And so it begins! TDI Syncro conversion

[Christopher Schimke]

Due to time constraints, this probably won't be an in depth log of my conversion, but I'll try to hit the highlights.

This the thread that started it all - http://www.thesamba.com/vw/forum/viewtopic.php?t=644299&highlight=conundrum

There is a TON of good info in that thread, but I decided to peel away from that thread for my actual conversion. Thanks to every one who contributed to that thread. Seriously awesome content! I'm going to cross post just a little bit, but I'll try to keep that to a minimum.

I'll have a bit more to share later, but this is my first hang up. I have an NOS diesel Syncro Doka/Sika fuel tank to use in the van. The van tanks and truck tanks are identical except for the fuel filler holes. Since this is a brand new tank, there is no baffle in it. I need to transfer the baffle from my van tank to the truck tank. The question is -

Why doesn't the diesel tank use a internal hose on the end of the return line inside the tank and the gasoline tank does? Did the gasoline return hose actually enter the baffle through the hole in the side or was it just pointed at the baffle? Any reason not to install a return hose on the diesel application?

The gasoline tank uses a filter at the baffle, but the diesel tank does not. The diesel tank just uses a plastic bolt to hold the baffle in place while the gasoline tank uses the filter itself to hold the baffle. I don't have the diesel-specific plastic bolt that holds the baffle. I'm going to use the gasoline filter to hold the baffle in place, so should I just reinstall the gasoline filter as is or cut away the filter screen?

Click on the following pictures for a larger image.

Diesel tank routing -

Gasoline tank routing -

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[Zeitgeist 13]

Fifteen or fifty?

[syncrodoka]

Fitting for inside the tank without using the filter.
http://www.foreignautosupply.com/parts-accessories/39-syncro-in-tank-fitting/#.VyamjPkrK70
I have no idea why they don't use that filter in the diesel version. Doesn't diesel change viscosity in the cold?

The gas version in tank hose does feed into the reservoir cup through the hole at the top

Good to see some kind of a build thread come out of that thread.

[Christopher Schimke]

[Zeitgeist 13]

Oops sorry, for some reason I thought you had an ALH. My question is invalid

[syncroserge]

[hans j]

Yay!

I don't think my baffle or prefilter is in there. Definitely doesn't have the return hose anymore... No issues for me. You can drive over 1000 feet with only the fuel in the filter, so a swirl pot is not needed in the tank.

And even though I raised the decklid for my 15* conversion, I have 11 inches of ground clearance at my skid plate, still with only an 18.5" center to fender ride height
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1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181

[IdahoDoug]

Besides the thickening of diesel at low temps accounting for the different tank strategy, the only other thing I can think of is the higher incidence of water contamination in diesel fuel. Perhaps it can freeze in the bottom of the tank? Dunno.

Looks like the beginning of a great build thread. Bravo!

Doug
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[ALIKA T3]

[Waldi]

[Christopher Schimke]

[lloydy]

Looking forward to following this

Will be rebuilding a spare 1Z engine myself soon.
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[flomulgator]

Christopher,
The in tank pre-filter would be a bad idea (heck I barely know why it's there in the gasoline version) because in a partially-gelled situation it would quickly clog the filter and stop flow if you accidentally push the envelope of diesel #2 in cold conditions (<20 degrees). This is even more true of pure biodiesel, take a look at this article on cloud points: http://articles.extension.org/pages/26611/biodiesel-cloud-point-and-cold-weather-issues

I'm naive to VW diesels but I've run an American truck for a while. It sounds as if just using the injection pump as the sole fuel pump is actually an option for VW builds?! That's something I would never consider; although a mechanical injection pump has the strength to pull thick diesel all the way from the tank (and up 2 feet in a truck), it is very hard on the pump in the long run and because you are sucking on the lines rather than pushing on them it could potentially introduce air into the lines which is no bueno. Also bad on fuel filtration, which is actually pretty important on a diesel due to the nozzle size on the high pressure injectors (and the fact that it could be running on used cooking oils, used motor oil, used ATF, kerosene, etc..) Trucks use a lift pump at the frame/bottom of engine that is very high flow rate, push diesel up and through a fuel filter (with integrated air purge at high point) and then on to the injection pump. The location of the pump also warms things up a bit.
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[Waldi]

Just to say it, a pre pump is not a must for our diesel engines. But it makes it sometimes more easy.

I have it installed primary because i drive with pure raps oil.

You cant use every kind of pump. It needs a self regulating pressure.

I use this one:

http://www.monopoel.de/catalog/vorfoerderpumpe-anschluessen-p-418.html

[MarkWard]

Algae and Fungus seem to thrive in diesel fuel. We had a generator backup for the company I worked for, and once a year, a company would come and clean the fuel we had stored on site.

I have no experience with the Syncro, diesel, but will be starting my project sometime this year. On my 2wd Vanagon diesel, from the factory it was fitted with a serviceable fungus filter in the tank. These were also found in Rabbits and Jettas of that era. They would collect so much fungus, that you'd have to remove them. Eventually VW sent a bulletin to permanently remove the fungus filter. On a rabbit, you could pull the back seat and the inspection cover over the fuel sender to access this screen. Not so easy on the Vanagon. I believe VW felt that the external filter was better suited for catching the crud from the tank and easily serviceable.

I have just acquired a used syncro tank from Europe. Thank you Karl. The return does go back into the tank via the sender. In my case the hose fitting on the sender is snapped off. For a return, I prefer to have it return under the fuel level. Diesel is prone to frothing and splashing the return fuel on top of the surface does not help the frothing. I am planning on using a gasoline sender since they are available and then using one of the two fittings to return the fuel.

Good luck Christopher. mark
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[MidwestDrifter]

Bacterial and Fungal growth occurs when liquid water is present in contact with diesel fuel. The microbial growth occurs at the water/fuel interface.

This growth can produce mats and fibrous material that can plug filters. For vehicles not fitted with a lift pump, a pick up screen is not strictly required, and can be disadvantageous in some situations. For example the microbial growth (fairly rare in vehicles with good fuel turnover) can plug the pickup screen/filter in the tank. Ice crystals from free water can also plug the pickup (though they may just as easily plug the main filter).

All that being said, for a vehicle that has regular fuel turnover, microbial growth is not a major concern. Having a pickup screen can prevent large contaminate particles from plugging the main filter, however in the event that the in-tank filter becomes blocked, it is very difficult to service.

For myself, I would personally install a pickup screen if it was reasonable to do so. I would not worry about dropping the tank to add one unless I was having problems.

In aircraft fuel tanks, the altitude changes and storage conditions on the ground make water accumulation a real problem. The resulting microbial growth wreaks havock with fuel control systems. We regularly test the aircraft fuel tanks for microbial growth, and administer biocide whenever it is detected.

My 2 cents worth.
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[ALIKA T3]

[vwwestyman]

Interesting discussion so far. Here are my general thoughts on the fuel system. I did a 1.6 NA conversion in a VW Cabriolet years ago and drove that for several years. I even mixed veggie oil in the tank 50/50 for most of that time (except for cold weather months) and more recently did an e-TDI conversion in my '78 Bus.

I would say that it is probably technically most "correct" to copy the diesel fuel system of the vehicle you're converting. However, I feel like I'm reading a lot of angst over things that in all practicality don't matter too much...

In the Cabriolet, I removed the fuel pressure pump, but left the in-tank lift pump as-is other than removing the screen (for the reasons mentioned). The lift pump was wired to be on any time the engine was turned on. This did prove handy for fuel filter changes (which I did a little more frequently owing to the veggie oil). It made purging air from the lines a snap.

I didn't really do anything with the old evaporative emissions system. I may have removed the charcoal canister but that was about it.

In the Bus, all I did was mount the TDI filter kind of lowish in the engine compartment. The fuel gravity feeds into the filter (so filter changes are easy-peasy) and returns using the factory return outlet in the tank. There are no socks or filters in the tank, and I think the outlet/return are both just open into the tank though there is a little bit of a baffle around it.

The easy to access water drain on the bus makes it real handy to draw off a little diesel fuel in the event I want to start a camp fire and the wood is a little wet or something.

All the factory tank venting is present on the bus all the way to where the charcoal canister was. Now it is just open to the atmosphere.

I have experienced no driving problems with either fuel setup. I suppose the fuel did warm up, but as far as actually driving I never noticed a difference.

I drove the Bus yesterday an hour each way with less than a quarter of a tank and didn't have any problems that might have been indicated by warm fuel.

I know that in even 5 gallons, the fuel will warm some over an hour's drive... Back when I was driving the Cabriolet, my usual procedure was to wait until the tank was low enough to need about 10 gallons to fill. I'd put 5 gallons of filtered veggie oil in the tank, and immediately drive from my house to the station to top off.

One time I had been working outside and needed to drive an hour away. I decided to do the veggie part just prior to showering and then was going to top off on the way out of town. Except I forgot to top off!

So about as I got on the highway, the fuel in the filter and pump had been worked through and the 90-degreeish (ambient temp) oil worked its way to the engine. I lost power for a while but over the course of the trip, the oil warmed up and I gained power back bit by bit. And I topped off when I got there!

Anyway, all that to illustrate that while it might not be "technically correct" I don't think one has to fret too much about making major changes to the fuel system when doing a conversion.

YMMV
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1978 Champagne Edition Westy, repowered to '97 Jetta TDI
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[MarkWard]

I did not realize the senders were different either, until I had a used diesel one sitting in front of me. The diesel sender has a hole where a hose barb would have been. It must have broke off when it was removed from the donor.

My gas sender is not working properly and I intended to replace it during the conversion. I don't think it is an issue adapting the gasser sending unit, you just pick one barb as a return and cap off the other. I should add, I am not speaking from any real experience only what I noticed recently.
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[hans j]

I am using a gas sender still on mine, without a hose on the other side. No discernible issues with frothing or anything else. No issues with fuel temp that I can see either. Fuel temp is only calculated in the ALH, there isn't an actual sensor for it.

Lift pumps are nice to add fuel to a new filter, but I've just been pouring old fuel out into the new filter. In over 15 years working on VW TDI's, I have probably only once been able to see any water come out of any fuel filter. Maintenance says replace every 20k and drain every 10k. I did a lot of services and checked for moisture a long time ago, never really stood out they were getting moisture in them.

The only thing I did different with mine is routed the over flow hose to before my air filter. It still gets mostly filtered air from my pre filter. I also added a Mk3 TDI one way valve before the fuel filter to prevent fuel from siphoning back into the tank. I don't know if that was the issue that I was having, but when I was first sorting my conversion, that seemed to fix an issue I was having.
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1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181