How dry should a dry sump be?

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schomosport
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How dry should a dry sump be?

Postby schomosport » Fri Aug 18, 2017 2:06 pm

Spiess pumped XE Dallara. Single stage pressure pump, single stage scavenge back to the oil tank via the oil cooler. Oil tank breathes into catch tank which then breathes to atmosphere. Crankcase breathes to same catch tank from what would have been the dipstick hole in a standard car. There is a baffle plate at the entry to this breather to stop the splashes in the crankcase going straight up the breather. All standard XE Dallara fit so far as I am aware.

Engine rebored with negligible mileage and satisfactory compression so it isn't blow-by pressuring the crankcase.


Immediately after switch off I removed the sump-to-scavenge stage collector pipe and drained approximately 0.8 litre oil out of the sump. The car also seems to be putting a lot oil into the catch-tank - can't make it do it in the garage but after the last test session I found best part of a litre in there. Scavenge pump gone bad because it has had too many bits of engine through it?

Was this the cause of my collapsing oil pressure and oil leak problems last time out because there was more oil in the sump than in the oil tank?

Frustrated and mystified. All offers of advice / help welcome.

Regards

Mark Schofield
Schomosport

Dermot Healy
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Joined: Thu Jul 10, 2008 9:59 pm

Re: How dry should a dry sump be?

Postby Dermot Healy » Sat Aug 19, 2017 4:53 pm

How about the pipes between sump & scavenge inlet or between scavenge outlet & oil tank?
presumably braided flexible pipe? Could one or other be compressed/internally disintegrating or otherwise unsavoury, reducing scavenge effectiveness? Also, has this 'rebuilt' engine ever held a proper oil pressure for the duration of a race and just now begun to misbehave? Or has this problem emerged since the rebuild? If the latter, are you sure all is right with the rebuild? Little puddles of silicone sealant lurking where they shouldn't? That oil cooler doesn't happen to still contain the innards of the engine from before the 'rebuild' restricting flow ? Suction side of scavenge pipework making a good seal? could it be sucking air rather than oil?

But you'll have thought of all these.

But, now that i think of it, maybe 0.8L oil lurking about after switch off doesn't necessarily sound so alarming given oil galleries emptying and oil floating about in the head etc Any engine supposedly drained of oil always seems to have at least a litre to spread over the van floor whenever i try to collect one!


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