8V71 Fuel Filter Change

[richard5933]

I've read so many stories of guys losing prime when changing the canister fuel filters on the 8V71 that I've avoided it till now. When I've had my bus in for other service, I've just had them do it. Now that I'm no longer at the shop so often it's time for me to tackle this and gain confidence.

I've got two sets of filters in hand from Luke. My understanding is that all that's involved to get to the filters is removing the bolt at the top center of each filter and removing the canister. Then swap out the filters & O-rings, refill the canisters with clean Diesel, and then reinstall.

If I do this correctly am I to understand that the engine should start up as normal?

Any advantage to doing them one at a time and running the engine in between for a few minutes?

Anything I've overlooked?

Thanks!

[luvrbus]

When it fires give it the throttle till it runs smooth if not 90% of the time it will lose prime

[chessie4905]

My opinion is to change that setup to spin ons.  The won't cost that much and avoids the mess with the elements and orings. Especially when the time comes to have to do it out on the road.
Cliffs right, keep it revved up when restarting. If you just let it idle, it'll lose prime and require refilling one or more times and unnecessary starter use till it runs again.

[buswarrior]

Shut off valve in fuel line from the tank?

Close while swapping, open once sealed up again.

And when he says give it throttle, don't screw around, governed speed makes for the fastest moving air bubble...

There has been lots of misadventure by those who did not understand that the fuel pump can't pump air. So long as you appreciate that, you will fill everything properly
Happy coaching!
Buswarrior

[richard5933]

Shut off valve in fuel line from the tank?...
Buswarrior

Does every bus have such a valve? Where would it be if my 4108 has a shut off valve?

[luvrbus]

Does every bus have such a valve? Where would it be if my 4108 has a shut off valve?

Nope mostly found on MCI's

[TomC]

When I first bought my bus, the oil filter on the engine and transmission were both the old fashioned canister type. I changed both to spin on-using a Cummins filter on the engine and a standard hydraulic filter on the transmission. The two fuel filters were already spin on.
If you want to assure that you don't loose prime, first run your engine for 5 minutes before you change them. Then only change one at a time, get the engine running for at least a minute, then change the other and get the engine running. Remember to fill the new filters with fresh Diesel (do not reuse the fuel out of the old filters). You should also carry extra fuel filters and at least a gallon of Diesel Fuel. Good Luck, TomC

[Geoff]

It's always been a good idea to have an electric fuel pump with bypass shut off valves for priming your fuel system; either if changing fuel filters or running out of fuel.  With a pump you can crack the outlet of each fuel filter and get the air out.

[luvrbus]

With the old sock filter and most people don't do it but they are supposed to be per-soaked it tell you that in the book

[Lin]

Installing the right electric fuel pump is probably the best backup for losing prime.  I have not done that yet.  I do, however, keep a garden sprayer on hand that is set up to pump fuel into the system (at the secondary filter, if I remember correctly).  There is also a small hand pump for Detroits that can be connected.  I had one but have not installed it yet.

If you do not have a shutoff valve to the tank, I would say that you should consider it.  Especially if you are not installing an electric pump. The first time I changed filters I did not close the valves not knowing what they were for.  Of course, I lost prime.  Since then I close the valves and there is no problem.

[Jim Blackwood]

I have diesel equipment here and I have sorta made it a habit whenever I work on the fuel system to grab an old electric fuel pump off the spare parts shelf and install it inline. It flows enough bypass fuel to run the engines and makes any work on the pressure side way easier. It can run all the time or on demand. Now on an engine with the fuel demands of a bus it might be better to plumb it a little differently, maybe around the shutoff valve with it's own shutoff for instance, but you can pick those things up for about $25 anywhere and worth every penny. Bleeding the system when it's under pressure is a whole lot simpler and easier especially if you have air in the injector pump.

Jim

[richard5933]

Am I correct that there is supposed to be a check valve to keep fuel from flowing backwards to the tank through the supply line?

[luvrbus]

Am I correct that there is supposed to be a check valve to keep fuel from flowing backwards to the tank through the supply line?

Yep but it is a one way check valve ,it doesn't prevent the fuel from draining out of the fuel tank supply line on the MCI's and other brands so they use a valve

[chessie4905]

The check valve should be at the firewall engine side

[richard5933]

Success!

I did the primary filter first. It wasn't horrible, but there was certainly noticeable rust-like particles and crud floating around the bottom of the canister. The filter was visibly dirty but not blocked, but the upcoming 2,000-mile trip would probably have ended with a filter problem if I had left it till after the trip.

Refilled the canister to the brim, re-installed, and then ran the engine at fast idle for a few minutes. Not even a single stumble, so I must have done something right.

Since the primary was not clean, I also changed the secondary filter. It looked pretty good with only a little brown coloring to the bottom of the filter paper. Same procedure with about 10 minutes of fast idle running afterwards. No problems noted.

On drive home to Wisconsin from NJ last fall I did have some noticeable loss of power as the trip progressed. I assumed it was the filters getting clogged, especially since the bus had not been used much over the past decades. Filters were changed in the fall after that trip while the bus was at the shop, and they confirmed that the primary was pretty clogged up. With that history, I thought it was important to change the filters again before heading west in a few weeks even though we haven't driven too many miles since the last filter change.

I have two extra sets of filters packed for the upcoming trip, just in case. Hope to not need them.

After all the various repairs and upgrades I've done on this bus it's strange, but changing the filters seems like an accomplishment. I guess I haven't really done that much of the engine work myself, so hopefully this is the start of getting my hands dirty again.