TDI install retrospective: Fuel System

Continuing the process of back-documenting what I did to put a TDI engine into an old (1972) air-cooled VW bus. Today's post is all about the fuel system. There was very little that needed to be changed with the TDI. Most of the work was on the bus side.

Tank Preparation

Because the coolant outlet flange and the vacuum pump on the TDI hang over the top of the transmission bell-housing, the TDI cannot be installed without modifying the fuel tank. OR, you will need to change how the coolant flows (super hard to get right) and the source of vacuum. For vacuum, there are belt-driven systems and electric pumps, but the coolant exits the head right there, so there are only so many ways around that. I looked into a custom flange that would route the coolant elsewhere, and even cut up a plastic one in an attempt to make one. I was, and remain concerned about fluid dynamics and whether I would create a situation where the coolant could not escape the engine at the right speed, causing overheating. So, I cut the tank instead. Well, I had someone cut and weld it. I didn't want to blow up.

The cut is 8-sided: straight across (left-to-right) on the top and bottom, straight up-down on either side and then 4 diagonals to join the other cuts. The measurements are at the bottom of the post. Once cut, a new piece of thin steel was welded in to close it off, leaving a depression into which the vacuum pump and outlet flange could nestle. I set the depression deep enough so that my hand could reach between the coolant flange and the fuel tank, so maintenance on the flange or the coolant sensor could take place without dropping the engine. This proved very fortuitous later. Since the old fill-vent is part of the sacrificed part of the tank, be sure to have a new one added.

After a failed attempt at lining the tank myself, I had the tank stripped, steamed and lined by Mac's Radiator. I think it cost me $100US, and it was returned painted with primer. I shot it with "Tank Tone" silver.

After the fuel tank is cut, welded, cleaned, painted and lined, it can be re-installed. The fuel tank install is fairly straightforward. Put the filler hose on the tank before you try to put it in the bus, but omit the clamp. Once the tank is settled in place, strap it down and then connect the fuel level sender and connect the other end of the filler hose. Clamp both ends.

Vent and Fuel Lines

I used Viton fuel lines from the get-go so I could handle BioDiesel. I encourage you to consider the same. The early bus was not shipped with fuel injection, so there was no facility for a return line. I didn't get one installed when I had the tank cut, mostly because I wasn't 100% sure where to put it. I'm still not 100% sure where I'd want it. Instead, I used the passenger side tank vent line for returning unused fuel from the injection pump. If you are similarly converting a non-fuel-injected bus, only re-connect the left side tank vent to the old vent system.

To the bottom of the tank, a nipple is threaded into the lowest point on the tank. The original nipple is quite small. I upgraded to a wider metal pipe insert so it did not limit the fuel flow. To this, I connected a fuel line and routed it along the original fuel line path back to the engine compartment. I was unable to find any pictures of the larger metal pipe; my apologies.

The low pressure lines between the injectors should be considered. If you don't know how old they are, replace them now. I used Viton for all but the stubby on the end which for some reason wasn't available in Viton. Not that it matters, it basically acts like a plug anyway.

Filtration
When I first did the conversion, I connected a clear plastic filter to the hose leading from the tank, and routed the output from the filter to the original fuel filter. Since then, I have replaced the little clear plastic filter with one that is diesel fuel rated and replaced the original TDI filter with a Caterpillar upgrade (See Green Diesel isn't BioDiesel). The original TDI routes unspent fuel back through the filter, increasing the fuel temperature along the way. Depending on your intended use, this could be a good thing. I have routed the unspent fuel directly back to the tank instead, in hopes of keeping the engine and fuel-related parts that little bit cooler.

That's it for the fuel system. It's actually very simple: tank to fuel line to cheap plastic filter to fuel line to big filter to injection pump. The biggest deal is/was removing, cutting and re-installing the tank. It is worth noting that after the cutout, the tank still holds 15 US gallons of fuel. At 30+ miles to the gallon, that is an effective range of 450+ miles per tank.

Tank cutout measurements:
across the top (and bottom) : 9"
top-to-bottom on the left and right sides: 7"
distance from right edge to right-side vertical cut:12-1/2"

Prior related post: Preparation

Next related posts:
Physical Mounting
Vacuum System
Air, Intercooler and Exhaust
Primary Electrical
Cooling
Secondary Electrical
ECU, dashpod and Sensors