I brought my car in for an early oil change (1997 A4 1.8TQM, 19,900 miles, lots of stop & go driving) Anyway I was going to perform this oil change myself and picked up an oil filter from another Audi dealership a week ago). Yesterday, I instead went to a local Audi dealership to have the oil change done (with dealership supplying filter and myself supplying the Mobil One). When I got home I looked at oil filter I purchased at other dealership and paperwork from dealership where change was performed. Numbers didn't match and I called dealership where car was purchased to verify number (wrong one at least on paper) Question, will 2.8 filter installed on 1.8T engine do any harm? Thanks for help.

I assume the filter physically fits and that there are no resultant oil leaks. The problem then is: Does the incorrect filter have the right filtering specs. The worst thing that could happen is that it completely blocks the oil flow, which won't cause any damage in the short term because it isn't a full-flow filter system.<p>If it were my car, I'd get the sucker out ASAP and replace it with the correct unit. You might also check with another Audi dealer to see if there is any harm in leaving it in, but like I said, I'd change the filter.

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The filtering specs are not as critical as the pressure valve. There is a spring-loaded valve in the filter that keeps oil in the filter, and prevents flow until the proper operating oil pressure builds up. This pressure is different for different cars, and is a critical factor.

Not to quibble, but the spring rate on the spring actuated valve IS part of the filtering specs. Furthermore, it isn't a critical value. There certainly is not enough difference in an A6 and A4 oil filter to cause anyone to lose any sleep over it. Furthermore, your oil light on your dash will indicate if there is insufficient oil pressure to operate the car safely.<p>There is a very wide latitude for operating conditions for oil filters in a car. For one thing, the pressure drop across the filter medium can change dramatically, as can the spring rate, over the life of the filter, and with varying operating temperatures, oil viscosities and ambient temperatures which can vary from -40 deg. F. to 120 deg. F. Filters are not sold for such varied conditions. One filter specification must suit all such conditions.<p>Like I said, replace the filter but don't worry about any damage that might have been caused.