Is it too late to switch too synthetic?
 

I know the synth question has been asked to death on here and, yes I have searched but I havent seen anyone mention switching on a car with very high mileage. My '99 has over 150k. The previous owner has been using dyno thus far and I have always used Mobil1, RP, Idemitsu, or ELF in my cars so Id like to continue doing so. I was figuring to use Mobile1 or RP since its just my daily driver. Thanks for any advice.

Also would an sTp filter be ok or should I buy a filter from audi?

YES!! Use full-synth Mobile1 please! And i don't know what the forum consensus is, but I buy my filters from audi (i get them cheap). The Mann filters are what you should be looking for if i remember correctly, you shouldn't really use anything else.

It really shouldn't hurt the engine to put synthetic in (if as much of the old stuff has been removed as possible), but to be on the safe side you'll probably want to change the oil after a shorter amount of miles than normal. Being synthetic, 2500-3000 I think would be a good time frame to change early, then follow a 4-7K routine after that.

Well, if you switch to synthetic then you are likely to develope oil leaks. If the car has been run regular motor oil and then switched to synthetic it is hard on the seals, especially on a 10 year old car with over 150k. It is typically ok to switch on a newer car with low mileage with no oil leaks, but i am sure your audi is at least seeping oil from the common areas. Once synthetic is used your car might begin to leak oil noticeably although there is no harm mechanically, your car will run fine with synthetic oil. An STP oil filter is fine. Filters these days are more less the same. Of coarse if you can get a mann filter without a hassel then go for it, obviously.

Changine to synthetic is always better for the motor, but you will notice some oil leaks if the previous owner has used dyno oil in it forever. Run the synthetic for a couple weeks and double check for oil leaks, especially around the valve cover/cam adjuster seal area, thats where you will find it if its gonna leak. Pull a couple coil packs out as well and look at the spark plugs, there may be oil in there also.

99 beat me to it.....

I think I might have a few small leaks here and there but I think the pro's of the switch outweigh the cons. Ill probably have the car looked over thoroughly before the switch, just to be safe.

I don't know about dyno but changing from a low-med detergent oil to a high detergent oil can cause problems on high milage - sludgy vehicles. The key word is sludgy!! All the crap gets loosend up and what dosen't get caught by the filter ends up in other unwanted palces.

I'd look inside the oil filler cap and feel the bottom inside of the pan thru the drain plug to see how much sludge is there. If it is minimal I'd make the switch and change the oil and filter often for awhile. If there is a lot I'd just forget it.

Another Oil Question
 

I switched my 2002 from "Normal" (i.e. whatever dealer put in) to Mobil 1 synthetic at 68K. At about 74K I was on a road trip and got the Check Engine Oil Level alert. I pulled over as soon as I could and checked the oil. It was low, and had a light colored foamy substance on the dip stick... I was/am concerned about that. I immediately planned another oil change and just did the change at 76K. I also flushed a quart through the engine once it was drained before re-filling. Not sure about any leaks, as I never saw any obviously leaking... Any ideas about that foamy substance? Should I be concerned?

It sounds like you have two issues: low oil level and light-colored foamy stuff. Given it has been about 6k miles since you changed oil, I assume you changed it last fall. It sounds like either the oil was not topped off or you are burning some oil (check tailpipe). The foamy stuff sounds like water has been churned with the oil. If you took a lot of short trips through the winter and did not really run the car for any distance at high speed, it's likely that you have accumulated condensation in the oil. Running it for an extended trip would boil it off, but if there is enough it will show on the dipstick. Of course, worse case, you could have a leaking head gasket that is allowing water into the oil, but I doubt that.

I'd get it changed, make sure it is topped off properly, and keep an eye on the level for a while. Also, run it at high speeds once in a while to get the oil good and hot and boil off the water -- it's a German car, it will enjoy it.

+1 Million what PPGoal said!

And I've used STP filters for the last 5 years on my wife's A6. No problems at all.