Oil pressure changes with ambient temp changes

[Snagglefoot]

Here is a chance to contribute your data with those having an oil temp, oil pressure and ambient temperature readout.

When cruising at a particular highway speed where the terrain is relatively flat and your transmission is not shifting, do you see any change in oil pressure with changes in ambient temp.

I can drive all day long ( recently did a 1250 mile trip) with the engine speed at 1800 rpm on a Chevy 6.0 gas engine and the oil pressure was 40 psi the whole time even with the temp dropping from 50 F to 15 F.
This engine has an oil cooler build into the rad so I would expect oil temps do not stray too far from radiator temps, which are very steady at 210 F.

The observation is the oil pressure is not drifting around with changes in ambient temp. I saw some graphs with those who had the data available, paricularily in Stelantis built vehicles.

Any contributions? Thanks.

 

[Lubener]

On my 87 F150 (4.9), I have an actual (SW) electrical oil pressure gauge which I installed. I always ran 10w-30 oil and switched to 5W-30 last year to help deplete my stash. Oil pressure hasn't really changed between the two oils. Pressure cold engine is around 47 psi while warm pressure @2000 RPM is at 40 psi and idle is 20 psi. Pressure is pretty consistant no matter what the outside temperature is. I have no actual engine temperature.

 

[Donald]

Why would you expect the oil pressure to vary with ambient temperature? The oil temperature is going to pretty much stay in sync with the temp of the engine. So once warmed up, the oil temp and pressure should remain constant regardless of the outside temperature assuming the RPM is kept constant.

 

[Snagglefoot]

Why would you expect the oil pressure to vary with ambient temperature? The oil temperature is going to pretty much stay in sync with the temp of the engine. So once warmed up, the oil temp and pressure should remain constant regardless of the outside temperature assuming the RPM is kept constant.

Yes. That is what I believe. I want to see if someone has evidence to the contrary.

 

[4wd]

Yes. That is what I believe. I want to see if someone has evidence to the contrary.

The oil and coolant temperatures are well connected on my Pentastar - and both will run cooler in January -vs- July …
The 850RE to a lesser extent … (cooler pending) …
GM units are certainly more consistent …
(and much lower transmission temps)

 

[Snagglefoot]

The oil and coolant temperatures are well connected on my Pentastar - and both will run cooler in January -vs- July …
The 850RE to a lesser extent … (cooler pending) …
GM units are certainly more consistent …
(and much lower transmission temps)

Of course January vs July in Texas can be a huge swing. Do you have any numbers that might help?

 

[4wd]

Of course January vs July in Texas can be a huge swing. Do you have any numbers that might help?

Oil in F? 208° -vs- 220° - hottest is 225° in 4WD …
(Only time I hear fans working hard) …
Just hot enough to cook moisture?

 

[Snagglefoot]

Oil in F? 208° -vs- 220° - hottest is 225° in 4WD …
(Only time I hear fans working hard) …
Just hot enough to cook moisture?

Any change in oil pressure with those temps?

 

[4wd]

Any change in oil pressure with those temps?

Maybe a psi or 2 … normally 31 psi on the highway unless a bird flies by - and suddenly it’s 78 psi

 

[dbias]

Never really noticed any Oil pressure change with temperature but I definitely do with rpm.

 

[Snagglefoot]

Never really noticed any Oil pressure change with temperature but I definitely do with rpm.

Yes, when I cruise at 1800 RPM and 40 psi, I will floor it, and the transmission will drop down a few gears and I will pass at 3500 to 4000 RPM. I will get about another 5 psi of oil pressure until I slow down and the transmission goes back to top gear (6th) in my case and the oil pressure drop back to 40 psi.

 

[OVERKILL]

Why would you expect the oil pressure to vary with ambient temperature? The oil temperature is going to pretty much stay in sync with the temp of the engine. So once warmed up, the oil temp and pressure should remain constant regardless of the outside temperature assuming the RPM is kept constant.

Depends on whether the oil temperature is thermostatically controlled or coupled to coolant temp with a heat exchanger or not. A large sump with an exposed pan can, during winter months, have considerably lower oil temperature than coolant temperature, because the pan acts like a heatsink. Lower oil temperature will of course increase oil pressure.

Unfortunately, most vehicles don't have digital read-outs for all of these temperatures, so it's not easy to track/compare.

That said, even with a heat exchanger, it's quite possible to see seasonal differences.

For example, when it was 23C, my oil temp is higher than coolant temp:

Here's another summer pic at 28C, temps are lower, but oil is still higher than coolant:

And here's -10C, oil is lower than coolant:

I'll try to remember to get a pic at like -20C and 100km/h, because I have one at 100km/h from the summer, so those would be good to contrast.

 

[Donald]

Hopefully the thermostat in the engine is working and is keeping the engine at the desired operating temp (regardless of ambient temperature) and so the oil should be very close in temp.

Now if in Eureka Canada in January or Mohave desert in the summer then maybe exceptions apply.

 

[Donald]

Depends on whether the oil temperature is thermostatically controlled or coupled to coolant temp with a heat exchanger or not. A large sump with an exposed pan can, during winter months, have considerably lower oil temperature than coolant temperature, because the pan acts like a heatsink. Lower oil temperature will of course increase oil pressure.

Unfortunately, most vehicles don't have digital read-outs for all of these temperatures, so it's not easy to track/compare.

That said, even with a heat exchanger, it's quite possible to see seasonal differences.

For example, when it was 23C, my oil temp is higher than coolant temp:
View attachment 325945
Here's another summer pic at 28C, temps are lower, but oil is still higher than coolant:
View attachment 325946

And here's -10C, oil is lower than coolant:
View attachment 325947

I'll try to remember to get a pic at like -20C and 100km/h, because I have one at 100km/h from the summer, so those would be good to contrast.

It may make a difference where the oil temp is measured. But when the oil flows into the block it will not travel far before it's the same temperature as the block. And then the viscosity should be the engine operating temperature viscosity.

 

[userfriendly]

I can head east from BC where the temperature is above freezing and the middle of the prairies is 30 below.
As the temperature drops the oil pressure goes up even with the front cover that comes with the duramax 6.6L.

 

[OVERKILL]

It may make a difference where the oil temp is measured. But when the oil flows into the block it will not travel far before it's the same temperature as the block. And then the viscosity should be the engine operating temperature viscosity.

Oil moves very quickly through the engine, it's bulk sump temp that matters and the temperature readings from the RAM come from the sensor that's just off the heat exchanger, and as you can see, these vary. As does oil pressure, which isn't measured until much further along in the system, up at the top of the intake at the front. Pressure and oil temp are almost perfectly correlated, which invalidates your theory.

 

[OVERKILL]

I can head east from BC where the temperature is above freezing and the middle of the prairies is 30 below.
As the temperature drops the oil pressure goes up even with the front cover that comes with the duramax 6.6L.

Yup, my M5, despite coolant temp being pretty consistent summer/winter, the oil temp (it had a massive valley-mounted oil cooler) had huge seasonal swings.

 

[k1xv]

As the oil is cooled through the radiator, and the radiator is thermostatically controlled, with constant driving conditions, the oil temperature and rpm/oil pump should not change much. So the oil viscosity should remain constant too. There isn't much left that would cause pressure to rise or fall.

So, as Alfred E Neuman says, :What, Me Worry?"

 

[OVERKILL]

As the oil is cooled through the radiator, and the radiator is thermostatically controlled, with constant driving conditions, the oil temperature and rpm/oil pump should not change much. So the oil viscosity should remain constant too. There isn't much left that would cause pressure to rise or fall.

So, as Alfred E Neuman says, :What, Me Worry?"

If it's cold out, thermostat operation will limit how much of the block coolant gets diverted to the rad, so rad bulk temps can be quite a bit different from engine bulk temps. So, if the oil is not on a thermostatically controlled circuit and getting cycled into the rad, if the rad is 15-20 degrees colder than the coolant in the block, that's going to reflect in oil temps.

On the other hand, applications with a block-mounted heat exchanger that uses block coolant as the heat transfer fluid, temps are going to be much closer coupled.

 

[userfriendly]

If it's cold out, thermostat operation will limit how much of the block coolant gets diverted to the rad, so rad bulk temps can be quite a bit different from engine bulk temps. So, if the oil is not on a thermostatically controlled circuit and getting cycled into the rad, if the rad is 15-20 degrees colder than the coolant in the block, that's going to reflect in oil temps.

On the other hand, applications with a block-mounted heat exchanger that uses block coolant as the heat transfer fluid, temps are going to be much closer coupled.

Stick your hand out the window at 75 mph when it’s 30 below and tell me it’s not going to affect the bulk oil temperature, especially when the oil pan is exposed to the elements.

Arctic outflow takes on a whole new meaning when nature calls and it’s 42C below.