Coolant sprays from secondary overflow uphill under load?

My 2018 F-250 6.7 sprays coolant out of the secondary overflow when towing heavy uphill. It happens only under load, like when I’m pulling my skidsteer (around 9,000 lbs). The radiator looks clean, and the fan clutch hasn’t thrown any codes. Anyone else dealt with this?

Sounds like the fan clutch might be the issue. Have you tried testing it yet?

Jatoprik said:
Sounds like the fan clutch might be the issue. Have you tried testing it yet?

Not yet, but I’ll look into it. I’ve cleaned the radiator recently, so it shouldn’t be a blockage.

Could be a sign of a partially blocked radiator or intercooler. Even if you cleaned it, debris could still be in there.

Christine01 said:
Could be a sign of a partially blocked radiator or intercooler. Even if you cleaned it, debris could still be in there.

I’ll double-check for blockages. Thanks for the suggestion.

Did it just start recently, or has it always done this with heavy loads?

Hadley said:
Did it just start recently, or has it always done this with heavy loads?

It’s a new issue. Used to haul similar loads without any trouble.

If the oil looks fine and there’s no fluid mixing, it’s probably not a head gasket issue. Check the fan clutch and maybe do a pressure test.

Carter said:
If the oil looks fine and there’s no fluid mixing, it’s probably not a head gasket issue. Check the fan clutch and maybe do a pressure test.

Good point. I’ll check the fan clutch first and see if that solves it.

I had a similar problem. Turned out to be a weak radiator cap. Might be worth replacing it to see if it helps.

Callum said:
I had a similar problem. Turned out to be a weak radiator cap. Might be worth replacing it to see if it helps.

That’s a good idea. I’ll pick one up and try it out. Thanks!