Do oil temps exceed operating temperatures?

[Robert_Gift]

Do we really need to be concerned about oil temperature extremes?
Don't cooling systems keep engine temperatures from exceeding normal operating range?
Parked in the house garage, I doubt our vehicle ever gets below 20 degrees F.
When driven somewhere and parked outside, the engine thermal mass retains heat for a long time.
By the time we leave from a store, etc., the engine has not cooled that much.
Does an engine really ever experience the extremes for which oils are supposedly formulated?
Thank you,

 

[Ugly3]

Given that you have an effective cooling system the hot end of the temperature scale is little problem, even on the hottest days (not on track or racing).

Cold on the other hand could be a problem if the vehicle is left in the cold temps too long. You never know what the future will bring.

So the simple answer is generally no as you describe the situtation, however, cold could be a problem on occasion.

Run the thinest oil your manual allows and enjoy your ride.

 

[TimVipond]

Motorcycles often achieve high temperatures and can overheat (especially air cooled ones) and destroy the oil when stuck in stop and go traffic. My son's girlfriend's clunker car overheated last summer when she ran low on oil. People have told me they have had high engine and transmission temperatures when towing in the mountains. Transmissions seem to last longer when they run cooler.

Many people can probably tell you stories about how it was -20F and their car wouldn't start. Maybe their oil was too thick. A friend of mine said he used to have to use Sterno to heat his oil pan to start his car in Wisconsin in the 60's and 70's. When he switched to synthetic he no longer had to do that. Others have to use an electric engine block heater to thin the oil to start in the morning.

Most owners manuals list the oil viscosity depending on temperatures likely to be encountered during the oil change interval. It is wise to pay attention to those recommendations.

 

[Kestas]

Robert, you're thinking in terms of bulk temperature. This thinking may be okay for transmission fluid, ps fluid, and transfer case fluid. But when it comes to engines the temperature is anything but uniform. There are localized hot spots that affect the oil. The piston rings are one example. Exhaust valve guides may be another. So there is some benefit to designing an oil that is more resistant to high temperatures.

 

[Blue99]

I share the same opinion as Kestas on this one! The oil stream will see a variety of temperatures during pumping circulation & splash lubrication.

I’m glad that the GF-4 certification requires an oil to pass the 100 hr & 300 degrees F parameters of the Sequence IIIG test.

Here’s a listing of some common engine component temperatures, in degrees F:

Upper Cylinder Wall 300-500
Exhaust Valve 1200-1500
Piston Crown 700-800
Hydraulic Valve Lifter 250-300
Crankcase 200-300
Top Piston Ring 300-650
Exhaust Gases 500-1000
Combustion Chamber 3000-5000
Coolant Jacket 165-230
Connecting Rod Bearings 200-375
Main Bearings 200-350

Note - The above numbers are from an Amsoil dealer site.

 

[AEHaas]

A typical 10W-30 wt oil may be used in your engine in an ambient environment from -30 to 130 F. One may think that 20 F or 50 F up to say 100 F is plenty safe and within the “normal” operating temperature range. Not correct. Oil and engines are designed to run at only one temperature range, say 190 F - 220 F. Anything else is less than optimal. This is why we have radiators. They allow the engine to get up to temperature faster and keep it at the right operating temperature.

Here in Florida for example an average trip to the outlet mall is 60 minutes drive, mostly on the highway. But even though the coolant in your radiator gets up to temperature in 3 - 5 minutes the oil takes 20 or 30 minutes to get to 200 F. If the ambient temperature was 75 F at start up then 95 percent of the wear and tear in your engine occurred during the first 30 minutes of your 60 minute drive and 5 percent of the wear occurred on the last 30 minutes on the highway.

The start up phenomenon is not so much dependent on the ambient temperature but rather the time it takes to get up to full operating temperature, 200 F. At any temperature below the normal operating temperature the oil is always too thick. One way to minimize this problem is to use oils that thicken less after engine shut down. A 5W-30 does not generally thicken as much and a 0W-30 is generally better yet.

You should read this:

http://theoildrop.server101.com/forums/s...ge=0#Post258506

aehaas

 

[brucelee]

The answer is that it depends on your driving habits.

My last Corvette allowed me to monitor average oil temps vs coolant temps. In any level of spirited street driving, the oil temp would exceed coolant levels pretty quickly and hit 275 pretty quickly.

Since I did not push the car hard, that is as high as I got.

However, one can certainly imagine how hot some Corvette engines can get when pushed hard.

 

[Steve S]

The oil temps are an "average" temperature. The oil temps vary depending where they are picking up heat .Also the pumping of the oil also creates heat.

 

[Steve S]

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The answer is that it depends on your driving habits.

My last Corvette allowed me to monitor average oil temps vs coolant temps. In any level of spirited street driving, the oil temp would exceed coolant levels pretty quickly and hit 275 pretty quickly.

Since I did not push the car hard, that is as high as I got.

However, one can certainly imagine how hot some Corvette engines can get when pushed hard.

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All engines heat the oil when pushed.

 

[ekpolk]

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Given that you have an effective cooling system the hot end of the temperature scale is little problem, even on the hottest days (not on track or racing).
. . .

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I'd say that's true, but also keep in mind that the oil system IS the cooling system for the bottom end/lower half of the engine, as well as some particular hotspots (such as the bottoms of the pistons). This may explain the low oil overheat described several posts up. But since few cars are instrumented so that you can easily determine oil temps, this is a hard question to nail down. One way, I suppose, would be to do a couple of UOA after OCIs reflecting a vehicle's normal operations. You could probably infer from that information whether or not you're overtemping your oil. Most cars probably aren't. Others clearly do. Does yours? Don't know.

 

[Quest]

TimVpond-

If you are talking about V-twin aircooled bike engines, they are known to overheat during excessive idling due to lack of airflow through it's cooling fins.

That's why a lot of high performance high tech bikes already done away with liquid-cooled engines for better heat management and combustion chamber temperature control, amongst a lot of other things...

My 2c's worth.

 

[TimVipond]

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TimVpond-

If you are talking about V-twin aircooled bike engines, they are known to overheat during excessive idling due to lack of airflow through it's cooling fins.

That's why a lot of high performance high tech bikes already done away with liquid-cooled engines for better heat management and combustion chamber temperature control, amongst a lot of other things...

My 2c's worth.

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I'm confused here. V-twin air cooled are more likely to overheat (that is likely why they now come with and recommend synthetic oils) and that is why liquid cooled bikes are switching to air cooled engines? Starting your Saturday night a little early?

 

[Gary Allan]

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Do we really need to be concerned about oil temperature extremes?

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Only in terms of how those extremes effect our oil selection. More extreme? More important.

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Don't cooling systems keep engine temperatures from exceeding normal operating range?

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For coolant? Yes, usually. For oil ..on some level. The oil temp is (mainly) the thermal back pressure of the engine in terms of btu's that aren't absorbed by the cooling jackets ..or sent out the exhaust.

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Parked in the house garage, I doubt our vehicle ever gets below 20 degrees F.

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Especially if you live in a region that never sees 20F. How about a unheated shed in North Dakota in February??

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When driven somewhere and parked outside, the engine thermal mass retains heat for a long time.

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It depends on the effective radiating surfaces, their thermal conductance, and the differential presented in ambient temp. That is, YMMV.

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By the time we leave from a store, etc., the engine has not cooled that much.

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Depends on how long you're in the store ..how long it was to get there ...how cold it is (see above).

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Does an engine really ever experience the extremes for which oils are supposedly formulated?

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Well, what do you mean by "formulated (for)" (the infamous "Well, first I think we need to define "completely destroyed" before I can comment")? When you're on the highway for a long enough period ..you'll reach the 200-220F temp range (probably). It will vary somewhat in non-exchanged/forced cooled engines depending on load and ambient temp.

If you mean hit 280-302F to test our HTHS ratings?? Not usually (unless racing or climbing some 8% grade for a long time at high load, as was mentioned).

As Dr. Haas explains ..coolant is quick to heat and is regulated to maintain a max temp limit in a narrow range. Oil typically is not and takes a long time to peak out at a normalized temp indexed for the load and for the ambient temperature in non-exchanged/forced cooled engines.

 

[saaz]

Most performance bikes are liquid cooled, and additionallt have separate oil coolers, the most recent bikes using a coolant/oil combined oil cooler in addition to the radiator. Oil temperatures can vary greatly from coolant temperatures

 

[cdherman]

Short answer summarizing all the above replies and answering you question with no doubts:

Oil temps DO exceed the operating temperature of the radiator coolant system under several circumstances.

Towing, racing, climbing, stop and go driving in hot weather, and just driving period in very hot weather, all qualify.

Add the fact that the temp of the oil in sump is an AVERAGE of all the returning oil. But as noted, there are hot spots in the system. And if you run "relatively" cool oil over a hot spot, you are still ok. But if you run already hot oil, close to the point that degradation occurs, over that same hot spot, then you get trouble.

I had the same question years ago -- it is a mistake to think that water temp is the same as oil temp. They are SOMETIMES, but not usually.

In fact I wonder if we are going to start seeing oil coolers on modern car engines in an attempt to control this variable. It might be necessary if they try and move to any lighter oils that would be more easily damaged by excessive low end engine temps. Looks like the two wheeled folks are moving in that direction. I wonder how much trouble it will be to thermostatically control the oil cooler so as to speed the warm up process, but then turn on the oil cooler so as to keep the oil at the optimal design temp.....

 

[mitchcoyote]

This thread reminded me of one of the reasons I'll always use Amsoil...

 

[saaz]

You can buy thermostats for oil coolers. Very useful for transmission and engine coolers. I have mine for my air cooled bike, as riding in winter conditions means even the hotted up engime takes a long time to warm up properly.

 

[johnd]

It was pointed out to me that the only thing that does cool pistons is oil. Some diesels actually spurt oil on the bottom of the piston for this very reason. I've driven trucks with oil temp gauges and I can verify that under load, oil temps can and will exceed coolant temps. If you have noticed, trucks that pull heavy loads like cement trucks virtually always have external oil coolers.

 

[Craig in Canada]

A lot more engines than just diesels use oil jets to cool the pistons.

 

[ekpolk]

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A lot more engines than just diesels use oil jets to cool the pistons.

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True. Even the ultra-common 2AZ-FE (the I-4 used in the current and previous generations of Camry) has had piston squirters added to it.