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Old April 28th 2020, 14:24
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owdlvr owdlvr is offline
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Join Date: Sep 2008
Location: Canada - West Coast
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Quote:
Originally Posted by Wally View Post
Hey Dave, I never quit understood how these exactly function. Can you elaborate a little how this one is plumbed?
The accusump is essentially a hard-anodized aluminum tube, with a piston inside dividing it into two halves. You have an oil chamber, and an air chamber. You set the pressure of the air chamber to the oil-pressure that you would like the accusump to become active at. On my cars I set the air chamber pressure at 20-25psi, but for this example let's assume I've set it for 10psi. (more on that later)

When the engine is running, anytime the engine oil pressure is higher than the air chamber setting, it will fill the Accusump with oil. In this case, with 1.5L of oil, if the engine is running at a pressure higher than 10psi. As the oil pressure builds, so does the oil pressure / air pressure in the accusump. So at full RPM, when the oil pressure gauge on the dash reads 50psi, the oil in the accusump is at 50psi, and the air chamber gauge will match (since you have the oil side of the piston pushing towards the air chamber at 50psi). As the oil pressure in the system lowers, so does the oil pressure in the accusump. But if the oil pump is providing anything over 10psi (in my example) and you will have 1.5L of oil waiting to be used.

When you corner the Beetle hard enough to starve the pickup tube, the oil in the accumulator will be used automatically to make up for the loss of pressurized oil from the oil pump.. So essentially, your engine sees no loss in oil pressure as long as the reason for oil starvation is solved before the full 1.5L of oil is used up. Now, keep in mind in my example the pressure has to drop below 10psi...which may not be desirable in a cornering situation. Typically if I'm starving the car for oil in corners, I'm turning a higher rpm and oil pressure than 10psi. So this is why I set my cars for 20-25psi. The trade off, though, is that at idle I have an EXTRA 1.5L of oil sloshing around in the crankcase, which increases the aeration of the oil. Not an issue in the dry sump car, can be an issue in the wet-sump cars. So, for typical street driving on a wet-sump car I set the air chamber at 10-15psi. If I go for a track day, or I know I'm going to be driving spiritedly through the mountains, I'll bump it up to 20-25psi knowing that I'm not likely to spend a lot of time at idle.

Before shutting the car off, I rev the motor up to get 40+ psi of oil pressure, and close the manual valve. Now I have 1.5L of oil stored at 40psi, so the next time I go to start the car I can open the valve, pressurize the bearings with oil, and then start the engine.

Determining the proper oil level is a bit of a guessing game. I typically start by overfilling the engine by 1/2L, fire it up, open the valve at idle. Close the valve, check the oil level, add another 1/2L and repeat. Once I've got it close, I then warm the car up, do the 40psi shut off and check the oil level, topping up as though the Accusump didn't exist.

This diagram shows how the system will be plumbed in the red car. The check valve is important, as it ensures the engine is filled with pressurized oil in a starvation situation, as opposed to wasting oil filling the oil cooler.

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