Overheating with antifreeze

T

Turkj40

Member
Sep 17, 2014
84
Plymouth Ma
Boat Info
320 sundancer
Engines
Twin inboard 350s
Have a friend w a brand new 6.3 merc and starting in June she overheats w antifreeze in the block. Run it w 100% water and she runs about 6deg hotter than the SB motor. He has replaced everything from hoses to sensors and all pumps with new and over from other motor and still with antifreeze it overheats. Has anyone run into anything like this.
 
Turkj40 said:
Have a friend w a brand new 6.3 merc and starting in June she overheats w antifreeze in the block. Run it w 100% water and she runs about 6deg hotter than the SB motor. He has replaced everything from hoses to sensors and all pumps with new and over from other motor and still with antifreeze it overheats. Has anyone run into anything like this.
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I agree with scoflaw Thermostat , heat EX , Risers , oil cooler restricted , etc!
 
All of the above has been inspected and checked. Like I said if we drain all the antifreeze out of the block and fill it with just water it runs normal. When we introduce antifreeze back into the block it over heats. We have tried different ratios with no luck. For whatever reason antifreeze makes the motor over heat
 
Turkj40 said:
All of the above has been inspected and checked. Like I said if we drain all the antifreeze out of the block and fill it with just water it runs normal. When we introduce antifreeze back into the block it over heats. We have tried different ratios with no luck. For whatever reason antifreeze makes the motor over heat
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Are you diluting it 50/50?
 
Almightys said:
Are you diluting it 50/50?
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We’ve tried every variation of mixture as well as different brands and pre mixes. As soon as the weather warms up the antifreeze fails however straight water works‍♂️ In September he will fill it with antifreeze again and it will be fine until next June then the cycle begins again.
 
Turkj40 said:
Have a friend w a brand new 6.3 merc and starting in June she overheats w antifreeze in the block. Run it w 100% water and she runs about 6deg hotter than the SB motor. He has replaced everything from hoses to sensors and all pumps with new and over from other motor and still with antifreeze it overheats. Has anyone run into anything like this.
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Brand new motor or brand new boat?
New boat should have a warranty.

incorrect ignition timing can cause it to run hot.
 
Espos4 said:
Brand new motor or brand new boat?
New boat should have a warranty.

incorrect ignition timing can cause it to run hot.
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Replaced one of the motors last year, def not a timing issue just overheats in June July August with antifreeze
 
Straight water would only cool it slightly better, so you must be on the verge of an overheat when on water only. So the HE checks out? I'd question that and the source of water to the raw water pump.
 
Antifreeze has poor heat transfer as compared to water. Something is introducing excessive heat into the cooling system. Could be a small head gasket leak, incorrect gasket installed somewhere, poor block casting maybe restricting flow, ignition timing, incorrect water pump etc. I’m not saying that these are the cause, but you’ve got something creating the excess heat or possibly affecting coolant circulation.

how about an IR temp gun. Scan the two motors at similar locations and see what you find.

For diagnostic purposes, how about running it without a thermostat. If the thermostat or it’s installation is the cause, it’ll stop overheating. If it wasn’t, it’ll Still overheat eventually.
 
Use heat gun and compare point for point between engines with both antifreeze and water.
 
I appreciate all the feed back but unfortunately we’ve checked off all those boxes. We swapped ever cooling part between the two motors down to the long block. This is a brand new short block and it doesn’t like antifreeze in the summer and we love in the NE, he runs it on water with no issues with temp until antifreeze is introduced. As mentioned the motor does not overheat when using only water in the block, if we fill the block with antifreeze it overheats. And there are no leaks because we have measured the amount of antifreeze we remove each time and it’s within a couple of ounces of loss. It’s the most baffling issue.
 
I will say this is an odd one. And I don't have an answer, but I would suggest trying to expand your scope of problems. I fully realize that you have swapped many components. But the antifreeze shouldn't do anything. Something else is up. I will ponder this for a bit and check back. Please keep us posted
 
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