12 minutes ago, weasley said:

 

A very cold oil will be thick, meaning a very thick oil film will form between moving surfaces.  This balances nicely with a cold engine, where the clearances are larger and need a thicker oil film.  However a cold oil will not be working fully - some of the chemicals used in it don't really activate until 60+°C, so although a cold oil will do a basic lubrication job, you won't get the full protection it can provide.  Hence why most engine wear happens during warm-up.

Well that ties in with my original gut feeling, so it's nice to have a guesstimate vindicated by an expert.

 

What I hadn't considered was that the increased engine tolerances when the engine is cold benefit from a thicker oil, that makes a lot of sense.  (I seem remember an old "fix" for worn engines was to use a slightly thicker oil.)

 

The giant book of things I don't know gets a few lines shorter today. 

Edited 15 October, 20205 yr by EnterName
Added notes on cold start-up

All right keep your hair on. I was respectful and gave you my opinion, without first resorting to wikipedia. I will go and educate myself again, but later. I have some real engineering to do first. 

Apologies if I came across as aggressive - absolutely not my intent.  I have participated in so many oil topics on the internet over the years that I try to present who I am and how I know what I am saying simply to try and establish some credibility.  I have great respect for engineers - I work with many and am interested in the subject, although am a chemist myself.

 

I also tend not to say who I work for because I want to present factual, objective information rather than being seen as a sales pitch.  Sometimes this means I have to bite my lip because I see people saying things about my company's products which I know to be totally untrue, but I have to be careful what I say as lots of it is confidential and to challenge any mis-truths may give away something proprietary.  Not saying this is happening here, just presenting you my background and the decades of oil topics I have tried to steer in the right direction!

44 minutes ago, weasley said:

Apologies if I came across as aggressive - absolutely not my intent.  I have participated in so many oil topics on the internet over the years that I try to present who I am and how I know what I am saying simply to try and establish some credibility.  I have great respect for engineers - I work with many and am interested in the subject, although am a chemist myself.

 

I also tend not to say who I work for because I want to present factual, objective information rather than being seen as a sales pitch.  Sometimes this means I have to bite my lip because I see people saying things about my company's products which I know to be totally untrue, but I have to be careful what I say as lots of it is confidential and to challenge any mis-truths may give away something proprietary.  Not saying this is happening here, just presenting you my background and the decades of oil topics I have tried to steer in the right direction!

You didn't come across as aggressive to me.

Going off subject very slightly, but oil related.

 

Back in around 1976 I bought a Ducati 860 motorcycle.

It was  a 90 degree air cooled in-line v twin, ie the front cylinder pointed towards the front wheel & the rear cylinder pointed towards the sky.

I had it from new, & at about 7k miles I took it to a motorcycle rally at Zolder race circuit in Belgium.

 

I took it around the circuit for a few laps, then returned to the camp site where it was running like a dog, misfiring & wouldn't tick over.

Checked the valve clearances & the rear cylinder clearance was massive, so the exhaust valve wasn't seating any longer.

I limped the bike back towards home,  got back to home soil before the engine expired completely.

 

Returned it to the dealer where it was repaired under warranty ( omitted to tell them it had been on the race track ), new valves & possibly guides in the rear cylinder.

Was told by the dealer that it should be run on straight 50 oil.

 

So seemed obvious to me that the rear cylinder wasn't getting cooled properly.

 

I bought an oil temperature gauge & fitted it to the sump plug, it regularly recorded 150-160 centigrade in road use & used Filtrate straight 50 oil from then.

 

At 12k miles exactly the same thing happened with the rear cylinder again, & thanks to the 2 year warranty ( very unusual in those days ) it was again repaired under warranty.

 

I sold it soon afterwards, & guessing 150 centigrade is getting past the maximum temperature that oil will protect the engines moving parts properly.

Presumably the oil temperature at the valve guides would have been way above this.

21 hours ago, Ads230 said:

You'll probably get 1000 different academic answers from this wonderful forum

Like I said @EnterName 😉

 

All proper useful info though, I've learned a lot reading through all this.

4 hours ago, PipH said:

Going off subject very slightly, but oil related.

 

Back in around 1976 I bought a Ducati 860 motorcycle.

It was  a 90 degree air cooled in-line v twin, ie the front cylinder pointed towards the front wheel & the rear cylinder pointed towards the sky.

I had it from new, & at about 7k miles I took it to a motorcycle rally at Zolder race circuit in Belgium.

 

I took it around the circuit for a few laps, then returned to the camp site where it was running like a dog, misfiring & wouldn't tick over.

Checked the valve clearances & the rear cylinder clearance was massive, so the exhaust valve wasn't seating any longer.

I limped the bike back towards home,  got back to home soil before the engine expired completely.

 

Returned it to the dealer where it was repaired under warranty ( omitted to tell them it had been on the race track ), new valves & possibly guides in the rear cylinder.

Was told by the dealer that it should be run on straight 50 oil.

 

So seemed obvious to me that the rear cylinder wasn't getting cooled properly.

 

I bought an oil temperature gauge & fitted it to the sump plug, it regularly recorded 150-160 centigrade in road use & used Filtrate straight 50 oil from then.

 

At 12k miles exactly the same thing happened with the rear cylinder again, & thanks to the 2 year warranty ( very unusual in those days ) it was again repaired under warranty.

 

I sold it soon afterwards, & guessing 150 centigrade is getting past the maximum temperature that oil will protect the engines moving parts properly.

Presumably the oil temperature at the valve guides would have been way above this.

 

A bulk oil temperature of 150°C is pretty high, although still well below the maximum it would see in the engine.  Of course if the bulk oil is hot that means it is getting heated up a lot somewhere around the engine, so it could be overheating there.  Oil film thickness varies with oil viscosity, so a very hot oil will be very thin which will lead to a very thin oil film - possibly thin enough to prevent metal-to-metal contact.

 

And as you discovered, an air-cooled engine is more accurately an oil-cooled engine.  Even a so-called water-cooled engine gets a significant cooling effect from its oil.

Edited 15 October, 20205 yr by weasley

Just to add a little more value to the thread, I found this link which explains the different types of viscosity as well as defining viscosity nicely.

https://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html

 

 

On 15/10/2020 at 08:48, TDIum said:

Gaaaa! I can't stand that Engineering Explained you tuber. Patronizing american twerp. 

As Bret says, once you get a reading from the oil temp display it's OK to consider it warmed up. 

The water cooling circuit on these engines (you and I have the same) is complex, designed to bring it up to temp quickly for emissions and fuel efficiency reasons. 

Just watched this, and I have to say I can see what you mean about him being patronising. Even just a quick search online returns tutorials on how to fix worn handbrake ratchets, which he claims never wear.

This video bothered me, and I'm still going to press the handbrake button when I lift the handbrake. (Mind you, I did wear through the chrome effect on my old car to reveal a nasty white plastic underneath.)

Grumble aside, he was right about the oil.

 

Just for fun,

 

I VCDS logged my coolant temperature and oil temperatures to show what's going on. Coolant clearly easier to warm than oil, not surprising really Ambient temps around 13C at the time, this was a normal run from home to an A road dual carriageway and at about 4.6miles my oil temp hits a reading on the Maxidot of 50C. 

 

I think the bump in the oil temp was probably just getting to around 60-70mph and I had to accelerate to get out into lane.  

 

On 10/11/2020 at 20:45, paulski said:

Just for fun,

 

I VCDS logged my coolant temperature and oil temperatures to show what's going on. Coolant clearly easier to warm than oil, not surprising really Ambient temps around 13C at the time, this was a normal run from home to an A road dual carriageway and at about 4.6miles my oil temp hits a reading on the Maxidot of 50C. 

 

I think the bump in the oil temp was probably just getting to around 60-70mph and I had to accelerate to get out into lane.  

 

Interesting! What are the 0-1400 numbers on the X-axis?

Time in seconds, I'd think.

5 minutes ago, EnterName said:

Interesting! What are the 0-1400 numbers on the X-axis?

 

At a guess, seconds since the log began 😉

7 minutes ago, Wino said:

Time in seconds, I'd think.

 

6 minutes ago, langers2k said:

 

At a guess, seconds since the log began 😉

Yeah, I initially thought that, but I figured it was best to check.

Now I want to change the settings on my car so it measures fluid temps from 0 deg C.

Edited 26 November, 20205 yr by EnterName

A couple of things, not quite directly on topic, but relevant:

 

No one in this thread has considered other thermal effects. As the oil warms up, it evaporates off any condensation in the oil. From this point of view, you want to get the oil up to somewhere around 80 C, to get any condensation to evaporate off moderately quickly.

 

I'm sure this isn't as bad on modern oils as it was on older oils, but I have had an issue with this back in the 80s, but the 'Aunt Minnie cycle' where there is stop-start cycling and the engine never gets up to temperature are always worrying, even if someone has done a test to show it is ok, under one specific set of conditions.

 

At the other end of the temperature range, HTHS ratings are usually measured at 100 C, If the oil temp is above that, you will be degrading the oil faster than has been allowed for in the service schedule, irrespective of what the schedule says.

 

(It may be that you are better off in the variable service schedule, in this case, because the software may compensate for the increased temp, shortening the service interval, not that anyone will know how much faster the oil degrades at the higher temperature. Well, maybe the oil manufacturer does, but they don't tell VAG. so that goes nowhere.) 

9 minutes ago, Camlobe said:

A couple of things, not quite directly on topic, but relevant:

 

No one in this thread has considered other thermal effects. As the oil warms up, it evaporates off any condensation in the oil. From this point of view, you want to get the oil up to somewhere around 80 C, to get any condensation to evaporate off moderately quickly.

 

I'm sure this isn't as bad on modern oils as it was on older oils, but I have had an issue with this back in the 80s, but the 'Aunt Minnie cycle' where there is stop-start cycling and the engine never gets up to temperature are always worrying, even if someone has done a test to show it is ok, under one specific set of conditions.

 

At the other end of the temperature range, HTHS ratings are usually measured at 100 C, If the oil temp is above that, you will be degrading the oil faster than has been allowed for in the service schedule, irrespective of what the schedule says.

 

(It may be that you are better off in the variable service schedule, in this case, because the software may compensate for the increased temp, shortening the service interval, not that anyone will know how much faster the oil degrades at the higher temperature. Well, maybe the oil manufacturer does, but they don't tell VAG. so that goes nowhere.) 

I think modern oils, particularly synthetics, are perfectly happy at 100 C. Oils really have improved enormously over the years.

Not sure about water condensation in the oil, never really thought about it, TBH.

 

 Vcds log outputs interval numbers to the CSV  but I cannot quite figure what it is, so I "cheated" in excel to get it to plot out correctly and just did 1,2,3 till the end of the log. It was about 15minutes.

 

It was interesting to see how stable the coolant temperature is maintained at 90C, it flat lines at the end. I don't think a mechanical thermostat would achieve that close control so the three electrically controlled cooling systems must play a part in that. 

 

Anyone else think of a log graph they want to see next. 

 

 

 

 

 

Edited 26 November, 20205 yr by paulski