what kind of oil does a four wheeler take

I'd go with 10W-40 synthetic in a Sportsman 500. That engine is air/oil cooled and synthetic handles heat better. I run Shell Rotella T6 5W-40 year-round in mine. Works great in cold starts too.

Stick with a JASO MA/MA2 rated oil because the wet clutch needs it. Car oil has friction modifiers that'll make your clutch slip. I use Yamalube 10W-40 but any brand that meets JASO MA is fine.

You don't need synthetic if you change it often. But if you ride hard in summer, synthetic helps with high temps. I've used conventional 10W-40 in my 2007 Sportsman for years with no issues.

Wait, the 500 is a single-cylinder, right? Those engines can run hot. I'd go synthetic 10W-40 for sure. Rotella T6 is popular but make sure it's the heavy duty diesel oil version, it's JASO certified.

Actually, the manual for the 2008 Sportsman 500 says 10W-40, API SG or higher, and JASO MA. I'd follow that exactly. Synthetic is optional but not required unless you ride in extreme temps.

I disagree with the synthetic being optional. That engine has some known valve guide issues if oil breaks down from heat. Synthetic gives better protection. I'd spend the extra few bucks.

Check your year because the 2008 uses a different engine than earlier models. Some 500s had a wet sump, others dry. The oil type is still 10W-40 but capacity varies. Get a service manual.

Just use Polaris Premium 4 oil if you want to be safe. It's pricey but it's specifically made for those engines. I ran it for years. But any 10W-40 JASO MA synthetic works too.

I run 5W-40 synthetic in my 2008 Sportsman 500 and it starts great in winter. But if you only ride in summer, 10W-40 is fine. Make sure it's not energy conserving oil.

Don't forget the filter! On those Polaris 500s the oil filter is a spin-on cartridge, easy to change. Use a good one like Polaris or Wix. Some cheap filters restrict flow and cause issues.

I made the mistake of using Mobil 1 car oil once. Clutch started slipping within 10 miles. Had to drain and refill with proper ATV oil. So avoid any car oil that says energy conserving on the back.

What about viscosity numbers in extreme heat? I ride in Texas summer at 100+F. Should I go up to 20W-50? I've heard mixed things. The manual says 10W-40 is fine but I worry about oil thinning.

20W-50 might be too thick for cold starts. If you're really concerned, run 15W-40. That's common in many diesels and it's available as JASO MA. I use it in my Honda Foreman with no issues.

Honestly, just pick a name brand JASO MA 10W-40. I use Valvoline ATV oil. It's affordable and meets the specs. The only time I'd special order something is if you ride in extreme cold.

Check the oil level after the first ride. Some 500s burn a little oil. If you notice it dropping, switch to a heavier viscosity like 10W-50 synthetic. But that's just a band-aid for worn rings.

I use Lucas oil stabilizer with my 10W-40. It helps with high temp protection and reduces noise. But some guys say it can cause clutch drag. I haven't had issues in my 2006 Sportsman.

You also need to consider the gearbox oil if your model shares oil with transmission. On the 500, I think it's separate. But double-check. If it's shared, the oil must be JASO MA approved.

I'd recommend using a magnetic drain plug. It catches metal shavings and you can monitor engine health. Cheap upgrade for peace of mind. I install one on all my quads.

A trick: after draining, pour a quart of cheap diesel oil through to flush out sludge before adding fresh oil. Then fill with your chosen high-quality oil. Works well for neglected engines.

Whatever you choose, record the brand and viscosity so you can replicate it. Mixing different brands might cause foam. I keep a logbook. Also, change every 50 hours or once a season, whichever comes first.