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Discussion and questions related to the course Engine Building Fundamentals
I am swapping a car and going with a dry sump mainly for engine fitment issues (all the other advantages are nice too). This will partly be a road car so I am trying to alleviate some of the race car inconveniences that comes with a setup like this.
The top of my tank will me mounted pretty much at the hood level and I expect to have problems with oil draining back if some time passes between engine starts. I don't really want to deal with a ball valve for fear of someone forgetting it closed and the general inconvenience of using it everytime I go drive the car. Are there obvious solutions to this that I am missing?
The simplest solution I could think of is looping the feed line above the desired lowest tank level to stop gravity from doing its thing. Is there something wrong with doing this that I am overlooking? I attached a simple picture of what I mean.
locate the oil filter higher than the oil tank
The top of the tank isn't the issue -- it's the bottom of the tank (pickup location) relative to the pressure stage output of the oil pump. We usually have a couple of quarts in this volume (pump height plus line volume), so the engine can start and the scavenge stages will quickly put the oil back in the tank.
As David said, it will leak (very slowly) through the pressure stage of the pump until the same level is reached in both - basic hydraulics - and the scavenge pumps should rapidly return the oil to the tank, anyway.
A loop, as you describe (no picture) is unlikely to work as it will just work like a syphon.
Is there any particular reason you can't mount the tank somewhere lower in the chassis, that will mean less is leaked back to the sump before equalising levels, slow the leakage, and it will lower the CoG?
If you're that concerned, there are at least three other options - set the ECU up so it doesn't power the ignition/injectors until oil pressure is present; use a separate starter switch to crank it over for, say, 15 seconds before starting proper after it has sat for a while*; use an ACCUSUMP with an electrically operated on/off valve that only operates when energised - it will fill during normal operation and hold the oil until the next time it's energised and feed oil to the engine.
*if you check the level sight glass/dipstick when it's been parked up, you'll soon get an idea what sort of parked up time passes before, or even if, you need to do this.
Thanks for the replies! Because of space constraints I am more of less stuck with a high tank location. You're right about siphoning, not sure how I didn't think of that. I'm assuming this would still happen through the filter if I mounted it higher than the tank oil level like TOWSN suggested?
I did think of having the ECU crank without ignition\injectors too and it seemed like the ideal solution but it might not be possible if I decide to stick with the engine's stock ECU. Worst case the separate starter switch is a good idea.
Hopefully this all ends up not being a problem as you said!
If the output from the pressure section goes to a remote oil filter before going to the engine, then mounting it higher will have the effect of raising the outlet of the pressure section of the pump.
Ah, I had thought aftermarket ECU. If it has a mechanical oil pressure guage, it would simplify things.
Back in the day, it was common to wire the fuel pumps through an oil pressure switch (and relay), primarily to shut down fuel pumps in case of a crash*, but you may be able to do a similar thing with the ignition/ECU power, so it isn't energised until there is oil pressure? There are high pressure, adjustable, oil pressure switches available from several suppliers, that could be used.
Hmmm, it may be possible to fit a level warning switch in the tank that is connected to a warning light in the dash, that indicates if the level is too low - crank until it goes out, then start the engine? The problem is that we don't know your specific system's characteristics, the easiest think may be just to check the oil level if it has been sitting and use a manual pushbutton switch under the bonnet (hood) to crank the engine over and scavenge oil to raise the tank level to an acceptable level to ensure an oil supply to the pressure pump, before closing the bonnet and actually starting the engine?
*You may have notice some old race cars had dash switches marked with something like "pumps on" or "pumps off!" - these referred to manual switches that powered the pumps to allow the engine to start, and that were then tuned off when the engine started as they would then be powered via the oil pressure switch circuit.