I have a 1999 XC70 2.4 T5 AWD with 105,000 miles. Last summer, the car's first in Texas, I experienced a weird problem after getting an oil change. The mechanic used 5W 30 in the car. After doing this, the oil light would come on when the car was hot (run for 20 minutes plus at highway speed) and the brakes were applied. The sequence was apply brakes, RPMs drop to just below 800, light flickers, RPMs kick back up, light goes off. After several visits to two different mechanics, the problem was seemingly solved by replacing the oil pressure switch, the seal on the oil cap, and changing to 20W 50 oil. Recently, I had an oil change where the mechanic doing the change "forgot" to use the heavy weight oil. As a result, I'm back in the same boat as last summer. Problem is, we just did all the same steps as last time, and the problem won't go away. There are no error codes, the system pressure tests fine, and there are no apparent leaks. The car has a new oil pressure switch, a new oil sending unit, and some nice thick oil to ward off the Texas heat. This morning, the mechanic came out with the owner's manual in hand to show me a note under the oil light description that indicated a flickering oil light was "normal' after "hard driving." Is he giving up or is this really just something that happens? The car was a Northeast car all its life, and this summer, so far, has been hotter than last ever got down here. Any help would be much appreciated! Thanks jeff in texas

Is it blowing smoke out of the oil dipstick tube (lift the dipstick out slightly and check with the engine at idle) also check the same with the oil filler cap removed... if it is puffing smoke out then your oil trap/crankcase ventilation system is blocked and may well be causing this problem.... Sorry if you know all this already! :blush: