Merc 90 Cooling Question

[CharlieZulu]

Hi Folks:

Late '80s Merc 90, oil injected. My water flow starts right from the get-go..... does this mean my thermostat is stuck open, or is this normal? If it isn't normal, typically how long does it take for water to flow from a cold start?

 

[electricjohn]

Re: Merc 90 Cooling Question

Mine has always flowed fast from start up, and faster up to WOT. A gage threaded into my head shows 7 psi at idle, and 14 at WOT. The water never gets hot, but an infra red thermometer shows my heads at around 140 to 145*F when engine is at normal operating temps.

 

[Hottip]

Re: Merc 90 Cooling Question

The water from the telltale should start flowing as soon as the motor starts to turn over.

 

[Maxz695]

Re: Merc 90 Cooling Question

I believe the is a bypass that allows water to flo even if the thermostat is closed.

 

[Chris1956]

Re: Merc 90 Cooling Question

Charlie, Depending on the model of that motor, you may not have a thermostat. Most/all inline sixes didn't have thermostats..... Telltale water flow was after a few seconds

 

[Faztbullet]

Re: Merc 90 Cooling Question

Thats a 3 cylinder 90 and it has a t-stat and poppet valve. The tattle tale is fed off the exhaust plate before the t-stat so it will pee within 10-20 seconds of engine start.

 

[Maxz695]

Re: Merc 90 Cooling Question

mine runs off the exhaust plate does that mean the thermostat has nothing to do with the tattle tail?

 

[CharlieZulu]

Re: Merc 90 Cooling Question

Yes indeed, it's a 3-cyl.

Thanks, guys for the great info.