2013 Jeep Wrangler – Sludge, Radiator Leak and Mixing HAT & OAT Coolant

I’m a Jeep owner that recently sold a 2010 Jeep Wrangler and bought a used 2013 Jeep Wrangler. Unbeknownst to my husband and I, Jeep models stopped using HAT (Hybrid Additive Technology) coolant and started using OAT (Organic Additive Technology) coolant in 2013. When these coolants are mixed because the person doesn’t know which kind to get, it turns into a sludge that can clog your system.

What happened to us has happened to many and I found so many forums online that I thought I would post about our experience in hopes that it helps other Jeep owners not only identify an issue, but make repairs rather cheaply. My husband spent less that $300 fixing our issue.

We were on the highway one day climbing a steep hill in 100 degree heat when the air conditioning dropped suddenly, water came spurting from under the front of the hood and the temperature gauge showed the Jeep to be overheating. We pulled over as quickly as we could and shut down the engine. After a tow home, my husband took a closer look at everything.

There was a hole in the radiator, no water in the reservoir and no indication what was going on. My husband tested the thermostat to see if it was working by placing it in a pan of boiling water. This may be an unorthodox way of doing it, but we are on a budget so… The thermostat was not working. I ran searches on radiator leaks and found all these forums on sludge that’s created when mixing HAT and OAT coolants. Sure enough, when my husband went to empty the reservoir there was about 5 – 6 inches of a sludge-like substance in the bottom – no clean water.


So far we knew that the radiator and thermostat needed replacing, but what about the water pump? My husband ran some tests, but only finally determined it was working fine by turning the engine over and inserting the end of a wire hanger into the area where the blades turn when it is working; basically using an appendage to “feel” for this moving part since there’s no way to see it from the outside. Again, unorthodox way of doing it, but we are on a budget so…

He had to flush the system at that point to make sure that this pressure buildup wouldn’t happen again with a new radiator. It was clear that there was no water going from the radiator to the overflow, so there was definitely a blockage. He bought the new radiator for around $200, but before he attached it, he disconnected hoses and the heater core hoses and blew air through everything to get as much of the old coolant out as he possibly could. He replaced the thermostat housing, but left the thermostat out of it to mimic the thermostat being open so everything would circulate. He then replaced the radiator, filled it up with distilled water and Prestone Flush and ran the Jeep with the heater on to make sure the heater core was blocked. After that he did the same thing 5 – 6 times; draining the radiator, draining the hoses )the ones he could get to without taking everything apart), putting more distilled water in it, topping it off and running it until what came out came out fairly clean. Finally, he drained one hose and the radiator just enough that it would make space for the right amount of coolant (50/50 mix) and added the correct OAT coolant.

He said the first couple of passes at cleaning it out there was definitely a brown, dirty substance, but it did eventually run clean and so far, so good! I found so many forums where people spent over $1,000 taking their Jeep to the shop and not getting their issue fixed that I had to post this. Hopefully, it will help a Jeep owner out there! Most important thing is to make sure you know exactly which coolant to use, as some 2013 models actually don’t use the OAT coolant. It was a switch that happened that year, so make sure you put in the research and if you have heater problems, check your overflow and see if you also have a sludge issue.

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