Coolant Tank Leak

[Drizzt]

Wanted to report an issue I solved on my truck, 2019 with 75k miles. Since about halfway through my ownership I've noted that between oil changes, my coolant level would drop from maximum to minimum. Well last weekend I developed an actual leak (left a small puddle on the ground after parking).

Investigation found that there was a small crack on the bottom of the tank that only opens up when the truck is at operating temperature (doesn't leak when cold). After swapping in a new tank, I noted that there seems to be a lot of stress cracking on the bottom of the tank.

Side notes / rants I discovered while doing the job:
1 - replaced the radiator cap, there is a newer revision. The old one was very stiff to get on, this one is much smoother (not sure if age or better design).
2 - The tank is only mounted with two bolts on the fender side, and a "pegleg" on the other side to hold it up. This makes it prone to a lot of vibrational stress as the tank bounces up and down on the leg. Horrible design effort by ford. Might consider strapping it down to reduce stress?
3 - The rectangular hole on the bottom of the tank is actually the overflow for the pressurized cap. So if you have coolant on the bottom of the tank, it could also be the cap is bad or high temperatures pushing the cap open. Another lazy design by ford not including an overflow hose.
4 - This bolt was a PITA to get to, probably easier to remove the airbox next time. Again a large miss by ford on serviceability, no reason the bolt couldn't have been 1 inch closer to the tank.

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[IdahoRanger]

Great write up James. If I remember there are some cases of coolant levels dropping on this forum so you may have solved the problem.

 

[airline tech]

Its a common issue with Reservoir Tanks to develop stress cracks with age on all makes, and Highly Common for the cap, with age the O-Ring swells, and creates a difficult to remove situation., as the swelled O-Ring will hold cap in place and the plastic threads are not strong enough to overcome it and let the cap back off. So it just spins in place and damages the threads on both the reservoir and the cap. If you are lucky the reservoir can be recovered, but always recommend replacing the cap (in this situation) at the very least.
The trick is to pull upwards on the cap while turning the cap (CCW) to remove it. I have dealt will that issue across all makes, I always replace my cap every few years as general maintenance for this reason. You can always just replace the O-Ring, but the cap is cheap enough to just replace the whole thing.

 

[Frenchy]

Interesting find.

That said for note 3 is is normal to not have an actual Overflow Bottle on a pressurized system like this regardless of manufacturer. If you pay attention you will notice when cold the coolant will be at the max line and when hot it will be at the minimum line. For a pressurized system like this that is considered normal operation.

 

[RangerBill]

Interesting find.

That said for note 3 is is normal to not have an actual Overflow Bottle on a pressurized system like this regardless of manufacturer. If you pay attention you will notice when cold the coolant will be at the max line and when hot it will be at the minimum line. For a pressurized system like this that is considered normal operation.

Mine is the opposite of that.

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