I'm working with a recent arrival that came in with a high oil consumption concern (1 quart/200-300 miles) and significant smoke, particularly out of the left side pipe, when the engine is cold or has been sitting for a few hours. Interestingly, the (visible) smoke appears to subside after about 5-10 minutes of driving.
When starting from dead cold, the engine sounds
like she isn't firing on all 12 cylinder, although OBDII data showed no evidence of a misfire. Idle quality was not what I would expect and have experienced in the past from these cars. After 5-10 minutes of running, the idle quality improved steadily.
Preliminary tests done by another shop indicated "good" compression in the 225 psi range, with minimal variation. Oddly, no leak down was done at this point.
Oil type used and quantity (in the dry sump tank) were verified. Both OK. Although some of the hoses to the/from the oil/vapor separator are a bot old and hard, the system was found to be free from any sort of obstructions. Next, a leak down test was done, revealing leakage from 18-33%, with the intake
and exhaust valves being the predominant leak source. Oddly, on some cylinders, leakage was stable at 2-3% for a few seconds and would then steadily rise to 30% and level out. This was noticed on several cylinders. There was evidence of "wetness" on one of the spark plugs that may prove to be troublesome as the repairs progress. Upon teardown, the intake ports revealed some evidence of oil/carbo blow back. However, most of the exhaust ports were heavily encrusted in an oily/carbon sludge. When the heads were finally removed from the engine, it was found that some of the exhaust valve guides were worn so badly that, even with the heads fully assembled, the top of the valve could be moved approximately 1/4" with just thumb pressure!
With a mere 15,000 miles on the engine, no less....
The last two photos are proof positive on just why it's so important to replace the coolant hoses (particularly those in the valley of the beast). There was evidence of coolant seepage and that coupler hose sure doesn't look like there's much life left in her!