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Like many of us, I have often wondered if there was an easy way to flush the oil in the oil coolers and their lines every so often (not every oil change, but maybe once every 5 changes or so). I would like to do this without disconnecting any of the oil cooler lines, not even from the oil filter sandwich plate. Of course, I am willing to remove the oil filter (after all, I am changing it anyway when I change the engine oil).

So, I am starting by trying to understand the oil flow through the sandwich plate. I have determined the following so far:
1) The oil flow through the filter is the oil goes into the filter through the outer ring, flows down the sides of the filter canister, flows through the filter material into the center of the filter, and then out the center into the engine. (I determined this by cutting open my old filter. It was pretty obvious which way the oil flowed.)
2) The oil flows through the sandwich plate and coolers as follows:
a) Oil under pressure from the engine goes into the sandwich plate on the outer ring (hidden when sandwich plate is attached).
b) When the engine is hot, a thermostat in the sandwich plate directs some portion of the oil (not sure how much fractionally) into the right hand oil cooler line (the one with the bleed nipple). The oil returns via the left oil line and flows down into the filter.
c) When the engine is cold, the thermostat causes most (all?) of the oil to flow through a bypass hole directly to the filter.

So, I thought, I could take the filter off, attach a tube to the bleed nipple, open the nipple, and flow oil through the tube (with a pump, or run the tube up high and connect a funnel), and it would flush the oil coolers. The oil would empty out the left hand hose via the oil filter location.

The thing I don't know is if the sandwich plate thermostat fully closes off the right hand oil cooler line when it is cold. After all, the bypass probably has much less fluid resistance than the oil cooler path, so the thermostat doesn't necessarily have to fully close off the oil cooler line to achieve the goal of not having much oil flow through the coolers when cool. If it doesn't shut off the oil cooler line, the fresh oil could just end up pouring into the engine or pouring through the bypass hole instead of flushing the oil coolers.

Does anyone have additional insight into how the sandwich plate works in this regards? Does someone want to try it? I just changed my oil last weekend, so it will be a while before I could try. Just leave the drain plug off the oil pan and see if the oil comes out the drain plug hole, or out the sandwich plate bypass hole, or out the left hand oil cooler line hole in the sandwich plate (this last one is what we want). If it comes out the bypass hole, it might be possible to plug it (say, with your finger), but I would guess that there would still be an issue of fresh oil flowing back into the engine.

Of course, a less desirable alternative is to remove the left or right oil line from the sandwich plate (note, you need a 28mm wrench), connect up an appropriate fitting which is in turn attached to a tube through which you can feed new oil. (If you disconnect the left hand line, make sure to open the bleed nipple.) I would just prefer not to remove any fittings. By-the-way, does anyone know the fitting specification (diameter and thread pitch) for the oil cooler line attachment at the sandwich plate?
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