I recently rebuilt my motor (~8,000 miles ago) and changed the oil regularly during the first 5,000 miles but now, after about 2,500 without a change, the oil appears to be really dirty. Do these motors need the oil changed more frequently than regular water cooled motors or is my dirty oil an indication of issues with my motor?

Thanks in advance!

Oil is cycled through major heat stresses being used as the cooling medium. It will break down faster. I change mine about every 2k to 2.5 k miles with Brad Penn or Amsoil. In what way is the oil "dirty"? Actual particles of stuff?

Just dark. No particles, just turns darker much faster than my other cars - including my 911?

Note I did the rebuild myself, so that could be one of the reasons?

Your mixture may be on the rich side.

Let's get straight with technology.

Contemporay motors are efficient. Old motors are not. If you have a motor from the 70's, rebuilt or not, it isn't efficient. Leaves a lot of unburned fuel behind. Makes the oil dirty pretty quickly, as it washes down from the cylinders into the sump.

The 3000 mile rule really applies to these ol motors. If they run rich, the interval changes.

Your dirty oil is not unusual. It's a cheap fix. Do it, accept it & move on.

It's an old car!
Pat

Amen, although some oils get dirty quicker than others. I would think the ones that get dirty faster are cleaning better but thats only a assumption on my part. If the oil is getting dirty faster than at the beginning it may be because the choke is making it richer in colder weather.

I once had a aircraft inspector neighbor that changed his 50 chev oil every 1k miles. Sometimes that was every 6 months, but usually every month. His chev didn't have a full flow oil filter either.