whats thicker 10w30 or 10w40

10w40 is thicker at operating temperature than 10w30. The numbers are viscosity ratings: the '40' is thicker than '30' when hot. But your manual says 10w30 for a reason. Stick with that unless you're riding in extreme heat or towing heavy loads. I ran 10w40 in my old Foreman once and it seemed fine, but I went back to 10w30 after reading more.

I've been running 10w40 in my 2005 Foreman for years without issues. The thicker oil helps with high-mileage engines that might have some wear. If your engine is tight and low miles, 10w30 is fine. But if it's got over 10k miles or you notice some noise, 10w40 can help. Just make sure it's a good quality oil that's JASO MA rated.

Don't just switch based on a buddy's advice. Oil thickness affects startup lubrication and engine clearances. 10w30 is designed for your specific engine tolerances. Using 10w40 when not needed can cause sluggish oil flow at startup and might even reduce fuel economy. I'd follow the manual unless you have a specific reason to change.

Actually, 10w40 is thicker cold and hot. The '10w' part is the cold viscosity, same for both. The second number is hot viscosity. So 10w40 is thicker when hot. For trail riding in summer, 10w40 might be okay, but I'd check your owner's forum for your exact model. Some Honda engines are picky. I use 10w30 in my 2007 Rancher and it's fine.

I'm a mechanic and I see a lot of guys overthinking this. 10w30 and 10w40 are both fine for most utility ATVs. The key is using the correct API service class and JASO MA/MA2 rating for wet clutches. If you're riding hard in hot weather, 10w40 offers better protection. But for light trail riding, 10w30 is adequate. Change it regularly.

I disagree with the mechanic above. Sticking with the manufacturer's recommendation is always safest. These engines are built to precise tolerances. 10w40 might be slightly thicker, but that doesn't mean better. I had a friend who used 10w40 in his Suzuki and it started making noise. He switched back and it stopped. Not worth the risk.

What about synthetic vs conventional? If you go with 10w40 synthetic, it might flow better at startup than conventional 10w30. But again, manual says 10w30. I'd try 10w30 first. If you notice oil consumption or high temps, then consider 10w40. Also check your air filter and cooling system before messing with oil grade.

I've run 10w40 in my 2004 Foreman for 5 years with no issues. Ridden in Arizona heat, mud, and heavy loads. The engine has 15k miles and still runs smooth. Some people say thicker oil can cause clutch slippage, but I never experienced that. Just make sure it's not too thick for cold starts. 10w40 is still fine down to -20°F.

You guys are forgetting the 'w' stands for winter. Both have the same cold flow. The difference is at operating temp. For a used 2006 Foreman, 10w40 might help if the engine has some wear. But if it's stock and healthy, 10w30 is better for fuel economy and clutch engagement. I'd check the oil pressure with a gauge to see if it's within spec.

I'd recommend using 10w30 for now. The manual knows best. If you want to experiment, do an oil analysis after a season to see if there's excessive wear. That's the only way to know for sure. Also, don't mix brands or types. Stick with a reputable brand like Shell Rotella T6 or Mobil 1 V-Twin. Both are JASO MA rated.

I'm a newbie too and I just use whatever the local shop recommends. They said 10w40 is fine for most ATVs. I put it in my 2008 Polaris and it's been good. But I don't ride hard. Maybe it depends on your riding style. If you're just trail cruising, either will work. Change it every 50 hours and you're golden.

Actually, the Foreman 400 has a wet clutch, so oil must be JASO MA rated. Many 10w40 oils are, but check the label. Also, consider the climate. If you ride in cold weather, 10w30 is better for startup. In hot climate, 10w40 offers more protection. I live in Texas and run 10w40 year-round. My 2005 Foreman has 20k miles.

I've read that some Honda engines have tight tolerances and thicker oil can cause foaming or aeration, leading to reduced lubrication. Not sure if that's true for the Foreman, but I'd be cautious. Stick with 10w30 until you've done more research. There's a reason Honda recommends it. They test these engines extensively.

I disagree with the caution. I've used 10w40 in multiple Hondas without issue. The difference is minimal. As long as you're within the recommended range (10w30 to 10w40), it's fine. Many manuals list 10w40 as acceptable for high-temperature operation. Check your owner's manual supplement. Mine says 10w40 is okay above 32°F.

I'd also consider the age of the bike. Older engines with worn rings might benefit from a slightly thicker oil to reduce blow-by. But if your compression is good, 10w30 is fine. Do a compression test before deciding. Also, look at the oil when you drain it. If it's very thin and dark, maybe go thicker. But if it's clean, stick with 10w30.

Another thing: oil filters. If you switch to 10w40, make sure your oil filter is clean. Thicker oil can put more strain on the filter if it's clogged. Also, check the oil pump. On some older models, the pump might not handle thicker oil as well. I'd inspect the pump gears if you're going to change viscosity.

I've been running 10w30 in my 2006 Foreman since new. Never had a problem. I ride in all seasons, from 20°F to 100°F. I change it every 30 hours. The engine is still strong. I think people overthink this. Just use what the manual says and change it often. That's more important than the exact grade.

I'd say try 10w40 if you want, but watch for clutch slippage. If you notice the ATV revving higher without acceleration, the oil might be too thick for the clutch plates. That happened to me with 10w50 in a different bike. 10w40 is usually safe, but each engine is different. Listen to your machine.

I'm a fan of using the thinnest oil that still provides adequate protection. 10w30 is likely sufficient for your riding. Thicker oil doesn't always mean better protection; it can cause more drag and heat. I'd stick with 10w30 and focus on other maintenance like valve adjustments and coolant changes. That will keep the engine happy.

I'd also check if your Foreman has any recalls or service bulletins about oil. Some years had issues with oil consumption. If yours is one, 10w40 might help. But overall, I'd follow the manual. If you're still unsure, call a Honda dealer and ask. They'll give you the straight answer for your specific model.