The Stanadyne Water Seperator Exposed

[Agnem]

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We all know that the factory 6.9 water separator is prone to letting air in the fuel system, and that a common remedy is to either remove it all together, or plug up the drain hose. What nobody has been doing that I am aware of, is repairing it, and it may be as simple as cleaning it.

At the 2007 IDI Weekend in Rising Sun, Indiana, I brought along a disassembled unit to take some of the mystery out of that silver cannister. Follow along with the pictures below to see how it works, and what could be done to get it to seal properly again.

The unit is made so that it doesn't come apart. The "bowl" is pinch seemed onto the head, and the only way to get one apart is to destroy it. However, there is one way, which we shall examine.

First, let's look at our "exploded view" model to see what exactly is in there.

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Inside the unit, there is a plunger, which serves to plug the bottom of the bowl, a rod, which senses the water and turns on the "Water in fuel" light, and the actual filter itself, which is basically nothing more than A SOCK! OK, it's probably a special sock, but it sure looks like something that had been on somebody's foot for a really long time.

Inside the bottom of the bowl is... well, nothing. This is where the sediment builds up, and collects around the rubber stopper. So when you pull the plunger up to drain it, all the sediment falls into the path of the rubber stopper so that when you release the drain, it seats on dirt, instead of a clean metal surface.

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Here is a better view of the 3 main parts, the sock, the plunger, and the rod.

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The good news is, that the one part that does come off on this thing, is the plunger assembly. Here we see my oldest son, Matthias, unscrewing the plunger from the head. The large nut under the pull ring is all that is needed to be loosened.

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Once the threads are disengaged, you can pull the whole plunger assembly out. There is one caviot.

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The "Sock" may try to get caught between the white plastic part you see about half way down the plunger assembly, and the hole that it is trying to pass through. Some determination and dexterital finagery may be required to get this part to clear.

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Once the plunger assembly is free, you can inspect the rubber tip for debris, or defects.

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Now it is just a matter of devising something you can insert in the hole in the top of the filter head, to get down to the bottom of the bowl and clean out the drain area. Perhaps a thin wooden dowel could be used to clean it out, or compressed air, or a vacuum. Armed with the knowledge of how it is made, it may be easier to fix it, then to replace it, and less costly too.

 

[FordGuy100]

Nice write-up Mel . I'm gonna have to replace mine (the stock 6.9 unit) cause when you pull up on the thing to let out the water, nothing comes out .

 

[69oiler]

when i first bought my 6.9 i has an air leak at the water seperator. the PO (a diesel mechanic) reground/cleaned the seat with the seperator mounted in the truck. i still use the stock seperator to this day.

 

[MIDNIGHT RIDER]

I never mess with them; BUT, why not throw away the ring/rod gizmo, mount a drain-valve in the bottom, and a vent-valve in the top.

The bottom drain-valve should be threaded into a fitting, that is fixed into the bottom of the canister, such that it can be un-screwed, occasionally, for cleaning.

A good way to get a leak-proof fitting into the bottom of the canister is to ream/drill the hole to 5/8", and install a tubeless tractor-tire air-valve into the hole.

This will provide a leak-tight threaded fitting to screw the drain-valve to.

In fact, if you can un-screw/replace the tractor stems valve-cap, without losing the cap and getting a fuel bath, the tractor valve is all that would be needed for a drain.

 

[Agnem]

I never mess with them; BUT,

That's the whole point of this write up, and Rob and Fordguy's comments speak to the point. You CAN and Should try to repair it, rather than re-engineer another solution. Fordguy's is plugged, and just needs to be cleaned. He doesn't need to get another one. At least he should TRY to fix it, now that we know they CAN be fixed.

Also, as a trivia item.... IN 1983 they came with a factory sepearator that was not the pull ring style. it DID have a screw in the bottom, like a radiator petcock, and a air valve in the top. The pull ring style was for VAN's only, and was remote controlled through the van floor. I guess they decided to standardize on the pull ring style after that model year. Mine was replaced with the pull ring style when my first injection pump went up, and I thought it was letting air in.

 

[MIDNIGHT RIDER]

While we are talking water-seperators, BE HONEST, how often does everyone check/drain their seperators??

I will admit that I seldom do, as I have never found anything in one yet that I thought was anything but diesel.

I have seven trucks in the yard, right now, and have driven numerous different diesel trucks for more years than I care to count, and I have NEVER seen a "WATER-IN-FUEL" light come on.

Is there an affordable consumer-available test-strip, or test paste, kit available that could be used to test the fuel drained from the seperator for moisture content??

I think it would be interesting for several of us to get the same test kits and, on a regular schedule, drain and test the fuel from our seperators, in somewhat of a scientific manner, then compare our results in a thread dedicated for it.

 

[Agnem]

The water in fuel light came on probably a week or two after I first bought the Moose Truck. It had a ton of water in it. I've drained it a few times since, but never saw as much as that first time. I usually drain it once a year.

 

[69oiler]

i have drained mine maybe 3 or 4 times since 2000 when i got the truck. once on the PSD when i changed the fuel filter.

 

[fsr7]

I drain mine every month or two... I don't rally think its necessary, but it gives me something to do when the truck is fueling.

 

[MIDNIGHT RIDER]

LOOK-OUT ANOTHER BRAINSTORM

This just popped into my head.

Without some kind of actual water-in-fuel test, there really is no real means of knowing if the water-in-fuel sending-unit/light system even really is in working order.

I propose this:

About once a year, drain the seperator and refill with fresh fuel; then, take loose the fuel supply lines at the seperator.

Add a temporary intake-side short line, such that drops of water can be added to the fuel that is in the seperator.

Add CLEAN water to the fuel that is in the seperator, ONE DROP AT A TIME.

Count the drops.

Have your assistant perched in the seat, with key on, watching the water-in-fuel light.

Keep slowly adding drops of water, until your assistant hollers "the light came on".

Write down, in your records, how many drops of water it took to light the light.

If you have purged all the fuel out and replaced it with water, then, you know that your warning system has a problem.

When the test is complete, drain the seperator, flush it out with some WD-40, and re-attach the fuel lines.

 

[FordGuy100]

What a second, in one of the pics I see that there is a rubber hose that attaches to the bottom of the seperator, does this rubber hose run come out under the drivers side door and about a foot in. If it is, mine is constantly leaking onto my side step bar . I'll go out and take a pic to give you guys a better idea of what I'm talking about. But if its constantly leaking that could mean my little rubber tip thing isnt sealing, is that a good or a bad thing?

 

[MIDNIGHT RIDER]

mine is constantly leaking onto my side step bar . But if its constantly leaking that could mean my little rubber tip thing isnt sealing, is that a good or a bad thing?

May be good.

May be bad.

Fuel is near three bucks a gallon; but, it will keep road-tar and bug guts from adhering to your running boards.;p

 

[FordGuy100]

Heres the pic of the rubber hose I'm talking about.

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[69oiler]

Heres the pic of the rubber hose I'm talking about.

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if fuel is leaking out, chances are air is leaking in. if the leak is bad enough you will have a no start or even a no-run situation like i had.

 

[FordGuy100]

I dont know if air is leaking in or not. I do know that my truck starts up in the first couple of turns of the motor even if its been parked for a week or two, and I'm not getting any surging during driving.