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JohnF2015
JohnF2015, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1013
Experience:  Owner/Service Technician at S & J Small Engines
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I have a Chaftsman 21hp engine. After I change the oil and

Customer Question

I have a Chaftsman 21hp engine. After I change the oil and filter the oil turns black. Any idea why?
Submitted: 2 months ago.
Category: Small Engine
Expert:  JohnF2015 replied 2 months ago.

Hi, my name is***** will be assisting you.

On these engines you will never get all of the old oil out when you drain it. There are several cavities in the oil pan that just won't drain out completely therefore when you add new oil and start the engine it will mix with the old oil that was left behind and look black. Even if you only run the engine for a couple minutes it looks this way.

Customer: replied 2 months ago.
I don't have to worry about having to add oil on a regular basis.
Expert:  JohnF2015 replied 2 months ago.

I would be concerned if you are having to add oil on a regular basis but there was no mention of that in your original comment.

Expert:  JohnF2015 replied 2 months ago.

You should always check the oil before starting your engine. I even recommend that you check it every time before starting, even if you checked it, started and ran the machine for 10 minutes shut it off and then went to restart it. You never know when you could develop a leak or the engine may start to burn oil.

Expert:  JohnF2015 replied 2 months ago.

If you are having to add oil constantly then it makes me think that you are having another issue. It could be as simple as a blown head gasket causing you to burn oil when running. It could be a leak but you would notice that if it was a problem.

Customer: replied 2 months ago.
My nephew has the same lawnmower and he told me the same thing happened to him. His oil started turning black and his engine blew. Could gasoline be leaking in the the cranksase
Expert:  JohnF2015 replied 2 months ago.

Yes it could but you would notice that anytime that you would check the oil level because it would always be overfilled with fuel/oil mixture.

I have seen several of these engines have a blown head gasket, it blows between the oil drain back passage for the valve train and the cylinder. You sometimes hardly notice a power difference when this first happens but it will cause the engine to begin to use some oil and the oil gets dirty quicker. Eventually it will get so bad that the engine will have very little power and will smoke a white or gray smoke constantly when running.

Expert:  JohnF2015 replied 2 months ago.

Normally if gasoline is leaking into the crankcase it makes the engine extremely difficult to start the first time you try it after it has been a sitting for a day or two.

Expert:  JohnF2015 replied 2 months ago.

Are you just having issues with the oil getting black right away or is it using oil?

Thank you it has been a pleasure to assist you.

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