You might give us a bit of an idea as to what the problem actually is, but I
presume that you simply have insufficient scavenge. Does the sump actually
overfill, or is the problem somewhat less?
How many scavenge stages are you using? If it's a cosworth type pump, you
can get pumps with several scavenge stages.
What type of engine is it? What type of oil pan does it have (purpose made
for dry sump, or modified standard pan?)
Most people run a simple mesh type filter between the pan and the scavenge
pump if they run anything at all. The full flow "real" filter should be on
the pressure side of the pressure stage, although you can also run a pretty
fine filter on the output of the scavenge stage. If you have a paper
canister type filter on the input side of the scavenge section, you'll
almost certainly have problems.
The usual order is: pan to scavenge stage to oil cooler to tank to pressure
stage to filter to engine input. The options are to add very free flow
filters between scavenge and cooler, and to add screen type filters between
the pan and the scavenge stage, just to catch big chunks!
You can sometimes get suction leaks when using hose and connectors not set
up to handle vacuum (input side of either scavenge or pressure stage) and
the tough part is determining that you have a leak - air gets sucked in,
rather than oil getting squirted out! Stainless Aeroquip line is normally
used, and I have good success using the blue fabric covered Aeroquip with
push-on hose-ends.
The temperature thing is just a factor of viscosity - the pump can overcome
problems when it has really thick, cold oil to work with, while the hot oil
is far harder to get pressures with. This exactly the same effect as you
see when you get very high pressures when the engine is cold, falling off to
normal pressure when the engine warms up.
The best discussions of dry sump systems tend to be in Circle Track
magazine, BTW, and they just happen to have an article in the current issue
(October) that gets in a fair bit of detail. Hope these ideas help to some
degree...
Brian
At 11:30 AM 9/2/98 -0400, you wrote:
>
>I am having a problem with the dry sump scavenge on 6 litre engine when
>teh oil gets hot (85 degrees plus). I have three main theories. Any
>suggestions as to the likehood would be much appreciated
>1. The pump is knackered (thought unlikely)
>2. The oil filter (full flow type) for some reason is not of sufficient
>capaacity
>3. I have some rubber tube on the scavenge side of the return pumps. This
>could be internally collapsing (no external evidence). A bit like sucking
>too hard on a thick shake!
>
>My feeling is that it is #2, but I dont know if pumping the air/oil
>mixture through a filter designed to take just oil is a problem. And if so
>why should it be temp dependant?
>
>Any ideas
>
>Geraint Owen
>
>
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