Oil & Correct Operating Temperature

[RTexasF]

At what time frame can you be assured that your oil is up to its operating temperature? I realize that ambient temperature is a factor as are other variables. Just because the coolant has reached its correct temp doesn't mean that the oil has. Is there a safe rule of thumb such as 20 minutes of driving from a cold start,30 minutes (Alaskan winters aside)? Thoughts? Opinions?

 

[Dominic]

I would probably take a good guess at around 15minutes the oil should be at least at 180degrees no matter what temperature it is outside so long that the driving conditions to that point have been "easy." Aluminum engines might take a little longer to get the oil to temperature though since they tend to expell heat better. I would give it a minimum of 10minutes in normal conditions and 15-20 in cold conditions.

 

[Patman]

One way to tell is if you have an oil pressure gauge. In my LT1, I know the oil is up to operating temperature when the idle pressure is down to 20psi, or when it's just under 40psi at highway speeds. When it's still cold, the pressure is much higher than this. In my car I've noticed it takes about 15-20min to reach this point. Cars with large cooling systems, such as mine, will take longer for the oil to heat up also. Oil temp always lags behind coolant temp. With a small cooling system, such as on my wife's Civic, it will heat up faster, so thus the oil heats up faster too. I would say in a small car that the oil should be up to temperature in 10-15min instead of the 15-20 of a larger engine. Obviously wintertime adds a few extra minutes to these times.

 

[Al]

I would have thought that when the coolant is up to temp the oil is too, since it is constantly circulating through the same piece of metal. However based on the oil pressure theory and what others have said- I guess I was wrong

 

[Patman]

I'm not sure on exactly why the oil temperature lags behind the coolant temperature after a cold start, but maybe it has something to do with oil being thicker than coolant? So therefore it takes longer to heat up? Am I way off base here guys?

 

[rugerman1]

Patman. It my have to do with the specific heat capacity of oil versus water/coolant. Mark

 

[OneQuartLow]

I'll take a shot. Water jackets surround the combustion chambers and absorb the brunt of heat production. Heating the oil means BTU's got through the water or pistons or were generated by friction. Way down the list, the in-block water capacity is generally smaller than the oil sump capacity. Total water capacity may be larger if including the radiator but only after the thermostat opens. More interesting to me is why an engine warms up so much more quickly driven lightly (say under 1500RPM) than when idled at that same speed. I'm assuming the cylinder temperatures are similar, but friction generates the additional heat. Any engine guys care to comment? David

 

[V6 Diesel]

I have installed an engine oil temp gauge and have the following results for Michigan temp's. In the winter if it is near zero it takes about 45 miles at 70 mph to reach about 160 deg. At the other extreme in summer 90 deg it will run about 200 deg in about 15 miles on the highway. Highway speeds always generate heat faster and usually runs hotter. Now for the details on the engine setup, it is a 4.3L Olds V6 diesel in a RWD Cutlass. Stock oil capacity is 6qts, it has an oil cooler in the radiator. I tapped into the oil cooler line and added an additional remote oil filter so car uses 2 oil filters. This was before I had heard about by-pass filters. The remote bracket uses a standard Chevy 1 or 2 qt filter. Oil capacity is now 7 or 8 qts depending on which filter I use. Temperature sending unit is located in a port on the remote oil bracket and readings are before oil enters the oil cooler. Temp readings do not really change any between the extra capacity of the 2 qt filter over the 1 qt.

 

[Al]

quote:

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Originally posted by rugerman1: Patman. It my have to do with the specific heat capacity of oil versus water/coolant. Mark

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hmmm.. but the heat capacity of oil is less than water. V6, how long does the water temp take compared to the oil??

 

[BOBISTHEOILGUY]

quote:

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Originally posted by OneQuartLow: I'll More interesting to me is why an engine warms up so much more quickly driven lightly (say under 1500RPM) than when idled at that same speed. I'm assuming the cylinder temperatures are similar, but friction generates the additional heat. Any engine guys care to comment? David

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When an engine is not under load it will not shear the hydrodynamic lube properties as when your pulling the wieght of you vehicle this puts more demand on the engine which actually is equivalent to a higher RPM than if you where to use the same RPM not under load.

 

[Dominic]

quote:

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Originally posted by Patman: One way to tell is if you have an oil pressure gauge. In my LT1, I know the oil is up to operating temperature when the idle pressure is down to 20psi, or when it's just under 40psi at highway speeds. When it's still cold, the pressure is much higher than this. In my car I've noticed it takes about 15-20min to reach this point. Cars with large cooling systems, such as mine, will take longer for the oil to heat up also. Oil temp always lags behind coolant temp. With a small cooling system, such as on my wife's Civic, it will heat up faster, so thus the oil heats up faster too. I would say in a small car that the oil should be up to temperature in 10-15min instead of the 15-20 of a larger engine. Obviously wintertime adds a few extra minutes to these times.

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Thats true I do this too, I completely forgot about it though for this post Thanks for reminding everyone! My oil pressure is roughly 60psi at idle when everything is warm, and its 70psi or so cold or when Im cruising

 

[V6 Diesel]

V6, how long does the water temp take compared to the oil?? Operating temp for water is around 5 miles +/- depending on outside temp's. Another factor on oil temp's is during the cold of winter a block heater is used so the oil is already partly prewarmed. The oil still would be under 100 deg with the block heater but sure helps. RPM and load make a diffence in oil temp's for this engine anyway. Of course the oil cooler is inside the radiator so it is somewhat kept warm by the coolant in the winter. I wish I had a gauge on a 350 chevy I have that uses an external engine oil cooler for comparisons of temps.

 

[RTexasF]

It seems then, for those of us without an oil temp gauge, that 15-20 minutes of normal driving should do the trick. Extremely cold temps could take that time interval to 40 minutes or so. Once again I have learned something here. Thanks to all.

 

[UncleS2]

I've gone by this for many years now: at least 10 minutes or 10 miles of *driving*, *After* the temp guage reads normal operating temperature. 15 min/miles is better, & at 20 min/miles, I figure it's guaranteed warm enough. Idling doesn't count. Of course, I'm in Texas too- in Minnesota, my standards might well be different.

 

[MolaKule]

Rugerman1 is correct. Water/glycol is a much better and more efficient heat conductor than is oil, since the specific heat capacities of oils are lower than water.

 

[Jay]

I'd say it varies quite a bit with engine design. Honda's K20A2 and A3 engines have oil coolers that circulate coolant around the base of the oil filter. This probably serves a dual purpose as oil heater when warming. These engines are also oil cooled as well as water cooled. They squirt oil under the piston crowns to cool the pistons. This also serves to heat the oil quickly.

 

[Patman]

I paid extra attention this morning to my oil pressure, and after 15min of city driving in 32F weather, my oil temperature reached operating temp. It only took about half that time for the coolant temp to reach 200F though. My car is a 1995 Firebird Formula with the 350 LT1.

 

[Soma07]

quote:

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Originally posted by Patman: One way to tell is if you have an oil pressure gauge. In my LT1, I know the oil is up to operating temperature when the idle pressure is down to 20psi, or when it's just under 40psi at highway speeds. When it's still cold, the pressure is much higher than this. In my car I've noticed it takes about 15-20min to reach this point. Cars with large cooling systems, such as mine, will take longer for the oil to heat up also. Oil temp always lags behind coolant temp. With a small cooling system, such as on my wife's Civic, it will heat up faster, so thus the oil heats up faster too. I would say in a small car that the oil should be up to temperature in 10-15min instead of the 15-20 of a larger engine. Obviously wintertime adds a few extra minutes to these times.

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FWIW I've noticed the same thing on my LT1. The coolant will come up to operating temp (~170-180) in about 5 min while it always takes at least 10min for the oil pressure to drop to normal levels indicating the oil is up to temp. This has always sorta worried me beacuse at the dragstrip the car will sit there for 30-45min between passes and then it gets run at WOT without much time to warm up at all... My car used to have the factory oil cooler that circulated coolant around the filter base but I removed it after hearing all the horror stories of it leaking coolant into the oil. I wish I had paid more attention to it back then, I'm sure it would help the oil heat up faster, especally during the winter months.

 

[Patman]

I too worry about the effects of racing my car with cold oil. In order to run the best ET in an LT1, a one to two hour cooldown is often the best thing. But I wonder what harm I'm doing to the engine by running it so hard on cold oil?

 

[Quattro Pete]

The oil in my 1.8T engine reaches approx. 180F after about 20 minutes of driving during winter (outside temps. in the 30s and 40s), and after about 15 minutes of driving during summer. Also, during winter, my oil temp pretty much does not go above 180-185F, and in summer, does not go above 200F. I've been told by a number of people (with 1.8T engines) that these temps are too low, and that my temps should be in the 200-225F range. Apparently, that's what their temps are. Do I have anything to worry about? Thanks!