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Information, speculation and anything else specifically related to Civic Type R EK9 and EP3
#3863265
Hi all,

I recently bought myself a EP3 30th Anny :D and wanted to make sure I had sufficient coolant in the system... you are all probably aware how much of a pain in the rear it is to check coolant levels especially if your reservoir tank has become opaque over time (even a torch doesn't help)... I ended up overfilling it and then syphoning the excess out.. Anyway during this process I couldn't help but think what the purpose of this tank was... I can see that the overflow pipe below the radiator cap pours in to this tank but I couldn't understand why there is a MIN and MAX marking on the tank... The tank doesn't feed back in to the cooling system (unless its via the overflow pipe and the overflow valve is a two way valve) and seems to only be used as a tank for the overflow to pour in to...so what the purpose of the MIN marking.. I understand the MAX can be for the maximum amount of overflowed coolant that should be in the tank before you need to empty it but I cant seem to understand why you would need a minimum amount of overflowed coolant? Any information would be much appreciated.
#3863266
Honda describe this as a "Reserve Tank" but on other cars it would be called the "Expansion Tank".
It allows the coolant to expand (and contract) with temperature so the water flows in both directions.
#3863267
Thank you @parsimony for your response. If this is an expansion tank how does the coolant contract back in to the system? Does it do this via the overflow pipe and a two way valve below the radiator cap? Also if this is a expansion tank i.e. a pressure holding tank, why is the cap not a pressure tested cap but instead a standard screw cap and where's the overflow pipe for it?
#3863286
@15repyt Thank you for your response. Could you give me more details as to how the tank supplies the radiator as I cant seem to find a connection between the two besides the overflow pipe which presently I believe works in one direction where the radiator feeds in to the reservoir tank via the over flow pipe.
#3863289
vtecjunky wrote:Thank you @parsimony for your response. If this is an expansion tank how does the coolant contract back in to the system? Does it do this via the overflow pipe and a two way valve below the radiator cap? Also if this is a expansion tank i.e. a pressure holding tank, why is the cap not a pressure tested cap but instead a standard screw cap and where's the overflow pipe for it?
I can't inspect the detail of this design first hand because I sold my EP3 11 years ago :lol:
Having said that, my understanding is that pressure is controlled by the radiator cap.
When coolant expands with temperature, the cap releases a small amount to the reserve tank (not under pressure).
As the system cools, a partial vacuum is created & that excess is sucked back into the radiator.
Having a minimum level ensures that there is always coolant available for the second of these two functions.
In many other cars, the tank is an integral part of the the overall pressurised system in which case the (radiator) cap will be found on the (expansion) tank.
#3863293
parsimony wrote:
vtecjunky wrote:Thank you @parsimony for your response. If this is an expansion tank how does the coolant contract back in to the system? Does it do this via the overflow pipe and a two way valve below the radiator cap? Also if this is a expansion tank i.e. a pressure holding tank, why is the cap not a pressure tested cap but instead a standard screw cap and where's the overflow pipe for it?
I can't inspect the detail of this design first hand because I sold my EP3 11 years ago :lol:
Having said that, my understanding is that pressure is controlled by the radiator cap.
When coolant expands with temperature, the cap releases a small amount to the reserve tank (not under pressure).
As the system cools, a partial vacuum is created & that excess is sucked back into the radiator.
Having a minimum level ensures that there is always coolant available for the second of these two functions.
In many other cars, the tank is an integral part of the the overall pressurised system in which case the (radiator) cap will be found on the (expansion) tank.
Right that makes sense. So the overflow pipe actually extends all the way down to the bottom of the reservoir tank and the pressure relief valve below the radiator cap is a two way valve which allows the coolant to move back and forth between the reservoir and the radiator as it expands and contracts! Thank you for your reply @parsimony

ps why did you get rid of it! They're such a pleasure to own and drive!
#3863297
vtecjunky wrote:
parsimony wrote:
vtecjunky wrote:ps why did you get rid of it! They're such a pleasure to own and drive!
I loved my Type-R but Honda didn't have a replacement on the market when I decided to get a new car in 2006.
Ended up with a Focus ST, subsequently replaced by an RS.
Brilliant though it is, the EP3 doesn't compare with my current car :D

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#3863340
parsimony wrote:
vtecjunky wrote:
parsimony wrote:
vtecjunky wrote:ps why did you get rid of it! They're such a pleasure to own and drive!
I loved my Type-R but Honda didn't have a replacement on the market when I decided to get a new car in 2006.
Ended up with a Focus ST, subsequently replaced by an RS.
Brilliant though it is, the EP3 doesn't compare with my current car :D

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Fair play! I can imagine, the RS is a beast!

Added in 2 minutes 46 seconds:
15repyt wrote:Pretty much as the previous post has said mate. Al I know is that in 5 years of owning my current ep3 I've never had to add a drop of water to the radiator or the expansion tank.
That's comforting to hear! Unfortunately I'm unable to see the level even with a torch on it due to the tank being so opaque so I wanted to be sure not to have it running too low which led me to wonder how the system works!

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