Higher viscosity in summer heat??

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Originally Posted By: Tempest
Originally Posted By: OVERK1LL

Precisely. Now think of this the other way.

Since oil and coolant temps are not 1:1, it would be fair to assume that in the frigid cold winter, oil temperatures may get nowhere near what they would reach in the summer. Even with the coolant the same temperature.

In cases like this, it may be beneficial, if conditions (both mechanical and ambient) allow the move to a lighter oil to improve start-up performance and to get closer to your summer "hot" viscosity, which is likely closer to "optimal" for your engine.

His question was about high heat, not extreme cold. If you live in areas that get deep into the negative F, then I agree that a lower grade maybe beneficial. This is because oil viscosity change is not linear. There is a much greater change at lower temps than there is at higher temps.


Yes, but my original reply was in response to this statement you made:

Quote:
The thermostat in your car determines how hot your engine runs.


Because of course the thermostat does NOT determine how hot your oil gets.

You then started talking about Death Valley and extreme heat testing, so I figured I'd mention that extreme heat isn't the only reason for somebody considering a deviation in viscosity from the manufacturer's spec.

And of course you touching on modified engines fits right in there as well.
 
You're right of course regarding the fact that most vehicles today don't unfortunately come with OP gauges but the OP spec's themselves are available in virtually every workshop manual.
And if you can't put your finger on the spec's, 15 psi/1,000 rpm at low rev's and 10 psi/1,000 at higher rev's will let you know if you're in the ball park.

As you mentioned, running the recommended oil, even a 20wt will rarely if ever prove to be too light even under the hottest ambient temp's you're going to encounter. And if one is going to do something extreme like tow a trailer through Death Valley in July, simply run fresh oil; preferably synthetic of the same recommended grade and that will guarantee no issues.
 
Quote:
You're right of course regarding the fact that most vehicles today don't unfortunately come with OP gauges but the OP spec's themselves are available in virtually every workshop manual.
And if you can't put your finger on the spec's, 15 psi/1,000 rpm at low rev's and 10 psi/1,000 at higher rev's will let you know if you're in the ball park.

On a factory located gauge, the factory knows where they are taking the pressure readings, so it is fairly easy to make a spec. If you add a gauge at some location, pressure could vary anywhere along the path due to diameter differences in the piping.

Or am I missing something?
 
Quote:
Because of course the thermostat does NOT determine how hot your oil gets.

I would have to disagree with that. A higher thermostat setting would end up having higher oil temps as well. Oil does move heat around in the engine, but the vast majority of the heat is removed by the cooling system.

At some point, at a given temp, there would be some equilibrium between the two. Oil temps definitely lag behind coolant temps though.
 
Originally Posted By: Tempest
Quote:
Because of course the thermostat does NOT determine how hot your oil gets.

I would have to disagree with that. A higher thermostat setting would end up having higher oil temps as well. Oil does move heat around in the engine, but the vast majority of the heat is removed by the cooling system.

At some point, at a given temp, there would be some equilibrium between the two. Oil temps definitely lag behind coolant temps though.


Again, you have to consider ambient temps here. How hot do you think the oil will get in an engine on a 30C day vs a -20C day if in both cases the coolant temp is at 195F?

While the oil most definitely acts as a heatsink when in flow through the engine, the pan/sump act as a cooler. Some vehicles have finned aluminum pans (my old Explorer for example) which of course has an effect on the temperature of the oil.

Oil volume is key here as well. An engine with a 12-quart sump is going to generally have lower oil temperatures than an engine with a 4-quart sump. Particularly if both engines are of reasonably high output.

And this of course drags in the topic of power density. Engines with higher power output have the potential for heating the oil to very high temperatures (see: Nissan GT-R). Often times these engines are spec'd for "heavier than optimal" oil, that will be "too thick" for the majority of conditions the engine is likely to operate in. However, when one is really pushing the engine to the limits, and oil temps continue to climb, then the spec'd oil is now doing its job. Ford's GT500 and Ford GT are good examples here, spec'ing a 5w50.
 
Originally Posted By: Tempest
Quote:
You're right of course regarding the fact that most vehicles today don't unfortunately come with OP gauges but the OP spec's themselves are available in virtually every workshop manual.
And if you can't put your finger on the spec's, 15 psi/1,000 rpm at low rev's and 10 psi/1,000 at higher rev's will let you know if you're in the ball park.

On a factory located gauge, the factory knows where they are taking the pressure readings, so it is fairly easy to make a spec. If you add a gauge at some location, pressure could vary anywhere along the path due to diameter differences in the piping.
Or am I missing something?

As long as the sender is matched to the gauge there is no issue.
 
Originally Posted By: OVERK1LL


Oil temp and coolant temp are not the same.
No they are not. But... With a stock engine driven normally across the desert the oil temp wont be much more than the coolant temp.

I've watched this on my motorcycle that uses the same oil that lubes both the transmission and engine. The coolant may be 200F, engine turning 9000rpm for an hr or more and the oil never got over 220F even though the bike does not have an oil cooler.
 
You run a thicker oil all it will do is degrade your fuel mileage as it has more drag on the engine to pump it when cold. In a stock vehicle your better sticking with what the book calls out for or just the thinner oil all year round as oils today are alot better than they were years ago when oil weight was thought to be important.
If your doing alot of towing then I would go with a grade up but only in this situation.
For everyday driving thinner is your best bet.
 
You can use a thicker oil during the warm months.
I've even used M1 EP 15W-50 in both of my Accords during the summer, with no ill effects, although I don't think I'd do so again.
Anyway, if you got a killer deal on a 10W-30, and wanted to use it during the warm months, it would be just fine.
If you buy oil as you use it, stick with whatever grade the manufacturer recommends.
It will do just fine, and you won't be experimenting.
Unless you want to, of course!
Engine oil temperatures don't vary that much through the year, assuming the engine is typically run long enough to reach operating temperature during the colder months.
 
There are different oil temperatures at different places inside the engine, just like there are different coolant temperatures at different places inside the engine. The added resistance of heavier oil does add a bit of oil temperature, but that doesn't thin the oil down a full viscosity grade. Keep in mind that, other things remaining equal, higher viscosity oil has greater film strength.

The oil temperature leaving the main bearings will be different from the oil temp out of the rod bearings, and different from the oil temp leaving the cams, and different being scraped down the cylinder walls by the piston oil scraper ring.

You want engine protection at the hottest points inside that engine. Because the oil in cars and light trucks is not carefully regulated, I'd agree with going one grade higher in very hot ambient temperatures, and certainly one grade higher than standard spec when run hot & heavy--towing heavy, etc. By the way, high humidity does not qualify as adding to the heat load for machinery.

By the way, my turbo Volvo has an oil temp regulating valve that sends oil to a cooler inside the hot tank of the radiator. (The transmission fluid is cooled in the cool tank of the radiator.) My Tundra has a coolant-cooled oil cooler in the filter base, but I don't know any details of it.
 
Originally Posted By: Ken2

The oil temperature leaving the main bearings will be different from the oil temp out of the rod bearings, and different from the oil temp leaving the cams, and different being scraped down the cylinder walls by the piston oil scraper ring.


If this chart is to be believed, oil in the bearings is much hotter than what's in the pan...

img104.gif
 
You guys are leaving out a critical aspect: engine design.

Overall, average oil temp is hugely influenced by design. If you have a new Ecoboost engine or a 6.1 Chrysler (and others) they have jets aimed directly at the underside of the piston.

These will change those oil temps! And the upside is no worries in the winter about the oil staying too cold!
 
Originally Posted By: MonumentOiler
Originally Posted By: glum
One thing I never see mentioned in these (endless) discussions is overheating. If your engine overheats and you manage to shut it down before something catastrophic occurs, aren't you better off with thicker oil, as far as heat-related wear?


If you are worried about overheating then I would focus on preventing that rather than using thicker lube. I don't think overheating is a common problem with good maintenance.

No mechanical failures should happen, but they do. My manufacturer advises using either 5/20 or 5/30. Guarantees or not, if my engine were ever to overheat, I'd much rather be using synthetic 5/30 than conv 5/20. I know someone will tell me I'm wrong (it's law around here to argue with everything... "Water is wet." "No, actually, water is not wet; it is definitional that it exists merely in a state of self-animus, the molecular embodiment not withstanding its interaction with itself.") but syn 5/30 could buy me a few seconds and it could make all the difference.

I would never go beyond what the manuf says but if they deem a range of viscosities acceptable, nothing wrong staying near the top.
 
Originally Posted By: Big O Dave
Originally Posted By: OVERK1LL

I've lived in a dessert for 20 years...


Do you know any Oompa Loompas?

Church on Sundaes?

Frosted windows?

Work as a fudge packer?


That was not my post dude
wink.gif


Originally Posted By: Tempest
Originally Posted By: OVERK1LL

Oil temp and coolant temp are not the same.

Car companies test their cars in extreme heat, to include Death Valley in summer time, with factory stock (obviously) cooling systems.

If the manual recommends going up a grade at a particular temp, then do it. Otherwise, I see no need. I've lived in a dessert for 20 years using just stock oil grades without issue.

If one has heavily modified their car or racing it, then the manual goes out the window.


Maybe Tempest knows them?
grin.gif
 
Originally Posted By: Big O Dave
Originally Posted By: OVERK1LL

I've lived in a dessert for 20 years...


Do you know any Oompa Loompas?

Church on Sundaes?

Frosted windows?

Work as a fudge packer?

For one added "s"? Nice to know the spelling police are out in full force.
43.gif
 
The bulk of you are going off the assumption that vehicles do not have some form of heat exchange taking place between the coolant and the oil somewhere in the engine.

I would bet that if the vehicle isn't designed with some form of coolant/oil heat exchanger (Like Porsche does with their liquid cooled engines), that there is an oil pressure circuit that feeds the cylinder head that goes right through part of the coolant jacket.

This would be pretty easy to develop on OHC engines too, if you think about it for a minute. That oil needs to get to the camshaft bearings in the top of the head, and the cylinder head has a lot of ports in it to flow coolant through. The oil pressure has to go through that engine block into the cylinder head somewhere, so chances are it is surrounded by the coolant flow in the head.

So even if there isn't a oil cooler on the engine block, somewhere there's a place in the engine where the coolant transfers heat into the coolant.

BC.
 
Originally Posted By: Bladecutter
The bulk of you are going off the assumption that vehicles do not have some form of heat exchange taking place between the coolant and the oil somewhere in the engine.

I would bet that if the vehicle isn't designed with some form of coolant/oil heat exchanger (Like Porsche does with their liquid cooled engines), that there is an oil pressure circuit that feeds the cylinder head that goes right through part of the coolant jacket.

This would be pretty easy to develop on OHC engines too, if you think about it for a minute. That oil needs to get to the camshaft bearings in the top of the head, and the cylinder head has a lot of ports in it to flow coolant through. The oil pressure has to go through that engine block into the cylinder head somewhere, so chances are it is surrounded by the coolant flow in the head.

So even if there isn't a oil cooler on the engine block, somewhere there's a place in the engine where the coolant transfers heat into the coolant.

BC.


It isn't an assumption. Most vehicles don't have oil coolers.

The CPVI's do, many HD trucks do (my Expedition), but my wife's Focus for example does not, and most regular, non HD vehicles don't.
 
Thicker oils create more parasitic drag and hence raise temps. 5w30 vs 10w30 isn't a big deal, but something like 5w30 vs 20w50 is.
 
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