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full closed cooling installed,temps?

Old 06-17-2015, 09:29 AM
  #1  
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Default full closed cooling installed,temps?

I have installed 2 new 5.7 carb engines connected to v drives in sea ray 30ft. I used parts I had on hand. The heat exchangers are both from 5.7 engines,not sure if they were 1/2 or full systems. I have mounted heat ex at back of engines[actually forward in boat cuz v drives] The thermostat housings are 2 outlet and are connected to bottom of NEW exhaust manifold. I followed full closed cooling water/coolant flow diagrams. The thermostat housings dont seem to have much of a bypass for coolant flow. I have a water heater that allows bypass by hose fitting next to thermostat housing on intake and returns to circulating pump.The other engine I installed a fitting in intake manifold and that hose runs coolant back to the heat exchanger coolant outlet[it does not get cooled just acts as a loop for coolant] New impellers in pulley driven sea water pumps, both pumping lots of water, exhaust risers are cool. The thermostat are 160. The engines run at 160-170 on guages at idle on hose water. Water coming out exhaust is warm. My question here is what temps should be seen at block and exhaust manifold log? I have had many raw water inboards and the exhaust logs are warm but not hot. i'm getting 190 on logs and block,heads. These are heat exchangers that I retrofitted. Basically i made a generic full closed cooling. My concerns are what is average temps. Please post only if you have a full closed cooling system and know what temps you are running I need to compare apples to apples. Thanks In advance
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Old 06-17-2015, 09:36 AM
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One potential problem (and I'm no expert) you say the heat exchangers came off of another 5.7 but you aren't sure if it was a full or half system. If they came off a half system engine, they may not be big enough to handle a full FWC system.
Just a thought....
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Old 06-17-2015, 10:02 AM
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My question here is what temps should be seen at block and exhaust manifold log?
What is the "block and exhaust manifold log" you are referring to?

Temps vary with the thermostat you have. What is it's rating?
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Old 06-17-2015, 11:08 AM
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On my 4.3 I'm seating about 160 to 170 on the gauge on the risers and elbows I am seeing about 180ish. My step father's boat has 4.3 and a open system and his gauge reads about the same but his risers are slightly cooler.

My kit was made by monitor and is a full system kit.
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Old 06-18-2015, 10:18 AM
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Thanks guys. The heat exchanger size seems to be the same as full,good point. I am running a 140 and 160 degree thermostat. 160 on hot water heater engine, the gauge reads 160-170 that temp is from sensor at thermostat and next to it in the intake passage. The block is the engine block and log manifold is the exhaust manifold, my riser has the cold water dumping thru them and they are slightly warm, water coming out exhaust is warm. I wonder do these closed cooling run cooler when boats in water? also hotter or colder when idle or cruise or stay the same cuz its a closed loop.
Thanks All
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Old 06-18-2015, 11:13 AM
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I installed 2 full closed cooling systems on my Mercruiser 7.4 MPI engines (twin engine with outdrives)

I was initially seeing temps in the 170-180 range with no load, using the thermostat provided in the kits. The exhaust manifold seemed to be heating up quite a bit before the thermostat would open. (160 degree).

I finally drilled a couple of bypass holes in the thermostat flange to provide some circulation to the exhaust manifolds while the engine was coming up to temp. Now I seem to run 155-165 all day long.
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Old 06-18-2015, 12:29 PM
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Yeah about 160 degrees small block V8 230hp 5.0L direct drive (inboard)
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