Why does my 2002 audi a4 quattro blow white smoke from the exhaust and from oil cap?, i replaced the engine head and turbo not long ago and it started out of nowhere

seems like you are having turbocharger problems the rattling may be coming from your turbocharger as well as the smoke may be the oil which the turbo its burning as it touches your hot manifold, hope this helps you .

It's very simply to find out if the turbocharger is causing white smoke from the exhaust vs a blown head gasket. So, remove the turbocharger's compressor inlet centre hose (from the aluminium side of the turbo). Then see if there's in plenty of oil coming out from the hose and from the turbo. I'm 100% convinced that the turbocharger is damaged in your case. You can remove also the exhaust pipe out from the turbocharger, and see if there's a lot of oil coming out.
Repair or replace bad turbocharger with a new one (or with a second hand in good condition one).
Good Luck!

White smoke is caused by engine oil being burnt. If your vehicle is turbo charged then it is most likely the turbo bushes that are worn, allowing oil to escape into the exhaust system. This can also be caused by worn piston rings but is unlikely on a vehicle of this age unless it has overheated badly in the past. To check turbo, remove main intake pipe from turbo. Check for excessive movement on impeller shaft in turbo by moving it up and down. To check piston rings carry out a compression test or if you have the equipment a cylinder leakage test will give you a better indication of cylinder condition. If the Turbo is at fault it will need to be reconditioned or replaced. Check oil feed pipe to turbo for blockage or restriction [common fault].

Your mechanic is spot on. The A4's are notorious for turbo overheating and failure. The oil burn is coming in the TURBO itself and then being distributed to 2.3.4 as a side effect. Your not noticing blue smoke because your catalytic converter is doing its job and the minor smoke being generated is being taken care of in the CAT. If you continue to drive as is you will run a certain risk of catalytic converter damage, cylinder damage from fouling (cylinder wash) build up, sludge, etc. If your mechanic has the knowledge on this specifc model there is a way to test the turbo output and turbo heat generation to absolutely confirm. One last thing. in ANY turbo car its imperative to run QUALITY oils not your local wal-mart brand or no name. Many people are not familiar with the demands on a TURBO engine and oil change facilities pull standard oil from 55 gallon drums via a pump.. so you arent feeding your car properly. The AVG (Audi/Volkswagen) company recommends FULL SYNTHETIC and either Castrol or Mobil 1. I have a Turbo Diesel and use Mobil1 as my choice. The recommended oil for your car via their web page is Current Vehicle: Year: 2003 Make: Audi Model: A4 Quattro Engine Type: 4cyl. 1.8Liter Turbocharged
Mobil 1 0W-40
A fully synthetic motor oil, Mobil 1 0W-40 with SuperSyn Technology exceeds industry standards and the major leading builder requirements, enabling the product to keep performing well after conventional oils cannot. Mobil 1 is recommended by leading car manufacturers as initial fill

Right side of the engine , on exhaust manifold.

Engine also smokes when car driving if turbocharger still faulty. Did you change the engine timing belt (the timing belt kit) meantime? What about engine oil consumption? When engine glow plugs (one or more) burnt then engine exhausts white smoke at idling. Also white smoke at engine idling when water is still present in diesel fuel.

I hope that you had the proper weight oil installed, at your oil change. If your oil is up to the proper level, and it's rattling ,this is VERY bad. White smoke usually means steam in the exhaust, and that means a blown head gasket. Check your coolant level. I wouldn't drive it anymore......until someone knowledgeable can diagnose it!!!!!

Alright there your on the money there. A4 audi's and The 2liter golfs do haed gaskets at around 145-150,000 miles. the oil's foamy kinda yellowie cream. Tip for ya When you do the head gasket cahnge the rad and water pump at the same time. Mine didthe same it's costly but worth it for piece of mind, Plus is the only time you get to the water pump apart from changing the timing belt.

Hello chris first thing you need to do is while the car is running go to the rear of your car have somone increase the gas pedal to get it to smoke now smell the smoke does it smell like antifreeze if it does most likely headgasket going wich means your head needs to be pulled to change the gasket if it smells like oil possible valve seals clogged oil returns this is all serviced under your valve cover if car is turbo turbo seal internal most likely ruptured and is letting oil get into the exhaust port side have your turbo checked if there is wettness around the housing areallook for exsesive oil leaking externally goodluck please rate

ok open your oil cap and see if its creamy inside there
if it is there is water getting into the head
caused by blown head gasket
if not just get back to me and ill find the other soulution