restricter plates?

[rons boat]

On a Mercruiser mcm 228 of 1984 vintage I am having problems with overheating of the engine block until the boat is at 1500 rpm or above and then all is normal. Bring back to idle and problem reappears. I have pleny of water from the impeller which is new. Elbows are cool. I wonder if someone has removed the restricter plates at the bottom of the elbow causing the recirculating pump to run out of water at low speeds. Can someone advise on this funny cooling problem?

 

[highaltitude]

Re: restricter plates?

check the spring loaded valves in the thermostat housing

 

[rons boat]

Re: restricter plates?

Highaltitude and others, I did check to see that there are no spring loaded valves as you suggested. I am fimilar with the valves that were in some pre alpha thermostat housings. My book does not say which models had the valves and which did not. I must defer to someone who has knowledge of the mcm 228 SN 63***xx which may not have had these devices and depended on restricter plates for appropriate back pressure. Perhaps someone else can shed some light. Thanks Ron