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Old 05-19-2017, 10:09 AM   #7
Live, eat, and sleep by TSL
Join Date: Mar 2005
Posts: 1,819
New vs old oil pumps?

From the Saab 9000 to the Saab 9-5 the oil pump changed a bit. I want to talk about that some.

Then 9-5 uses a Gerotor pump. This is basically just two gears. Most gear pumps operate on the same principle. As the gears separate they draw in oil, and as they come together they force it out. The old 9000 used a crescent pump. The two are shown here, one from a B234 engine and the other from a B235. Whats the difference!?!? Not much really. As you see above the volume of the pump is determined by the cavity between the inner and outer lobes. Want more volume, make the gearset bigger! Clearly the B234 pump is larger but not significantly. So the B234 motor should have more volume. That's good for a worn engine where your are pouring most of your volume back to the sump. What about Crescent vs Gerotor? Gerotors always have one more lobe on the driven gear than the drive gear. You can see that the Crescent pump has many more lobes on the driven gear. This is beneficial to even out the flow of oil. More lobes results in a more steady flow (less lumpy). Is the B234 oil pump more expensive? You bet. Probably substantially. There is WAY more machine time in the gears themselves. In addition, the housing is more complex. In a crescent pump the clearance between the "crescent" and the gear lobe is critical. So from a manufacturing perspective Saab would have to hold tight tolerances on both the gear teeth, and the Crescent shape (on both sides). On a Gerotor, they are only concerned about the gear mesh, and likely you could theoretically mix and match gear sets to get a really good mesh. That's easier than trying to machine them all perfectly, and all the same.

Is the B234 pump better than the b235 pump? Yes, but in my opinion the difference is negligible. This is probably what saab thought when they made the changes. You could probably argue that the b234 pump is better at chopping up little pieces of junk with all the sharp teeth it has. I would agree, but it is not like a 5 mm piece of steel is fragile! And either way, there should not be little pieces of gunk floating around in your engine. Saab made that an issue with an ineffective PCV system of course. Just looking at the pump the B234 pump looks bigger, with more capacity. True, but probably this goes un-noticed until your bearings wear out. I've heard some people say they want to run their bearings on the loose side for turbo applications. I think this is complete garbage! It is just an excuse to use a worn out engine and hopefully you have an oil pump with enough umph to make up for your poor judgement or lack of ability to measure clearance.
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