I've had the same coolant in my 97 civic for over 7 years now, so I figured it's time to change it. Over the years, the coolant level has gone down slightly so I topped it off with some cheap store-bought stuff. I want to flush all of this out and put genuine Honda coolant back in, but I've been reading mixed things on how to do this. I will be replacing the thermostat at the same time, so the upper radiator hose will be disconnected. Here are my questions:

- Is it necessary to take the engine block drain off? Most websites never mention this, but the official Honda manual does.

- Should I use a garden hose to rinse all the old stuff out of the block?

- Should I use a coolant flush solution prior to filling back up?

Thanks.

 

well if the fluid doesnt look dirty i wouldnt bother with flush kit....

i just flush the motor with a garden hose with it running... but if your pulling the thermostat just stick a hose in it and let it flush itself.... just remember to do the heater core as well. just pull the heater hose and hold the hose to it to flush it....
if you want to be really flush the system sure draining the block is a great idea but i dont see it being that big of a deal.... plus with my old 94civic i couldnt get that drain plug out.LOL i just drained it as much as posible after flushing it and then filled it back up with oem fluids... good old blue stuff

just be sure to allow the system to bleed itself... with the front end raised preferably simply start the car up and keep toping off the radiator with fluid for afew cycles.... it typical takes me about 10-15mins for the system to system to keep full then i just top off the reserve bottle and put the cap back on and take it for a drive.

 

I agree, just flush the radiator, heater, and engine with plain water. Run it for a few minutes full of plain water and then flush again.

You don't have to get all the water out. Don't mess with the drain plug on the engine. Remember a Civic holds about 1 gallon total. Drain the radiator to get most of the water out. Then add 1/2 gallon of concentrated antifreeze-coolant (not the "ready to use" type which is already half water). Top up with plain water. The two will mix in the system so you have the proper 50% mixture.

 

well the factory stuff is already premixed..
as long as your not in canada or really freezing temp area then its nothing id worry about...
you can always use a fluid tester to see how low temp your fluid can go before it should freeze.. if its to low for your area then simply drive the car for a day or so depending on how much the engine is ran... then drain the fluid again by simply pulling the heater hose and drain plug and radiator cap and once its done draining simply put it all back together and refill it again with the new stuff again and bleed the system again....

that will allow plenty of time for all the old water/fluid trapped in the system to be mixed very well with your new fluid so when you drain it out and refill with brand new stuff you should have a perfect mixture of coolant now

tho i recomend flushing it with the motor running with the hose always filling the radiator with the drain open as well... that just helps keep the factory parts cool so you can work much easier around the area without it being so hot... just easier to work with so quickly...

 

If I take the hose to the radiator, thermostat opening, and heater hose, I'll still have tap water in the system after doing that. When I fill it back up with the factory stuff (which is premixed), I'll have more water than coolant... Is the amount that will be sitting in the heater core and engine block so small that this won't matter?

 

I think the heater core drains itself, you can blow air through it to be sure. But quite a bit sits in the engine block unless you take the drain plug out. So it seems you need to do that.

 

well to get the most of it out. pull the heater core hose top or bottom doesnt matter... easier to take it off the back of the head tho rather than off the heater core directly... when you pull the one hose off just hold it down and gravity should take care of the rest see the heater core is up and down with the hoses on the bottom so it drains right out
if in doubt about your water/radiator fluid mixture buy one of those testers and just check the fluid after the motors been driven awhile... if its to weak for your cold area then simply drain and refill the system. any left over weak mix will be so minor it shouldnt effect anything....

 

Cool, thanks. I was considering pulling the engine block drain, but after stories on here about them being stuck I guess I'll leave it as-is and flush all but the block.

 

"Top up with plain water"

shouldn't this be distilled water or does it really matter?

 

suposedly distilled water or premixed radiator fluid is best for the system.... but ive used regular whellwater from my house in alot of vehicles in my past with no problems...