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Discussion Starter · #1 ·
On my 02 Odyssey, the initial coolant change interval is 120,000 miles or 10 years, then 60,000 miles or 5 years thereafter. Can anyone tell me the reason for the shorter interval after the first change? Is it perhaps based on the assumption that, during subsequent changes, not all of the coolant will be replaced? If so, and if I elect to get a complete replacement (not just a drain and full), then why wouldn't I be safe waiting another 120,000 miles? Thanks.
 

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Your assumption is correct. The service interval is halved upon replacement, due to the fact that a drain and fill (as recommended by Honda) will not get all of the old coolant out of the engine. Therefore, what remains in the engine somewhat dilutes the new coolant, thus not making it 100% as effective as the factory fill.

If you want to see if you can go another 120K miles, periodically monitor the chemistry of the coolant and change it when it is needed.
 

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Discussion Starter · #3 ·
When the dealer replaced my timing belt and water pump, is it likely that they replaced ALL the coolant, or only drained part of it?
 

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Heater Cores! You have two. Doing the water pump gets the fluid in radiator and engine block, but your heater cores and lines still have fluid in them. That is why you have a shorter interval after the first interval at 105k miles.
 

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Discussion Starter · #5 ·
Heater Cores! You have two. Doing the water pump gets the fluid in radiator and engine block, but your heater cores and lines still have fluid in them. That is why you have a shorter interval after the first interval at 105k miles.
How much coolant gets left in heater cores approximately?
 

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There's coolant left not just in the heater cores, but especially in the lines leading to and from the rear heater. I estimate about 4 liters if the lines are 1 cm in diameter and 2.5 meters (8 feet) long.
 

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Has anyone used a backflush kit to replace coolant? I know about 20 years ago I did this on my first car and it seemed to work pretty well.
 

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wynns has a machine u hook up to it and put in 12-16 gallons of coolant and actually run the car the car while it changes the fluid. hooks up to the top rad hose and the radiator. few other ways to do it tho.
 
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