1977 mercury 115 outboard cooling system

I have a mercury 115 that after starting, water flows for a good little bit, thens stops. I have put in a new impeller kit and housing. You can idle for about 4min then stops and keep running in about 30seconds it starts again real slow. If I try to idle up it stops in about 1 min from take off.

Is there a switch or thermostat that does this, I do not hear any alarms, and water seams to be warm to touch when it is flowing. I can't tell if someone else has bypassed something or is there some thing I need to by pass.

Please help.

Re: 1977 mercury 115 outboard cooling system

Trent, That motor does not have any thermostat or valves that would do slow or restrict water flow. The telltales do clog easily and you can clean them up with a piece of wire.

On the flusher, water should come out the gratings above the antiventilation plate, as well as from the prop hub. Some water may come out the square holes higher up on the midsection. The exhaust cover (flat plate on port side of motor) should be cold when running on flusher at idle. If it is warm at idle you have a cooling problem.

Re: 1977 mercury 115 outboard cooling system

Chris
I don't understand why some engines don't have a thermostat? I thought that the reason for one was so the block temperature wasn't quite so drastically different than the combustion chamber. I've read forum threads where people asked about just not putting in thermostats, and the answers were that by having the block be too cool, the engine would be ruined in no time do to the block not getting warm enough. I've got an 115 HP merc (approx 1973) and my friend that's working on it told me that the block seems so cool that he could probably put his face against it! Anyway, if you or someone else can explain to me how these engines perform and not wear out with this set-up. I would be grateful.
Thanks
Richard (Camano Island, WA)

Re: 1977 mercury 115 outboard cooling system

Is this a newer to you engine? There could be something in the watertube so that when you accelerate it's forcing more water into the tube and pushing the object up and restricting it, maybe a piece of the impeller.

Just my .02

Re: 1977 mercury 115 outboard cooling system

Rich, Merc designed a lot of their motors in the seventies and eighties without thermostats. These motors ran very cool at idle and warmer at speed. As long as you had the correct prop for the boat and load, and a good waterpump impeller, they worked pretty well. They were carborated to work under these temperature differences.

Johnny/rude had thermostats on their outboards in the fifties, or earlier. They thought it necessary, and probably had better running motors in cold conditions.

The bottom line is if you have a thermostat, make sure it works properly. If not, make sure you keep an eye on the water flow (water pressure gauge is a good way) to keep the motor from overheating.