Originally Posted by FJ55guy
Definitely dont want to mix your HOAT and OAT, first thing they tell you in tech school. They say a cup of the Oat in the Hoat can gel the entire systems.
However, jwmbishop hit the nail on the head, Chrysler is far from the first ones to introduce a system specific coolant.
That's a good safety rule. Because SOME oats will sludge up in SOME hoats... and all oats will sludge up in most IATs avoiding mixing altogether is the safest way.
Antifreeze has traditionally been ethylene glycol (EG) with Inorganic Acid Technology (IAT) corrosion inhibitors added since 1926. (and closed - pressurized - systems were developed in 32-34).
American vehicles have traditionally been designed to use antifreeze with silicates and phosphates as corrosion inhibitors.
European vehicles have traditionally used antifreeze that does not use phosphates.
Japanese vehicles have traditionally used antifreeze that does not use silicates.
Newer corrosion inhibitor technology includes Organic Acid Technology (OAT) and Hybrid Organic Acid Technology (HOAT). Both may be referred to as “extended life” antifreeze and were introduced in the 1990′s and use propylene glycol (PG).
IAT antifreeze has a 2 year or 30,000 mile service life, where OAT and HOAT have a 5 year or 150,000 mile service life.
OAT based antifreeze is not compatible with IAT antifreeze; although, some HOAT formulas claim compatibility with certain OAT formulas or IAT formulas.
OAT and HOAT antifreeze is designed for use in aluminum radiators and components. You should NEVER mix OAT based formulas (which includes hoat) with IAT formulas. The result is typically turning your coolant into sludge due to a chemical reaction. Keep in mind, OAT based formulas are still a developing technology. There are some “universal” formulas that claim compatibility with other IAT and OAT formulas, but the only safe bet is to use the same formula that is already in your vehicle
. This may change as the OAT based formulas continue to develop; however, always err on the side of caution and use the same type of formula that the manufacturer recommends
See why the "safe" rule is best - and should be taught to every tech?
If you were designing your own system the rules are REAL simple:
If you have a mix of cast iron, aluminum and ANY brass in the system (old school radiators) - do not use oat or hoat - use IAT (ethylene glycol). propylene glycol does not do well controlling electrolysis in a three metal environment (or even a two metal when one is brass)- and can actually speed up the process of molecular distribution. The organic additives actually help carry the brass molecules trying to swap places with the iron.
If you have an cast iron\aluminum system - never use IAT - use oat (hoat as second choice). This is where Dex-Cool was designed - for the cast block aluminum head GM engines.
If you have an all aluminum system - again no IAT - use HOAT (oat as second choice).
Anything organic can be broken down. With Organics the additives becomes more sacrificial than the metal surfaces - that is they break down before they can piggy back the metallic molecules attempting to be transferred via electroysis. Mixing organic (PG) with inorganic (EG) - causes the organics to break down faster, fall from suspension at the molecular level AND the inorganics to attach to them. Sludge.