Originally Posted by spearfish25

I was working on the cars with two other Z owners today and recognized a very important issue with my oil cooler. As many people have oil coolers with the cooler fittings facing down (toward the ground, as Modshack's DIY shows), this is a potentially very important issue.

The cooler is mounted above the oil pan. This means that a good quantity of the oil in the cooler will backflow to the oil pan when the system isn't pressurized (engine is off). This has important ramifications on dipstick measurements! When the car is running, the oil pan oil level will be nearly 1 quart lower than when the engine is off. This became readily apparent after draining the oil from the pan and the cooler (disconnected one line). We refilled the system with 6 quarts (stock without cooler is 5 1/8), ran the engine for about 30 seconds to self-prime the system and then turned off the engine. Checking the oil level by dipstick immediately after shutting off the engine gave a full reading (even with top dipstick hole below H). Waiting five minutes later gave a reading well above the H. Yes, some oil drains down from the engine internals. However, the more important phenomenon here is that the oil cooler back flows to the pan if the fittings are toward the ground. Thus, if you don't keep your oil pan level near the high mark with the engine off, you may be running at or below the low mark when the engine is running with the cooler fully primed.

I brought this up with Modshack once and he dismissed the idea. He said that he got 1 quart of oil out of the cooler when he disconnected one line and drained it into a measuring cup. This may be due to the type of oil filter or sandwich plate he was using. Today I used a Purolator PureONE filter with a Mocal 200F thermostatic plate and there is back flow. Very little oil drains out when a line is disconnected with the oil pan already drained.

You've been forewarned!