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Coolant circulation in GD3

Old 12-13-2018, 05:37 PM
doctor J's Avatar
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Coolant circulation in GD3

I'm sure this is another boring topic for copy and paste experts with master degrees in aircraft restroom cleaning and bachelor degree in scan gage reading, but, nevertheless I would like to post few illustrations explaining how the coolant circulates in 2007-2208 Fit cooling system

This is picture from the manual with added arrows. A bit hard to read

Close up view with thermostat housing attached to the block; outlets are labeled. Arrows indicate direction of flow

Side view shows circulation with engine hot. The coolant goes all way up from the radiator via lower hose, passes through main thermostat valve , and goes down via return pipe to the water pump.

This is the coolant flow in the head (engine hot). The bypass thermostat valve is closed (red X) and main valve is open, allowing cooled coolant (pardon the pun) enter the thermostat chamber , mix with coolant returned from heater and go to the water pump via return pipe. The coolant is going through the heater core at all times

With engine cold the coolant enters the thermostat chamber via bypass hole and goes to the water pump after mixing with coolant returned from the heater. There is no circulation from the radiator (main valve closed)

So you need to feel lower hose to verify that thermostat is open, not the upper hose. I can speculate that such location of the thermostat makes burping air from the system a bit difficult (especially after clanging coolant in the radiator only )

Last edited by doctor J; 12-13-2018 at 05:44 PM.
Old 12-14-2018, 11:15 AM
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Good info. Thanks.
Old 12-14-2018, 11:35 AM
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Originally Posted by doctor J View Post
I can speculate that such location of the thermostat makes burping air from the system a bit difficult (especially after clanging coolant in the radiator only )
Yes, it does. I'm a veteran.

What you need to do is run the engine for 10 minutes, then shut it down for another 10 minutes so that heat-soak will open the t-stat. Then the system will allow the coolant to pass, as with normal cars.

This procedure works with most Honda cars (as they usually incorporate that reverse-flow system).

EDIT: Do NOT look at a scangauge during the initial 10 minute run...
Old 12-14-2018, 02:25 PM
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Great info! Thanks!

Not exactly intuitive to me so the diagrams and pics help.
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