I heard less than 1/4 tank when replacing fuel filters on 6.7 power stroke. This true?

 

I did not have any issues when doing mine with about a 1/2 tank. I disconnected the upper filter and connectors first, then did the lower. Drained maybe 1 quart or so of diesel, then completed the job of replacing both filters.
Mine's a push button start and the process was to push the start button w/out your foot on the brake a few times to get the fuel / lift pump to pressurize the system. I could hear the pump running for the first couple times then it seemed to be pressurized. Repeated that process a half dozen or so times.
Truck fired right up with no issues.

 

I've successfully changed mine with more fuel than 1/4 tank. Haven't lost more than the up to half gallon of fuel that the manual states. I open the drain then go up to the engine bay filter and replace it first. After that, the lower is about done draining, ready to open up.

Edit- If you have a 2017 it might be best to stick to that 1/4 tank suggestion. In the OM, it mentioned disconnecting a fuel line to avoid siphoning on the 2017MY only..supposedly resolved in later years. Maybe the 1/4 tank or less avoids the need to disconnect the fuel line?

 

On the 11-16 models, loosen the primary filter 3 full turns, then open the drain. It won't siphon if you do that. I changed mine with my 60 gallon tank nearly full. The only fuel that drained out was what was in the filter and the lines. Still a mess, but manageable.

 

The truck can have a full tank... does not matter. Just have to break the filter cap suction... it is different for the 17 plus Alumina Duty trucks with different fuel system with in-tank primary pump and larger primary fuel filter housing in different location.

Don't know what the OP has year wise, but x2 for the 11 to 16 trucks. Mine has a skid plate on it so that has to be removed first so the DFCM (diesel fuel conditioning module aka pump housing with fuel filter/water sepator) can be turned off. Remove WIF sensor connector.

Turn three times completely to break the suction, open drain and about a large coffee can sized container will be big enough for the drained fuel. Pull off old o-ring and use new one that came with the FD4615 Motorcraft set of filters. I use new engine oil on the pump threads (male part of pump) and new o-ring (once installed). Some guys use Vasoline I've seen here I believe and even lithuim grease. The engine oil trick I learned from a Ford tech who posted here. It also makes it easier some to screw off the cap to get it loose IMO.

Remember to prime the system at least 6 times... about 30 second intervals. You can hear the pump running with driver's door open. (RTFM) factory manual says six times. I go over double to at least 15 times. First time I changed the fuel filters with 6 priming cycles, it took at least a few seconds to start so overkill... I went at least double the next time.

There are two stops (tabs) on the cap (female that holds the fuel filter) which meets the stop on the male (top which cap screws onto). They can be broken off by going to far... I shine a flashlight up there when they get close to avoid this.

 

The very early trucks with the new style filter ( probably 2017 if I remember) had a problem with siphoning too much full if the tank was full.
Ford fixed that part way thru the year. My Late in th year 2017, didn't care how full the tank was.
My current 2023 doesn't care.

 

On my 2016, I have started just unscrewing the housing all the way (carefully) and dumping it out like a cup of water vs opening the drain. If you’re going to open the drain, others are correct with 3 full turns to break the suction.

Overkill above is also correct about tightening the lower housing. The first time I changed filters I had this issue. The truck died a couple seconds after the filter change from sucking air. I had intermittent long cranks from not tightening it enough.

 

Adding to what @Overkill2 stated, make sure that you are on level ground or if at an incline your engine is on the high side. Otherwise, it is possible to create a gravity siphon. Generally, cracking the cap works but I have been a bonehead a couple times, not paying attention, truck pointed hood first on a down slope and wondered why in the hell my tub had over 2 gallons of fuel in it and still coming. On a side note, after switching to the SPE MS filter relocation kit, changing is absurdly simple. I would say I lose less fuel but with the size of the filters I probably lose more!

 

My driveway angles up towards the garage... a real treat when checking the oil level after a change, have to take it out into the street to get the max level dialed in but I'm used to it.

As to fuel filter changes, I remember having an issue the first time, but didn't Crack it enough to break the suction and luckily, always had it pointed up hill so never ran into the down hill problem you described...

 

I have never had an issue with a full tank on my 21'.

 

Same for my driveway, it angles up towards the house but not a huge amount. I tend to back in and the couple times I just couldn't be bothered to turn it around. Both times thinking, meh it won't happen and both times it did. As for doing it now, I ended up swapping over to the SPE solution so both are spin-on at the tank now. I've only put 8K miles on the rig since swapping over so I won't know for awhile yet if a gravity siphon is even possible with that setup.

When I do the oil, I have the same, I have to get it on the street to level to check. I have a 24 HO and I have put 4 gallons in at each interval; I've got lucky on this rig as it sits right at full on the stick. I'm planning on swapping over to the PPE oil pan at some point so we will see how what that does as far as capacity goes.