overheating

[dennis cudd]

i have a 76 233 mercruise in board. the water pump has been changed the impeller has been changed ihave put a new sea pump on and it still runs hot.ihave taken the thermastat out some times you can swtch the motor off and let it sit for a while and start it back up and the boat will run fine for the rest of the day. several weeks during the summer it didnot run hot at all then all of a sudden it started back again. i put it in the shop hoping to get some help. the shop cleaned some rust out of the exhust mainifolds and said that took care of the problem since then it runs hot all the time.he put some clear hoses and said one would bubble up for a while and then clear up. he thinks its, the exhaust manifoldbut doesn't know for sure and i have already spent 400 bucks and still have the same problem and do not want to spend any more unless it is going to be fixed can you give some advise./

 

[Walt T]

Re: overheating

is this raw water cooling or closed cooling system? When exacly does it over heat? At speed? at idle? does it overheat at speed and cool down at idle? does it cool down at all? Are you still there? Dennis?

 

[dennis cudd]

Re: overheating

it is a raw water system.it will heat up at an idle or at high speed. you can switch the boat on and off and let it set. then after a few trys the temp gauge will go down and the boat will run fine for a while.any time you get around 5000 rpms the motor will heat up more.

 

[f_inscreenname]

Re: overheating

I know in my case I didn't run a thermostat at the beginning of the summer for a couple of months and I found that if I ran for more then a mile or so at anything over 2000 rpm's you could watch the temp clime about five degrees a mile after that. I was told that some motors need a thermostat to create a little back pressure so all the water moves around inside the block. With out a thermostat the water runs through the motor like a stream that has current in the middle but on the banks the water sits still. A old marine mech told me they used to take a 140 degree thermostat and drill three or four 1/8" holes in it to cool down motors that didn't have any reason to run hot. It worked for me. I still have my fingers crossed (been four months with no cooling problems).

 

[dennis cudd]

Re: overheating

one thing i didn't mention when my boat runs hot it will peg the gauge and i switch off till it cools down to 160

 

[Walt T]

Re: overheating

You got something blocking cooling ports in the engine. It's moving around, that's why it seems to work ok sometimes. Could be impeller pieces?