'97 Passat TDI Build

[Caddylackn]

My next mod is to add 4"-6" strakes between the rear tires and the diffuser to clean up the air going through the diffuser. I may extend it to curve close to the front of the rear tire to block some flow to the tire.


something like this:



I will re-use the 6" lawn edging I removed from the air dam, I have to find a good way to attach it to the coroplast. I probably will have to remove the undertray to put a steel stud reinforcement strip to hold the strakes in. The coroplast is curved and the lawn edging doesn't curve well in that direction. I will try the heat gun and stretching the bottom edge. The exhaust tip is rattling on the metal diffuser opening and I will bend the metal up.

The center strakes are really for structural support to keep the curved surface and are not doing anything with the air flow. I probably will cut those flush.

But first I have to figure out what is rattling and scraping while driving. It gets louder as I go faster, so it has to be the wheel. Sounds like right rear wheel. Doesn't look like the skirt is rubbing.




Unfortunately I did not refill my tank and get my gas mileage before my heater core job. Didn't occur to me that I would lose my odometer reading when I unhooked my battery and removed the instrument panel. Rats, I had at least 650 miles on the odometer, probably closer to 700 miles.

And double rats that my blend door for the heater is hanging up and I still have some heat on in the car while driving. There is no way in hell I am pulling the dash apart again. I may just bypass the heater core until it gets cold out, then hook it back up when it gets cold.

[Piwoslaw]

Looking through the last page got me fantasizing about A-B-A-B testing of that air dam.

One series of tests to see the effect of the stock, dirty underside, and another to see the effect with/without the air dam when you have the undertray.

[oil pan 4]

Air dams give most of what you would get with a full belly pan but with about 10% of the work, materials and hassle.

[seuadr]

nice! thanks for sharing!

[Caddylackn]

The edge of the coroplast with the sheet rock corner support on the left, screwed to the framing strip on the right. Viewed from upside down.





Here is the undertray deflector that diverts flow back out of the exhaust tunnel, viewed upside down, see below.

The deflector goes around the exhaust pipe and is to keep air from going under the undertray via the exhaust tunnel. The main flow through the radiator will make it through the tunnel around the cat where it will hit the deflector about 1' past the cat. The deflector is held together by gorilla tape but that won't last too long. I will make a duplicate shield in sheet metal to replace it when this one fails.



There is a slight exhaust leak where my cat back exhaust attaches to the factree exhaust pipe. It is only a slip on U bolt connection. I need to fix the small leak as I can smell diesel exhaust fumes slightly now, when stopped at lights. Must be exhaust fumes trapped under the undertay. No smell when driving though.


So far I have seen a 13% bump in trip gas mileage with the installation of the undertray on my commute. Some of this bump is probably from the new front wheel bearings (one was bad), and some may be from the improvement of the undertray to the diffuser. The diffuser was installed first, which kind of traps air until the undertray is installed. I also have new rotors, the old ones were warped which may have caused some drag.

There is no doubt that I can coast farther with the undertray, and my terminal velocity of hills has increased where I need to use brakes now in a few places where I never needed to before. It accelerates much faster coasting on hills. Also after disconnecting my battery to do the heater core, when battery hooked back up, my idle fuel usage went from 0.16 gph to 0.12 gph, so 33% less fuel used now when coasting. I must of cleared some code. It got rid of an excessive vibration at idle.

[Arctic Fox]

I had a Passat once. A B5.5

Every time I looked at it, I wanted to beat it with a baseball bat.

It was the worst car I have ever known - it made me hate Germany.

Strangely, the one [and only] time it drove right and didn't give me any problems is the day I finally took it to the junkyard.

[Caddylackn]

Originally Posted by Arctic Fox

I had a Passat once. A B5.5

Every time I looked at it, I wanted to beat it with a baseball bat.

It was the worst car I have ever known - it made me hate Germany.

Been there, agree 100%. I parked mine for over 7 years after getting another vehicle. I had no intentions of driving it again or selling it whole for next to nothing, but was keeping it for the TDI 1Z drivetrain only for a swap, like into a Caddy pickup, or maybe a Jetta TDI A3. It was on my bucket list.

I only started driving it again recently when it was costing me towards $100/week to drive my Crown Vic. My passat has only two working doors and no windows that work correctly. The driver's window won't go up all the way and slips on stripped gears, one window is unhooked from the motor (since it is shorted to stay down) and slides down when the wedges come loose, Passenger front window is cocked at the top and protrudes out of the track an inch at the top, and passenger rear window won't come up if lowered all the way and only works off the door switch.

My cruise control doesn't work, and my heat is currently stuck 25% on. My a/c isn't working and most of the plastic interior pieces are cracked or has a broken piece out of it. Until recently I only had one working speaker and no heat and a leaking heater core. The stock head lights completely suck and are down right dangerous without auxillary lights. My first gear synchro is about gone, and my second gear is starting to grind. The brakes suck though, and no ABS. Parts are expensive as new Audi parts and there is no longer a supply of Passats at the junkyard, they have all been crushed. Not many older Passats left on the road, the owners have given up on them.

If you lower your expectations, it isn't too bad as a commuter. It actually handles really well and feels stable at speed, and has a ton of cargo room for hauling sh.t. If you don't care about your interior or working accessories, doors, or windows it makes a good dog hauler or muddy bike hauler.

[Arctic Fox]

Lol! I had a bunch of similar stories with my Passat, too. 😁

The first was a CEL that no one could fix. I took it to the VW dealer, the mechanic came out, said "this is a Passat."
I said yep.
He said "nope."
"What do you mean, 'nope'?
He said, "Every Passat between [years] gets a CEL and no one can figure out why. Scrap it and buy a Toyota."
He wouldn't work on them!

Timing belt tensioner gave out on I-40, miles between cities, in a snow storm. $400 to get it back home. Found out the valves got crushed and piston heads scored.

The alarm system would randomly close all windows and lock the car (the tire dealership was pissed when this happened to them, with keys in the ignition).

Or, usually sometime in the night, the alarm system would disarm itself, unlock the doors and lower all the windows. I come out the next morning and everything is opened up.

The rust underneath!!

I held onto it for about two years after buying another car ('08 Dodge Caliber R/T) because I was thinking of converting it [somehow] to all electric. But my hatred for it got me to just junk it.

🔥🤬

[freebeard]

Or, usually sometime in the night, the alarm system would disarm itself, unlock the doors and lower all the windows. I come out the next morning and everything is opened up.

Now there is a car with a sense of humor.

[Caddylackn]

Some A B A B A B A B A Testing results with the full undertray and no air dam.
compared to A B A B A B A B A B results with the air dam and diffuser only.

-Using Scan Gauge II trip, no fill up yet.
-Using my GPS speedometer my car is showing about 3% off (speedometer reads high) so Scan Gauge II is probably reading 3% high. Not calibrated yet
-A = ride to work 20.8 miles.
-B = ride home from work 20.8 miles. 1,400' elevation gain 1,500' elevation drop (100' net elevation drop) to work, 100' net el' gain home.
-Drives are 57- 60 mph on interstate (speed limit of 60 mph), and 45-50 mph in 45 speed limit. About 2/3 of the commute is interstate and 1/3 at 45 - 50 speed limit.
-Coast in neutral with engine on, as much as possible. About 1.5 miles of trip is 30 mph speed limit and steep.

At least 3 miles of entire trip is just coasting.

With air dam and diffuser;

To work (trip mpg)..............Home (trip mpg)
67.9 .................................64.3
71.7..................................67.7 3 mile shortened trip
66.9..................................62.2 3 mile shortened trip
68.2..................................64.2
68.3..................................69.4

With Full Undertray tied to diffuser
78.2....................................77.4 To work from gas station to work only
81.7....................................76.1
83.7....................................78.6
82.5....................................79.4
81.8....................................79.5
85.3...................................... - New all time high trip this morning

I can easily see the difference driving and coasting. I can reach 75 mpg on flat road at 60 mph and I can coast way farther now. I am getting 35 mpg on the big hills that I used to struggle to get 32 mpg on. I can now link several shorter coasts into one long coast.

I did install new front wheel bearings the same time as I installed the undertray so that does skew the data a little.