DIY Coolant change - what if I do not get all old out?

I was considering doing my overdue coolant change myself, but then got the nagging thought of maybe not getting all the old stuff out.

Could this be an issue?
I understand that old coolant loses its ability to ward off corrosion, and that is what bothers me.
Advice?

 

You'll never get all the old fluid out. Just like any fluid change. Old and new coolant mix perfectly fine as long as they are both the same type.

I did mine a few years ago and ponied up for the premixed 50/50 pink coolant directly from the dealer

There are a few good threads on here showing the process of draining (dont bother with both block drains, just the one everyone recommends). They also explain getting any air out of the system after the flush

 

Coolant is kinda same deal as ATF or power steering fluid.
If you do it at all you've done more than many owners ever will.

You can do a little drain/fill now, another drain fill later, maybe a 3rd later than that if you have funds or concerns.

I am more worried about snapping one of the coolant drain bolts than I am about getting all coolant out. I only use drain at bottom of radiator for however much comes out, then refill it and drive. After 10k or 20k miles later do it again.

 

These are questions the dealer doesn’t concern themselves with when they do it for you.

 

You only need to drain and replace most of the coolant. When new Toyota SLLC is good for 10 years or 100K miles. After 100K, drain the radiator, and the right side block drain. Refill the system with Toyota SLLC (pink) and you should be good for another 5 years or 50K miles.

 

You don’t get all the old fluid out.

there are additional drains if you’re concerned.

if the interval is every 50 then you do it every 50. If it’s overdue and you’re concerned you do more than one.

the beauty of a 50/50 change is you have 50/50 remaining in the truck, you add 50/50, therefore you have 50/50.

it is a binary equation.
Either the truck does not get its coolant changed. Or it gets its coolant changed like it’s supposed to.

 

I am learning form the above posts, thanks.
My main concern is corrosion, not much else.

I like TacoTuesdays idea of gradually getting fresh in - approximate amount, see below. Note: it is the 4 cyl. 2.7L here!

With any method, what is the safest coolant to agree with whatever is left of the factory one?

 

Go with the OEM pink fluid if the current fluid is pink.