Curious - why thicker visc for summer versus...

[Ramblin Fever]

winter if the overall engine temp should be staying the same - irregardless of hot ambient temps?

My owners manual in 2 vehicles recommends different viscosities for different temps, and I have no problems following that. In fact, I prefer a thicker oil in the summer; however, I've noticed the BITOG board is split in this regard.

Some are opting for thicker visc, some say there's no difference in outside ambient temp versus overall engine temp.

So, which is it? Curious, personally.

 

[1sttruck]

What is the temperature range of hot and cold ? I notice in my 5.9L diesel that it takes longer to warm up in the winter (down to the teens around here, single digits aren't that common) than it does in the summer. My cooling system is large with good capacity, so I need to use a 'winter front' to block part of the radiator in colder weather. Performance is off a bit in hotter weather (in the low hundreds) and the engine that I have access to when checking oil and such is much hotter.

Based on my impressions at least parts of the engine will be warmer/cooler in corresponding ambient temperatures.

 

[Tempest]

I don't get this either. The inside of the engine will be hotter than the ambient temp no matter where you are (even at the 115F temps I see here), and the thermostat will keep the engine temp constant no matter what oil you run (as long the cooling system is sufficient).

So the gist of this is that the oil will be at the same temp in the engine, and better flowing oil is always better for start up/short trips no matter the exterior temp.

 

[JohnBrowning]

It is simply that the thicker oil offers greater protection from wear and loading. The problem is that this same thicker oil could cause an increase in wear if the ambient tempatures gets low enough. Every one on this site get obsessed with flow but flow is only important to a point. Like wise HTHS is important but only to a point. It should be easy enough to undersant that all the HTHS in the world is no good if the oil can not be pumped to the part's in a reasonable amount of time and in suffcient quanities. Like was all the flow in the world is not going to day any good if the film strength is not sufficent to hydrodynamicly seperate the parts.

Too many people think that flow is always going to help prevent wear but this is not the case. Until you reach a certain viscosity the difference in flow is so minor that any difference would be hard to detect even under lab conditions in the engine. As temp.'s get colder though the difference in the cold flow,pump,crank properties of an oil can change drasticly. ALl things being equal usualy the thicker the viscosity of the oil the the poorer the performance inthese area's as the tempature drops.

I can tell you from experince that even on old detroit V8's that as soon as you cranked the engine oil was shooting out of the head area. I once had to get a ladder and clean a ceiling that was between 25-30 feet high. I had the valve cover off an engine and was cranking it with the coil wire off and oil shot up that high. We had nice automotice artwork onthe walls and ceiling so I had to clean it off. The oil shot out on the first crank.I have also been dosed with oil on OHC imports also with the valve cover off and in this case the engine running.Oil pressure and displacement is instant. The oil pump on a car is a positive displacement and the oil circuit is preety much a sealed circuit if all is right. The oil while not newtonian does not suffer compression at the pressure levels inside the oil galley from the pump. The viscosity that the pump see's when you go to crank it is all that matter and like it or not ambient tempature has a bearing on this.

No each oil circuit is going to have an upper and lower limit. Too thin and the bearings will not get the protection they might need too thick and the top end might suffer at start up under cold condtions. So lets say that a particular car can do just fine with any viscosity that is below 90W but above a 10W on a standard day. This means that bareing CAFE goals the engineers can recomend any viscosity in that range for a standard day. Now as you leave "standard" either higher in temp or lower this is going to effect the base viscosity rateing on the side of the oil can. So while a 90W might be fine at 59°F with X% humidity and a barametric pressure of 29.5 inch's of mercury it would be way to thick for use in the engine at say-30°F etc..... THe same applies to a 10W it might be fine for use below 0°F but at 120°F pulling 11,000lbs at 100MPH it might not hold up.

No long ago all owners manuals had oil viscosity recomendations based on ambient operateing tempatures. These charts preety much gave you a good idea on what was best for preventing wear at various tempatures. It gave the owner some freedom to make intelligent choice. Today for what ever reason they have dumbed it down to the lowest possable denominator.

 

[AEHaas]

I respectfully disagree with some of the above. It will be more obvious when I get permission from SAE to show you some of the current research data out there.

aehaas

 

[M1Accord]

you got inside connection with SAE, thats' tight.

 

[Dr. T]

I used to think that too....that the temps. were the same regardless of outside ambient temp., but that's not true.

The engine certainly has an 'operating range'. It runs hotter the hotter is outside as it has more difficult time cooling itself. Secondly, there is usually more strain put on it by summer a/c, increased traffic, less dense air, high speed driving, towing, etc..

Ever park a car after hours of driving in the summer heat...the temps. actually escalate compared to winter where they drop quickly. Hence, the potential requirement for oil with more cojones than is required for winter conditions....especially those running thinner grades.

For the rest of us, a broader spectrum antibiotic

...ahhmm, I mean oil viscosity range eg. 0/5-40/50 handles the large winter-summer temp. variability already.

 

[farrarfan1]

I find it amusing that people recomend 5W30 in the winter and "thicker" 10W30 in the summer. Does anyone use 0W20 in the winter and switch to the "thicker" 5W20 in the summer? Or 10W40 in the winter then the "thicker" 15W40 in the summer?

 

[Brian Barnhart]

It’s common for oil temperatures in some engine designs to increase significantly under certain summer conditions, even when coolant temperatures are still “regulated” by the thermostat. A friend’s GTI oil temps rise significantly above 65MPH with the AC on in 90F+ heat. He reports he can easily reach 240+ oil temps if he’s running over 70MPH/AC/90F+, all the while with only a small increase in coolant temp. He even reports a 5 to 10 degree F increase in the oil temp with the A/C on versus off. Interestingly, he also claims that the oil temp will also fall relatively quickly if he comes to a stop and let’s the engine idle (even though coolant temp doesn’t really change much).

Many seem to think that oil temp closely tracks coolant temp, but such is not the case with some engines under some conditions. Thermostats regulate coolant temp at one spot in the engine but do not directly regulate the oil temperature or even the coolant temp in other parts of the engine.

In most engines, oil temps may closely track coolant temp under most conditions. But there are probably also certain conditions under which oil temp doesn’t closely track coolant temps for many engines.

Then there’s also the case where normal coolant temps run about 200F, but can easily climb to 220F+ when towing up a mountain on a hot day with the AC on. In those conditions, oil temps can easily climb 20F or more above “normal” as well.

Since it’s possible to achieve relatively high oil temps in some engines under certain conditions in the summer, it’s no wonder higher viscosities are sometimes recommended or chosen during the summer.

 

[Seth]

Quote:

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I respectfully disagree with some of the above. It will be more obvious when I get permission from SAE to show you some of the current research data out there.

aehaas

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Unfortunately, there are articles like these still floating around adding to confusion.. Not sure how much of this is relevant even now..

http://www.machinerylubrication.com/arti...oup=Maintenance

Edit: Please do not post the full text of copyrighted articles.

 

[75003]

Great post Seth. I learn something new every week.

 

[AEHaas]

It is sad that this article has some good information mixed with some very bad information. It is best to ignore this article.

aehaas

 

[Pablo]

I agree with Dr. Haas. Although this article is from 2003, it's dated.

 

[Curious Kid]

FWIW - during the winter the coolant temps rarely reach the tripping point for my aux fan to turn-on, and my oil temps seemed to go no higher than 190 degrees F. In the summer months however, the fan engages regularly unless I'm driving a steady pace of something like 15mph or above. The oil temps have increased to something like 220 degrees F. at one point since I've started monitoring over this past year.

My vehicle doesn't have an oil cooler (oil-air or oil-coolant), so much is dependent upon the amount of air and it's temperature around the oil pan, and just how much heat can bleed-off into the coolant system by transfer through the engine's block (to some extent this phenomena works in reverse, limited by surface area, flow characteristics and transfer rates, etc.). My coolant stat temp is for 193 deg.F IIRC.

I don't have a graduated coolant temp gauge to see just how closely oil temps are following along with coolant temps, but I imagine that with the rates of transfer that seem to occur with the oil taking something like 3 times as long to reach operating temp, things could differ when under sustained loads and potential coolant system failure as mentioned in the paper posted above.

Take care.

 

[Drew99GT]

Quote:

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It’s common for oil temperatures in some engine designs to increase significantly under certain summer conditions, even when coolant temperatures are still “regulated” by the thermostat. A friend’s GTI oil temps rise significantly above 65MPH with the AC on in 90F+ heat. He reports he can easily reach 240+ oil temps if he’s running over 70MPH/AC/90F+, all the while with only a small increase in coolant temp. He even reports a 5 to 10 degree F increase in the oil temp with the A/C on versus off. Interestingly, he also claims that the oil temp will also fall relatively quickly if he comes to a stop and let’s the engine idle (even though coolant temp doesn’t really change much).

Many seem to think that oil temp closely tracks coolant temp, but such is not the case with some engines under some conditions. Thermostats regulate coolant temp at one spot in the engine but do not directly regulate the oil temperature or even the coolant temp in other parts of the engine.

In most engines, oil temps may closely track coolant temp under most conditions. But there are probably also certain conditions under which oil temp doesn’t closely track coolant temps for many engines.

Then there’s also the case where normal coolant temps run about 200F, but can easily climb to 220F+ when towing up a mountain on a hot day with the AC on. In those conditions, oil temps can easily climb 20F or more above “normal” as well.

Since it’s possible to achieve relatively high oil temps in some engines under certain conditions in the summer, it’s no wonder higher viscosities are sometimes recommended or chosen during the summer.

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Yup. All it takes is an infared temp gun to find that out.

On my Corolla, coolent remains at about 190 regardless of outside temps; once up to temp, it's there whether it's 10 degrees or 100 degrees ambient. But when it's really hot out if I stop and record the temp at the oil filter, I can get 230. It's about 210 idling. In 10 degree weather, the hottest I've seen at the oil filter is about 210 after getting off the highway. It'll drop to 190 while idling.

Don't think I'd want 5w-20 knowing my oil temps are getting to 250+ on the interstate with the A/C on crossing Kansas when it's 100 out, but that's just me!

In winter, based on what I've seen with my car, 5w-20 would be thicker than 10w-30 in max summertime operating temps.

 

[Steve S]

Why does an truck pulling a heavy load up a long grade over heats when it is 110 degrees F. but not when it is 75 degrees f?

 

[Panzerman]

The temps alot of people consider controlled are on the combustion chambers and not the oil it is basically air cooled by the pan or a oil cooler. Ill bet Pablo and the Good Doctor have never been in Sub zero temps to see oil performs quite well, even thicker and monogrades. This is coming from someone with experience with Diesels in temps down to 40 below, the old Detroits speced a straight 40 wt and they did start in 0 weather. Cat engines are well known to start in 0 weather without the aid of block heaters. The oil 15w40 in this case, in extreme cold did work. Ive heard these engines fire up and Ive checked the oil before hand and it was quite flowable. I will agree with Mr. Browning, and believe in a thicker oil especially living now in the Sunshine state where the extremes are the heat. Pull the drain pan on a N14 Cummins and that "thick" comes out like water, now imagine a 5w20 or 0w20. They dont get the abuse a diesel gets but they dont hold 10 gallon of oil either.

 

[Brian Barnhart]

Quote:

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Why does an truck pulling a heavy load up a long grade over heats when it is 110 degrees F. but not when it is 75 degrees f?

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The capacity of a cooling system is dependent on the difference between the ambient temperature and the desired (higher) engine running temperature. If the ambient temperature is increased, the amount of heat that can be dissipated by the cooling system decreases (assuming the desired engine running temperature remains the same).

Therefore, if a cooling system is operating at 100% capacity to maintain an engine temperature of 200F while pulling a load up a given grade at 100F, any increase in ambient temperature above 100F will increase the engine temperature. Under the same conditions at 75F, the cooling system maintains the desired 200F operating temperature by operating at less than 100% capacity (since it has more capacity at 75F than 100F for a 200F engine temp).

 

[mitchcoyote]

So this means using a synthetic oil for a 5k mile OCI is NOT a waste of money!!!!

 

[Brian Barnhart]

Quote:

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So this means using a synthetic oil for a 5k mile OCI is NOT a waste of money!!!!

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I’m not exactly sure what was posted in this thread that led you to that conclusion. However, if you operate a vehicle under conditions that cause it to run significantly above normal operating temperature for long periods, a synthetic oil will be less likely to deteriorate under those conditions than a non-synthetic (generally speaking).

If you don’t operate your vehicle in extreme cold (less than -10F or so) or under conditions that bring the operating temperature significantly above normal (200F or so), there is probably little to be gained from the use of synthetic even with a 5K OCI. Of course, I still frequently use synthetics even though those conditions don’t generally apply!