Low end of "Normal" for engine oil temp

[EnterName]

I watched this video and the first point on operating temperature piqued my interest on oil temperature.

 

So I monitored my car on warm-up, and sure enough after about 5-6 min, my car water temperature was in the middle of normal, however my oil temp was still reading "--", and only after a few more minutes did the oil temp hit 50 deg C and start registering.

On the motorway in summer, I recall it being around 95 deg C, but pootling around town today at 13 deg outside temp, oil temp was around 80 deg C.

 

Does anyone know what the minimum oil temperature is for an engine to be regarded as fully warmed-up?

[Ads230]

You'll probably get 1000 different academic answers from this wonderful forum, since it's all dependent on the engine make/model/tolerances & oil spec used within the engine 😉

 

As a general rule of thumb (& as I'm sure you're well aware), the indicated coolant temp meets its 'normal' level much faster than the oil itself. Oil takes a while for it all to warm up and become less viscous, therefore putting less friction on the engine components & doing its job properly.

 

Personally with my VRS, for example, typically sits between an indicated 95 deg C (which I regard as the 'cool end') to 105 deg C (usually 'middle' - e.g. motorway driving). I'd consider 'Hot' to be 115 deg C+ in normal driving, unless doing track days etc. 

 

I'll take it gently for the first 5-10 minutes of driving where it starts increasing from the indicated oil temp from 50 deg C -->.  My personal approach is to wait until it hits 90 deg C, where I (subjectively) feel that it's "warmed up" to allow more spirited driving etc; but appreciate others might think differently.

 

I'm not sure there's any definitive answer online unless someone is a verified VAG engineer, but typically anyone with mechanical sympathy & understanding will limit any spirited driving or overrevving until the oil meets at least 80 deg C, where it starts to reach its operating temperature. 

[Ootohere]

Simplified with a TSI.

The Coolant is when up to temp around the low 90*oC's, and the oil which is also a coolant gets to the efficient temp of around 90's C, and get hotter and the coolant system of the radiator, cooling fans at lower speeds are trying to bring the oil temp back down to a lower temp when it can.

 

So the oil can get hot, but you do now want it staying there when the engine is not under load.

You also do not want it going low, so in very cold weather there might be grill blinds, pieces of board etc used to stop the flow of very cold air to the radiator and engine department.

[brettikivi]

as far as I'm concerned, if I can read a number, the engine is warm. Especially from a -20C start. I might only see 65-70C in winter.

 

 - Bret

[Ootohere]

With a 1.4 TSI Twincharger @ over 200 ps with 5w 30 FS oil & 99 ron minimum petrol i could do a few hundred miles including Dual Carriageways & Motorway at NSL when the ambient temp was below freezing and the indicated oil temp would not get above 88*oC.

The oil capacity is given as 3.6 litres, i would have 3.9- 4 litres in.

That was when i got the very best MPG as long as driving more than 30 miles.   Cold dry roads & cold dry air and it loved that conditions.

http://briskoda.net/forums/topic/282056-at-what-oil-temperature-in-a-vrs-or-other-fab2-do-you-back-off

 

Edited 14 October, 2020 by e-Roottoot

[Phil-E]

Sounds normal.

 

I've only had my MK2 1.4 TSI a couple of months and only just started driving it in colder weather.

 

I do 7km to work and by the time I'm there the temp guage is on 90 and oil temp at early to middle 60s.

 

In the summer I never saw the temp go over 97c and that was even driving on mountain roads with 3 adults, a dog, boot full and 3 bikes on the tow bar rack.

 

Also to note is my car has the factory fit tow bar which on the 1.4 TSI includes an upgraded radiator.

 

I also have under bonnet insulation which wasn't standard on the 1.4 TSI.

[paulski]

Subjective subject. Who's getting their vcds to log it then for a few days real world driving, would love to see some graphs of that.

 

2.0 TDI. From cold on dual carriageway runs when coolant has warmed to 90C (~5miles) oil is just reading 50-60C. Another few miles beyond that I'm happy to stamp the gas if required 

[TDIum]

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. 

[EnterName]

Thanks for your posts, folks.

I had a Google to see what temperature the oil changed viscosity, assuming it gets thinner as it heats up, but I couldn't find anything specific on it.

My own gut feeling is that 60 deg C would be the minimum oil temp before really booting the throttle, but I'm surprised at just how long it took for the engine oil to warm up, in my car compared to the water temp.

It'll be interesting to see just how long the oil takes to get up to 50 deg C in winter, after a frost.

I was just curious to know the relationship between temp and viscosity, beyond what I know, which is simply "warm oil flows better than cold oil". Doubtless someone somewhere has a few graphs plotting viscosity/temperature.

 

Oil temp something I never gave a moment's thought, assuming the water temperature gauge was all I had to pay attention to.

[EnterName]

15 minutes ago, 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. 

I've worked with engineers for nearly 40 years now, and we can be quite odd. He doesn't seem at all unusual to me.  

[Breezy_Pete]

18 minutes ago, EnterName said:

I had a Google to see what temperature the oil changed viscosity

A continuum, surely. 

@weasley would probably be my go-to person for knowing where to find such info.

[TDIum]

23 minutes ago, EnterName said:

I've worked with engineers for nearly 40 years now, and we can be quite odd. He doesn't seem at all unusual to me.  

 

Only been in the profession 28 years and I deal with tiny electronics. But that guy - well put it this way, I would have sat a the other end of the lecture room. 

[EnterName]

5 minutes ago, Wino said:

A continuum, surely. 

@weasley would probably be my go-to person for knowing where to find such info.

Yes, I realise there is a load of different grades of oil, and presumably a whole load of different graphs.

But I'd expect the typical graph to look a bit like this. (Highly technical, took me hours to come up. )

I just need a reliable source of the numbers. (I also realise I may be well off the mark with my graph.)

[weasley]

As @Wino says, oil viscosity varies continuously with temperature, down to the point at which it 'freezes' and up to the point it boils or catches fire.  The viscosity classification (eg 5W-30) gives some idea of how the oil behaves when cold (the 'W' number) and when at 100°C (the second number).  100°C is considered to be a typical bulk operating temperature but obviously in the course of doing its job the oil experiences a wide range of temperatures, from cold start to the top piston ring or piston undercrown.  If you can look at the technical data sheet for an engine oil, the value that helps you understand the effect of temperature on viscosity is the viscosity index (VI).  The higher this number, the less the viscosity changes with temperature.  So, an oil with a VI of 120 will vary more than an oil with a VI of 150.  If both of these oil have the same viscosity at 100°C then the lower VI oil will be thicker when cooler and thinner when hotter than this.  The relationship is not linear - it is a fairly complex logarithmic relationship.

 

I would consider an oil to be 'warm' around the 60-70°C mark - this is the temperature that some of the active ingredients really start getting to work properly.  This isn't the final operating temperature and I wouldn't expect an oil temperature (measured in the sump) to stabilise here.

 

In an engine the oil does warm up significantly slower than the coolant, largely because the coolant is thermostatically controlled and only the small portion within the block is circulated at first, whereas all of the oil is circulated all of the time, so is a significantly larger mass to heat and is exposed to the cooling effect of the sump.  I recall that in my Yeti TDi the oil would just about reach 90°C on my 30 minute work commute in the winter and would cool noticeably during any time spent idling.

[weasley]

17 minutes ago, EnterName said:

Yes, I realise there is a load of different grades of oil, and presumably a whole load of different graphs.

But I'd expect the typical graph to look a bit like this. (Highly technical, took me hours to come up. )

I just need a reliable source of the numbers. (I also realise I may be well off the mark with my graph.)

 

Pretty close!

 

Take a look here.  Your "runniness" is effectively the inverse of viscosity.

Edited 15 October, 2020 by weasley
Updated info

[EnterName]

2 minutes ago, weasley said:

 

Pretty close!

 

Take a look here.

Bingo! That's just the job. Thanks @weasley

[Breezy_Pete]

Cheers for the input. Looking at the numbers on the graphs for the lower viscosity oils, it does appear that @brettikivi is about right.

[TDIum]

21 minutes ago, weasley said:

As @Wino says, oil viscosity varies continuously with temperature, down to the point at which it 'freezes' and up to the point it boils or catches fire.  The viscosity classification (eg 5W-30) gives some idea of how the oil behaves when cold (the 'W' number) and when at 100°C (the second number). 

 

Sir, with all respect I do believe you are mistaken. A multigrade oil specified as 5W30 means, its like a 5-grade in Winter and a 30 in summer. This goes back to when multigrade oils were invented, before which you would have to change it twice a year. 

[TDIum]

The oil remains liquid and will lubricate your metal bits even when very cold.

What you are concerned with is the metal bits and how they expand with temperature. This is the thing you want in the normal operating range before giving it some right boot. Moving parts expanded to their normal operating clearances. 

[Breezy_Pete]

.

Edited 15 October, 2020 by Wino

[Breezy_Pete]

9 minutes ago, TDIum said:

5-grade in Winter and a 30 in summer

No, see here: https://www.opieoils.co.uk/t-multi-grade-car-engine-oils-explained.aspx

100°C is the point at which the right-hand number is measured. "Winter" and "summer" would be too vague.

[weasley]

1 minute ago, TDIum said:

 

Sir, with all respect I do believe you are mistaken. A multigrade oil specified as 5W30 means, its like a 5-grade in Winter and a 30 in summer. This goes back to when multigrade oils were invented, before which you would have to change it twice a year. 

 

That's how the nomenclature was first developed, but it isn't really like that any more.  What you say is largely correct, but doesn't quite go far enough.  The "5W" is saying the oil is behaving like a '5' grade would when cold and the "30" bit is saying it is behaving like a '30' grade would when hot.  In this case a monograde 30 would be too thick when cold and a monograde '5' would be too thin when hot, hence the multigrade performance and nomenclature.

 

In reality the two halves of the visc grade are tested under very different conditions.  The 'W' (for "winter") number is tested under very cold conditions to determine if the oil can flow and pump when cold - one test is called the 'cold cranking simulator' (CCS) and one called 'mini rotary viscometer' (MRV).  For an oil that is "xW-yy", the CCS is tested at -(35-x)°C and the MRV i tested at -(40-x)°C.  An oil has to flow and pump effectively in these tests in order to pass them.  The yy number is mostly derived from a simple viscosity test at 100°C (oil falling through a tube and timed between two marks).

[EnterName]

9 minutes ago, TDIum said:

The oil remains liquid and will lubricate your metal bits even when very cold.

Yes, but not as well as when warm.

 

11 minutes ago, TDIum said:

What you are concerned with is the metal bits and how they expand with temperature. This is the thing you want in the normal operating range before giving it some right boot. Moving parts expanded to their normal operating clearances. 

Yes. I was trying to learn what "normal" is in the original post. Anything over 50deg C should be fine, looking at the graphs Weasley linked to.

[weasley]

12 minutes ago, TDIum said:

The oil remains liquid and will lubricate your metal bits even when very cold.

What you are concerned with is the metal bits and how they expand with temperature. This is the thing you want in the normal operating range before giving it some right boot. Moving parts expanded to their normal operating clearances. 

 

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.

[weasley]

22 minutes ago, TDIum said:

 

Sir, with all respect I do believe you are mistaken. A multigrade oil specified as 5W30 means, its like a 5-grade in Winter and a 30 in summer. This goes back to when multigrade oils were invented, before which you would have to change it twice a year. 

 

And just to present my credentials, if I may, I have been working in lubricant R&D for 28+ years for one of the well-known oil brands.  I've worked on everything from motorcycle to ship engine oils, as well as transmissions, turbines etc.