than 1/2" tall ; and is air and water freindly, in a water tight plug that can be clamped into a 3/4"diameter x 1/2" deep hole. Any body know where I might find one?
 
You need to specify model year and HP, and usually serial number.
The EzPartsWeb Online catalog is https://www.mercurymarine.com/en/us/parts-and-accessories/parts-catalog.
"Force" (Bayliner) bought out Chrysler outboards in 83. They never made a 6cylinder, largest being the 5 cyl 150 hp.
Boats.net and https://www.crowleymarine.com/parts.html also have lookups.

The 6cyl inline is "Blind cylinder" meaning cyl head is part of block casting. a temp sensor must be in contact with the coolant or water, as there is time lost transfering heat thru the block.
The most proven and reliable method of monitoring temp is water pressure guages. those "Pee streams" on most outboards are simple yet extremely effective.
** Start with what is supposed to be in the port hole you mention. 6 cyl, and early merc had liquid mercury switches to shut them off in event of striking submerged object at high speeds, so a runaway motor would'nt be flopping around in the boat with you.
80's Force had thermoswitches to operate alarm buzzer
 
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