Volkswagen 1998 Jetta TDI

Empty Space Under the Car

Once the tank was completely installed, it was apparent that this would be impossible. The HotFox fittings would obstruct all side-layout scenarios, so I moved to the space between both tanks under the car.

This space was eight inches deep at its highest point, which forced the filter head to be horizontally or angle mounted. The filter head was 9 inches tall.

The filter head required a custom metal angle to set it at fifteen degrees. I wanted it to be as steep as possible to reduce spilling oil when a filter required changing, but fifteen was the most I could get.

Next, I placed the 20-plate heat exchanger up against the tank and underside of the trunk floor. To secure it, I fabricated two bent aluminum strips on each side.

If I needed to pull it out for some reason, I could just push back this harness. They hook and connect to the top of the exchanger, which is upside-down.

I thought the fuel pump could still be mounted on the side, but that proved difficult again because of potential hose kinking. A spot directly the heat exchanger worked best.

Glenn predicts my cheapie fuel pump will give out soon anyway, so mounting where it’s easy to remove would be good. I didn’t even bolt it in place; the mounting was accomplished by using some aluminum wire loops.

Hose Routing

Since most of my fittings are all pointed downwards, I needed to be creative to avoid kinks.

AutoZone sells Goodyear brand heater hose coils that are meant to hold a specific bend in a specific location. They slide onto the hose and have a metal backing that retains the desired shape. This is important for my design, for I can’t have any hoses dip below the tank; if it did, not only would I lose all my heat, but also it could get caught on something when I drive.

I found that these coils have a secondary effect that reduces kinking for moderate turns. Since the store-bought coils still have a little play with the hose, it can still kink or stretch, so I used some of my aluminum wire to produce my own. It doesn’t have the backing, but it still works really well if it’s snug.

I would have used more 90 degree bend fittings, but in most cases, it wasn’t possible. The heat exchanger had some crazy custom hose fittings that I could replace.

Exhaust System Bypass Mini-Bundle

For most of the bundle, I used large extruded insulation with Hose-On-Hose (HOH) heating.

This insulation had a wall thickness of 3/4” and averaged a diameter of 3.” There was a small distance from the back of the car to the suspension system that couldn’t accommodate this large bundle.

So before I installed the large insulated HOH setup, I made a thin segment out of 3/8” copper and aluminum bendable pipes. Just in case you don’t already know, you shouldn’t use copper hoses or fittings for the VO system. There has been a lot of research on this topic and copper can react with vegetable oil.

This smaller bundle is probably a better conductor of heat transfer anyway, because I connected the two copper and single aluminum tube with silver solder.

Start of the Bundled Tubes

Since my major HOH bundle starts by the muffler, I was able to make some steep bends in the copper and aluminum tubes from the mini-bundle.

This lifted the tubes up against the floor boards to clear the suspension system. As you can see, I wanted to have a lot of insulation to protect the bundle.

These were 6-foot segments from B & B Hardware and I used zip-ties to make an A-A-B pattern.

The make-up of the bundle comprises three 3/8” fuel hoses (coolant-in, coolant-out, & fuel-supply) and a 5/32” vacuum tube for a VO return.

Potential Rework

The only part of the system that makes me cringe is the mid-section of the bundle. There wasn't a lot of room for a three-inch diameter tube to go for this 3-foot distance.

If you look at Jeff’s configuration, he ran HIH and that afforded him a low-profile system. On mine, it does hang down pretty far. I’m tempted to remove this section and make another mini-bundle to run closer to the floor boards.

If I had to start from scratch, I’d contemplate doing the whole bundle with aluminum 3/8” bendable pipe. It’s only 89 cents a foot and if you can solder certain places together, you’ll essentially have a twenty-foot long heat exchanger.

Glenn said it would be a pain in the ass to route the lines, but since it’s not being tracked inside the car, I don’t think it’s that difficult.

Coolant Return Splits Away

I split the coolant return away from the bundle right behind the passenger-side tire. This saves some space when I set up the front heat exchanger.

From the Image above:

• R: VO Return
• S: Coolant Supply
• T: VO Supply
• U: Coolant Return

Once again, I used a section of the copper and aluminum bendable hose to manage the transition through the fender. If I just bent the rubber hose into the fender, it could kink.

I then re-bundled the three remaining tubes after the interstitial metal segment. Also, this metal area is insulated with reflectix (not in the picture).

Fender Area

This was a good find for hiding the bundle. If you remove the plastic inner fender, there is a whole bunch of room for not just the bundle, but if wanted to install a third heat exchanger, this would be the place.

I’m even tempted to move my front heat exchanger to this location, because the upper left side has a lot of extra space. I don’t have an image of the system with the inner fender removed, but this picture shows how the three tubes work.

Coolant Return

The coolant return hose emerges up the firewall and connects in the heater core hosing in a series configuration with a simple brass 3/8”-to-5/8” reducer. The coolant supply hose (not pictured) runs continuously around the engine and follows the VO lines from the selector valves to the rear mini-bundle.

Later, I came back through these areas and added some lower profile extruded pipe insulation to this line. Due the conversion, the heater core is now the last element in the series circuit. Saving as much heat as possible will decrease my warm-up time.

Also, the image displays the 14-gauge pink wire that is the load for the fuel pump in the rear. I ran it from the back to the front, which may have been a mistake.

Later I found that the Jettas have a few extra slots for diesel supply and return. Look in the engine compartment near the diesel can filter; if you see a blue plastic line, follow that to a metal tube that runs down through the floor boards.

If you can fish your electrical down this path, you can have a really clean system.

End of the Bundle

The bundle completes it run in front of the air filter housing. I found a reasonably-sized hole that accommodates an uninsulated cluster of hoses.

I ran a 5/8” hose from the heater core for the first part of the coolant supply line because I have a theory that the thermal mass will retain more heat.

At the bottom of the air filter housing, there is a heat exchanger that you’ll see later in the thread. The heat exchanger has a 3/4” coolant fitting so this works pretty seamlessly coming directly from the heater core hosing (avoiding a reducer).

This was all post-insulated once the engine portion of the conversion was completed.

Coolant Splice

Heat Exchanger

I realize this is a horrible image, but the center hose is half of the old heater core hose. Since the coolant return came up along the firewall and the coolant supply line wrapped around the engine, it was easier to cut the existing heater core hose in half and use brass reducers to match up directionality of flow.

You’ll notice that the darkest hose (center, below) is the coolant supply hose at 5/8” diameter. It’s connected using a 5/8” 90 degree plastic heater hose bend from Kragen, to the right of the brass fitting in the middle.

Engine Pics

Conversion Source

• Nickpisca.com