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Author Topic:   Mercury Four-Stroke: Water Pressure and Temperature Gauges
high sierra posted 12-15-2005 09:16 PM ET (US)   Profile for high sierra   Send Email to high sierra  
On a Mercury 115-HP four-stroke outboard, how can both a water pressure and a temperature gauge be installed? There is only one port, for one or the other. I figured on using a tee or such but space is limited. SOSMERC said he fastened it to the block. SOSMERC--was that the solution? Is there a better solution? I already bought the water temperature [gauge and sensor]. The water pressure [fitting] was already installed before I owned the boat. high sierra
jimh posted 12-15-2005 11:19 PM ET (US)     Profile for jimh  Send Email to jimh     
Most engines have a tapped hole in the cylinder head near the top for fitting a temperature sensor. The temperature is usually cylinder head temperature, more so than water temperature.
sosmerc posted 12-16-2005 01:11 AM ET (US)     Profile for sosmerc  Send Email to sosmerc     
I mounted the sensor against the block on the starboard side of the powerhead, right next to the factory "engine water temperature sensor. The sensor supplied with your guage can be used to monitor either block temp or water temp, depending on how you install the sender.
As I recall the first 115 Merc EFI 4 stroke I rigged was a repower on a 17ft. SeaRay that had a 125hp Merc 2 stroke.
It had already had a temp guage, and the sender was installed "in" the water jacket such that it was monitoring water temp. I used the same sender, but found it convenient to mount it against the block in the above described position.
After further study of the Merc Factory Manual for the 115 EFI 4 stroke, I see there is a plug in the block, low and below the oil filter, that the manual describes as an "Access Port, Water Pressure/Temperature". It requires an Adaptor (22-86306) to allow for installation of a 1/8 inch pipe fitting temp sender...or a water pressure fitting...whichever you prefer to use. With the appropriate fittings you could probably rig both at this location if you really wanted to.
I hope this info is helpful.

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