With twin 500EFI's and starting this season, starboard engine is pinning the water pressure gauge when under load (which is mechanical) and thermostat is cycling quickly on same engine? It is going to 150 then cooling down to 130F, then climbing back to 150F and then going down to 130.Where should start? Switched the gauges and same thing so it is not the water pressure gauge.

Thanks in advance.
Dan

Look for a restriction in the water system on the pressure side of the pump, clean out the oil cooler, check the ps cooler, and the exhaust. Could also be the tstat sticking.

The thermostat was installed in the top of the housing, it was moved to the bottom position in the housing and cured it :-)