Marine: Boating, Sailing, PWC, GPS and Navigation - Boat running HOT!!!

I have a 1985 OMC 3.8 205 hp engine that is running hot. At 3000 rpm unplanned the boat doesn;t run hot at all the only time it gets hot is when the boat planes out even with the rpm at 3000. As soon as the boat unplanes the temp drops right down. I have removed the t-stat and it has not helped at all. The boat had set for 3 years with the stern drive off and uncovered, I flushed the engine with water the best I could and the stern drive has been rebuilt.... ANY ideas of what to do next.....

are u sure the impellor in the outdrive is ok? starting it out of the water without earmuffs for only a second could burn is up...

Yes I have checked it and it seems to have good water flow. Since the new impeller has been put it it has never been ran without waterflow.

I have Same Exact Problem My boat gets hot when it plains out it usually gets up to 180 temp at plane then goes down to 160 temp when not planeing and running at lower speed.
Before boat ran below 140 temp.
I have a 1973 Glastron I/O 130HP Volvo Penta with 270 outdrive
The impeller works fine becouse i had Garden hose hooked uo with flush to the outdrive and water was running through and out outdrive at idle. I am thinking it might be the thermostat but I am looking for other causes before I replace thermostat.

if the impellor is a few years old, it can go bad just sitting. the rubber looses its elasticity, so to speak, from being bent over in the housing. i dont know if my point is being made properly, but the impeller may be bad. they are cheap enough to replace just in case.
also, the timing could be off.

I agree with Terry..... I replace my rubber impeller at least every two years.... and have yet to regret it. Impellers are cheap... head gaskets and all the other heat related problems get spendy quick

You had better put that THERMOSTAT BACK IN.You can overheat your motor not having one in.If you think that your thermostat was bad replace it with a new one.Without one you have to much and too fast a water flow going thru the block.NOT GOOD.Will definatly overheat a marine motor.

I have a 1985 OMC 3.8 205 hp engine that is running hot. At 3000 rpm unplanned the boat doesn;t run hot at all the only time it gets hot is when the boat planes out even with the rpm at 3000. As soon as the boat unplanes the temp drops right down. I have removed the t-stat and it has not helped at all. The boat had set for 3 years with the stern drive off and uncovered, I flushed the engine with water the best I could and the stern drive has been rebuilt.... ANY ideas of what to do next..... :thinker: You are sucking air in your hoses or hose somewhere in back by Transom. The faster you go with your boat the water table goes down in the back of your boat.If you are sitting still your drive is in water all under water but the faster you go your water table goes down in back of boat ,so you are sucking air in one of the inline hose that goes to your sea pump this will make your engine run HOT ,also never run without a Thermostat because of pressure differance. This sure Help You ALL.

I have Same Exact Problem My boat gets hot when it plains out it usually gets up to 180 temp at plane then goes down to 160 temp when not planeing and running at lower speed.
Before boat ran below 140 temp.
I have a 1973 Glastron I/O 130HP Volvo Penta with 270 outdrive
The impeller works fine becouse i had Garden hose hooked uo with flush to the outdrive and water was running through and out outdrive at idle. I am thinking it might be the thermostat but I am looking for other causes before I replace thermostat.--------------------------------------------------------------------------------------------------------------------------------------------------- You are sucking air in your hoses or hose somewhere in back by Transom. The faster you go with your boat the water table goes down in the back of your boat.If you are sitting still your drive is in water all under water but the faster you go your water table goes down in back of boat ,so you are sucking air in one of the inline hose that goes to your sea pump this will make your engine run HOT ,also never run without a Thermostat because of pressure differance. This sure Help You ALL.------------------------------------------------------

You are sucking air in your hoses or hose somewhere in back by Transom. The faster you go with your boat the water table goes down in the back of your boat.If you are sitting still your drive is in water all under water but the faster you go your water table goes down in back of boat ,so you are sucking air in one of the inline hose that goes to your sea pump this will make your engine run HOT ,also never run without a Thermostat because of pressure differance. This sure Help You ALL.

You are sucking air in your hoses or hose somewhere in back by Transom. The faster you go with your boat the water table goes down in the back of your boat.If you are sitting still your drive is in water all under water but the faster you go your water table goes down in back of boat ,so you are sucking air in one of the inline hose that goes to your sea pump this will make your engine run HOT ,also never run without a Thermostat because of pressure differance. This sure Help You ALL. In Volvo where the gooseneck is on the drive This is a known place to suck air . if you put two or more gaskets there this will work. I had the problem myself . I have a 1982 Glastron SSV-177 . I run cool now all the time never over 180 degrees in my boat.

i have ran my boat without a thermostat in it for 12 years