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More a car building question than a tuning one but here it is anyway.
I'm installing an external differential oil pump and oil cooler. The pump, lines and cooler will be higher than the actual differential. Do I need to install a differential breather higher than the highest point of the other components in the system?
No, the stock breather will still be fine. You're still going to need to maintain the same level in the differential and all the pump is doing is drawing the oil from the drain plug on your diff and pumping it back through the filler plug.
how do you set that level since all the oil will drain to the diff when the pumps off? (assuming the cooler and lines are higher than the oil level in the diff?
assuming just measuring the oil and going off oem fill recommendation? but then how to check it?
I've drawn a sketch (attached) which has helped me decide this won't be a problem. As the oil return line is higher than the fill plug/oil level then I think the oil will slowly drain back into the diff when the pump is off. It will just be the oil from the return line and maybe the pump but not the cooler itself. This should be only a very small amount of oil - not nearly enough for it to overfill the differential and out of the breather.
To set the right oil level I guess I fill it with the pump running. If a little drains back and the level is too high when the pump is off, then so be it.
n.b. The pump is after the cooler to ensure it pumps cool oil and not hot and hence improve the lifespan/reliability of the pump.
You might find you get pump cavitation trying to draw through all the lines and a cooler. Listen to it carefully on testing.
Thanks Michael. I'm planning on using the Tilton pump which apparently is self-priming up to 8 feet of lift. I still may fill the cooler with a funnel before I connect the lines and start it just in case.
i would also think you want to cool the oil when its hottest, this make your cooler the most efficient it can be as the temperature differential between the air and media is at its highest.
The Tilton pumps that I've used tend to seal reasonably well so you won't end up with all of the lines draining into the diff. I would suggest checking the oil level with the pump running.