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Old 12-03-2019, 15:21   #1
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Changing engine oil

I've always warmed up the engine and oil before changing the oil, thinking that it would flow out of the dipstick hole easier. But my buddy says better to do it with a cold engine because the oil has settled in the crankcase and you will get more quantity whereas with a warm engine it is spread out. This makes sense. What do the old salts think?
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Old 12-03-2019, 15:31   #2
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Re: Changing engine oil

Pretty much every engine manual that addresses the issue will tell you to warm up the engine before changing the oil. I then let it sit for half an hour and I think everything that is going to drain back into the pan has done so.
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Old 12-03-2019, 15:35   #3
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Re: Changing engine oil

Nope. Two reason for warming the oil before changing:


1) it thins the oil so less is likely to cling to the walls of the engine or stay within the galleries. And makes it easier to pump.

2) (and most importantly) it helps to mix any sediments or stratification (especially moisture) that might otherwise stay at the bottom of the sump where it won't be extracted.
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Old 12-03-2019, 15:48   #4
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Re: Changing engine oil

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Originally Posted by DEAN2140 View Post
I've always warmed up the engine and oil before changing the oil, thinking that it would flow out of the dipstick hole easier. But my buddy says better to do it with a cold engine because the oil has settled in the crankcase and you will get more quantity whereas with a warm engine it is spread out. This makes sense. What do the old salts think?

Both true,
warming up the engine as well as making the oil fluider is needed to prevent any waste from remaining on the bottom of the sump;
but after warming up the engine you need to wait for some minutes, to let all the oil ricollect into the sump.
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Old 12-03-2019, 15:52   #5
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Re: Changing engine oil

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>>>>>>>>>>>>>>
but after warming up the engine you need to wait for some minutes, to let all the oil ricollect into the sump.



i can never do it that fast! By the time I've warmed up the engine and even gotten the gear out to pump, I still wait until the engine is OFF before I connect my hand pump to the hose that goes to my engine oil pan. And I have to remember to wear a pot holder around the pump. By this time, I'm really getting to lust after those new Betas with the pump built in!
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Old 12-03-2019, 16:13   #6
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Re: Changing engine oil

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i can never do it that fast! By the time I've warmed up the engine and even gotten the gear out to pump, I still wait until the engine is OFF before I connect my hand pump to the hose that goes to my engine oil pan. And I have to remember to wear a pot holder around the pump. By this time, I'm really getting to lust after those new Betas with the pump built in!

When I say "after warming up the engine you need to wait for some minutes" I mean "wait for some minutes after the engine is off", I thought it was understood

P.S. I've a Perkins with a pump built in, it's gorgeous
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Old Yesterday, 15:26   #7
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Re: Changing engine oil

I think my vacuum pump takes 20 minutes, so I'm pretty sure everything has drained back to the oil pan by then. In the olden days we would flush our engine out with diesel fuel, does anyone do that anymore?
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Old Yesterday, 15:51   #8
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Re: Changing engine oil

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I think my vacuum pump takes 20 minutes, so I'm pretty sure everything has drained back to the oil pan by then. In the olden days we would flush our engine out with diesel fuel, does anyone do that anymore?

the proof of the pudding is in the eating - or...no. Maybe some people do it but it doesnt have any effect - more important by far is to change the oil regularly (measured by engine use rather than time, in the case of boats) and, if you DO subscribe to the diesel flush, consider more frequent oil changes instead. I've a lifetimes experience of nursing old engines of all types and, while I may have done a bit of flushing 40 years ago, I've found the frequent oil change to be the best method of ensuring longevity in old engines. Kinda hoping good red wine is having the same effect on myself...
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Old Yesterday, 18:37   #9
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Re: Changing engine oil

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I think my vacuum pump takes 20 minutes, so I'm pretty sure everything has drained back to the oil pan by then. In the olden days we would flush our engine out with diesel fuel, does anyone do that anymore?
Wouldn't you need to do at least a partial second oil change so that the diesel that was left didn't dilute your new oil? At least if you are using the dipstick method to suck it out and can't ever be sure you got it all.
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Old Yesterday, 19:44   #10
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Re: Changing engine oil

Good points Charlie and Rob...
Long before modern oils and additives, I learned it from my father on our cars, trucks, and tractors... Drain the oil. fill with diesel, turn the engine over a few times, drain, and put in the new oil. I think the idea was that the diesel fuel was a solvent to dislodge and clean out grime and deposits.
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Old Yesterday, 20:08   #11
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Re: Changing engine oil

Without a bottom drain plug, you’re never going to get ALL the old oil out....and it gets expensive to try flushing by filling, running, and draining again, so best is just change often.

The cup or so of old oil you leave in there is diluted into the gallon plus of new oil you put back in...not the end of the world. Your new oil has 1 20th of the contaminants in it the old had, and as you use it, it will work back up to contaminant-full, at which time you change it again.

No sense in getting it super clean, then after 5 hours running you are where you would be with that one cup of old oil mixed in with new. While I always change filters at oil change time, theoretically the filter should last much longer than the oil. Acid buildup is the real problem with diesels and oil - I go no more than 100 hours between changes.

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