install temp sensor and gauge

I have a 1999 merc 175 efi [FONT=&quot]serial #[/FONT][FONT=&quot]0G843863. I would like to add a temp gauge and water pressure gauge. I am wanting to know if there is already a temp sensor that I can just wire to a gauge. Also is there a port already for a water pressure gauge?[/FONT]

I don't know but probably not. The preferred method of monitoring engine cooling is with the water pressure gauge. Other option is via a temperature sending unit embedded in the block's cooling water. As I recall my son't 150 of that vintage had 1/8" NPT plugs in the water jacket cover(s) on the rear of the block....spark plugs protrude through them (if in doubt as to what cover plate to which I am referring.

Since you have two thermostats you really need to monitor both rows of cylinders....I would guess. Water pressure would tell you if the water pump is supplying water and can be monitored over time for decreases pressure at a certain RPM as an indication as to the impeller needing to be replaced. The thermo sending unit(s) would only tell you of current conditions and would not necessarily indicate pending replacement of the impeller....but it/they might if you find the original lower RPM temperature runnning high.

These engines have high volume popoff valves that open a larger port allowing for increased coolant flow and when open bypass the stat. I have a stat on my 115 and once up to themperature it sits rock solid on the pellet stamped value. Once I get on plane and RPMs increase over about 2500 the popoff opens and the temp gauge immediately drops to the ambient temp of the surface water plus a few degrees, definitely lower than when running on the stat at lower speeds.

The temp sensor would have to be screwed into the water jacket cover plate. You might put a pressure gauge on one bank and a tstat on the other. Using a Tee such that both could be connected to one port wouldn't work as unlike a hose barb for water pressure, the temp element has to stick down into the cooling water of the block to monitor it and a Tee would prevent that.