I own a 2015 honda fit exl and have never done a complete coolant flush. Though I've seen some videos and read stuff online, I have a few questions since I'm reading conflicting things.

1) is using distilled water necessary for the flush? www.hfitinfo.com manual doesn't mention it at all yet people on Youtube add distilled water once the drain valve and bolt are drained.

2) how much approximately of distilled water and antifreeze/coolant do I need for the job? is it as simple as however much it takes to top off the radiator cap?

3) do I need to drain the valve (petcock) and drain bolt? I see some people only drain the valve petcock and not the bolt

4) do I need to empty the coolant reservoir as well and add new coolant? If so, at what step do I do this?

thanks for the help in advance. any other tips for a first timer doing this job are welcome.

 

Personally I would just drain the rad, either removing the hose or from the petcock.
Then remove the upper hose or just the cap. Flush the radiator with a hose if you're feeling feisty.
This removes the majority of old coolant.

Remove and clean out the overflow. Refil to the cold line with fresh coolant.

Put it all back together.

Get premixed coolant compatible for your system (blue?), fill till you can't fill anymore.

Then you need to burp it to remove any trapped air. Get a funnel or there's a fancy tool basically this:
Ship it.

I don't like to really flush with anything. Because you don't know if you've got all the water out, could end up really diluted coolant.. which I think is worse then mixing some old coolant back in.
This is also what just about any mechanic would do.

 

People use distilled water just incase you don't get it all out, like borner said. Distilled water won't rust/ corrode anything. Most race tracks require you run ONLY distilled water for track safety.

 

The other issue if it's diluted it can change the freezing point.
Probably not enough to really matter, but better safe.. also seems silly to me pouring a couple $1.50 gallons of water down the drain, for no huge benefit.

But that last bit is just my.. $3.00 I guess ($0.02, if you will)

 

I mean the coolant is only designed to last like… 10 years! So even if you only get 80% out… you’ll have a mix of old and new at at your next flush it’ll be like 4% left of old coolant… however if you don’t get all the distilled water and end up diluting you coolant to more than a 50/50 ratio, who knows what will happen.

 

I've never heard that before and it's simply not true. Any water will cause corrosion - it absorbs carbon dioxide from the air to become acidic. The antifreeze component itself has to contain anti-corrosion inhibitors to offset any water corrosion. The inhibitors get used up or deteriorate over time which is why any radiator fluid has to eventually be changed.

The reason for not using tap water is because it contains minerals like calcium. Put it in your radiator and the calcium will coat the inside of the cooling fins reducing the cooling ability of the radiator. This is especially a problem in areas with very hard water which has a high mineral concentration. It was more of a problem many years ago when people replaced their coolant much more often, every couple years or so. Every time you did that you'd get another fine coating of minerals inside the cooling system if you used tap water. It just keeps building up. Distilled water contains no minerals, so no problem.

The radiator fluid which my Honda dealership sells is the 50-50 pre-mix. I'm not sure if they even sell the concentrate,