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I have a 2001 7.3 Super Duty with around 469,000 miles on it. It started leaking diesel fuel about a week ago and appears to be coming from the front of the engine almost from the radiator. It doesn’t happen all the time I drive it. Sometimes it’s a small dipping and a few times it’s left a puddle. It looks like it is coming from the radiator or bottom of it. I took it to the local shop and they have no idea where it is from other than it’s getting in the coolant somehow and when it under pressure it leaks out. They don’t really work on diesels other than minor repairs. Any thoughts from anyone who may have experienced this? THANKS!! Randy
 

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The fuel drain valve discharges just above one of the radiator hoses, so might appear to be leaking from the radiator. If you have an injector cup leak it would get fuel into the radiator and would wind up floating on top of the coolant tank. If there's enough fuel, it might eventually leak out of the radiator cap, but if there's no sign of fuel there, it would NOT be leaking from the bottom of the radiator, because fuel floats on the coolant.
My money's on the fuel drain valve on the back of the fuel filter. It takes a T20 bit on a small ratchet to get the 4 screws out to replace the o-rings that seal it. IIRC they're 1/8 ID x 1/4 OD, or -205 size. You should replace them with viton o-rings, not the garden variety you can get at the plumbing shop or big box hardware. If you can't find viton o-rings locally, here's a couple of options.
Drain valve o-rings
Fuel Bowl Reseal Kit
 

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99 F250 7.3 2000 F250 7.3 2001 Excursion 7.3 mostly stock all 3
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I have a 2001 7.3 Super Duty with around 469,000 miles on it. It started leaking diesel fuel about a week ago and appears to be coming from the front of the engine almost from the radiator. It doesn’t happen all the time I drive it. Sometimes it’s a small dipping and a few times it’s left a puddle. It looks like it is coming from the radiator or bottom of it. I took it to the local shop and they have no idea where it is from other than it’s getting in the coolant somehow and when it under pressure it leaks out. They don’t really work on diesels other than minor repairs. Any thoughts from anyone who may have experienced this? THANKS!! Randy
 

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99 F250 7.3 2000 F250 7.3 2001 Excursion 7.3 mostly stock all 3
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Youch! So the way I read it is there's fuel in the coolant? In the degas tank?
Have you taken a sample of the coolant? If not, definitely take one. Put it in a tub, bowl, whatever.
If there's fuel in the coolant it will separate from the coolant after you let it sit, plus do the smell test.
If you've already done that, I apologize for assumption.
I had some cracked injector cups and had that issue. Had to replace ALL my hoses, everything that coolant touches, and engine flush. On top of replacing all the cups, also did the injectors, cuz the coolant ate the orings, plus already in there anyway.

Is it knocking also? (More than the average diesel knock)
You sure it's not coming from the fuel bowl?
my 2001 7.3 Excursion fuel bowl drain valves leaked and it hit a line and went forward first, then dumped down, the 99 F250, just leaked toward the back.
Worth a gander.
Hope that helps a bit.
You got a diesel shop nearby?
I'd opt for that over the dealer, especially since your local one is clueless.
 

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x2 on what klhansen said. Fuel leaking into the cooling system will come out of the cap on the degas tank - had that happen on the '03 I used to have. You would see a steady stream of fuel/coolant coming from under the cap. The fuel bowl drain is a metal tube that runs down the front passenger side of the engine and could give the impression that the leak is coming from the radiator based on its location.

Should be easy to eliminate the possibility of a fuel leak into the cooling system - just check the degas tank level. If it's in the normal range between the "cold fill" and "hot fill" marks, then there is nothing leaking in. If it's completely full, you might have a problem.
 
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