I like the idea of having a gauge so I can monitor trends. I have not worked on an Optimax, but if there is a place for a sender in the head, it is a simple matter to install the sender. There is usually a spare wire in the wire bundle to run to the gauge. The senders are cheap. On the 2.5 the sender mounts in a recessed hole in the head. It does not go through to the water, so, it reads head temp. On a 2.5 there is room to drill a hole in the top of the head and mount a water temp sender. The sender would be just behind the thermostat. On my motor, I have the sender mounted on the opposite bank from the overtemp sender. If I can find a similar gauge, I am going to mount one on the other bank also. It is possible to run an ammeter with a shunt if the gauge is designed for that. In my opinion the voltmeter makes the ammeter unnecessary. I think there is a provision in the electronics on the newer motor to read out total engine hours too. It may take a special test device to do that though. I will try to find some info on the Opti for you. My guru is fishing right now. jim
I took a look at the Merc site and it looks like their sc100 temp gauge will work with the existing sensors. It is a white faced gauge. Gauges and sensors are usually matches pairs. The next question is whether Faria makes a temp gauge that is compatible with the Opti. If they don't, then the only way to use a Faria instrument is to use their sensor. I took a look at a picture of an Opti 3 liter head, and I don't see anyplace for an aftermarket sensor. It is probably possible to drill and tap into the water jacket at the top of the head for the Faria sensor and actually read water temp on both sides. I would not hesitate to do that, but you might not want to. I think I would call Faria and Merc if I were you. The factory, not the dealer. jim
Thanks, Jim. That is a good idea. I dealt with the factory tech at Faria once before and they were very helpful so I'll E-Mail them today and ask if the guage will work. If so, I'm going to buy it and then probably I just won't use the Ammeter guage. I'll let you know what I learn.
