[T3] fan rubbing something

[Jim Adney]

On 15 Feb 2016 at 19:17, Keith Park wrote:

> Most builders have told me high volume oil pumps are a major mistake. 
> you dont NEED anything more than the stock volume and a high volume pump
> is higher in volume but lower in pressure, so you run out of pressure
> when the engine gets older. 

The pressure is regulated by the pressure relief valves in the case, 
which bleed off excess volume to get the pressure down to what the 
engine was designed for. A higher volume pump gives you more to work 
with, but too much can overwhelm the relief valve system. On a badly 
worn engine, that excess can come in handy, allowing the system to 
maintain pressure even in the face of increased internal clearances.

Most of our engines came with pumps with 21 mm gears, but starting in 
'72, VW introduced 26 mm pumps. Those late engines have had really 
good reliability. Given that fact, I don't see any problem with the 
aftermarket 25 mm pumps, IF the quality is good, which is not a safe 
assumption. I would steer clear of anything larger than 26 mm, simply 
because there's a downside and no upside.

This becomes just another example of more not being necessarily 
better.

One other argument against larger pumps is the fact that the power 
required to drive the pump is flow x pressure. Since a larger pump 
increases both of those numbers, you deplete your hp output to the 
tranny by the extra amount used to drive the larger pump. It's not a 
free lunch. 

I take issure with the high volume/low pressue argument. Nothing 
supports that.

> Most aftermarket pumps have such poor quality control
> that they are a problem anyway.

This is, unfortunately, very, very true, and it's probably the cause 
of most of the problems with larger pumps.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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