Advice on coolant leak

[robeward]

For week or so I noticed my radiator fan kicking on high while sitting at stop lights. Up until recently I did not know the coolant had a dipstick. Shame on me. I am use to the remote reservoir and just assumed the coolant was a sealed system so I have not been monitoring. Once I learned this I checked the coolant level and it was low enough that it did not touch the dip stick. I also had this brown paste on the dipstick. It was not slimy or sludge. More like a dried paste. Close to peanut butter. See attached pictures.

Took my truck to a shop and they checked for visual leaks, completed a pressure check and also added die for further inspection. They could not find any leak. To date I have not smelled coolant, have not seen signs on garage floor of leaks and do not have any white smoke from exhaust on startup. My last truck developed a cracked head so I am familiar with the white puffs of smoke.

Assuming the shop is correct and there are no external leaks what are the next things I should be looking for or researching?
I would also like opinions on the brown paste and what that could be?
I still have the die in my coolant and am also concerned with buildup in the system so was considering flushing the coolant system.
Can anyone point me to a procedure specific to these trucks?
Should I use a cleaner like the prestone product?

Advance Auto Parts - Down for Maintenance

I will keep a very close eye on the level now to determine rate of consumption. Thanks for any advice.

 

[Darksteel165]

Imo just add coolant and see how it is.
Also monitor engine/coolant temps.
Oem stat is 203 degrees so should be around that while in motion. If it not in motion it will climb but I think would still be under 230 degrees.
If temps are good then I don't know if you really need to buy that cleaner because it's flowing, maybe remove the tstat and confirm it's not gunked on?

 

[SD Rebel]

Also note that there is a known cooler issue that causes oil to leak into the radiator, there is a thread here that mentions it: Brown Sludge on Coolant Dipstick?

The brown paste is likely oil getting into the radiator from the leaking cooler and creating sludge on the dipstick, seems to be a common issue and relatively easy to fix. I believe it starts on Post 41. There is another thread that talks more in-depth about the issue, which I can't find right now.

Essentially you can replace the cooler with an updated one that is less likely to leak, 2019 - 2020 RAMs have the older style cooler.

 

[Bubba67]

I had a radiator fluid leak in my 21 Ram Big Horn, 5.7. I first noticed the sweet smell of a leak after driving it just 30 minutes, I took it in at least twice, before they replaced the t stat. Then, I finally told them I could smell it in the cab, and they replaced heat exchanger. Even though they did all this, and pressure tested it, I could still smell fluid till the day I traded it, not sure if it was residual from leaking on carpet from the Heat Exchanger or something else. I never saw brown color in it.