I think it would be a great to know if the engine water coolant system was working, via a pressure switch screwed into the block. Absense of pressure an idiot light comes on. Any idea of practicality and the expected min and max operating pressure.

If you are looking for a way to determine if the impeller has died this is not it. Pressure rises with heat, so if the impeller dies and the engine gets hot the pressure light would not go off. Most "production" engines are pressure tested to 28psi.

Has this been tied, you seem very sure it won't work.

<a href="http://overtons.com/cgi-bin/overtons/order/pdetail.cgi?28239%2B%2B" target="_blank">http://overtons.com/cgi-bin/overtons/order/pdetail.cgi?28239++</a> <BR> <BR>looks like that's for an outboard, but still a water pressure gage. IMHO a pressure switch would work. generally pressure of a liquid is much less sensitive to temp than gas pressure.

we have a little jet boat, and it overheated on me twice, once pulling some guy, and the other was just cruising around the lake. Not sure if this will help or not, but it felt like someone was picking the back end out of the water. In any case, I took it for service,and they took off the impeller case, and there was a lot of weeds, and even treeback in there. That's what the prob was. It's run fine ever since. And we were lucky cause that stuff could wreck the impeller. Also the guy told us that a jet intake could suck up most things at full throttle from 2 feet below the hull. That's quite a bit. <BR>b

When operating at a significant RPM I would expect there to be a few PSI of water pressure from the raw water pump. It would be possible to configure a pressure switch that could operate off of this low pressure, but you would have to sense it at the output of the pump. <BR> <BR>If you attempted to tap off the engine block, such as at the water temperature sensor, then the thermostat would mess things up big time, as it blocks the water flow (and thus reduces the pressure) to maintain a constant temperature. <BR> <BR> Given that there are paths that have little or no restriction the pump would not be generating much pressure, especially at idle. You may get a lot of false indications at low RPM, so don't make the indicator too annoying. <BR> <BR>

rather than a pressure switch, you should look for a flow rate guage (similar to the ones you can install in the fuel lines to monitor how much fuel you are using). It would be a lot more accurate than a pressure switch for all the reasons stated above and probably a lot easier to find.

Oh sh** kick me self for overlooking the therostat. <BR>Areed a flow sensor would the best way to monitor but that is going have to be a sucka. Big $$$. 1 inch in dia. <BR>what about a ps switch on the engine water pump. Mine has a 1\2 inch npt pipe plug in it. <BR>I've found a 5-15 psi ajustable set point. $35.us. <BR>Normally close out put so a light comes on when the ps swicth does not have, adjustable, 5-15 psi.