Fuel Filter Not Full When Changing

I have been changing my own fuel filter on my 2006 LBZ since new. Current clock is at 220,000 so I have changed the filter a lot (every 10,000 miles). I always use Baldwin filters (thanks John).

A few months ago the original filter housing needed replacing. The change was done by a GM dealer. A few days later I noticed a leak on top of this new housing which turned out to be a flawed casting. When the prime pump was pushed fuel would come out of the top of the casting. It was replaced by the same dealer (no charge obviously). All has been normal since that time and approx 8,000 miles added to the clock.

Yesterday it was filter change time and I replaced the Delco filter the dealer put on when they changed the housing. I have always hated spilling a bit of diesel when working this filter out. I always remove the right side battery to make more room, but you still have to tilt it a bit. Yesterday I didn't spill a drop. Why? The filter was almost empty. It was probably 1/4 full of diesel maybe. I had just returned from a 1,000 mile trip and everything worked fine and fuel economy was as always.

Why would this Delco filter not be full of fuel like all of the Baldwins I have been using for the past 15 years? I did put a Baldwin back in.

Is there still something still not quite right with this new housing?

Thanks guys.

I just changed the fuel filter on my truck a few days ago. I used a Baldwin as well. Properly primed, a fuel filter can accumulate air over time due to a slight vacuum present as the high pressure pump pulls fuel from the tank - fuel has molecules of air in suspension. A more restrictive fuel filter will increase the vacuum when measured at the fuel test port near the right side front of the engine. Why Baldwin doesn't do this and the AC-D filter did is a mystery. Maybe the dealership filter wasn't properly primed? By the way, this is an argument for a lift pump - though neither of my trucks have one.

My LB7 filter assy has a drain valve on the bottom. I usually drain a cup's worth of fuel to keep the spills to a minimum.

Thanks for the reply. Obviously I have no clue what the dealer technician did when changing the filter. I just know I prime mine correctly.

This may remain one of life's mysteries.

I know the lift pump would keep the filter full, but my truck has never had one and continues to work perfectly. Just the question of the not full filter came up.

I expected JK to respond to this, although most of what he'd have to say is somewhat predictable: install a lift pump, etc.

I've used many different filter brands over the 20+ years I've had my Duramax, and have not seen any of them not collect some air over time. All of them were never full at service. I also have an original Mega Filter, which has an air gap. I do not have a lift pump (although it's been on my short list for years). Over time, regardless of the OEM filter brand, air builds until it will stall after a cold start. I can determine the state of the OEM filter by the time/miles between stall episodes. Once it begins, it becomes more frequent. I only bleed the Mega Filter, as previous experience has shown that also bleeding the OEM filter has very little, if any, noticeable effect on the cycle. I also monitor the filter performance with a restriction gage (Kennedy). After it reaches about 5" Hg, it declines more quickly, so I base my service interval according to that. I have yet to notice any degradation of the Mega filter. The Difference from old to new is less than 1" Hg, and I replace it at 50K miles. I'm not concerned with filtration with my setup, but the air has always been a concern. If the original, single media, simple, Parker filters were available, I'd use them. Until they were no longer available, air wasn't ever an issue. They were less restrictive, but I suspect GM was correct in the redesign, for OEM-only applications. The increased restriction rate is a fair indicator of filter efficiency, or perhaps a lesser media area that may increase restriction at a higher rate. I dunno, and haven't spent much thought on it. I just replace the filter as restriction increases.

On another note--
If you have a repeat with the air, or for no reason at all, change the fuel cap. Any change in its venting may have an effect on the condition.

Went to dinner this afternoon and came out to start then quickly stall. Popped the hood and pumped up the filter and noticed a small amount of fuel on top of the filter housing before I bled any out. Is the something that might need rebuilt/replaced on the filter housing that would cause this?
Recently replaced the filter and WIF plug on filter. New filter in rear CAT prefilter in rear wheel well.

If the primer pump is leaking, there's a kit for that. Elsewhere may be a problem. Locate the source and go from there.

Quote:

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Originally Posted by a5150nut

Went to dinner this afternoon and came out to start then quickly stall. Popped the hood and pumped up the filter and noticed a small amount of fuel on top of the filter housing before I bled any out. Is the something that might need rebuilt/replaced on the filter housing that would cause this?
Recently replaced the filter and WIF plug on filter. New filter in rear CAT prefilter in rear wheel well.

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I had the same problem with a brand new replacement housing. It was a flaw in the casting. Fix was a new one.

Quote:

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Originally Posted by DmaxMaverick

On another note--
If you have a repeat with the air, or for no reason at all, change the fuel cap. Any change in its venting may have an effect on the condition.

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I'm sure glad you mentioned the fuel cap. To me that is one of those items that is out of sight and out of mind. Mine is original on my LBZ and now with 220,000 on the clock. I'm going to replace that sucker today. That may be the cause.

Thank you sir.

Caps are often neglected. A diesel fuel cap is supposed to vent at 2-psi positive or 1" negative pressure. Pressure on the fuel return line increases as fuel tank pressure increases. I thought about this while sealing the injector fuel return lines, during a recent head gasket replacement, since they're mostly under the valve covers (fuel in oil is bad).