Briggs 3.75hp - oil is BLACK after 5 hours

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Some of you have read that my lawnmower's 6.5hp intek had an unfortuneate death. Right now I've temporarily put on a 3.75hp B&S engine. This engine is a little worn, but I recently replaced the crankshaft and made sure the inside was nice and clean. I've been using Mobile 1 10w30, and I just changed it after about 5 hours use. The oil is BLACK. Why did it get so bad so quickly?
 
Sounds Like the Air filter is Letting some dirt in or the carb is running rich. I have always had good luck with Dyno 30HD oil. Just a Idea.
 
well, that is the nature of that engine. Check the air filter and im sure the carb is running rich. Make sure all the extra oil on the air filter is sqeezed out. The L head engine burns dirty but it is reliable. The engine temps cook dino oil into submission but hey what do you expect from 20 oz of oil that is heated to its limits and beyond. Dont worry, what you are expiriencing is normal for your engine and the oil. The design of the L head allows for the oil to absorb dirt and carbon and to hold these in suspension, while the engine is in use, which is what oil is supposed to do. The aluminum block rapidly transfers heat out to the atmosphere and inside to the engine oil, which is what cools the engine on the inside. If your oil is dark after a few hours then it is doing its job. Change the oil every 20-30 hours and it will be ok. These engines are durable and run for years with proper maint. The L head design runs even longer if you dont maintain it. My Dad never changed oil on our old briggs push mower he just added oil to it once in awhile. We had that mower for 16 years. The intek engine burns fuel more efficiently and the ohv design allows for better fuel economy and combustion versus the L head design, but unfortunatly water is not an approved lubricant for the Intek engine.
 
No, this is most certainly not normal. The oil is BLACK. It looks like what they use to resurface driveways. It shouldn't ever get this bad...even if it's in there for years. Not to mention this is Mobile 1. It's not running rich, and the air filter is brand new.
 
If it turned syn black right away then there must be some blowby getting to the oil. Have you broke in this engine on dino? Was the engine rebuilt properly?
 
ZmOz, yeah, it looks like you've eliminated everything but rings and excessive blow-by ... unless something went horribly wrong with that crank install and the blackness is a lot of lead.
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--- Bror Jace
 
Zimmer - This may be more of a characteristic of the M1 oil.

I use M1 10W-30 in my Chevy Silverado 4X4 during the Wisconsin winter months & am always amazed at how black the oil looks at a 4K mile OCI.

Try a honey yellow dino SAE 30 HD, such as Mobile or Chevron, for 10+ hours and see what color the drained oil is. In my opinion, the dino oils are a dark brown vs. M1 which turns black.
 
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