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440 Chrysler Marine Overheating

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toddster1280

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Hello all, I am working on a 36 foot Trojan with a dual 440 Chrysler marine. I stepped into this job with one motor out and the long block rebuilt. Since Day 1, that motor (port side-counter-rotating) has been overheating. I have tried all the basic, usual items: cleaning out heat risers and manifolds, which were plugged (and probably the cause of the original failure of the motor), a new raw water impeller was installed (and am getting very good flow out of the exhaust, with heat risers and manifolds cool to the touch). Fresh water thermostat and water pump have been replaced.Heat exchangers were cleaned and Starboard heat exchager was put on port side, since starboard side has always been running at operating temperature (170 degrees). RPM's up to 1,000 on port motor, stays cool, but rapidly climbs at anything over 1700 RPM's. Antifreeze is at 50/50 mix. Timing is good. Not advanced to cause overheating. Heat gun was put onto top tank, and is accurate with gauge on dash. I even went as far as checking the head gasket to see if the person who overhauled the motor put it on backwards, ie, water passages misaligned, but that is not the case. Hoses are clear. I have been a mechanic for 30+ years, but this overheating problem child has me stumped. Any suggestions would be helpful, so I can get some sleep at night. Thanks, Todd.
 
What year? Single or dual pocket pump? Have you back-flushed the two oil coolers? Couls be partially blocked with debris or impeller pieces.
 
toddster1280 said:
Hello all, I am working on a 36 foot Trojan with a dual 440 Chrysler marine. I stepped into this job with one motor out and the long block rebuilt. Since Day 1, that motor (port side-counter-rotating) has been overheating. I have tried all the basic, usual items: cleaning out heat risers and manifolds, which were plugged (and probably the cause of the original failure of the motor), a new raw water impeller was installed (and am getting very good flow out of the exhaust, with heat risers and manifolds cool to the touch). Fresh water thermostat and water pump have been replaced.Heat exchangers were cleaned and Starboard heat exchager was put on port side, since starboard side has always been running at operating temperature (170 degrees). RPM's up to 1,000 on port motor, stays cool, but rapidly climbs at anything over 1700 RPM's. Antifreeze is at 50/50 mix. Timing is good. Not advanced to cause overheating. Heat gun was put onto top tank, and is accurate with gauge on dash. I even went as far as checking the head gasket to see if the person who overhauled the motor put it on backwards, ie, water passages misaligned, but that is not the case. Hoses are clear. I have been a mechanic for 30+ years, but this overheating problem child has me stumped. Any suggestions would be helpful, so I can get some sleep at night. Thanks, Todd.
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At least you didn't say that you've checked everything. If that were the case, you'd have found the problem. Seriously, you did check most everything. But, how about the water pickup and sea cock? Maybe a piece-o-crap is lodged in there. [A stretch: excessive bottom paint on water pickup?]

Good luck, Noel.
 
Thanks for all the quick responces. Raw water is flowing out the exhaust better than the starboard side but will back flush the coolers anyway (heck, I have cleaned everything else!).The bottom was cleaned and water is flowing very well from the seacock. At first I did take out the thermostat with no differance in temp but found out latter I was thinking like a car mechanic and not marine. The thermostat restrices the fresh water flow so the raw water from the heat exchanger has a chance to cool the fresh water passing thru the tubes. When the thermostat is removed, the water races thru the cooling tubes without getting cooled. I did replace the fresh water circulating pump (straight fins, not directional) from the starboard side with no differance in temp reading from both motors. I beleive the problem is in the fresh water circulation. I don't undrestand the "single or dual pocket pump". Are you refering to the raw or fresh water pump? Both are what came from this motor when I stepped into this job. This may be a long shot, but is there a differerance in the rotation of the fresh water pump housing on the block? Both outlets on the motors are rotating the same way even thou this is a counter rotating motor. This was installed before I put the motor in. Could the previous mechanic put the wrong one on (this looks like it was with this motor because of the paint)? This is a 1972 motor. Again, thanks for all your input on this problem child. Todd
 
Didn't know the vintage at first. You most likely have a single pocket (one impeller) raw water pump. Early models had dual pocket (two impellers) raw water pumps. Have come across dual pocket pumps serviced where only one impeller was changed. Hard to miss but people didn't realize there were two impellers in there.
 
I found full sized oysters under my intake screens. I unscrewed them and cleaned all of the oysters out. They blocked the thru-hull just enough to make a difference. I never would have found it if I had not taken the scoop/screens off.
 
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