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Ask DR.Cummins Your Own Question
Category: Heavy Equipment
Satisfied Customers: 3691
Experience:  16 Years working on Cummins Diesel engines,
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What happens when you mix red antifreeze coolant with green?

Customer Question

What happens when you mix antifreeze types i.e. long life red coolant with standard green coolant?

Submitted: 6 years ago.
Category: Heavy Equipment
Expert:  DR.Cummins replied 6 years ago.

Hello and welcome to Just Answer!

I would be more than happy to assist you today. It is one or the other when it comes to this and this is why - the difference between the two colors is that red antifreeze contains a different type of corrosion inhibitor that has a much longer service life than silicates, phosphates and borates. Red antifreeze contains organic acids that protect engine parts from corrosion. Silicate (green) type antifreeze does not mix with red type antifreeze. Never mix the two colors in a cooling system. The organic acids in red type will cause precipitation of silicates in the green type and corrosion protection is greatly reduced. Red type antifreeze is good for five years.

Customer: replied 6 years ago.
What happens when the coolants are mixed in engine?
Expert:  DR.Cummins replied 6 years ago.

You can put red in green, orange or whatever color it is for emergency purposes, but you cannot fill the system with half extended life and half regular 50/50; it will break down each other and cause premature corrison of the cylinder liners and wipe out the DCA (additive to prevent pitting) in the liners and block. 1 gal is ok, I would not do any more than that.

Customer: replied 6 years ago.

We have a gray mud like substance in the cooling system and we know the coolants have been mixed. Is this from mixing the two coolants?

Expert:  DR.Cummins replied 6 years ago.

Nope that is oil. The cause of that is a failed oil cooler.

Customer: replied 6 years ago.

We had the mud like substance tested in a lab. No signs of oil. Can these two types of coolant being mixed cause this?

Expert:  DR.Cummins replied 6 years ago.

No, we have never seen the 2 coolants create a substance like that. You have 2 50/50 mixes, all they do is protect the internal metal parts from corrosion. When you have that type of mixture in the coolant, it is always oil. Forget the lab and have the oil cooler testes for leakage in hot water. Over 190 degrees. The 2 coolants just reduce the chemicals of each other. If a lab checked it out they should have told you what the origin substance was, without question. We do it all the time and they are 100% correct with today's technology; better find a new lab.