TC35 fuel filter problem SOLVED!

[jedjoe]

While your experiment does seem to have solved your problem and may work going forward, I'm still curious and I'm sure you are as well as to what has changed that caused your filter housing to lose its fuel level. Yours as well as thousands of other TC35A's have run without a clamp on the return line.

Its almost like your tank has a vacuum on it and will not allow the fuel to flow into your filter, but with a vent line being on your filter the fuel is allowed to be pulled from it and replaced with air from the vent. Its an example of the path which offers the least resistance will be taken.

Is there a pressure rating on the pressure required to open the check valves that you purchased?

I just looked it up on this small valve. Opening pressure is 0.5 Kilopascal or 0.0725 psi

 

[jedjoe]

Opening pressure for the 1/4" inline check valve is 0.5 Kpa or 0.0725 psi.

 

[jedjoe]

I don’t think there’s enough pressure to open a check valve..
Do u have a knob on your inlet banjo bolt.??
If yes, try turning it the other way and see what happens..

the check valve has an opening pressure of 0.5 kPa or 0.0725 psi

 

[jedjoe]

While your experiment does seem to have solved your problem and may work going forward, I'm still curious and I'm sure you are as well as to what has changed that caused your filter housing to lose its fuel level. Yours as well as thousands of other TC35A's have run without a clamp on the return line.

Its almost like your tank has a vacuum on it and will not allow the fuel to flow into your filter, but with a vent line being on your filter the fuel is allowed to be pulled from it and replaced with air from the vent. Its an example of the path which offers the least resistance will be taken.

Is there a pressure rating on the pressure required to open the check valves that you purchased?

0.5 kpa or 0.0725 psi

 

[thclimer]

0.5 kpa or 0.0725 psi

That's a very small amount of pressure, I'd install it to give it a try.

 

[jedjoe]

Here is an update that will have you all scratching your heads....

Please examine the attached photo as you read this post.

So, I ran the tractor for a few days leaving the hemostat crimping the return line section that connects to the filter bowl. The tractor ran perfectly, with no symptoms and no loss of power even when throttled up for most of that time. Probably 4-5 hours of full use and there was no drop in the level of the filter bowl...it stayed full. Excellent.

Today the 1/4" check valves arrived. I removed the hemostat, returning that one section of return line (from the "T" connector to the filter assembly)to use. I added the check valve on the part of the return line that travels from the "T" connector back to the tank. Based upon past conversations with others (and with my agreeing with them), that check valve (which has a VERY LOW opening pressure) SHOULD have stopped any air from being sucked down the line (and yes, I tripled checked the valve to ensure it was operating properly and I had installed it with the correct direction of flow (flow allowing fuel back to the tank but not allowing air from the tank).

Guess what? The problem RETURNED! Within 15 minutes of use, the bowl was only 1/2 full.

Anticipating the questions of all of these smart tractor minds, let me say this: 1) The filter bowl assembly itself is fully intact, without any cracks or damaged "o" ring; 2) the return line from the injectors to the "T" connector is brand new, as is the line I crimped for my previous experiment.

As far as I can understand this, the problem is stopped when I shut down the hose from the "T" connector to the top of the filter assembly. The problem returns when I unclamped that small run of return hose. The "T" connector is brand new, so the air is not coming from that connector. The air CAN'T be coming from the main return line to the tank, as there is now a check valve that works perfectly, stopping any air from being suctioned from the return line. So....what's left? Unless I am dementing, the ONLY place left for that air to enter is somewhere along the line from where it exits the injectors but before it reaches the "T" connector. Right? Or am I missing something??? This weekend, I will remove the fiberglas panel that blocks access to where that line connects to the injector exit. Maybe when I replaced that line I didn't tighten it sufficiently.

For those of you much wiser than me about fuel injection systems, is it possible that air is leaving the injectors along with the excess fuel? And if so, why is it ending up in the filter assembly rather than being pushed back to the tank?

 

[Harry in Ky]

No, you're not the only TC owner to experience this, and for what it's worth, there are Kubotas out there doing the same thing. Probably other brands as well. That return line connection is not a "new Holland only" concept. Your "heating the fuel" theory may hold some water, but I see many newer tractors, at least those with common rail systems now have a fuel cooler in the mix. Fuel is sent up front and through a small cooler placed near hydraulic coolers, A/C condenser, etc, before going to the filters and the engine. I guess no added heat needed there.

 

[jedjoe]

So I believe I have solved this ongoing problem to my satisfaction. After checking to ensure that the return line from the injectors was not loose (and therefore not a source of air), I did a bit more research on diesel fuel injections systems. It seems that well over half of the available diagrams of such systems don't even include the return line that runs back to the fuel filter assembly, the excess fuel instead simply returning to the tank directly. When I did see that extra line, the orifice on top of the fuel filter assembly was typically identified as an "overflow". This led me to believe that if fuel is moving along that one small line, it's more likely exiting the assembly, NOT entering it. So....I installed one more check valve, this time on that line and oriented so that fuel can leave the assembly but nothing can enter it (fuel or air) from the return line. See attached image.

I then ran the tractor at high throttle for about 2-3 hours today (end of year field mowing). NO DROP IN THE FILTER ASSEMBLY! Just as important, there was no loss of power nor any signs that pressure was building anywhere in the system (no leaks, no popped connections, nothing).

What I learned from this process (beside now really understanding the fuel delivery system) was that the source of the air into the filter bowl was DEFINITELY coming from the return line orifice at the top of the assembly. Adding the first check valve (preventing air from being suctioned down the return line from the tank) DID NOT FIX the problem. Surprising, as that seemed the logical source of the air. Adding the second check valve (on the short section of the return line that runs directly into the filter assembly) DID FIX the problem. Moreover, preventing fuel movement back toward the filter assembly via that return line has (so far) created no problem at all. If that top orifice is really an "overflow", then my check valve will still permit such overflow, as the opening pressure on the check valve is very small (0.07 psi).

I think I can live with this solution and move on. The check valves are cheap, so I'd encourage anyone else with this same problem on a TC to try this solution if nothing else has worked to date.

Thanks all!

 

[thclimer]

Wow, what saga, thanks for sharing your progress and documenting your modifications with pictures. I hope you have many hours of running now without a loss of fuel in the filter housing.

 

[dieselscout80]

So I believe I have solved this ongoing problem to my satisfaction. After checking to ensure that the return line from the injectors was not loose (and therefore not a source of air), I did a bit more research on diesel fuel injections systems. It seems that well over half of the available diagrams of such systems don't even include the return line that runs back to the fuel filter assembly, the excess fuel instead simply returning to the tank directly. When I did see that extra line, the orifice on top of the fuel filter assembly was typically identified as an "overflow". This led me to believe that if fuel is moving along that one small line, it's more likely exiting the assembly, NOT entering it. So....I installed one more check valve, this time on that line and oriented so that fuel can leave the assembly but nothing can enter it (fuel or air) from the return line. See attached image.

I then ran the tractor at high throttle for about 2-3 hours today (end of year field mowing). NO DROP IN THE FILTER ASSEMBLY! Just as important, there was no loss of power nor any signs that pressure was building anywhere in the system (no leaks, no popped connections, nothing).

What I learned from this process (beside now really understanding the fuel delivery system) was that the source of the air into the filter bowl was DEFINITELY coming from the return line orifice at the top of the assembly. Adding the first check valve (preventing air from being suctioned down the return line from the tank) DID NOT FIX the problem. Surprising, as that seemed the logical source of the air. Adding the second check valve (on the short section of the return line that runs directly into the filter assembly) DID FIX the problem. Moreover, preventing fuel movement back toward the filter assembly via that return line has (so far) created no problem at all. If that top orifice is really an "overflow", then my check valve will still permit such overflow, as the opening pressure on the check valve is very small (0.07 psi).

I think I can live with this solution and move on. The check valves are cheap, so I'd encourage anyone else with this same problem on a TC to try this solution if nothing else has worked to date.

Thanks all!View attachment 763461

Where dI’d you get the check valves and what part number are they?

 

[jedjoe]

I got these check valves from Amazon. Here is the link to the correct product.

https://www.amazon.com/dp/B087PFHNTZ?psc=1&ref=ppx_yo2ov_dt_b_product_details

There are metal valves that would probably be more durable, but I went with these for two reasons: 1) It was an experiment that I didn't know would work and thus didn't want to waste money if ineffective; 2) these were the only valves where I could clearly determine a small opening pressure. I didn't want a valve that would require too much pressure to open. These valves have a documented opening pressure of 0.5 kpa or 0.07 psi. There were some nice aluminum alloy valves, but their opening pressure was 2.9 psi (or 20 kpa) and I was afraid that would be too high a pressure to operate on these low pressure return lines.

 

[jedjoe]

Have now used the tractor for high throttle work for more than 15 hours with no loss of fuel height in the filter bowl and no compromise to the workings of the tractor. I think I can now recommend that anyone out there with this same problem could use my fix; namely, two low pressure check valves with one preventing suction flow from the return line to the tank, and the other permitting only outward flow from the filter assembly out to the return line.

 

[jedjoe]

This is just an update on the solution above. It has now been over three months and a couple hundred hours of tractor use. I've had no further problems with the fuel lines and filter bowl assembly since installing those two small check valves. While I still cannot say definitively WHY the problem occurred (and has occurred apparently with my other TC owners), the above fix really did FIX the problem. Happy holidays all!

 

[Steve in ATL]

Attached is a diagram of the fuel system and a description of how air is bled from it.View attachment 761130

I ran across this thread because I have / had basically the same issue. Here's something interesting: I have a 2000 model year TC 35D. In the repair manual for the above section (Fuel Flow Chart), MY manual shows the Lift pump *ahead* of the fuel filter (with everything otherwise the same plumbing-wise).

This makes me think that the original design intent was to have the fuel bowl / filter pressurized. Which would make a return line to the tank necessary.

As the tractor's fuel system is currently constituted (as per your diagram, with the lift pump *after* the fuel filter, there is no need for a return to tank line from the filter bowl to the tank - the main supply line would provide all the equalization of pressure needed. It's ONLY purpose would be to provide a path out of the filter bowl for AIR, not for fuel (which should never be needed).

Thoughts?

 

[jedjoe]

What you say makes complete sense. In my case, however, air was definitely ENTERING, rather than leaving, the filter bowl assembly. The check valve solved that direction of flow, while still permitting either air or fuel to leave it. What makes this so weird is that the original arrangement (no check valves at all) worked perfectly fine from 2004 until 2022, when the symptom first appeared. A real head scratcher! My “fix” is still working, so I’ll take what I can get!

 

[Steve in ATL]

My thought is that as the main fuel supply line ages and degrades, restriction goes up and flow goes down. When that results in there not being enough fuel supply to the bowl, the suction from the lift pump draws air down the relief / return to tank line as you originally posited.

 

[jedjoe]

Your theory of increased friction in a degrading line makes perfect sense to me. If the lift pump produces a constant suction at the intake and pressure on the output side, then that friction in the main line would create resistance and the pump would seek a source of fluid or air to compensate. Hence, air being pulled down into the filter bowl from that return line extension. Once I installed the one way valve on that line, the lift pump had no other source for the suction than to pull more forcefully from the main line. If the friction isn't too high, it could do it. That's probably what is happening!

 

[BlueMachine]

Thanks for this very comprehensive analysis.
I'm having a similar problem except that in addition to a nearly empty filter bowl, mine loses power while mowing on slopes but does not stall unless I refuse to push in the clutch.
You've given me some new ideas for things to check.

 

[Harry in Ky]

Thanks for this very comprehensive analysis.
I'm having a similar problem except that in addition to a nearly empty filter bowl, mine loses power while mowing on slopes but does not stall unless I refuse to push in the clutch.
You've given me some new ideas for things to check.

I still maintain that the check valves are just overly complicating the situation. If you have good supply from tank to filter base, then eliminate the vent hose entirely. Cap both ports it's now connected to, and go back to work. The issue will go away. It has in every case I've been involved with.