MK1 gas conversion to diesel

DieselAlltheWay · Post by **DieselAlltheWay** » Fri Jun 25, 2010 1:14 am

Here's the next project that we're very close to starting and could use some advice, especially from folks that have done this, like Fatmobile and I'm sure others.

Car is a gasser 90 Cabrio. Donor cars: a 83 Jetta NA diesel and a 94 Golf TD (1.9L of course).

History: as someone that wants to go diesel all the way

the obvious thing to do is to convert a gasser Cabrio into a diesel. After successfully putting in a 1.9L into the 84 Rabbit TD, myself and my expert young VW friend mechanic are going to attempt to put this superb powerplant into this topless MK1. I was lucky to find a running 83 Jetta diesel for virtually free. And luckier to have found a superbly well maintained and beautifully driving 94 Golf TD for FREE

So I saved the fuel cell and all the lines from the diesel Jetta, along with several other parts. First and most important question is: do I really need to replace the gas tank in the Cabrio with the "proper" diesel one? It was a major pain in the ass to just remove the one from the Jetta and I'm not looking forward to replacing the cells unless needed. Heck, removing the line alone was a very difficult thing and I'm not even sure if I need to replace that too.

This is the first big question of many to come, I'm sure.

tylernt · Post by **tylernt** » Sat Jun 26, 2010 1:04 pm

I'm doing an '88 Jetta gas-to-diesel and will be using the original gasoline tank. As long as you replace any rubber fuel lines with diesel-compatible material, I don't forsee a problem.

DieselAlltheWay · Post by **DieselAlltheWay** » Mon Jun 28, 2010 1:23 am

Possible issues with fuel delivery as the diesel work on a gravity basis, contrary to the gas one that requires an electric pump. Some people even drill a hole at the bottom of the tank and connect the line there, which may mean you cannot run too low on the tank and possible issues with the indicator gauge.

The more I read up on this the more I think I'll stick to swapping the tanks. It's a bitch but at least it would be done right.

BlueDog · Post by **BlueDog** » Mon Jun 28, 2010 8:33 am

When I did my conversion I took the diesel tank out of the '86 Golf donor car and installed it into the '89 Jetta. It wasn't that bad of a project. Fussed around with the straps and bolts. Would have been easier with a helper. Strangely, I ended up not installing the water separator. Had too many air leaks when I tried. Been running three years without it and no worries.

82vdub · Post by **82vdub** » Mon Jun 28, 2010 9:03 am

Will a Golf or Jetta tank fit in a Cabrio chassis? Isn't the Cabrio gastank even different than a non-convertable Rabbit's tank? If it were me, I would install a $50 low flow low pressure pusher pump in the fuel line to pull the fuel from the tank. I've got one of these on my old winter Jetta to solve a siphoning issue years ago. No problems.

Concerning the fuel lines, if a line is rated for fuel, is there a different rating for gas v's diesel? I'm not aware of any difference in rating as any vacuum line that's purchased at the auto store is rated for fuel systems, with no specification to gas or diesel. Biodiesel is yet something different. Am I wrong on this?

BlueDog · Post by **BlueDog** » Mon Jun 28, 2010 9:11 am

I for one can't speak about the Cabrio chassis; just don't know. But the Golf tank fit the Jetta like a glove. Obviously VW engineering designed both cars to use the same tank. I'm not aware of specs nor ratings but biodiesel fuel requires use of Viton hoses and seals. Standard fuel line gets mushy falls apart eventually.

tylernt · Post by **tylernt** » Mon Jun 28, 2010 10:28 am

I'm not sure of the materials science either, but I recall the Bentley has a caution against spilling diesel on rubber coolant hoses, as it degrades them. Viton is probably the way to go, petro- or bio-diesel.

82vdub · Post by **82vdub** » Mon Jun 28, 2010 10:45 am

Fuel (gas or diesel) does degrade certain types of rubber. But, if the hoses are rated for fuel, fuel doesn't degrade them. Coolant hoses are not rated for fuel and do degrade when fuel gets on them. A fuel rated hose is always rated for gas or diesel as far as I know. You get into alcohol, methanol, ethanol, and some of the other more exotic types of fuel, and there's likely different ratings required. I'm more referring to the common types of fuel, gas and diesel.

DieselAlltheWay · Post by **DieselAlltheWay** » Mon Jun 28, 2010 1:05 pm

Good question as to whether or not the fuel cells are a match. I am assuming so since they share the same chassis. Of course as per my other thread the last time I ASSumed something with VWs it bit me in the ass.

Anyone knows if the cell from a 82/3 diesel Jetta would fit a 90 Cabrio? Any easy way to find this out short of pulling them off?

I suppose adding the low flow pump to be an OK way to go although I'd rather not have yet another part that may fail in the future. This discussion has also confirmed that if I do stick with the gas tank in the Cabrio that I hope not to have to switch the lines, seeing what a headache it is to fit the metal lines from the diesel.

82vdub · Post by **82vdub** » Mon Jun 28, 2010 1:07 pm

DieselAlltheWay wrote:Anyone knows if the cell from a 82/3 diesel Jetta would fit a 90 Cabrio? Any easy way to find this out short of pulling them off?

hollander interchange manual should say what fits what. A call to a salvage yard will probably answer what fuel tanks will fit into a 90 Cabrio.

surfcam · Post by **surfcam** » Mon Jun 28, 2010 1:30 pm

Hit Pick-and-pull in the morning and they should have time to print it off for you.

82vdub · Post by **82vdub** » Mon Jun 28, 2010 5:46 pm

I have an 84 Hollander foreign interchange manual. It's the newest foreign one I have.

According to this manual, here's the following:

- #52709 - fits 82 Rabbit gas (exc pickup), 82 Jetta and Scirocco, 83 and 84 Rabbit (fuel injection), Jetta (gas) and Scirocco
- #52710 - fits 83-84 Rabbit with carb
- #52711 - fits 82-83 Rabbit diesel (exc pickup), 84 Rabbit diesel and Jetta diesel

Clearly the Jetta and Rabbit shared the same tank under some situations, but I have no information on anything newer than this. The interchange manual went back to 1975, so the early Rabbits had a different tank in them.

Post by **Fatmobile** » Mon Jun 28, 2010 10:29 pm

I think the cabby tank has a pusher pump in it.
There's a chance that it won't cause a restriction if you don't power it,.. and a chance it won't push TOO hard if you do use it.
Either way the external fuel pump will need to be removed.

I'd try to use the cabby tank,.. and it's internal pump if it will work.

Quantum TD · Post by **Quantum TD** » Sat Jul 03, 2010 10:20 pm

I've thought about this in the past. If it were me, I'd get a Rabbit convertible gas tank up to 1984. Those years had a gravity feed to the main external pump. So, essentially, it's just like a diesel tank.

Cabriolets from 1985-1993 had internal pumps that fed the from the bottom of the tank, out the top of the tank, despite using the exact same fuel system (CIS).

That would be the easiest.

Now, would your 84 TD tank fit in there??? I think you can make it work.

Be advised, you'll have to drop the rear end if you swap out the tank (at least that's the case for most MK1 cars).

bscutt · Post by **bscutt** » Sun Jul 04, 2010 9:42 am

Yes it took me 7 hours Friday to swap the tank in my 79. Not a fun job but if you disconnect the rear brake lines and drop the front swing arm bolts, then remove the exhaust hangars you have room to get the tank out with some finagling. ON the diesel there are 5 lines going to the tank plus the filler hose.