What thermostat for a 454 Mercrusier Inboard 330 HP with closed cooling?

[Finnerty]

I have a question about my Mercruiser Inboard 330 with closed cooling. Mercruiser Manual #3 says I need a 143 degree thermostat. When I tried to buy this at our local Mercruiser Authorized parts dealer he said "no, you need a 160 degree". Is he wrong or has the recommendation changed since 1977...? and will it make any difference? Also sold me a 13 psi pressure cap as "this is what is used now" instead of the (manual specified) 14 psi cap. Wondering....

 

[Bondo]

Re: What thermostat for a 454 Mercrusier Inboard 330 HP with closed cooling?

Ayuh,... Running antifreeze in the motor, I'd probably go with a 180? T-stat...

The 143? is to keep the iron from absorbing salts...

As for the cap, I really doubt 1 psi makes Any difference what so ever...

 

[Don S]

Re: What thermostat for a 454 Mercrusier Inboard 330 HP with closed cooling?

160? is what Merc recommends. The engine will then run in the 170? to 175? range under load. With a 180? stat, you will run 190 to 195 range, while that won't hurt the engine, it makes vapor lock a real problem in the enclosed engine compartment.