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I'm with Nesism on this.... Take it to the extreme and see how the issue is entirely possible.... Let's say your new oil cooler take 3 quarts of oil to fill up... However you crankcase capacity is 3.7.... When engine is running 3 Quarts are in the cooling system. leaving .7 Quarts to do the rest of the lubrication, This can be nothing but far from ideal.....
Anytime you lower a crancase, be it engine ,transmission, rearend or even the coolant system, that fluid must be accounted for, or the recommendations were given way to high....
My 2006 Silverado with the towing package,which includes a auxiliary oil cooler,takes 6 Quarts vs NO Cooler taking only 5 Quarts

I'd never use Castrol GTX unless I also used a Fram filter.

Now Castrol R is a whole different kettle of fish.......

So I should change my oil once a year eh

Once a year seems a little excessive

Oil breaks down and becomes acidic, attacking steel, the old 3 month standard was based on this fact. Oil is better now than it was, I wouldn't go a full year myself, but hell it's all up to you really.

With everything that's happened with my motor the last couple years I guess it averages out every 4 months. 5000 miles out of a rear tire, time to change the oil?
Steve

Not sure what this says about me but I love a good OIL debate...

A couple of tidbits obtained in various older oil threads I've participated in...

The British formula Castrol GTX is quite different from the stuff sold in the USA. Way more zinc and phosphorus for one thing. Good stuff for motorcycles, unlike the swill they sell us which (like most auto oils) has drastically less ZDDP than it used to.

Combustion byproducts make the oil acidic with use, but the oil manufacturers add buffers to neutralize this. The amount of buffer added varies with formula (denoted by TN number) but there should be plenty to last 7500 miles or more with normal use, so unless you are abusive, acid accumulation in the oil is a non issue.

The computer in my daughter's car goes crazy at 3500 miles. The 5/15 oil they put in it seems to evaporate. I keep trying to get her to get Rotilla but she won't listen to me. It's the newest car she's ever had and listens to the dealer.
Steve

I was being facetious. I think that 3,000 miles is long enough; 2,000 is better.

Also, fully synthetic oil should never be used with an oil cooler. It is so much slipperyer that it will go through the cooler too fast to cool off.

The tone of this whole thread took that turn ages ago. Dont worry I'm thinking of asking in a few weeks, had to pull my motor out and I've got a set of jugs and pistons that are 1200cc, along with a cooler, so I'll be asking myself

If you ask yourself, you are less likely to get an argument.