Quick question, hopefully somebody knows the answer. I've had a sealed 5 litre container of Honda premixed coolant sat in my garage for just under 6 years, will it still be okay to use for a coolant change?

 

A couple of years would probably be fine but six, no I wouldn't use it.
It's not that expensive either so just get a new container from Honda, coolant type 2.
5l #08CLA-G02-6L0 or #08CLA-G01-6S0 for 1l.

 

It will last forever in the bottle so it's fine to use, once it's in the car the corrosion inhibitor degrades over time so it's recommended to change it every completely every five or six years.

Hondas schedule says "first change at 100,000 miles or 10 years then every 5 years" as yours has been doing nothing for years theres no problem using it.

 

Come to think of it, I've had an unsealed bottle in my garage for a couple of years. Does it degrade once opened?

 

How do you know this richmc, are you a chemical engineer?
I'm not asking to be a smart ass I'm just curious if sebacate or any of the other additives really are stable forever.
If you do some searching you don't find much info from the manufactures, most just say a sealed container is good for years.
Some say 5 years, highest I found was 8.
This is for the silicate free coolants, which I guess that the OP must have. If it's the older green stuff it's probably a lot less.

 

I did some research a while back and that's what it came up with. the fact that The Honda service schedule says first change at 100,000 miles or ten years is good enough for me, that's in the "hostile environment" of the engine, being constantly heated and cooled, tearing around the block contacting lots of different metals. In a plastic bottle on a shelf in a garage doing nothing it must be good for 10 years as that's how long it would be in the car. If the bottle is sealed it won't lose any of it's volatile elements and it certainly won't freeze in winter. I can't remember the web sites I got the information from, but I do recall a safety sheet that had something like "shelf life N/A"

The time to change your antifreeze is when the rust inhibitors are exhausted, The S2000 having an alloy block (like most modern cars) will probably mean it will last a lot longer, I recall reading somewhere that Toyota say their cars coolant last for the life of the car, assuming it's topped up and checked for gravity.

If you do a search I'm sure you will find the same information I did a while back.

 

The 10 year service schedule is a good point, but it also makes me wonder why it has to be changed at 5 year interval after that.
At the factory they can guarantee fresh fluid is used but the containers from the dealer could probably get pretty old before even reaching the customer.
Just some thoughts
I think Toyota use the same schedule as Honda btw, it does make sense because they also use the same type of coolant, but with a pink dye

 

If shelf life was a problem, then it would have some sort of expiry date on the bottle.

 

Good point, there is no obvious expiry date on the container.
I've just done a load of searching on the web and there's lots of conflicting information. Although I'm fairly sure it'll be absolutely fine, for the sake of £20 I think I'll get a new bottle. I'm planning on keeping the car for a good few years.

 

Better safe than sorry
I think there is lots of stuff that do go bad without having any expiry date stamped though.
Had a couple of ~5 year old unopened bottles with Motul RBF600 that I was unsure about and contacted Motul.
They told me minimum shelf life was 2 years and recommended me not using it since they were more than double that.