Changing Dexcool too often damaging ???

[BillJ99]

I had to have the LIM changed on my 1999 5.7L Vortec. I don't know if the Dexcool was ever changed before the failure, but I have become a bit obsessive about changing it for now on.
The strategy I have adopted is the following: Once a year (every 10k or 15k miles) I will simply drain the radiator and refill it with new Dexcool. This will be about 5 quarts of fresh coolant.
Now ... I have read that when you completely flush a cooling system and replace it all with fresh Dexcool that it takes a few thousand miles before the internal parts of the engine are protected from corrosion. The protective layer created by the old Dexcool has been washed away and the new stuff has to build a new layer.
My question is this: Will just changing 5 quarts of coolant remove the protective layer in the same way? If it is, I may be doing more harm than good.

Bill
1999 Roadtrek on a Cutaway Chassis with a 5.7L Vortec and a 4L80E transmission

 

[JHZR2]

I've read before that changing can disturb the passivating layers which then causes new corrosion (slight) until re-passivated. Not sure I believe it 100%, but it makes some sense as if you drain, the local surface is no longer in a true hydrated aqueous state, so things can change.

I can see this more with a chemical flush or even a freshwater flush than a drain and refill. If you do go that short an interval, I'd just drain and refill with the right blend.

Dex is good stuff. Some systems weren't really designed for it, and had issues, but even then, 10-15k may be a bit much. I'd probably go for a 3/36 interval.

 

[Rand]

I'm pretty sure thats only if you are changing to a different chemistry coolant

ie from old green to dexcool etc.

 

[BillJ99]

Originally Posted By: JHZR2
Dex is good stuff. Some systems weren't really designed for it, and had issues, but even then, 10-15k may be a bit much. I'd probably go for a 3/36 interval.

Agreed, 15k might seem like overkill, but remember that I'm only changing about 30% of it each time. My objective is to always have it as fresh as possible.

 

[FXjohn]

why keep the Dexcool? I got rid of that stuff in my GM vehicles and never looked back.

 

[JHZR2]

Originally Posted By: BillJ99
Originally Posted By: JHZR2
Dex is good stuff. Some systems weren't really designed for it, and had issues, but even then, 10-15k may be a bit much. I'd probably go for a 3/36 interval.

Agreed, 15k might seem like overkill, but remember that I'm only changing about 30% of it each time. My objective is to always have it as fresh as possible.



I hear ya, but on a well maintained engine without dex issues, it's a 100k coolant as factory fill and subsequently. So if you never depleted the original, and keep topping up,the chemistry, you're fine. IMO the interval you mention is just adding a lot of extra work and cost.

Why? Because in reality at some point the engine will need to be opened up, and you'll do a full flush, and start anew.

I don't see harm being overly conservative, but unless your engine and cooling system is known for big issues, I'd probably save my time, effort and energy, myself. I get that you may not know all the history, and that it is an older model. That said, my 98 43 v6 is [censored] and span, and I have had no issues at the interval I've mentioned.

 

[FXjohn]

there is no advantage to dexcool.

 

[The_Eric]

There is no disadvantage to it either.

O/P, while you're changing your coolant, make it a habit to change your radiator cap too. It's very important for several reason that it's maintained.

 

[SteveSRT8]

Originally Posted By: BillJ99
I had to have the LIM changed on my 1999 5.7L Vortec. I don't know if the Dexcool was ever changed before the failure, but I have become a bit obsessive about changing it for now on.
The strategy I have adopted is the following: Once a year (every 10k or 15k miles) I will simply drain the radiator and refill it with new Dexcool. This will be about 5 quarts of fresh coolant.
Now ... I have read that when you completely flush a cooling system and replace it all with fresh Dexcool that it takes a few thousand miles before the internal parts of the engine are protected from corrosion. The protective layer created by the old Dexcool has been washed away and the new stuff has to build a new layer.
My question is this: Will just changing 5 quarts of coolant remove the protective layer in the same way? If it is, I may be doing more harm than good.

Bill
1999 Roadtrek on a Cutaway Chassis with a 5.7L Vortec and a 4L80E transmission



Bill,

We own a fleet of all GM V8 trucks, some Silverados and a few 3500 Vans. I ran many of the exact same powertrain as you for a LONG time. Great combo.

We never had the intake gasket issues, and we didn't change coolant unless something broke first. If you have the updated gasket design there is no reason NOT to use Dex.

The gaskets were bad, not the coolant.

And remember the cap as noted above^^^

 

[BillJ99]

Thanks all for the comments.

As for the radiator cap, it was probably the original so I changed it last year. I realized, mostly from comments on BITOG, that with Dexcool the cap is doubly important.

Bill

 

[BillJ99]

Originally Posted By: JHZR2
I've read before that changing can disturb the passivating layers which then causes new corrosion (slight) until re-passivated.


"Passivating layer" ... that is the term I was looking for! Following your message, I did a bit more research on the term. While I haven't found a definitive answer to my question, I was left with the impression that just removing 1/4 or 1/3 of the Dexcool won't disturb the passivating layer. Using a chemical flush would probably destroy it and it has to be re-passivated.

Thanks