At operating temp, why does outside temp matter?

[OceanRuns]

This is a bit of a noob question.

Regarding an oil weight...

Once and engine reaches and maintains its operating temperature, why would the outside, ambient temperature matter?

Say in one case it's 70 degrees outside. Say in another it's 105 degrees. An owner's manual might spec a xW-30 versus an xW-40.

But, in both cases isn't the internal engine temperature the same? The internal engine temperature isn't 35 degrees hotter right? So, why is the thicker oil spec'd if the engine operating temp is the same?

 

[RamFan]

I've never fully gotten an answer on this either, in for responses.

 

[eljefino]

Let's say a bearing designer says it'll work great with 5-100 cSt. A 30 weight would be around 11 cSt at 100'C but on the bitter edge if it heated up to 120-130.

So while it's water cooled there is some oil cooling going on as well, and some engine designs have more of an internal lag between oil and a cooling force-- either a water jacket or the pan that gets air cooled. (or a oil-to-water cooler etc.)

So it kinda comes down to where you measure, and if there are temporary hot spots during a few second WOT run. They also use oil in "piston squirters" to keep the pistons cooler, this heat has to go somewhere.

Just my take, someone will elaborate I'm sure.

 

[d00df00d]

Remember that the gauge in your car shows the temperature of the coolant, not overall "engine temperature" or oil temperature.

When it's hot outside, your engine's cooling system can maintain a good cooling temperature by keeping the thermostat open and running the fans more. Some parts of the engine will still be a bit warmer. But more importantly, the oil will be a lot warmer because in most cars there's nothing controlling its temperature except air flow over the bottom of the pan. Some cars have oil coolers, but most of those are just passive radiators.

Oil temps can get very, very high in hot weather even when coolant temp is still in the normal range.

 

[Nick R]

Short answer: It doesn't.

Slightly longer answer: The oil temp may be slightly warmer if it is hot outside, but not really a huge difference. Not enough to warrant getting a thicker grade of oil. Extremely heavy loads will do more to affect oil temp than anything. Hauling/driving up a long, steep grade with the engine working hard will raise oil temps sure.

 

[Trav]

Remove the coolant and the engine will seize if let run. Higher ambient air temps reduces the amount of heat transfer, the cooling system becomes less effiecient.
Seeing as the cooling system plays a large part in keeping the oil cooled as well as the engine itself oil temps will increase also.

 

[Nickdfresh]

My (older Ford Contour) temperature gauge does go up a bit on a hot day after exiting the highway - but not significantly...

 

[OVERKILL]

Originally Posted By: Nick R
Short answer: It doesn't.

Slightly longer answer: The oil temp may be slightly warmer if it is hot outside, but not really a huge difference. Not enough to warrant getting a thicker grade of oil. Extremely heavy loads will do more to affect oil temp than anything. Hauling/driving up a long, steep grade with the engine working hard will raise oil temps sure.


You've never owned a car with an oil temperature gauge, that's very obvious

I haven't been able to get it even close to the level of the first photo after over an hour of driving ALL WINTER.

And this car has an oil cooler. These swings would be far greater on a car that doesn't have one.

 

[Vikas]

PSA:

If you want to brag about your instru///Mentation display, don't do it if the check engine light is on!

 

[MolaKule]

Quote:
Say in one case it's 70 degrees outside. Say in another it's 105 degrees. An owner's manual might spec a xW-30 versus an xW-40.



Keep in mind most of the oil temperature charts are for conventional oils verses ambient temperature, with a built in margin of CYA.

Just in case you drive through Death Valley and are using mineral oil, you might need an extra margin of safety to keep the oil from thinning out too much when going across the desert at 100 MPH.

Warmer ambient temperatures simply mean that the coolant and oil will heat up faster, that is, the rate of change of temperature will be faster in hot weather than in cold.

Once the coolant reaches operating temp after thermostat opening, the engine coolant temp should stabilize unless air flow is somehow restricted through the heat exchanger or radiator, or the cooling system was somehow underdesigned for the intended operating temperature and driving conditions.


Oil and coolant temps differ with vehicle and engine size, but as a rule of of thumb the oil temperature is about 20F above coolant temp.

 

[weasley]

Holy c***! Did you really get through that much fuel in 6 km?!

 

[bmwtechguy]

Some GM trucks with towing packages would have (or may still have) the engine oil cooler in the hot side of the radiator, and the transmission fluid cooler in the cooler tank on the other side of the radiator. I like this design for the engine oil cooler because I think it helps to get the engine (and transmission fluid) oil up to operating temp sooner on a cold day and helps keep peak oil temps down on a really hot day or when towing, etc.

 

[mechtech2]

Originally Posted By: Nick R
Short answer: It doesn't.

Slightly longer answer: The oil temp may be slightly warmer if it is hot outside, but not really a huge difference. Not enough to warrant getting a thicker grade of oil. Extremely heavy loads will do more to affect oil temp than anything. Hauling/driving up a long, steep grade with the engine working hard will raise oil temps sure.


Nonsense.
Oil gets much hotter in summer than winter. Esp shorter trips.
For a quick paradigm, I note that after performing uncountable oil changes, oil is much hotter when draining in in summer vs. winter. And my experiences with oil temp gauges show this effect as well. Common sense tells us this, as well.

 

[Falken]

Outside temp does matter. If you are in Texas on a hot day, the car can only manage so much thermal shedding.

The car operates in a different thermal envelope and have different oil requirements, than say a vehicle that is in Quebec, with -25 deg C.

Oil viscosity has a lot to do with outside temps. Such as when someone picks a 0W20 for Winter use. Or decides to tow up a mountain in the Summer.

 

[V8man]

A thicker oil could make your engine run hotter in the summer versus a thinner oil.

 

[Trav]

Originally Posted By: MolaKule
the rate of change of temperature will be faster

Any idea of much the performance of liquid to air coolers diminishes with higher ambient temps?

This is my problem with the rate of change being faster only thing (i assume you meant only because you bolded it).
On my now gone Caddy the electric fans would never come on in the winter months during normal driving (excluding fan operation for the A/C on).
In the hot summer it would be going on an off pretty regular without the A/C on of course which automatically turned the fans on.

Engine temps in winter rarely saw above thermostat 195f but in summer 226f was common.
So the question is how much higher do the temps on the internals like cylinder walls, cams, etc need to rise to raise the whole cooling system temp by over 30f?

Oil temps on my CBR1100XX routinely ran at 260-280f while the coolant was 190f even though it had a large oil cooler.
Hot summer 220-280 Kmh 7-10,000 RPM extended running. The air could not remove enough heat from the oil quick enough.
In spring and fall running the same speeds oil temp rarely broke 220f

 

[antonmnster]

On the Audi during the winter, the oil might make it to 180F, but it takes a half hour. Driving around town it might never even get to 160F.

During the summer on the highway it will easily get to 220F. And it doesn't take long if the engine is loaded (on the highway).

In both summer and winter, the coolant gets to 180F and is pretty stable. But the oil varies greatly.

And that's with a water/oil heat exchanger. I feel completely comfortable running two grades seasonally.

 

[dieselbass]

might take into account the heat passing through the AC condenser on a hot day. Much also depends on airflow (or lack thereof in traffic). When the vehicle is moving along with sufficient airflow and rpm, all is well, but diminished airflow (like behind a truck) will change all of this. Plus with cooling systems running hotter by design and some radiators the size of a textbook...... Add in some blockage to the radiator due to lack of service, that heat will also head for the oil.

just my .02 however

 

[steve20]

I have a digital oil temp gauge in the Corvette- I can say after watching them for years, the oil temp runs about half of what the coolant temp is all the way to 150 degree coolant temp. After 150, the oil starts catching up and eventually exceeds the coolant temp by 20-30 degrees
After the stock 180 thermostat opens:
Winter running oil temp 185-200
Summer running oil temp 210-235
Winter coolant temp 180-195
Summer coolant temp 195-230
After fully warmed up a full throttle run to redline in one gear increase oil temp by only 5 degrees

 

[dieselbass]

seems like when the Baja trucks start getting hot, they do some WOT as the incoming gas/air charge serves to help cool things off. Air passing through a ventury and cooling as it expands.....

so, it would seem elevated ambient temps do have an effect. 160 pieces of equipment at my job tell me so ;-)