Optimum operating oil temp for passenger cars

[peterlonz]

I'm new here & just getting the feeling of the website.
I hope my question is not a repeat of many before - I could not see a search facility to check this.

My question is this: what is the optimum operating oil temp in modern passenger cars, given everyday driving in climates as varying as Australia.
I was very recently surprised to be advised the range considered best was 90 to 100 Deg C (195-210 Deg F). That seemed high to me but who knows?
If the temp was to be measured can anyone suggest the suitable positions to take data permanently. Temporarily I could bind a thermocouple wire to the dipstick.

 

[Kiwi_ME]

My last car (a 2009 Swift Sport) would run at 85 to 110 C, at the sump. Once warm, which took around 20 minutes, mostly it varied with engine RPM rather than load.

I've attached a thermocouple to the sump of my recent cars. Jaycar has a nice little electronic one, or use a coolant temp kit from Repco.

 

[expat]

Originally Posted By: Kiwi_ME
My last car (a 2009 Swift Sport) would run at 85 to 110 C, at the sump. Once warm, which took around 20 minutes, mostly it varied with engine RPM rather than load.

I've attached a thermocouple to the sump of my recent cars. Jaycar has a nice little electronic one, or use a coolant temp kit from Repco.


Those temps v time are almost exactly what I see for my 74 Triumph Spitfire.

Higher RPM's (as on a track) might push the temps a little higher.

 

[901Memphis]

100C is optimal since the oil is specified by viscosity at this temperature and you want to be hot enough to burn off water contamination so it doesn't build up.

A good probe would probably be down the dipstick in the middle of the sump. The closer you get to the pan the lower the reading I imagine as the fins cool it.

A good synthetic can handle upwards of 300F in the sump but a 5w30 is no longer a 30 weight at 300F since viscosity decreases with temperature. This is why a real oil pressure and temperature gauge are important if you track, since a car that specifies a 5w30 for normal use might move up to a 10w40 on the track to keep it oil film sufficiently thick.

 

[ac_tc]

Above 60 degC up to say 140 degC is okay.
It´s usually 10-30 degC hotter than the cooling water
once warm and thats perfectly ok

 

[peterlonz]

To everyone who replied - thanks.
I will investigate the Jaycar & repco kits mentioned.
Basically it looks as though the initial advice I received was correct.
I am now uncertain about where water (mentioned in one reply) might come from; surely you don't need 100 Deg C to boil off water in an engine which is normally running at above 70 Deg C?

 

[Ducman]

At 100 c the water will boil off quicker than it will at 70 c, where it will be inclined to evaporate slowly.
Most bulk oil temps are around 90-100 c under normal operating conditions, but may well be less in some engines, and quite a lot more more in others depending on operational conditions.

The water can come from condensation which forms inside the engine under a number of normal circumstances.
An internal coolant leak of some description, can also contribute to water in the engine oil.

It's most damaging in engines when it combines with the compounds that are produced from the normal combustion process(mostly Sulphur).
The resulting acids break the oil down, and to a lesser extent they continually eat away at the engine internals.
The water itself contributes to destructive sludge build up, and causes corrosion/rust in extreme conditions.

That's why TBN is an important feature of the engine oil, to combat the effects of acids in the oil as they build up.
The acids are expressed as TAN(Total Acid Number) in Used Oil Analysis, and eventually overwhelm the TBN to render the engine oil unfit for service.

Assuming there's no internal engine coolant leak.
Most of the water in the engine oil will eventually boil off/evaporate, and out of the oil on a longer trip. To be consumed buy the engine through the PCV.
With shorter trips the water ultimately accumulates.

That's one of the reasons why the manufacturers have always deemed that a low mileage vehicle with mostly trips of less than 16 kms, put the vehicle into the severe service category.
This requires a higher service schedule/more frequent engine oil changes as a result.
It's due to the negative effects of the acids that build up in the engine oil.

 

[Doug Hillary]

Hi,
peterlonz - Welcome to BITOG - whereabouts in QLD are you?

Engine manufacturers will establish the desired bulk oil temps range(s) at the design and manufacture and intended application stages

One heavy diesel engine manufacturer I worked alongside had these parameters inbuilt (in one engine family/application) as part of the engine's ECM unit;

Programmed Shutdown - 120C P
Audible/lights Warning - 115C
Normal >110C (P 350C)

My averages with this engine family across my Fleet and application was - 103C (P 380C)

Some time back I did some work on this issue with a V8 Porsche engine family. This application had a thermo oil cooler and engine vents - it all stabilised the oil temp in a range 86-92C. This was confirmed over a quite significant sample running in various climatic conditions - freezing alpine to severe tropical

I have seen this temp range programmed in a wide range of German engine families over many years

Oil temperatures reach some high very points in travelling around within an engine - the tempos noted above with a ( P ) are the pyrometer temps often seen with >580C being reached when working hard!

 

[Doug Hillary]

Hi,
peterlonz - Sorry I forgot another tid-bit - the Porsche Museum's cars in Zuffenhausen have their engine lubricants warmed up to 80C before any significant revs or loads are applied

The priceless pre-war Mercedes Benz and Auto Union racing cars exhibited at Goodwood (in 2012) were also treated the same way prior to use