You have a 1989 jetta gl runs very well while cold and after it warms up gets very noisy and the oil pressure light comes on Once you get the engine over 3500 rpm it goes back off. help?

Answer 1

You probably have excessive clearance in the rod bearings that causes rod knocking when the oil thins from the heat. While the oil is thick it provides a little cushion between the rods and the crankshaft but after it warms up the oil is a little too thin to help out. You can try using thicker oil, (Higher number on the viscosity. If you've been using 20W try 40 or 50) or you can add some engine oil treatment such as STP but generally the best solution is to have the engine rebuilt. Most larger communities have shops that can do a good job on VW engines but make sure it is someone who specializes in VW's, not a general mechanic. If you keep running the engine while the rods are knocking, you will have one of the rods come apart inside the engine and potentially send pieces through the side of the block. Then the engine cannot be rebuilt.