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Old 09-04-2012
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Question about oil viscosity in a diesel genset

I rarely use my genset, but I have notice that the oil seems a bit runny, like water, at times. In the past I just changed the oil. However, recently I ran the genset for a good 12 to 20 hours and I notice the oil was very, very thin, as well as really low. I put more in and it just seemed to be unnaturally runny. I use straight 30 diesel oil.

Is this normal, or does something seem wrong?

I am planning on changing the oil again but use 15w-40.
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Old 09-04-2012
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Re: Question about oil viscosity in a diesel genset

you might be getting diesel into the crankcase,how worn is the cylinders/compression,I would stay with the straight 30 wt or maybe even 40,a good diesel machanic can determine diesel fuel in oil by the way it drips off the dipstick
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Old 09-04-2012
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Re: Question about oil viscosity in a diesel genset

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Originally Posted by sawingknots View Post
you might be getting diesel into the crankcase,how worn is the cylinders/compression,I would stay with the straight 30 wt or maybe even 40,a good diesel machanic can determine diesel fuel in oil by the way it drips off the dipstick


You can also get an oil analysis done that will tell you for sure. Also may show abnormal wear.

Blackstone Labs

or other sources, Google "Engine oil analysis"

Paul T
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Old 09-04-2012
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Re: Question about oil viscosity in a diesel genset

Done engs all my life , Blowby is just something diesel engs do mostly due to such high comperssions ...the older thay get the more thay do blowby.
Don't put a multi vis oil into an eng not built for it .

Just use what the eng requires / designed for , doesn't hurt to put heaver oil in like in hot weather , heavy use / like a duty eng running 24/7 , or as it gets high hours on the hobbs .

You can tell if the oil has a lot of fuel in it just by smelling it ( well I can lol) if it's a lot of fuel in the oil you could put a little in a spoon ( go outside) and put a flame to it and it will flash but that would be a lot of blow by , like Sawingknots says piston to cly fit & valve guide fit have a lot to do with it .

Check your valve adjustment and fuel injector timeing & pressure , it all starts with valve guides getting worn , diesels are Very Robust engs and designed with blowby in mind if it starts drinking oil a lot just change more often..

good luck.
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Old 09-04-2012
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Re: Question about oil viscosity in a diesel genset

Leaking or cracked injector can cause fuel to get into the crankcase as excess fuel is sprayed into the cylinders during the power and exhaust strokes due to the leak/crack.
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