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 Post subject: * FUEL FILTERS *
Post Number:#1  PostPosted: Sun Dec 18, 2005 5:30 pm 
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[I originally wrote this in another venue; now I am reposting it here. I'm splicing several posts together here.]

The 1981 720 diesel has no primary filter, it has only one filter, and I've covered that down in the Secondary filters section.

PRIMARY FILTER

This is the small, plastic filter on the passenger firewall. It is used in 1982-86.5 models, and comes in two styles: 1982 (and '83 w/SD22) and 1983-on (w/SD25).

olpeppy wrote:
> Is the Fram p6415 a correct primary filter for the sd25? i know there has
> been some discussion on the possibility of getting one for a gas engine that
> is wrong.

Image

The correct primary fuel filter for 1982 (from Jul-81) and 1983 w/SD22 is Nissan 16401-36W01. I have not found an aftermarket substitute that is identical to it. Both the inlet and discharge lines are on the side of the top end. Philip took a comparison photo of the wrong (left) and correct (right) filters:

Image

In 1983, for the SD25, Nissan changed to a filter that is nearly identical, but whose inlet/outlet are top/bottom. OEM No. 16401-29W00 :
Image

Apparently, the Fram P6415 and the AC Delco GF630 are available aftermarket replacements.

Fram P6415:
Image

AC Delco GF630:
Image

I would usually never recommend a Fram product, but this may be one of those instances where quality truly doesn't matter (much). Anything that the pre-filter (primary filter) passes will get caught in the (much more expensive) main filter.

It appears, from the pics, that these filters would probably work fine in '81-82 trucks. But I think I'd rather go the other way: use the early filter in the later trucks, because the crap shows up very nicely in the early filters, and I'm not sure it would, in the later ones.

The OEM filter for 1982 costs about $11 from the dealer. The AC Delco GF630 for '83-on seems to cost approximately the same (RockAuto).

[tale of woe]
The firewall-mounted plastic filter seemingly isn't available from anywhere except the dealer. I had been fighting this fuel system off and on for about a month, and finally figured out why I was still having problems: that little plastic filter.

While Wix does not have a listing for the firewall primary filter, the Wix 33214 (note the '1' in the part number) is physically identical to the OEM version, and that's what I had been trying to use. Unfortunately, diesel does not readily pass through the media in it, which is designed for gasoline use. With new fuel and a new Wix filter, I pulled 8-11" vacuum out of that filter by the lift pump! Just for reference: that's a LOT of vacuum for a lift pump. Not surprisingly, this truck will run for about two miles with cold fuel, and then it'll slowly starve. On a warm day, I can run it 50 miles (I know, because I did it last week), but in the morning it is two miles, tops.

The vac test identified the problem, and on a hunch, I drove 60 miles to the dealer and bought the OEM filter (see first picture, above). The OEM filter's body is translucent, and you can see plainly that the OEM filter media is wire mesh! Obviously, it flows diesel a lot easier than a paper element, which is what is in the Wix unit I was using.

Summary: do not substitute a gasoline fuel filter for the OEM primary fuel filter: it won't work! The Wix secondary filter (spin-on) is fine, but there's a reason Wix doesn't list a replacement for the primary filter.

[/tale of woe]

[Edit, added Aug2013]
The Wix 33972 filter is a plastic mesh filter that appears to be an acceptable non-Nissan filter for this application, and might be a drop-in replacement for 1983-on:

Image

Wix wrote:
Principle Application: Plastic Universal In-line fuel filter w/ 5/16" lines - can be used w/ gasoline or diesel fuel.
Applications
Style: Fuel (Complete In-Line) Filter
Service: Fuel
Type: Full Flow
Media: Plastic Mesh
Height: 3.636
Outer Diameter Top: 1.828
Outer Diameter Bottom: Closed:
Burst Pressure-PSI: 58
Max Flow Rate: 1 GPM
Nominal Micron Rating: 50


[end Aug2013 edit]


SECONDARY FILTER

This is the larger, metal spin-on filter on the passenger fenderwell.

1981 uses the Wix (33393/NAPA (3393):
Image Image
They're pretty cheap (about $15) and fit other rigs like Isusu NPR, Nissan UD, so they're in stock most everywhere. No "Water in Fuel" sensor hole in the bottom. Because the 1981 720 has no primary filter, and this filter is smaller than the 1982-on filter, this might make necessary more-frequent fuel filter changes.



1982-86 uses the Wix (33224/NAPA (3224) (NLA Aug2013):
Image ImageImage
This filter is used ONLY on '82-86 Nissan SD diesels, so availability is sparse; plan on ordering it up in advance. Pricey: about $30 is list, often you can get it for a bit less than that, depending upon the store.

This later Secondary Fuel Filter has provision for a Water-In-Fuel sensor, hence the threaded hole in the bottom. The black o-ring shown in the left pic above is the sensor seal, and is often included with a replacement filter. The "sensor" is merely a steel probe. The real sensing is done by a module under the dash, that measures the resistance of the probe to the filter shell: water at the bottom will conduct (a little) from the probe to the shell; fuel will not. There's no float switch, as in a brake fluid reservoir.

Image
There's a decent tutorial (with nice line drawings) at an Autozone page, for the diesel fuel filter change procedure. It includes the fuel system bleed procedure, with drawings.

_________________
Regards,
Al S.

1982 Maxima diesel wagon, 2nd & 4th owner, 165k miles, rusty & burgundy/grey. Purchased 1996, SOLD 16Feb10
1983 Maxima diesel wagon, 199k miles, rusty, light yellow/light brown. SOLD 14Jul07
1981 720 SD22 (scrapped 04Sep07)
1983 Sentra CD17, 255k, bought 06Jul08, gave it away 22Jun10.


Last edited by asavage on Sat Aug 10, 2013 7:25 pm, edited 11 times in total.

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Post Number:#2  PostPosted: Tue Mar 07, 2006 4:57 pm 
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BURIED in the above AutoZone link is a very important bit of information about bleeding the Diesel Kiki injection pumps found on the SD engines.

If you replace the secondary filter and then operate the priming pump by hand until you feel some firmness, you will end up with a significant amount of air trapped in the secondary filter. Sure the engine will have enough fuel to idle for a bit and then get you about 2 blocks when ... brrrrrrrrrr .... no fuel. And no amount of cranking is going to purge this much air through the injectors.

Warning: ANYTHING that gets the engine going with first couple of ignitions producing SHARP COMBUSTION knocks is hazardous to pistons because these diesels have a lot of compression (22:1). For this reason, I would not use ether, WD, or other light aromatics to start any SD series diesel. There is no justification for "aerosol starting assistance" after a filter change simply because a filter change does not drain fuel between the injection pump and the injectors. Air removal before the injection pump is what the priming pump and bleed bolts on the injection pump are there for.

So be SURE to purge the air from your newly installed filters using the vent screws shown here:

Image

Regarding the smaller 'pre-filter', I found out that air in your new pre-filter will move to the secondary filter and possibly stay there. Why? The banjo bolt on the secondary filter adaptor marked "OFV" is low pressure pop-off valve with a TINY orifice in the end (about the size of a #50 drill). If this orifice is clogged or the spring valve inside the bolt stuck, there will be no return path from the secondary filter to the fuel tank. Remove this banjo bolt and poke through the tiny orifice in the end to verify proper valve operation. This banjo bolt is also a "pass-thru" for the tiny trickle of overflow fuel from the injectors (#4) back to the fuel tank. See OFV Fuel Pressure Regulator

_________________
-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


Last edited by philip on Mon Nov 27, 2006 11:42 am, edited 7 times in total.

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 Post subject: Re: Little Pre Filter
Post Number:#3  PostPosted: Mon Jun 26, 2006 3:27 pm 
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asavage wrote:
philip wrote:
Do we know yet if the ACDelco and Fram replacement pre-filter is actually a wire mesh screen like the OEM Nissan part or the dreaded paper element with a hefty price tag?

-Philip


Certainly I don't know. Wanna go look 'em up at your local Pep Boys?

For the price, I'll stick with OEM.

_________________
Regards,
Al S.


Well ... I was motivated today to find out.

The Nissan part for the SD25 (inlet on the bottom, outlet on the top, wire mesh media) is #16401 29W00. As it turns out, this "pre-screen" has an opaque housing. :roll:

The FRAM part (# P6415) is identical in every respect. I was able to verify personally that the media is wire mesh. $14.99

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-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


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Post Number:#4  PostPosted: Sun Jul 02, 2006 10:00 pm 
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You were not getting a discount. I payed $11.03 with tax for the SD22 fuel strainer here in Hawaii.

aloha

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- Zoltan -
________________________________
'82 Datsun 720 SD22 California model
'86 Ford Escort 2.0L Diesel


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 Post subject: Re: Little Pre Filter
Post Number:#5  PostPosted: Tue Jul 04, 2006 12:44 pm 
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asavage wrote:
Do you know how much the OEM filter is? The SD22 version is $11.

Correction: that's what I paid for it. I may have been getting a small discount.


The SD25 screen from Nissan was $12-13.

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Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


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Post Number:#6  PostPosted: Sun Aug 06, 2006 2:01 pm 
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I was wondering if it's possible to disassemble the primary fuel filter and rinse it out without replacing it. There is quite a bit of gunk accumulating in mine, but since it's just a wire mesh I don't see any reason to completely replace it. I thought I would ask before I break it in half trying to open it.

Thanks,
Clayton


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Post Number:#7  PostPosted: Sun Aug 06, 2006 2:21 pm 
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claybodie wrote:
I was wondering if it's possible to disassemble the primary fuel filter and rinse it out without replacing it. There is quite a bit of gunk accumulating in mine, but since it's just a wire mesh I don't see any reason to completely replace it. I thought I would ask before I break it in half trying to open it.

Thanks,
Clayton


Yes, you can backwash these screen / filters but if you have a paper one (which is the wrong part), these cannot be backwashed. None can be "disassembled."

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-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


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 Post subject: Thanks.
Post Number:#8  PostPosted: Sun Aug 06, 2006 3:32 pm 
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Of course - silly me. I guess I didn't think about it long enough before posting...I just have the screen so it should clean out easily. It would be a bonus if it screwed apart but I'll just backwash it.
Thanks,
Clayton


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 Post subject: Re: Thanks.
Post Number:#9  PostPosted: Sun Aug 06, 2006 10:06 pm 
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claybodie wrote:
Of course - silly me. I guess I didn't think about it long enough before posting...I just have the screen so it should clean out easily. It would be a bonus if it screwed apart but I'll just backwash it.
Thanks,
Clayton


You have "just the screen"?? Is there no secondary spin-on filter as shown earlier in this thread?

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-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


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Post Number:#10  PostPosted: Mon Aug 07, 2006 7:46 am 
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No no - Thanks for the concern but I have both a primary and secondary fuel filter. With 'just the screen' I was referring to the fact that my primary fuel filter is a wire mesh instead of the other material shown above. That made it pretty easy to backwash the screen out yesterday. It's weird as hell though - there are a couple small sticks about 1/2" long that hang out inside the primary filter. They'll just have to sit there until I can replace it, but I guess the primary may serve a useful purpose after all.

Thanks,
Clayton


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Post Number:#11  PostPosted: Mon Aug 07, 2006 8:40 am 
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claybodie wrote:
SNIP
It's weird as hell though - there are a couple small sticks about 1/2" long that hang out inside the primary filter. They'll just have to sit there until I can replace it, but I guess the primary may serve a useful purpose after all.

Thanks,
Clayton


YETCH. I wonder what's in your fuel tank! There is a drain plug on the bottom of the fuel tank. All you need is a 3/8ths square drive ratchet. Drain off a half gallon in to a container that allows you to examine the contents.

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-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


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Post Number:#12  PostPosted: Mon Aug 07, 2006 11:25 am 
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Yeah, No kidding.
I was planning on draining the fuel tank to see what’s in there, but also to see how accurate my gas gauge is. The shop manual says something like 13 gallons, but my gauge tends to read at E after 10 gallons. I haven’t thought about this too deeply, but would it cause any issues to drain what’s left in my tank and then re-fill it? Or is there a better way to do it?
I seem to remember something about it being a bad idea to run out of fuel in a diesel, but I don’t know if draining the fuel tank would cause a problem.
-Clayton


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Post Number:#13  PostPosted: Mon Aug 07, 2006 12:01 pm 
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claybodie wrote:
Yeah, No kidding.
I was planning on draining the fuel tank to see what’s in there, but also to see how accurate my gas gauge is. The shop manual says something like 13 gallons, but my gauge tends to read at E after 10 gallons. I haven’t thought about this too deeply, but would it cause any issues to drain what’s left in my tank and then re-fill it? Or is there a better way to do it?
I seem to remember something about it being a bad idea to run out of fuel in a diesel, but I don’t know if draining the fuel tank would cause a problem.
-Clayton


There's stuff that floats, stuff that sinks, and stuff that clings in diesel fuel. In his library, Al has a photo of some weird algae he found floating in a tank of diesel. Stuff looked like suds floating on dark stout beer.

No fuel meter is supposed to read EMPTY right before you start sucking air. The EMPTY mark on my truck is at 10 gallons ... and that's just as well.

Take a look at OFV Valve for "When this happens (nearly always associated with running the fuel tank at or near the Empty mark on hilly terrain or frequent traffic stops), "

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-Philip
Passed 08May2008
My friend, you are missed . . .

1982 Datsun 720KC SD-22

"Im slow and I'm ahead of you"


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