Why is mixing coolants not recommended?

[xbrotherx]

So I've never had a diesel before so be gentle. I have read that mixing coolant brands is not recommended. Why is that? I need to add more coolant to my degas bottle and I have no idea what coolant the previous owner had in there.

Hopefully, within the next few weeks I will have the time to do a coolant flush but until then, is it ok to put some good coolant (something like Fleetguard, Delo, etc.) and distilled water to top off?

[superduty4x4]

The big beef is to not mix extended life coolants with conventional coolants. If your truck has conventional coolant in it, any brand conventional coolant should be fine. The bigger issue is making sure you have enough SCA (sacrificial coolant additive) in the coolant.

[xbrotherx]

Originally Posted by superduty4x4

The big beef is to not mix extended life coolants with conventional coolants. If your truck has conventional coolant in it, any brand conventional coolant should be fine. The bigger issue is making sure you have enough SCA (sacrificial coolant additive) in the coolant.

Ok good. I want to do this right because I think the previous owner beat the snot out of the truck but right now, I just don't have the immediate time available to flush the coolant and do it right. I have other pressing issues, one being the timing cover was cracked when I bought the truck so I am taking it in to have that fixed in the next few days. That's one reason I have to keep an eye out on the coolant level. Good times.

[Dave]

brand mixing is ok as long as they are the same color/style coolant.

Different color coolants tend to react differently to each other

[superduty4x4]

Originally Posted by Dave

brand mixing is ok as long as they are the same color/style coolant.

Different color coolants tend to react differently to each other

Exactly. If you mix an extended life coolant with conventional, it turns into a jello like substance.

[xbrotherx]

Originally Posted by superduty4x4

Exactly. If you mix an extended life coolant with conventional, it turns into a jello like substance.

Well, shoot, I don't know what they had in there before. I guess I will just keep it topped of with distilled water until I get it in the shop and when they do the timing cover let them do a flush as well.

[superduty4x4]

Extended life coolant is usually red or gold colored. If you have "normal" green coolant you should be fine.