Coolant reservoir peanut butter

[WhiteWillysWheeler76]

Hello all. Just bought a beautiful '16 Willy's Wheeler Wrangler that has had a TON of upgrades added. Only had the truck home for a couple of days and decided to change the oil and coolant. Everything was fine until I took the plastic coolant back up reservoir out to clean it and found a handful of what honestly looked and felt like peanut butter caked to the inside bottom. Washed right out with hot water though. No signs of blown head gasket (ie: no coolant in oil, no bubbles in radiator, no milkshake in the radiator etc). Car runs great, heater works, no white exhaust, plenty of power, etc. Any ideas?? Thanks in advance.

 

[Eulalio]

Just rusts from the system and blown out to the reservoir when its hot and expands.
No big deal but if you want to clean it, buy this to clean all the rusty gunks in your cooling system.

 

[Mr. Bi-Polar]

In case you haven't checked the 16 wrangler require OAT coolant and other wrangler could use HOAT coolant. At some point the previous owner/s could have mixed the two different coolants even if was just a small amount. Once the two coolants mix, they create a gel that will harden over time thus clogging your system.

Just to be on the safe side make sure you burp the system by parking in on a hill (nose up) so that any air bubbles can be filtered out.

 

[Eulalio]

In the event of mixture, not only the bottom of the reservoir jug is gooey, it should be the entire coolant.

 

[JKTim]

I would flush the entire system before winter. Oops. Never mind. Just saw you were in Florida. I will change that to “soon” or before the summer heat. You will want maximum cooling capacity plus then you won’t need to worry about it for a while.

 

[Chris]

If I had to guess, someone used tap water in your system. Never, ever, ever use anything but distilled water (if you must use water at all, since coolants these days come pre-mixed) as it will cause your cooling system to rust and do exactly as you described.