What Sending unit? What pressure gauge?

[rost495]

200 hp Johnson 94.

Want to put a water temp gauge on it. What size NPT sending unit? Where do I find info on where to look to connect it? Also my book says, different NPT sizes but mentions inboards?? Is this not for outboards? Sorry if its a dumb question but want something to tell me if my outboard is running hot for some reason?

Also water pressure gauge. 15psi or 30 psi?

Thanks, Jeff

 

[Silvertip]

Re: What Sending unit? What pressure gauge?

Water pressure = 30 PSI gauge. As for the engine temp gauge, make certain the temp gauge and the sender (one for each head on a "V" engine) are compatible with the gauge. A sender and gauge for an inboard or I/O will not work on an outboard as an outboard runs much cooler. Some engines like my Merc have a port tapped for a 1/8-inch pipe thread that allows the sender to extend into the water jacket. Other manufacturers of gauges and senders have the sender mounted on a bracket bolted to the head using a head bolt. The sender then contacts the cylinder head (essentially making it a cylinder head temp gauge rather than a water temp gauge) but that's another discussion that gets out of hand. You need a gauge that reads 60 - 200 or 210 or so. I/O and inboard gauges generally read 100 or 120 degrees to either 240 or 260. You could use those gauges and senders but the gauge would rarely move since normal idle temp is in 140 range and overheat occurs about 175 give or take a little. Just make sure you know what you are buying.

 

[rost495]

Re: What Sending unit? What pressure gauge?

Thank you for the reply!
Got the pressure issue covered then.

About the temp gauge... outboard V6. Does that mean I need 2 gauges and 2 sending units??
I know boats are not cheap, but double gauges are not either, if I need 2, do I really need a temp gauge? I was suspecting that the horn alert or whatever the overheat alert is on a 94 Johnson saltwater 200 would be too late, IE like a dash light, once its on its probably burned up?

ALL help is totally appreciated!!

Jeff

 

[Silvertip]

Re: What Sending unit? What pressure gauge?

You certainly don't need a temp gauge provided the existing overheat warning system is functional. However, the overheat warning system sounds when the engine is "already" overheated. The temperature gauge allows you to monitor temperature at idle (normally higher than at wide open) and at wide open. It can tell you both the thermostat and the poppet (bypass) valve are functioning properly. Just so you know, because the tell tale shows a good stream of water does not mean the engine is being properly cooled. That stream merely indicates the water pump is working. If you install a pressure gauge, install a new impeller at the same time. Then note idle, cruise and wide open throttle pressure readings. Any future deviation from those values indicates a problem. As for the temp gauge, you need only one, but ideally you need two sensors, one for each head since it is possible for one side of the engine to run hot and the other normal. A simple three pole two position switch allows the gauge to display right and left head temps. If you go to E-bay and search on outboard temperature gauge you will currently find one for a Mercury so you will have an idea what a cylinder head mounted sensor looks like. The gauge is calibrated Cold-Hot and those outboard gauges calibrated 60 - 210 are now getting hard to find. If you decide to add the temp gauge, private message me and I'll help you with the switch wiring.