Macrobb
Full Access Member
Well, the only problem I see with long oil change intervals is that the IDIs have huge ring gaps. These huge ring gaps produce a lot of blowby.
As far as I can tell, you get lots of carbon in the oil. The oil itself is probably good for a long long time... if you can keep the carbon in suspension. If you get too much carbon, some will drop out resulting in sludge. How much is too much? I'm not sure. But I've also seen IDI heads where they were obviously run past that point... with lots of oil sludge/carbon debris on top of the heads where oil slowly flows.
Also, I'm convinced that you really want to keep the oil going through your lifters clean of much of anything... every old lifter I've taken apart has had a heavy layer of crud on the check ball inside, which may prevent it from seating correctly and either allowing the lifter to soak up more of the cam lobe, or "pump up" and cause problems there.
As far as I can tell, you get lots of carbon in the oil. The oil itself is probably good for a long long time... if you can keep the carbon in suspension. If you get too much carbon, some will drop out resulting in sludge. How much is too much? I'm not sure. But I've also seen IDI heads where they were obviously run past that point... with lots of oil sludge/carbon debris on top of the heads where oil slowly flows.
Also, I'm convinced that you really want to keep the oil going through your lifters clean of much of anything... every old lifter I've taken apart has had a heavy layer of crud on the check ball inside, which may prevent it from seating correctly and either allowing the lifter to soak up more of the cam lobe, or "pump up" and cause problems there.