Thermostat bypass valve

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My Rio engine G4ED has a cooling system I have not encountered before. The thermostat is connected to the lower radiator hose and the upper hose is unrestricted. The thermostat has a bypass valve that is attached to the bottom. Does anyone know the purpose of the bypass valve on the thermostat? The thermostat is the same size as a small block chevy's except for the bypass valve. I'm not understanding the purpose of the bypass valve.
 
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It's probably so coolant can flow through the engine block when the thermostat is closed. I think all engines have a bypass loop like that. That water pump is still pumping water when the thermostat is closed - the water has to have a place to go.
 
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On many American engines, the coolant flows through the heater core, even if the thermostat is closed (cold engine). I've heard of some folks drilling a small bleed hole in their theremostats to allow trapped air through and allow a small bleed off of coolant prior to it opening. Where is the water pump on this engine? I've heard of some engines that use reverse flow (cool in at top/hot out the bottom) system.
 
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Some engines use a second valve like that to CLOSE the bypass route when the thermostat opens, forcing all the water to go through the radiator instead. Older systems boosted engine efficiency by always mixing radiator water and bypass water to make the engine temperature more uniform. Some systems are reverse-flow wherein cool water goes into the hottest part of the engine first (the heads), and don't need to do that as much. Without a full cooling system diagram, I can't really guess at what its for in your particular engine... but in general its to block the bypass once the engine warms up.
 
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 Originally Posted By: Drew99GT
It's probably so coolant can flow through the engine block when the thermostat is closed. I think all engines have a bypass loop like that. That water pump is still pumping water when the thermostat is closed - the water has to have a place to go.
Its not just so the water can have a place to go, its to make sure that the engine warms up uniformly. If the thermostat STOPPED water flowing through the engine when it closed, some parts would get boiling hot (like the cylinder heads) and others wouldn't even get warm for a long, long time (like the lower block water jackets.) Also the thermostat itself wouldn't be exposed to hot water in order to open.
 
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 Originally Posted By: dwendt44
I've heard of some folks drilling a small bleed hole in their theremostats to allow trapped air through and allow a small bleed off of coolant prior to it opening.
that works as well as putting a tylenol tablet in the t-stat to keep it open. the pill will dissolve and let the t-stat operate normally while bleeding the system.
 

Cup of Joe

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 Originally Posted By: 440Magnum
Without a full cooling system diagram, I can't really guess at what its for in your particular engine... but in general its to block the bypass once the engine warms up.
I wish I had a full system diagram, no such luck. Some of the universal replacement thermostats are of a more conventional design without the bypass on the bottom. I'm wondering if there would be any issues using a thermostat that does not have a bypass? The OEM design with a bypass valve comes in factory temp of 180F and 192F. I don't know why you would want 192F but its offered.
 
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