Dipsticks

[Arthur Marshall]

This is probably a stupid question, but after a day's run and with the engine cold, when I hoick the dipstick out to check the oil, before I wipe it and stuff it back in, it shows oil at the minimum mark. After I wipe it and put it back to check properly , it shows oil at the full level. 

I assume the second reading is correct, but why doesn't the oil equalise to the correct level initially? 

[RLWP]

Do you think you might have too much time on your hands?

[dmr]

35 minutes ago, Arthur Marshall said:

This is probably a stupid question, but after a day's run and with the engine cold, when I hoick the dipstick out to check the oil, before I wipe it and stuff it back in, it shows oil at the minimum mark. After I wipe it and put it back to check properly , it shows oil at the full level. 

I assume the second reading is correct, but why doesn't the oil equalise to the correct level initially? 

I have noticed something similar and have not thought up an explanation yet. Maybe the forum will give us the answer, but hopefully not because its nice to ponder things like this, much better than worrying about serious stuff.

 

..............Dave

[NB Esk]

I'll fall for it and it's only my opinion.  When the dipstick is wet with oil it has lost its surface tension (and therefore the oil struggles to stick to it) When it's dried off the surface tension is restored and, hey presto.......

[RLWP]

15 minutes ago, NB Esk said:

I'll fall for it and it's only my opinion.  When the dipstick is wet with oil it has lost its surface tension (and therefore the oil struggles to stick to it) When it's dried off the surface tension is restored and, hey presto.......

So, when the dipstick is covered in oil, it makes it hard for oil to stick to it?

[Onewheeler]

Pure guess, but looking at pictures of dipsticks and tubes (not a euphemism but private browsing might be advised) it looks as if in some models the stick doesn't emerge from the bottom of the tube. So, in a hot engine if there is a good seal at the top where the dipstick goes in (that's a big if) air in the tube expands and the level at the bottom of the tube drops. Pull it out and oil settles to its proper level.

 

Or something completely different.

[RLWP]

3 minutes ago, Onewheeler said:

Pure guess, but looking at pictures of dipsticks and tubes (not a euphemism but private browsing might be advised) it looks as if in some models the stick doesn't emerge from the bottom of the tube.

That won't be true of Arthur's Lister

[Sea Dog]

1 hour ago, Arthur Marshall said:

This is probably a stupid question, but after a day's run and with the engine cold, when I hoick the dipstick out to check the oil, before I wipe it and stuff it back in, it shows oil at the minimum mark. After I wipe it and put it back to check properly , it shows oil at the full level. 

I assume the second reading is correct, but why doesn't the oil equalise to the correct level initially? 

Obviously, your engine realises you're not happy with the first result (or why would you do it again?) so, like a faithful Labrador, it trys to please you with something it thinks you might like better the next time.  You should be pleased and give it a biscuit.

[David Mack]

Does the dipstick vibrate upwards a bit while the engine is running? Try pushing it down before you pull it out the first time.

 

 

[RLWP]

4 minutes ago, David Mack said:

Does the dipstick vibrate upwards a bit while the engine is running? Try pushing it down before you pull it out the first time.

 

 

Clever!

[MtB]

1 hour ago, Arthur Marshall said:

This is probably a stupid question, but after a day's run and with the engine cold,

 

 

That's one weird engine you have there. After a day of running my engine is HOT.

[OldGoat]

12 minutes ago, David Mack said:

Does the dipstick vibrate upwards a bit while the engine is running? Try pushing it down before you pull it out the first time.

 

 

Now that makes a bit more sense: and if the engine is an SR, there's not a lot of difference between the two marks? Can't be bothered to go outside to check my SR2 genny to check in case I'm wrong....

 Having been motoring for years bot bikes and cars, I was taught to always remove the stick, wipe it, check the level and repeat. Dunno why - but old habits die hard. 

 

(My modern car doesn't have a dipstick only some option somewhere - but not intuitive to find, however it's a Volvo so doesn't use oil between services)

Edited June 12, 2018 by OldGoat

[Sea Dog]

2 minutes ago, OldGoat said:

Having been motoring for years bot bikes and cars, I was taught to always remove the stick, wipe it, check the level and repeat. Dunno why - but old habits die hard. 

 

I think you might be onto something there OG.  That very action is possibly why no-one experienced in engines has yet solved the conundrum - they haven't noticed the phenomenon in order to be able to give a definitive answer.

[Boater Sam]

Sump contracting.

[WotEver]

Oil in all the pathways drains back into the sump. 

[dmr]

 

3 minutes ago, WotEver said:

Oil in all the pathways drains back into the sump. 

Could be, I have thought about that, but that infers the dip stick is creating an air tight seal to stop the oil draining till stick is removed, but the crankcase ventilation should provide an alternative route for the air????

 

.................Dave

[WotEver]

13 minutes ago, dmr said:

 

Could be, I have thought about that, but that infers the dip stick is creating an air tight seal to stop the oil draining till stick is removed, but the crankcase ventilation should provide an alternative route for the air????

 

.................Dave

Okay then... oil can’t move up the dipstick tube because of the seal at the top. Remove the dipstick, seal is released, oil flows up the tube...

 

Thats probably as much garbage as my first idea

 

 

Edited June 12, 2018 by WotEver
Tryping

[Arthur Marshall]

2 hours ago, RLWP said:

Do you think you might have too much time on your hands?

Certainly, I'm on holiday sitting on the back deck in the sun. But it's an interesting question as you'd think the levels should be the same. Just struck me as an anomaly and I thought someone here would know the answer. 

Anyway, I've stuffed a biscuit down the air intake, so that should help... 

 

PS no I haven't, not really... 

[OldGoat]

4 minutes ago, WotEver said:

Okay then... oil can’t move up the dipstick tube because of the seal at the top. Remove the dipstick, seal is released, oil flows up the tube...

 

Thats probably as much garbage as my first idea

 

 

That only has credence if the tube is actually immersed in the oil. On some engines - especially with a deep sump, the dipstick  "waves in the wind" at its lower end...

[dmr]

I've seen inside a few engines and think the dipstick usually protrudes well below the bottom of the dipstick tube, but dunno how universal this is.

 

Just been and done a couple of test readings and can't replicate this effect. Engine has not run for well over 24 hours though.

 

................Dave

[Chewbacka]

My guess - Oil splashes all over the dip stick when running and after stopping and cooling  you remove the dip stick, the oil drains off the end off the dip stick but does not have a clean cut off, so you look at the drip on the end.  Then wipe it, reinsert and there is a clear line between oil and no oil, so the true level is easier to see.

[WotEver]

9 minutes ago, OldGoat said:

That only has credence if the tube is actually immersed in the oil. On some engines - especially with a deep sump, the dipstick  "waves in the wind" at its lower end...

Ahh yes. I’d venture probably most engines. 

[NB Esk]

2 hours ago, RLWP said:

So, when the dipstick is covered in oil, it makes it hard for oil to stick to it?

Correct 

[cuthound]

Could it be capillary action? Probably not on such a short dipstick and relatively viscous oil, but on the largest diesel tanks I worked on (circa 100,000 litres each), the diesel oil would visibly creep up the dipstick if you took too long to read it.

[Dr Bob]

5 hours ago, Arthur Marshall said:

This is probably a stupid question, but after a day's run and with the engine cold, when I hoick the dipstick out to check the oil, before I wipe it and stuff it back in, it shows oil at the minimum mark. After I wipe it and put it back to check properly , it shows oil at the full level. 

 

...erm...." I agree with MtB, after a days run, my engine is very hot. Well by very hot I'm talking 70 degs ish. If you have problems with the estimating the temp of the engine, may you also be having problems with assessing dipsticks? Dipstick science is notoriously difficult!?