OAT vs HOAT Coolant

[Corey G.]

I'm going to flush the coolant in my LJ since it has 100k (bought it at 71k, 2 years ago), and I have no idea the last time it was done, or what's in there now.

Mopar specifies HOAT type coolant for all 2001+ TJ's (and pretty much all 01+ Daimler vehicles). It's pretty hard to find, and kind of expensive. $25/gal at Jeep dealer or a couple bucks less on Amazon.

I understand if you mix OAT (common coolant) and HOAT it will form sludge. What I'm trying to find out is if I can use OAT in a system that calls for HOAT, after a complete flush. It's easier to find, cheaper, and more likely someone on the trail would have a bottle of OAT in an emergency. Does anyone know if the components in a HOAT system are really any different, or is it just another way for the dealers to charge more/environmental thing/whatever??

[Blacky]

from what ive been taught, HOAT is compatible with both conventional and OAT antifreeze types. its made with additives that contain ingredients of both OAT and conventional coolants. HOAT has much better anti-corrosion properties and you can use it longer.
personally i wouldnt mix, and i would use the HOAT that the factory specifies

[Posimoto]

I'm going to flush the coolant in my LJ since it has 100k (bought it at 71k, 2 years ago), and I have no idea the last time it was done, or what's in there now.

What year is your LJ?

I understand if you mix OAT (common coolant) and HOAT it will form sludge.

Yes, also OAT (orange) isn't common coolant, IAT (green) is.

What I'm trying to find out is if I can use OAT in a system that calls for HOAT, after a complete flush.

After a “complete” flush including the block and heater core you can change between IAT, OAT, and HOAT however, switching fluids may not give the best protection for the engine it was designed for this is why you should stick to OEM specs. 

Does anyone know if the components in a HOAT system are really any different, or is it just another way for the dealers to charge more/environmental thing/whatever??

Yes, components in IAT, OAT, and HOAT are different and can't be mixed. This is why universal antifreeze doesn't work, if it contains silicates it doesn't meet OAT specs, if it contains no silicates it doesn't meet HOAT specs, see where I'm going, universals just don't work for OEM specs.     

It's pretty hard to find, and kind of expensive. $25/gal at Jeep dealer or a couple bucks less on Amazon.

$15 @ walmart

[Corey G.]

I'm going to flush the coolant in my LJ since it has 100k (bought it at 71k, 2 years ago), and I have no idea the last time it was done, or what's in there now.

What year is your LJ?

I understand if you mix OAT (common coolant) and HOAT it will form sludge.

Yes, also OAT (orange) isn't common coolant, IAT (green) is.

What I'm trying to find out is if I can use OAT in a system that calls for HOAT, after a complete flush.

After a “complete” flush including the block and heater core you can change between IAT, OAT, and HOAT however, switching fluids may not give the best protection for the engine it was designed for this is why you should stick to OEM specs. 

Does anyone know if the components in a HOAT system are really any different, or is it just another way for the dealers to charge more/environmental thing/whatever??

Yes, components in IAT, OAT, and HOAT are different and can't be mixed. This is why universal antifreeze doesn't work, if it contains silicates it doesn't meet OAT specs, if it contains no silicates it doesn't meet HOAT specs, see where I'm going, universals just don't work for OEM specs.     

It's pretty hard to find, and kind of expensive. $25/gal at Jeep dealer or a couple bucks less on Amazon.

$15 @ walmart

I have a 2006.
By components, I meant water pump, hoses, radiator, t-stat. Is there anything different about them that would be non-compatible with OAT or IAT?
I hate wal-mart, but I'll check it out.


Some info from someone on jeepforum.com...

The decision to use Hoat was made when Daimler-Benz bought into Chrylser. It is fine for newer non-ferrous metals such as aluminum and closed (non-vented cooling systems. The main reasons for OAT & HOAT coolants was for manufactures to make the claim of "5 year maintenance free". On the old iron 4.0 the best coolant for rust protection is the OLD IAT (ethyl glycol,silicate coolant as long as it is changed every 2 years. There is no advantage what-so-ever of using HOAT in the 4.0. HOAT does a poor job of protecting iron and once it starts to break down it turns into the most nasty,acidic mess that you could possibly put into a coolant system. Silicate anti-freeze has been used for over a century without any problems and nothing protects ferrous iron better than silicates...,period.
All the brown sludge,corrosive gasket eating and overheating problems did not evolve until the introduction of organic coolants. IMO once the engine is out of warranty or past 5 years I flush (throughly) and switch to the old conventional IAT. After that I change every two years with the satisfaction of seeing nice green coolant and not HOAT mud.

[SPYDER]

It can cause the radiator and heater core to start to corrode at the seams.  The aluminum compounds are slightly different.   Or at least that is what the Chrysler rep told me when I asked this same question. 

[Posimoto]

I have a 2006.

Your lj is out of warranty, put whatever you want in the coolant system, just don't buy it from walmart.

[jps4jeep]

I have a 2006.

Your lj is out of warranty, put whatever you want in the coolant system, just don't buy it from walmart.

Troof!

I've never run anything but the cheapest green stuff, never had a problem in any of my vehicles.

[jeeptech]

The HOAT coolant sucks.  It will corrode the heater core and cause intermittent leaks from the cap and hose terminations.  Do not mix IAT and HOAT, it's result will be sludge.  Do flush the entire system with water until it runs clean and fill it up with the Green stuff.  Most important part, don't buy anything for Walmart!