First of all, this all hinges on where you live and how you ride... none of which is given. In AZ you might be good; in cooler, wetter western NC not so good. The Airhead is NOT a hot running engine. Previous experience with 4-cylinder Jap bikes, Brit twins, and big V-twins simply does NOT apply.

Secondly, I don't like the oil cooler. They are all mounted higher than the filter and the oil can drain out over night. So if the thermostat isn't working, your engine starts out dry. They also make working on the front of the engine and routine oil changes a PIA. 

The extended sump offers several advantages. 1) The extension becomes, in effect, an oil cooler. 2) If you have one of those bikes that seems to always throw out a 1/4 quart, you can safely use that level as your "full level", knowing there is reserve in the sump. And 3) your oil change routine stays the same. You're not working though external hoses and having to buy a different type of oil filter.

And please clarify, are you talking about installing a deeper stock pan off an R100, or are you talking about a third party "extended sump" ?

 It is a Bowman/Mac or very similar. It came off an 81 r100rs. It comes with the pickup extension @ $170. I will pass on the oil cooler install. I'm in Savannah,ga. Todays temp is 95+.

Just so you know, I'm about 100 miles north-northwest of you, so our riding environments aren't exactly the same, but not drastically different either. It is also in the low 90's here.

• I've usually used the MAC extended sump, and had very good results. They add about 1 additional quart to the engine. When I started Airheads, these sold for $125 new, but Mac has apparently gone out of business and re-sale prices have soared. The key to buying a used one is to insure you also get the oil pickup extension, which lowers the suction point for the oil pump to the new lower level. This small but important part is most often missing in used Ebay sales. (It's a simple part that could be made in the average home shop, and it should be fitted.)

• For the cost conscious shopper, there is also the Siebenrock oil pan extension, which simply lowers the oil pan you already own by 30mm. The only seeming disadvantage is that you end up with 2 sump gaskets in place of the one. Those new are $120 CLICK HERE.

• Your third choice may be a stock pan off an R100. These will definitely improve the flat pans used on the /5 engines... I'm just not sure which pan is on the R80. Of course, take-off pans are much cheaper and are in the $40 to $70 range.

Back in the 80's, there were several vendors for the first 2 types. So you'll see those on Ebay occasionally. I keep hearing of an Israeli vendor whose pans show up for sale in Europe, but they seem to be closer to racing spec and not a good idea for road use. It's important to remember that you NEED the oil to get hot in order to lubricate properly. And as I already said, the Airhead is one of the coolest running engines out there, so adding more than 1qt could actually be detrimental, unless you're something like an iron butt rider. The primary advantage I see is not having to carry extra oil with you when going to a rally 4 states away.

Hope this helps.

I have followed discussions of oil coolers on other forums (Guzzi and Commando) and consensus seems to be that they don't do that much. Folks have measured oil temps before and after installing a cooler and differences are minimal. My take has always been that disadvantages outweigh the advantages. I do have a factory-installed oil cooler on my 2008 Moto Guzzi 1200 Sport so presumably somebody at Guzzi thought it was worthwhile.

Again.... it greatly depends on Where you ride and How you ride. There are places in the deserts of western US and northern Mexico... and I suppose North Africa... where a 2° or 3° drop can be meaningful. So this is not a "one size fits all" type question. 

And I suppose that if you motocross your Airhead, a deeper sump may not be the best answer either !

► But, for the typical rider who...

• Experiences loss of oil due to crankshaft proximity
• Typically rides further than 350 miles in a single day
• Typically experiences average air temps above 88°F

Then the "deep sump" oil pans are the cleaner, faster, easier solution to install and maintain. I have used both the "sump extension" loops and the "extended pan" types on several years and models, and found them to be equivalent solutions over the long term.

Hope this helps.