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So my brother and I changed some differential oil in the truck. We used a small hand pump to push clean oil in the case. Oil was like 75w/140 or something crazy

Fast forward. I got a generator and needed to have oil added to it. Because of the fill location my wife used the same pump to put oil in it. The oil she needed to put in was 10w/30, which she did.

She did not clean the pump of the 75w. But we are talking maybe a tablespoon worth of oil of mixed weight. Would that cause any harm???

I’m also curious because I’d rather it be oil mixing instead of washing the pump with soap and water and having water mixed in with the oil.

Any input is appreciated!
 

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Don't even think about it. The only thing I'm careful of, is foreign objects like dirt, metal shavings, etc. that always seem to stick inside a funnel and a quick wipe with a rag takes care of that. A tiny bit of different oil won't hurt a thing. It's like the gnat in your potato salad last 4th of July............:eek::D
 
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If you're sure if was only a tablespoon of the 75W, I wouldn't worry about it.
 

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Heck even if you used half 75W, doubt it would hurt anything though probably wouldnt run it long term like that. Be enough additives in the 10W30 to make the 75W safe as motor oil and gear oil have different additives from factory. And guess I am just old, but air cooled engines always used to run straight 30W or even 40W in warm weather. Modern automobile engines have closer tolerances so maybe not want to run straight 30W in them though in warm weather doubt it would actually hurt anything. I would doubt significantly closer tolerances in small air cooled engines. Thin oils more to please EPA and official fuel mileage than for your personal benefit. They want engines to warm up faster and less drag while running cold.
 

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Heck even if you used half 75W, doubt it would hurt anything though probably wouldnt run it long term like that. Be enough additives in the 10W30 to make the 75W safe as motor oil and gear oil have different additives from factory. And guess I am just old, but air cooled engines always used to run straight 30W or even 40W in warm weather. Modern automobile engines have closer tolerances so maybe not want to run straight 30W in them though in warm weather doubt it would actually hurt anything. I would doubt significantly closer tolerances in small air cooled engines. Thin oils more to please EPA and official fuel mileage than for your personal benefit. They want engines to warm up faster and less drag while running cold.
not that long ago we added STP oil treatment which is only slightly thinner than alemite grease. I would buy a new can and wedge it in on top of the block to heat it up before I tried to pour it in.
 

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Don't clean your pump with soap and water.
Run some diesel or kerosene through it to flush out oil.
 

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No need to "clean" the pump. Oil is oil-- the different weights are just measures of how "thick" that particular stuff is under hot & cold conditions. The small residue left over from the last use of the pumps is insignificant.

Heavier weights are used when the tolerances between parts is large- gear boxes & differentials--tolerances measured in 100ths & 10ths, while lighter oils are used in engines where crank, cam & piston bearing tolerances are measured in 1000ths of an inch.

Heavier weights also make it tougher to crank the engine on start-up, particularly when outside temps are low. That's why block heaters are used in winter- to keep the oil thinner (and increase tolerances).

They say 90% of engine wear occurs on that first cold crank in the AM when the oil has drained down into the sump. That's one reason to use oil additives like Z-Max-- it penetrates metal parts and doesn't drain completely after the engine is shut down.
 
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