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Thermostat question

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Old 07-12-2008, 10:43 PM
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Default Thermostat question

Have an issue with an engine overheating. I plan to remove the thermostat and see if thats the problem. The manual says running without a thermostat will cause the engine to overheat. Doesn't make sense to me. The engine is a small block chevy, mild horsepower with raw water cooling, and still has the circulating pump.

Anyone know why I can't run it without the thermostat?

Going boating in the morning so any quick answers will be appreciatwed.

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Old 07-12-2008, 11:00 PM
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It will make the engine run rich as it will not be up to temp most of the time.Take them out and test them use a propane torch its usually pretty apparent if the open slow or not all the way they are bad.Just put new ones in
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Old 07-12-2008, 11:05 PM
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Thanks expensive date

But back to my basic question, running without the thermostat can't cause it to overheat, can it?
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Old 07-12-2008, 11:09 PM
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Probably not but if its a newer motor it will run cooler and the ECM will dump fuel into it.Probably would not hurt for a short run but why do it twice.Take them out test them and install new.If they are good you have another problem.What exactly is it doing?
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Old 07-12-2008, 11:18 PM
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Its an older carb motor. Temp up slightly at idle, normal at 3000 rpm, approaching 200 degrees at 4000. Timing isn't too high, and raw water pump has new impeller. No leaks in hoses or circulation pump.
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Old 07-12-2008, 11:58 PM
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Mine did the same thing last year.Salt water tears up thermostats.I changed the impellers(they were not that bad)still had problem.I put a torch on the thermostats heated them to 400 degrees and the only opened 1/2 way
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Old 07-13-2008, 08:15 AM
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A thermostat is used to regulate water flow, the same as on a open cooling system you sometimes need restrictors to keep the block pressure up and the slow the waterflow down. When combined with a ciculator pump it keeps water in the block long enough to draw out enough heat.

In some cases without a thermostat the water will run through the engine too quickly and it won't have a chance to remove enough heat. Therefore your water temperature will appear to be lower on your gauge but your internal engine temperature will be higher because your not taking out enough heat.

In other cases removing the thermostat will change the path of the water flow and allow it to bascially bypass the block and go right to discharge so your circulating pump continues to circulate mostly the same water and not the cooler water that is being brought to it, that water exits your transom.

It can overheat and you won't know it till it's too late.

There are plenty of diagrams out on the web that deal with this, find them and you'll see what I'm talking about.
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Old 07-13-2008, 12:54 PM
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HabanaJoe

Think you have a point there. I've run plenty of engines without thermostats but always used a crossover, and did not have circulating pump. The circulating pump might just keep the cooling water at the front and allow the block to overheat.
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Old 07-13-2008, 09:00 PM
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Habana Joe is exactly right. The cooling system is not designed to run without a thermostat. If you have a good impeller maybe your risers are clogged and keeping the water in the system too long.
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