Oil Leak AG4 01N: Troubleshooting & Location

Hey everyone,

My AG4 fuel pump in my Audi A4 (engine code AFN, manufactured in December 1998) is malfunctioning. (Mileage: 280,000 km)

'I've been experiencing a significant oil leak for the past few days. After it became so heavily oiled (and covered my garage), I replaced the transmission pan gasket (including the oil). However, that didn't solve the problem. I simply couldn't pinpoint where the leak was actually coming from.'

Somewhere in the front area, near the transition between the motor and the AG4 unit.

From the top, everything is dry, but from the bottom, it's dirty. The front right axle shaft is damp, and underneath it's wet; somewhere around there is where it's leaking. But it's definitely ATF oil coming from the transmission, not from the differential. The color is red, like fresh, new oil.

I'm confident about this because now, after the oil change, it smells quite strongly of fresh ATF transmission fluid, which wasn't the case before; the old oil had already started to smell bad.

Does anyone know of a common weak point in the transmission that is prone to leaks?

I suspect the propeller shaft on the right side is running in differential gear oil, not in ATF oil, correct?

If it's running in the ATF (Automatic Transmission Fluid), then it would be the seal.

I've now been able to pinpoint the problem; it only occurs when the device is warm, but then it happens constantly.
It's leaking right in between the transmission block and the engine block.

I suspect there's a leak at the transmission inlet. That's probably where it's coming from.

Okay, removing the gearbox.

Or does anyone have a better idea?

Hello,

There is a shaft seal located at the inlet of the ATF pump (transmission input shaft) - part number 095 321 243A, radial shaft seal 51x65x7, approximately €10 - which is easy to replace after removing the transmission or engine. However, there is also an O-ring (0953 321 386) and a gasket (01M 321 385) located beneath the ATF pump, where this seal sits, which can also leak.
You should also have 3 new nuts (M10x1, part number N102 223 01) on hand to secure the torque converter to the flywheel, as well as 2 sealing rings (N906 660 01) for the oil cooler lines. It's also helpful to have a filler cap (01M 321 423A) and a retaining clip (01M 321 435A), as well as a new oil pan gasket (01N 321 370), an intake filter (01M 325 429), plus a sealing ring (01m 325 443). Personally, I won't use any filters or gaskets from the aftermarket. Last time on my G4, I had to reinstall the oil pan several times until it sealed properly with a VAG original gasket. The gasket from a well-known filter manufacturer was clearly too soft and twisted inwards after a few days, causing a slight leak . Because of all the removing and tightening, the thread then became damaged, and I had to install a Heli-coil.
By the way, Ravenol offers ATF products with the correct specifications at reasonable prices.

Please verify the part numbers for a Passat manufactured in 1998 with an AFN engine and a DMX AG4 transmission.

Regards,

Jürgen.

Hello Jürgen,

'Thank you. I had already resigned myself to scrapping the car because a transmission specialist told me that the input shaft seal was leaking due to a defective input bearing.'
Therefore, a complete overhaul would be necessary.

Is there a way to determine the difference between just a shaft seal (Simmerring) and an input bearing?

Hello Garth,

I looked at the pictures and I can imagine that a faulty bearing in the ATF pump could also cause quite a problem, leading to reduced pump performance, which would impair the proper functioning of the transmission. Also, I'm surprised that it only happens when the transmission is warm. Taking out the transmission, replacing the oil seal, and reassembling everything isn't rocket science – I estimate it would take about a Saturday on a lift. It might be worth trying.

Regards,

Jürgen.

Still available: Passat Variant AFN/AG4 and Golf 4 AHF/AG4, both manufactured in 1999 and with approximately 290,000 kilometers on the odometer.