Re: 70hp idling characteristics?

[Don]

Does your thermostat set up look like this?
http://www.marineengine.com/parts/johns … +Crankcase
If so, what you have is a "vernatherm", along with all that other jazzy stuff. All those bits/pieces must be oriented properly, and the diaphragm must not be split, along with proper vernatherm operation, or the engine won’t warm up…
Higher RPMs bring more water pressure which can overcome the big spring’s ability to keep the diaphragm sealed on the vernatherm face, so seeing the temp gage go down a bit at higher RPMs is normal and a good thing. I would not try to heat up that vernatherm, or the pin might just pop out. I don’t have a dimension for closed/open lengths though…
PS, another glitch in the ointment is that some of the water pumps may develop too much pressure at idle, causing the diaphragm to blow off its seat…This is truly a pain, most of the water pump kits have extensive directions about this though. Moving the elbow to the top of the powerhead, and removing the restrictor nipple at the end of the overboard hose should lower the pressure enough to solve this situation…So, for now, just pull the plastic restrictor off the overboard hose, and hold the hose overboard to see if the engine warms up this way….
Good luck with this jig saw puzzle!