Oil Consumption high in some GTS's
I have talked to many GTS owners and Porsche about the oil consumption of GTS'. The fact of the matter is that the oil consumption is usually in specification, and the technical reasons for the consumption are valid.
The GTS pistons have unique oil scrapping system (combination of ring tension, type of ring and drain back capacity) designed to leave more than the usual amount of oil on the wall during each stroke, this is to improve piston to wall lubrication, so more oil ends up in the combustion chamber to be burnt. There is also a change in the material of the piston. Keep in mind that it is the first forged piston used in a 928! There are also specifications on cylinder to piston clearances, which fall within a specified tolerance, and may be responsible for variances in oil consumption within models. Since I have measured many GTS pistons, I have found that the tolerances do vary slightly even within any one group.
The design of the piston is very different than S4 or earlier pistons, both in design and material. Why they made this design change is simple, Porsche wanted to improve the durability of the GTS under extreme driving conditions. It is the same reason that they added a oil cooling system to the manual transmissions! Constant improvement! But it did have a "down side". In my view, a quart of oil is a lot less expensive than an engine rebuild? Of course, I can revise your pistons and eliminate the oil consumption..... but it costs more than a quart of oil!
I have seen GTS with 2000 mile per quarts, and I have seen them with 450 miles per quart. Porsche made a decision on a design and the jury is still out.
So, If the oil consumption is out of the spec, then there is generally another reason why...breathers, guides, etc. Always check the plugs as indicators of internal engine condition...also use compression and leak down testing.
Drive hard and drive safe, and have fun! (and keep a quart of oil in the back)
Marc M. Thomas
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