^ When the water pump bearing, which is not lubed by coolant, wears and starts wobbling, this causes the seal to fail and let coolant into the oil. Coolant flushes are not a magic bullet. That might help the seal last a little bit longer but once there's the wobbling, it's of minimal benefit.
There is no "maintenance" to solve this, lots of people never noticed any coolant coming out the weep hole before their oil was contaminated. I suppose you could call it maintenance for people to check their oil before every drive or even stop and check it in the middle of longer trips, but this is not something most owners know or want to do, at least not these days... I do recall decades ago when my father took the family on vacation road trips, and he would check the oil when fueling up along the way, so once for every tank of gas. Once my 3.5L gets to about 75K mi, I'll be doing that.
I have a 2015 Explorer 3.5 XLT FWD. 171k miles.
Heat airflow acted up approx 6-8 few wks ago and noticed a negligible reduction of coolant mx in reserve. Added some coolant, brought pressure up and got hot air. Approx wk later, drip noticeable by oil filter/compressor area, et. Getting messy, and prayed it wasn't what I thought. 2021 failed WP put coolant in crank, et, and replacement 1.8K, for WP $60-170 part. No coolant in oil presently, all clean, and water is moving throughout the system. So the pump isn't dead, so far. But the leaking increased and over the next few weeks and the system just wouldn't reset. As I prepped for WP reset, i decided to at least do a complete flush. I flushed the radiator first, drained it all out, closed valve.
Added Prestone flush and distilled water to the top, started car and a 4 cycle flush with strictly distilled water. 10 min run. Stop and drain, et. (4-6gallons) over at least an hour. When drainage coloration showed reasonable signs of the system cleared, I drained the remainder of last cycle out. Presumed 1/2 of the water in the engine was workable given drainage results, filled system with MotorCraft Concentrate, and the system only took approximately 8/10ths of the gallon bottle. Started car and idled to thermostat open and all moving through the system. Purged the air in the system, then would add concentrate into the system as needed as reservoir emptied into the system over next 48 hours. After a coupld days i ended up, in total, using about 1.8 gal Motorcraft concentrate coolant into system. In the first day or two I still noticed a drip and leak in same areas per WP weep hole symptoms, but eventually the leaks diminished and diminished, and the necessity to monitor/regulate level in resevoir suggested it was all stablizing and good to go. I suspect the bad orange coolant I used when air flow tripped and I added, could have compromised the WP inner seal, besides the fact I hadn't regularly performed adequate system necessities in a timely fashion. So there may have been a lot of clog and ??? in the system and my bleeding it out, and all over several cycles may have bought some time on the inner WP seal. So - FYI. Before your ?? tells you otherwise. Master flush the system over several cycles and re-infuse MotorCraft coolant, only if you know the pump is still moving the water throught the system. Otherwise, if you waited too long and coolant is in the oil - gameover.
