Lead in oil

[Weasel]

I have been doing oil samples on my engine every 100hrs since overhaul and I always have higher than I would have expected lead content in the sample.

Samples are taken with the engine warm and approx. 1/2 way through the oil drain.

Engine is started full rich then when running evenly leaned aggressively (just rich enough to run) until ready for take-off.

Full rich on take-off then leaned in the climb to maintain approx. 200-150 rich of peak.

At the end of climb go to Lean of peak for the rest of the flight including descent, landing, and taxi.

Compression is ~75-78/80 on all cyls. bore scope inspections indicate cyl walls look good.

Does not "seem" to have excessive blow by (normal looking belly).

Blackstone Labs indicate averages for a IO-540c4b5 to be 3645ppm.

Mine range from a low of 5175 to a high of 8043 and not necessarily in a trend.

The only other think I can think of is the fuel pump diaphragm. The fuel pump was new from tempest at the engine overhaul. possibly bad?

[Geico266]

Run 75% mogas and 25% 100ll.

Change the oil more frequently.

[Walt]

Oil change interval? 50 hrs = twice as much lead as 25 hour

[RV10inOz]

I would not recommend 75/25 mogas/Avgas.

Oil interval is correct, and check other variables, such 7qt sump fill VS 10?

Oil sampling is full of variables and YOUR normal method creates YOUR NORMAL benchmark. and it may differ to most others.

[Weasel]

Originally Posted by Walt

Oil change interval? 50 hrs = twice as much lead as 25 hour

That is probably it. I use a 50hr oil change. I just assumed that would be the fleet average but perhaps its something less.