Mechanical AND electric lift pump installed by previous owner

[Enforced_Leo44]

So… after having some problems with oils in the geared hubs randomly rising above the fill plug after making sure that the levels were right, I stumbled upon a strange and possibly stupid thing done by the previous owner, which is what the title states

Now, could this be why the oil levels in the hubs rise? Could the electric pump push diesel fuel through the mechanical pump vent line and into the hubs?

The truck is a 1988 M998, 6.2L 3 speeds, I don’t really know the condition of the mechanical pump so I can’t say for sure if the diaphragm is gone for good or not

 

[TNDRIVER]

So… after having some problems with oils in the geared hubs randomly rising above the fill plug after making sure that the levels were right, I stumbled upon a strange and possibly stupid thing done by the previous owner, which is what the title states

Now, could this be why the oil levels in the hubs rise? Could the electric pump push diesel fuel through the mechanical pump vent line and into the hubs?

The truck is a 1988 M998, 6.2L 3 speeds, I don’t really know the condition of the mechanical pump so I can’t say for sure if the diaphragm is gone for good or not

YUP, the mechanical pump can do it by itself if the diaphragm leaks. Guess how I know!

 

[Enforced_Leo44]

YUP, the mechanical pump can do it by itself if the diaphragm leaks. Guess how I know!

Who doesn’t love a good sniff of diesel fuel while changing oils in the geared hubs

 

[Mogman]

YUP, the mechanical pump can do it by itself if the diaphragm leaks. Guess how I know!

Been there done that! No more mechanical pumps for me.

 

[Enforced_Leo44]

Been there done that! No more mechanical pumps for me.

So, could it be a good/viable idea to just remove the mechanical pump and just keep the electric one the previous owner installed?

 

[Mogman]

That depends on what type of electrical pump is installed.
The engine will run on very little pressure but you need or want about 10-14psi, the reason is you want to bypass as much fuel as you can to keep the IP cool.
Anything over 15psi starts to affect IP timing.
I use a low pressure Raptor pump and a spin on filter to replace the mechanical pump and that PITA factory filter.
You definitely don't want one of those cheap impulse pumps (looks like an inline filter or a square block)
The Raptor is not cheap but unless you buy it from some discounter or used they have a lifetime warranty.
As you can see in the picture it takes about 3psi to overcome the check valve in the return line fitting in the top of the IP, this truck can sit for weeks and still have a static 2-3psi sitting on the feed line

 

[Enforced_Leo44]

That depends on what type of electrical pump is installed.
The engine will run on very little pressure but you need or want about 10-14psi, the reason is you want to bypass as much fuel as you can to keep the IP cool.
Anything over 15psi starts to affect IP timing.
I use a low pressure Raptor pump and a spin on filter to replace the mechanical pump and that PITA factory filter.
You definitely don't want one of those cheap impulse pumps (looks like an inline filter or a square block)
The Raptor is not cheap but unless you buy it from some discounter or used they have a lifetime warranty.
As you can see in the picture it takes about 3psi to overcome the check valve in the return line fitting in the top of the IP, this truck can sit for weeks and still have a static 2-3psi sitting on the feed line

Gotcha, I’m gonna see what kind of pump he installed and put a pic in here

 

[Mogman]

PureFlow AirDog #R1SBU369 Universal Raptor 100 gph, Preset to 8psi, (Pump Only)

This is a 100GPH (Gallon Per Hour) Raptor-4G fuel pump that is preset to 8psi from the factory. This pump is adjustable up to 30psi. This is a fuel pump only and does not include any installation parts other than the male fittings that install in the pump itself.

pureflowairdog.com

So if you purchase the pump under the MAP price of $332 you have no warranty.
The kicker is you can purchase it direct for $317 which is under the MAP price, I have sent them a message and ask them to clarify why the factory is selling pumps without warranty...
This is the same company that makes Air Dog, I have had good luck with Air Dog products for around 10 years now, the Raptor is the same pump only without the air separating (removes entrained air not a problem for the 6.2/6.5L) and built in filtering.

 

[Enforced_Leo44]

PureFlow AirDog #R1SBU369 Universal Raptor 100 gph, Preset to 8psi, (Pump Only)

This is a 100GPH (Gallon Per Hour) Raptor-4G fuel pump that is preset to 8psi from the factory. This pump is adjustable up to 30psi. This is a fuel pump only and does not include any installation parts other than the male fittings that install in the pump itself.

pureflowairdog.com

So if you purchase the pump under the MAP price of $332 you have no warranty.
The kicker is you can purchase it direct for $317 which is under the MAP price, I have sent them a message and ask them to clarify why the factory is selling pumps without warranty...
This is the same company that makes Air Dog, I have had good luck with Air Dog products for around 10 years now, the Raptor is the same pump only without the air separating (removes entrained air not a problem for the 6.2/6.5L) and built in filtering.

This is the pump that the previous owner installed, it fits your definition of “inline filter look-alike” so I’d scrap this and just replace the mechanical pump with a new one

 

[Mogman]

It looks like a better pump than the cheapo ones, but not having any data on it I would have to put a pressure gauge in line with it.
Might be better at this point to remove it and install a new mechanical pump.
BTW the trans would be a better ground that the frame, the M998 I stripped down had no connection from the batteries to the frame so all grounding would be through things like the parking brake cables etc, One reason why those brake cables fry when the starter shorts to the frame..

 

[sue]

So… after having some problems with oils in the geared hubs randomly rising above the fill plug after making sure that the levels were right, I stumbled upon a strange and possibly stupid thing done by the previous owner, which is what the title states

Now, could this be why the oil levels in the hubs rise? Could the electric pump push diesel fuel through the mechanical pump vent line and into the hubs?

The truck is a 1988 M998, 6.2L 3 speeds, I don’t really know the condition of the mechanical pump so I can’t say for sure if the diaphragm is gone for good or not

I have to ask the obvious question, after reading post after post….etc. about the mechanical fuel pump pushing fuel through the vent line? Why not run this
“Vent line” to a tee to the fuel tank vent line?

 

[TNDRIVER]

I have to ask the obvious question, after reading post after post….etc. about the mechanical fuel pump pushing fuel through the vent line? Why not run this
“Vent line” to a tee to the fuel tank vent line?

As ACTION pointed out to me recently the later trucks actually do something to this effect. I plan to cheat the process a little and rout my 9 and 11 series trucks vents up behind the air intake where the system is currently vented. It's my humble opinion that is one of the few improvements that can be made to the early truck. If the pump starts barfing fuel better to find it on the fire wall than in a hub.It's on my summer todo list. My two cents. THANKS ACTION!