overheating problems please troubleshoot

mercrude

Seaman
Joined
Oct 29, 2002
Messages
67
overheating problems please troubleshoot

this motor is a 1983 mercruiser 485 185 hp<br />I rebuilt carb adjusted air/mixter screws idle screw put on water and the temp guage shot up to 240 burried all the way motor steamed just like a car overheating this motor has a closed cooling system. well I changed the thermastat pulled the exhaust manifold and on the top of exhaust manifold there are two cut outs seperated by a wall this wall had a crack in it so I cleaned it up and JB welded,d it, rubber bellow tube coming off back of exhuast manifold had a long gash in it so I replaced it, then I rebuilt the water pump in lower unit. still overheating very quikly<br />I noticed a hole in the large rubber coragated tube that comes out of transum to lower unit but have not changed it can anyone please help me I feel like I'm parts hanging and my wallet is getting thin. :confused:
 

karayj

Chief Petty Officer
Joined
Aug 4, 2002
Messages
468
Re: overheating problems please troubleshoot

Re: overheating problems please troubleshoot

Did you buy this boat like this and its the first time out or was it fine and then after rebuiling the carb all this started..???
 

mercrude

Seaman
Joined
Oct 29, 2002
Messages
67
Re: overheating problems please troubleshoot

Re: overheating problems please troubleshoot

the overheating problem started the first time I took it out after the carb project :confused:
 

mercrude

Seaman
Joined
Oct 29, 2002
Messages
67
Re: overheating problems please troubleshoot

Re: overheating problems please troubleshoot

I purchased a new t-stat and it looks differant then the one I pulled out can I leave the t-stat out to see if my overheating stops or is this a bad idea?
 

navigator336

Petty Officer 1st Class
Joined
Jul 27, 2003
Messages
270
Re: overheating problems please troubleshoot

Re: overheating problems please troubleshoot

When was the last time you changed the water pump impellor? If it was recently and the old one was shot (i.e. missing blades) did you find all the old blades? When they break, they usually end up at the tranny cooler and block this little heat exchanger which will cause you to overheat at normal operating speeds but not typically at wakeless speeds.
 

crazy charlie

Vice Admiral
Joined
May 22, 2003
Messages
5,581
Re: overheating problems please troubleshoot

Re: overheating problems please troubleshoot

Mercrude,pull the new thermostat to see if there is an immediate change.This will rule out 1 part of the equation or nail the problem.Never leave the thermostat out after checking it out.Dont go crazy until you check the thermo. Charlie
 

mercrude

Seaman
Joined
Oct 29, 2002
Messages
67
Re: overheating problems please troubleshoot

Re: overheating problems please troubleshoot

crazie charlie<br />I checked the t-stat it was fine took boat to marine they did a compression check all four cylinders varried from 105-125 1b each not good they think it's a blown head gasket<br />what I would like to know what would cause head gasket to blow?
 
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