1986 350 Merc Alpha 1

I own a 1986 Sea Ray 30 ft Sundance with a heating up problem! We use the boat in fresh water since new. We have changed outdrives from Right to left side to weed out the problem of drives and still its heating up at idle and WOT. There are new water pumps in both drives and both engines are with stock thermostats. Today I removed the power steering cooler to see if there was some kind of blockage. Next thing is manifolds??? Does anyone else have a possible reason for heating up in the ranges I have. There are new water pickup hoses and they are not kinked. This problem has hauned me for 3 years, so when I'm by the dock i must watch the gauges with great care. Is there a way to flush the manifolds? Thanks Randy Canada..

Re: 1986 350 Merc Alpha 1

You might be able to flush the manifolds with acid.More than likley the manifolds and risers need to be replaced.If they are 1986 model they are due for a change.They usually last 15-20 years you have way more than that.
Bite the bullet and get new.J

Re: 1986 350 Merc Alpha 1

Thanks for the reply, that is what I'm looking for tomorrow.

Re: 1986 350 Merc Alpha 1

..stock therostats..as in new of the recommend heat range or...the original stock theromstats....surly these are not the orginals..

Re: 1986 350 Merc Alpha 1

You are right the therms are new and stock as in Mercury. I heard the manifolds could possibly be cleaned as in boiled or a solution to add to the inside and leave for a period then flush??? Any thoughts. thanks for the in put...

Re: 1986 350 Merc Alpha 1

Manifold, maybe 10-12 years, risers, 4-6 .when you try to remove the corrosion your removing the cast iron .The walls are getting very thin and prone to cracking and filling the motor with water. Just replace them and you will be better off in the long run.

Re: 1986 350 Merc Alpha 1

Well the boat was just taken out of the water for the season and we did a check on the manifolds and all are good. Now it is out of the water a new mechanic asked me if the balls on the thermostat housing has been replaced or switched around and the spring has to be stretched to put more tension on the balls??? Has anyone ever done this and would this help my heating problem at lower RPM's? Thanks Randy...

Re: 1986 350 Merc Alpha 1

Has anyone ever done this and would this help my heating problem at lower RPM's?

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Ayuh,... Those have to be Functioning with the Alpha 1 waterpumps....
That's probably the Idle problem,...

I'm running a motor out of an Alpha 1, Gen.II with my Alpha 1...
I experinced some overheating at trolling speeds, til I swapped to the check-ball T-stat housing...
It didn't seem to bother at WOT though...