86 Ski Supreme overheating

If you are getting water through initial screen and trans cooler and on to the Raw water pump then the impeller might be need to inspected and or replaced.

Raw Water Pump is an external belt driven pump.  Pulls water from the bottom of the boat and supplies all cooling to your marine engine.  There is usually a filter on the supply hose.  Raw Water Pump impellers usually last no more than 3 years in my area before they either fall apart or get stiff and no longer suck water up properly.   Each pump design has its own unique impeller.  They are usually around $35 and take a 1/2 hour to install.  If you have never replaced one study up you want to get it right.   When you pull yours apart make sure all the blades are intact.  Many times blades peel off and will go into your cooling hoses and plug those.  Don't stop chasing the lost parts till you have them all and could reconstruct your old impeller.  Lost pieces cause overheats later so take the time and find them.  Flush hoses clean after removing them.

If you pop that housing off, right in front of the carburetor just like you said, you'll find the thermostat.

You can test the old thermostat in your kitchen if you have a Meat Thermometer or a IR gun.  Put the thermostat in a pan of Cold Water.  Slowly heat the water like your engine would do, so in 3-5 minutes take the water from cold to 150, hold the temp at 150 and see what happens.  It takes a little time for the thermostat to heat up and open.  If you wait a minute or so and it does not open at 150 try 170, then maybe 200.   The thermostats are usually stamped with the opening temp.  143* for example and they usually open almost exactly at that stamped temp. There is no repair if it does not open replace it.  Your old boat should open around 140 and it should be fully open.

Got a picture of the thermostat?

Start by replacing the impeller.  Then look downstream of the raw water pump for chunks of old impeller.  Or do like most and hope they went on through.  

Young545 wrote: Took off the pump today and the impeller is mostly gone. So I know to check hoses. Remove main pump? Engine inspection? I’m at the cottage on phone and can’t figure sending pics yet. I’m

Forgot the most important pic.

Those pieces are in your cooling system somewhere.  

Do I need to precharge hoses with water before starting?

Ski Supreme back up and humming!!! Big thanks to KENO, MrMcD, and fanofccfan for all the help. I changed the impeller and decided to reuse the old thermostat since it tested ok. I cut off the ends on 3 hoses as they were splayed and cracked. Started right up and stayed around 150. Thanks again for taking care of a newbie. 

The first Lake test will confirm if your boat is ready to go.   Pay close attention to the temp the first outing.  Good Luck.