A couple of years back (about 15 or so) I thought of putting an oil-cooler
 > >>on my BMW R100S, but got warned by some people, that if you would not
bleed
 > >>it right, it would not work - it seems that both inlet and outlet where
 > >>pointing down as this was the shortest connection to the pump, the
cooler
 > >>was up in front of the engine on the frame. The oil would feed into the
 > >>inlet tank and start to compress the trapped air in the cooler, so

only

the
 > >>one or two lowest cross tubes would feed oil to the outlet tank,

wasting

the
 > >>majority of the cooler on trapped air! The solution was to change the
outlet
 > >>to the top so any trapped air would be pumped out. As it was it still
 > >>worked, if it was bled correctly on installation, as the oil pump

would

hold
 > >>the oil. However over time air would get in and the original cooler
 > >>configuration had to be bled on a regular basis.
 > >>
 > >>Any chance something similar could have happened to your 12A cooler?
 > >>
 > >>Thomas J.

Good point. I haven't seen this mentioned.

This is a problem with any fluid cooler installation. There is a hard and
fast rule that you can follow, or suffer the outcome. "Fluid out is at the top"
always.

If you fill the oil pan to indicate a specific level, and after running for a
short while, the oil level is increasing. What could be the cause?

    (1) The engine is saving lubricant from the fuel, air, and oil mixture
and mixing that with the lube oil in the pan. The oil scraper rings on the side
of the rotors are there to keep oil spill from the rotor bearings and the
rotor cooling spray nozzles, from getting into the combustion chambers. Oil film
from the top oil leaks past the side seals and is also collected by the scraper
rings and is added to the crank case oil. This is a very slow process and
takes some time.

    (2) The oil cooler outlet is not the highest point on the cooler, and
normal foam in the oil is condensing in the cooler into a slug of air above the
oil outlet level. This can happen very quickly on the first start up, and keeps
introducing some air back into the oil from time to time and results in oil
pressure that wiggles the gage from time to time. Over time there will be oil
temp problems, and if you don't fix it, maybe bearing problems. Because the
effective size of the cooler is being reduced by the amount of air being trapped
in it.

    (3) Both of the above. The engine saving top oil goes on all of the time
anyway. The amount of oil required to support the top end is microscopic. So
unless you are mixing a bunch of oil with your fuel, this problem should be
minimal.

In racing the apex seals are approaching the speed of light. There is a
centrifugal load added to the spring load. So I mix 6 oz. of RedLine 2 cycle oil in
5 gallons of 87 octane. So we make a little oil each week, and change it
every three weekends.

The stock coolers are double pass with both inlet and outlet on the same end.
There is little volume above the upper fitting where oil could collect. So as
long as the upper fitting is used for fluid out, air collection should not be
a big problem.

The ideal would be with the cooler tubes running vertically, with oil (or
water) in at the bottom and out at the top. Like almost all water radiators.
Ideal, but not practical in all cases.

Lynn E. Hanover

 
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