The CB1100 Community Forum

At the risk of groans from the readers at another oil change related thread, I wondered if a step had been missed in the various oil change procedure threads, or if it just had not been mentioned because it was considered a "given".

I am of the "old School" group about changing oil hot/warm, for smoother drain flow, suspending particles immediately prior to drain, and the Shop Manual calls for Hot/warm drain. What I noticed is that the various previous threads did not mention the first step in the drain procedure, after the bike is warmed up and shut off, is removing the oil filler cap. This is also the first step in the Shop Manual.

Back in the day, an old time mechanic taught me the finer points of oil changes. Aside from the warm up in order to drain hot/warm oil, he also said to remove the oil filler cap before removing the drain bolt. I asked him why, and he said it eliminated some vacuum in the crankcase so that the drained oil would flow out more smoothly and completely. Same principle as modern gas cans. You can take the cap off the cans pour spout, and gas will pour, but not smoothly. However open the small vent cap on the can first, then take the cap off the pour spout, and the gas will then pour much more freely out of the can.

I thought I would post this small step for those just starting DIY maintenance, as well as those that might not have a Shop Manual. I imagine this will be "old news" and "second nature" to all the other dinosaurs out there like me.

Exactly!

crankcases are vented the idea of removing the filler cap first is just an old wives tail!

Tale.

Certainly can't hurt but it seems to make little difference in flow when I forget to remove it first.

I’ve never removed the fill cap first. Oil pours out without hesitation.


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But it would do no harm. I have found it much easier to get the new oil in if I remove the cap. YRMV.

It is my habit to remove the drain bolt, start the flow, then remove the filler cap. On most vehicles, the flow will increase when the filler cap is removed.
Then I find something else to do and let it drain to the last drop.

If I recall correctly, my Moto Guzzi V7II did not like to drain much until the filler cap was removed and it had two drain bolts for the engine.

I certainly did not intend to imply that leaving the cap on would not work, because yes, the oil will still drain. That said, it has been my experience that removing the cap first does work a bit more efficiently for most of the vehicles I have worked on. When in doubt I defer to the Shop Manual, and in this case, step one is to remove the oil filler cap. Just food for thought, and use the procedure you have the most confidence in.

(05-02-2018, 04:47 AM)SportsterDoc_imp Wrote: [ -> ]It is my habit to remove the drain bolt, start the flow, then remove the filler cap. On most vehicles, the flow will increase when the filler cap is removed.
Then I find something else to do and let it drain to the last drop.

If I recall correctly, my Moto Guzzi V7II did not like to drain much until the filler cap was removed and it had two drain bolts for the engine.

So do I.

Cap first, drain plug second = common sense with fluids

pb