Boat overheats?

Question

What would be the Best way to Dyignose a Water circulation problem with out putting the boat in the water, our boat ramp will not allow Boat Repairs dockside the man says No acceptions, the Boat is I/O 305 V8. Guage stops at 240, it got up to about 220 I shurdown we never went over 1500 RPM,s not much more aver Idle, we arent in a position to just start replacing parts untill we find the problem.

the Engine was removed for a Gimbal replacement and a Transom replacement, the Outdrive is about 2 years old (Jasper) everything is back were it belong to be.

If I left any info out feel free to email me and Ill try to answer your question.

Thanks.

Answer 1

First I'd have the lower unit pulled and have them check the impeller.  This should be the first place you need to check before continuing on.

If you have a service shop do this, make sure they get it right the first time.

Afterwards, do the cooling test on a flusher hooked up with water hose flow at home running at idle.  Do not exceed 1500 RPM or you may risk having the engine overrev uncontrolably and burn up your engine.

If you get water flow into the cooling system and significant water comming out of the exhaust, that should tell you that the impeller and water pump is doing its job.  However, that won't tell you if the thermostat is working, or if you have a blockage somewhere in the engine or cooling system elsewhere.

Second, if impeller in lower unit is not the cause, it would either be a thermostat problem, water pump on the engine, heat exchanger clogged if you have dual coolant system (internal/external), or primary coolant obstruction somewhere.

Answer 2

Well you need to start somewhere to check out the cause.

First is make sure that your pump is working correctly, that the impeller is okay.  If you have not replaced the impeller that is cheap place to start. If your boat is fresh water cooled, you could check the thermostat in the engine block to make sure it is not stuck. The heat exchanger could be stopped up, this is a big problem in salt water use.  

You can get an engine cooling flush kit, hook up to a hose and run the boat setting on the trailer. You should do that anyway, just to keep the engine and cooling system clean, really important in salt water use.

Answer 3

It's hard to say.  I know you don't want to just start replacing stuff, but I would go buy a new thermostat.  They are easy to replace and if it doesn't fix the problem, take the thing back.  The people that sell you the thermostat can guide you as to how to replace it, but its easy to do.  Thats where I would start.

Answer 4

you can test the thermostat in a pot of water on the stove with a kitchen thermometer, observe and see what the temp is when it opens.  most stats have the operating temp stamped on 'em.

Answer 5

A lot of times if a closed system it's the exchanger> & if not it's the risers where the water come out where the 4" hoses connect too> look inside as there are small holes that plug up> Drill out or replace them>

Answer 6

Even inboard, not sure how you cool this puppy down but I'd betcha it's your waterpump. Have you had any luck there?