2000 Civic with 160k miles. I've replaced the two main radiator hoses but am still running the original 3 heater hoses and 1 bypass hose. I have heard the heater hose directly under the distributor is common to fail. Also, I'm still running on the original thermostat. The car has zero heating and cooling issues; and I don't see any obvious leaks or cracks in the hoses.

Should I start replacing these parts, maybe the next time I do a coolant replacement?

 

I would recommend replacing the hoses. Your call on the thermostat - it's cheap.

 

The one under the dizzy should be replaced 100%. It often gets oil on it there and gets soft, ask me how i know :p. Heater hoses are cheap and easy, i would do them all and flush the coolant at the same time.

 

The back heater hoses are easy? It looks kinda tight in there, lol; I was also reading that the 'nipples' on the heater valve and the ones on the firewall/heater core are fragile and to not use pliers to pull off the old hoses.

When the heater is not in use; does hot water still travel towards the closed heater valve? What about the bypass hose; when the car is at operating temperature, is hot water still circulating through the bypass hose?

 

If you're replacing them just cut it and peel it away. If you use pliers you might end up messing up the heater core pipes

 

The rear hoses aren't fun no but the repair is easy compared to many other car repairs imho. Intake manifold is easy enough to pull if you really wanted some space to work. Cutting off the hoses is a good plan aswell. If you do use pliers make sure you only use them to spin the hose and break it loose. Try not to squeeze the actual nipples to much.

I dont know a ton about how the cooling system flows exactly. Ide assume being as its a sealed system and under pressure at operating temp all passages would be filled with coolant at all times if the system is properly bled. The only difference is whether or not it flows depending on heater core valve / thermostat stopping it. Hopefully someone else can call me out if im wrong on that one.

 

For the heater hoses at the firewall, the brass heater core hose ends are VERY thin and fragile. I always use a sharp razor blade/knife and gently cut through the hose fully and then GENTLY peel it off the hose ends. As for water flow through the bypass hose, if you are using an OE thermostat, the water flow through the bypass hose is closed off when the thermostat opens.

 

I agree with the other suggestions to remove the clamp, split the hose with a razor, then peel it off the heater core and valve nipples. I would not get pliers anywhere near the heater core nipples, because as JRCivic1 said, they are thin wall brass and you will crush them, and they won't seal. For installing new hoses, I like to add a VERY small amount of Polyurea grease to the nipple and the inside of the hose. It helps it slide on with minimal effort.

 

Gates hoses should be a suitable replacement, yeah? It's not like I have to buy OEM Honda hoses? I actually bought one of those blue silicone hose sets years ago but never installed the heater hoses and I'm not sure if they are built to last.

For getting the hose off the heater core, is it still best to tackle it from above or under the car? And the distributor has never been removed before this; am I gonna need to replace that o-ring?

 

I like Gates hoses.

I usually like to access heater hoses from the top. At least pull off the intake tube. Unbolting the heater valve from the firewall also helps get to the shorter heater hose.

I would replace the distributor o-ring if it looks flattened or if it's leaking.