Air in the Fuel Line

[Car959]

Hello TDI Club,

I am new to the forum but have benefited significantly from the threads regarding the MKIV. I am "remodeling" a 2000 golf TDI ALH/Manual transmission with 239k miles. I replaced the motor mounts, water pump, timing and serpentine belt, clutch, alternator, steering rack, one axle, vacuum pump, rear brakes, fuel sending unit, fuel filter, battery and the fuel line going from the injector pump to the filter.

My suspicion is that the car was owned by someone that thought they were a TDI expert. NOT! There were several modifications including an EGR delete, a manual transmission swap to a CIN tranny out of a Jetta and some weird modifications of the glow plugs I haven't figured out yet.

That being said, the problem I am having is consistent "champagne" like bubbles in the clear fuel line that runs from the injector pump to the filter.

Is this normal? Full disclosure; I did not do all this work myself, but had much of it done at a local shop that did not necessarily specialize in VW TDIs.
Any ideas would be greatly appreciated.

 

[AndyBees]

There is a Thermostatic Tee (T) at the fuel filter. Fuel from the Injection Pump returns to the fuel tank via that T. If the ambient temp is cold enough, the T will re-cycle some of the warm returning fuel back into the fuel filter for obvious purposes.

The T has two O-rings that are prone to allow air to be sucked in. The Injection Pump has a very strong internal centrifugal pump. So, it's suction can pull air into the filter via those O-rings. The good is that the air is filtered. The bad can result in hard starts.

Yeah, you should find the correct transmission for the TDI engine.

Welcome to the club...

 

[Car959]

Thank you!

Should I replace the O rings with something thicker? I read on one of the threads someone did that. Or, replace the fuel filter?

Also, if I replace the fuel filter, should I fill it with Diesel Purge?

 

[AndyBees]

Anytime you change the fuel filter, you should fill it with Diesel Fuel. Diesel Purge is okay but will not solve the air issue.

Yeah, you can replace the O-rings and give it a try. I'd do that before doing a fuel filter change. The filter is not the problem unless it has not been changed in 100 years...... point is, throwing fuel filters at it will not solve the problem. I wish I had invested in the #1 fuel filter company when purchased my first VW Diesel back in January, 1980. The consensus (pun intended) of TDI owners is to throw a fuel filter at any problem under the hood ........ easiest thing to do but with newbies (especially) results in more problems because the procedure gets botched more often than not (air in the IP, fuel pipes to the injectors, etc.).

For what it is worth, my brother let the original fuel fuel go for over 171k miles on his 01 Jetta TDI with zero issues (lives in North Georgia). I have that engine, totally intact, including the IP, in my 03 Jetta with over 325k miles on it. With my formerly owned 2000 Jetta TDI, I always changed the fuel filter in November or early December so it would be fresh for the winter, regardless of miles (generally it had 36k miles or more). My son owns it now and it is pushing 389k miles.

I suggest that you purchase a new Thermostatic T which will come with the O-rings. In the meantime, if the engine is starting and running fine, just drive it until the T comes. Then, install a new filter at that time.

Also, check the rubber hose connections on the filter. Those things are 22 years old....... cracked and may not be sealing well. I'd wait for this procedure and do it when you get the new T.

Summary options from my ramblings:

1. Change O-rings (this would be the last option that I'd attempt and I've never done it)
2. Install new T with new filter (unless the filter is fairly new)
3. Check the hose connections at the filter (when you install the new T and filter)

Lastly, if all the above fails, there are connections to the fuel tank under the back seat. Remove the seat and then remove the round cover ......... you will see the connections. I've never had an issue there.

 

[Car959]

Thank you very much, this is really helpful.

 

[fatmobile]

Air in the line going from the injection pump to the filter???
Or air in the line going from the filter to the injection pump?

Fine air bubbles or foam going from the pump to the filter could be a bad mainshaft seal.
Commonly followed by air coming out the pump inlet when the engine is shut off.

 

[Car959]

Thanks for the info, the bubbles go from the filter to the pump via the clear fuel line. I am not noticing any air coming out of the pump inlet when the engine is shut off.

 

[super1]

Hello TDI Club,

I am new to the forum but have benefited significantly from the threads regarding the MKIV. I am "remodeling" a 2000 golf TDI ALH/Manual transmission with 239k miles. I replaced the motor mounts, water pump, timing and serpentine belt, clutch, alternator, steering rack, one axle, vacuum pump, rear brakes, fuel sending unit, fuel filter, battery and the fuel line going from the injector pump to the filter.

My suspicion is that the car was owned by someone that thought they were a TDI expert. NOT! There were several modifications including an EGR delete, a manual transmission swap to a CIN tranny out of a Jetta and some weird modifications of the glow plugs I haven't figured out yet.

That being said, the problem I am having is consistent "champagne" like bubbles in the clear fuel line that runs from the injector pump to the filter.

Is this normal? Full disclosure; I did not do all this work myself, but had much of it done at a local shop that did not necessarily specialize in VW TDIs.
Any ideas would be greatly appreciated.

Curious to know what a CIN Transmission is?
Was it a Gas or Diesel Jetta ?

 

[Car959]

Not sure about gas or diesel. When we pulled the engine and transmission, CIN was stamped on the top of the tranny casing. It does fit the car, however, the dog bone mount had to be modified to fit.

 

[super1]

You don’t want a transmission that came out of a gas motor the gear ratio be all wrong you won’t be saving any fuel actually using more fuel

What year Jetta?

Are you sure it says CIN ?

 

[Car959]

I’m not sure, however, I am fairly sure it came out of a deisel jetta, possibly a 99 if my research is correct. The car ran really well prior to a motor mount breaking. In repairing the motor mount, one thing led to another and we decided to pull the engine and redo the timing belt, water pump, clutch etc…

 

[super1]

I’m not sure, however, I am fairly sure it came out of a deisel jetta, possibly a 99 if my research is correct. The car ran really well prior to a motor mount breaking. In repairing the motor mount, one thing led to another and we decided to pull the engine and redo the timing belt, water pump, clutch etc…

Ok