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Coolant vs. oil

The question is simple, in a cold engine after start up which one is warming up to operating temperature first?

oil because of friction and hot piston coming into contact with oil, etc

Yeah I thought so, plus the coolant is a cylinder wall away from the real action. Unless you blow your headgasket…

Think of it. Until the motor, including the oil, gets up to temperature, coolant iisn’t allowed to circulate through the motor. Circulating oil is in much closer proximity to heat and is really the first line of defense for overheating. Without adaquate oil, your motor would over heat a seize long before the loss of adaquate coolant…

Coolant heats much faster than oil. I always warm my engine before changing the oil with at least a short drive until the temperature gauge is well along toward normal. At that time, the oil is warm but not so hot that it is painful to my fingers as it always spills on them when the drain plug is removed. The oil filter is also not too hot to grasp. I have drained oil from a completely warmed engine many times also and have noted the difference.

Not an either/or thing, everything’s warming up as soon as you start the engine.

Coolant always circulates through the engine when it is running. Without oil, the coolant will still keep the engine from overheating…for the very brief time it will run before siezing due to lack of lubrication. I think the best way to determine which heats up faster is take a car with an oil temperature readout, start it cold, drive it and see what happens.

Interesting question
Coolant (1/2 ethelyn glycol and 1/2 water) transmits heat much faster than oil.
Water (unmixed) transmits heat faster than coolant.
oil transmits heat relatively slowly.

However, oil washes heat down from the surfaces of of the cyliners…and the combustion temperatures can get over 3,000F. Coolant, while not directly exposed to the combustion temperatures, actually has far more exposure than oil to high temperatures because it’s spread out over the suface opposite the cylinders, ittentionally to soak up the heat. But then it’s rapidly cooled, which the oil is not.

There’s also the issue that materials that transmit heat more readily can feel hotter than materialos that do not. And vice versa. Aluminum at 70F feels cool. Wood at 70F feels like it’s the same temperature as your hand. Sit on a 40F aluminum stadium seat and it’ll suck the heat right out of your lower cheeks. Sit on a 40F wooden seat and it’ll feel just a bit cool.

So, IMHO, while the oil is soaking up heat from cylinder walls areas of which are being exposed to a few thousannd degrees and more, and the oil has no cooling system, it probably gets hotter…but doesn;t feel it because it transmits heat relatively poorly. It’s slow transmission of heat, however, probably means it takes longer to get hot.

Oil can get much hotter then coolant which is designed to remain at a fairly constant thermostatically controlled temp. Operating temperature of the oil is variable. The question has no real answer as the oil will reach operating temperature at lighter loads quicker the coolant but the motor and the oil lubricating it may take longer to reach a higher operating temperature while hill climbing or towing. Heck, theoretically, the coolant will never reach the temperature of the oil under these conditions so will lag behind oil temps well over 200 degrees while coolant could remain well under.

And you thought this was a simple question…

"The question is simple, in a cold engine after start up which one is warming up to operating temperature first? "

It says so in the first 4 words ;=)…now the answer ?

From my experience I do believe the coolant comes up to operating temp first, then the oil follows. Just warming a car up for an oil change kind of confirms it because just because the coolant is at operating temp, the oil can come out luke warm.

Point made.
The coolant. No, wait, the oil is subjected to much higher temperatures, so it must be the oil. No, wait, aw, nevermind…

Well the operating temperature of the coolant is around 180° where the operating temperature of oil is closer to 300°. I remember someone who had an oil temp gauge and a coolant temp gauge, along with a bunch of other gauges in his car and the coolant came up to a stable temperature before the oil did, but I don’t remember if the coolant was actually hotter than the oil when it first stabilized.

Bottom line:
if both had the same exposure to the same tempertaures, the coolant would heat up much faster than the oil. It simply is a much better heat conductor.

But they don’t. They each have very different exposures to very different temperatures. The coolant has far greater exposure (via much of its volume being in contact to the other side of the cylinder walls) to lower temperatures. The oil has far less exposure to much higher temperatures.

They also have very different exposure to surfaces that dissipate heat. The oil’s only real direct ability to disspate heat is by radiation via the vottom of the oil pan (assuming the exhaust isn;t near it) and by convection via gasses in the pan traveling up the oil return passages and being drawn in through the crankcase ventilation process…with a bit being dissipated by the valvecovers (which is why I like valve covers with vanes cast in). The coolant system…well, it’s designed to dissipate heat. It even needs a special device (T-stst) to prevent it from dissipating too much heat to allow the engine to get and stay at operating temperature.

So which one reaches the engine’s ooperating temperature more quickly isn’t that easy to figure out. And it might vary from engine to engine. Or by engine type…a V8 might profile differently than an I-4.

Si I contend that the question really isn;t simple at all.

Thanks for the replies. Sorry I believed that this has a simple answer…
I guess the only way to know it is have a car with both oil and coolant temperature gauge on it…

To 252525:

Now that you have my and Bing’s replies, what will you do with this information?

By the way, you may have heard the old saying: You can lead a horse to water but you can’t make him drink!

To Wha Who:
I appreciate all the info you guys given to me. Here is the situation, I spend more time driving around and sitting in traffic than I should. I do have a lot of time to think and I am a curious person. It is great to see other peoples opinions and reasoning. There is nothing behind it. My motto is: every day is a good day to learn something new…

If you have a working thermostat, I don’t see how the coolant could get to operating temperature before the oil. The oil is circulating and heating up from the start. The coolant doesn’t get exposed to the warm engine until the engine (and the oil) have both already reached operating temp.

Now, if you don’t have a thermostat, or if you have one that is stuck open, this question gets complicated (and I don’t know the answer). However, if you have a working thermostat in place, the answer is simple.

My car has both a coolant and an oil temperature gauge, which both display in Fahrenheit. (or Celsius if you prefer) The oil temp is accessible, while the actual coolant temp is buried in a ‘hidden’ menu on the “EVIC” (Chrysler’s acronym for the electronic display on the dash), along with a ton of other interesting and useful information. (the car also has an analog coolant temp gauge on the dash)

I have noticed that the coolant heats up much faster than the oil on cold days. I’m sure this is because of the thermostat being closed to purposely heat the coolant faster, and the car’s fairly large oil capacity of 7 qts. But the coolant will always be at a higher temperature than the oil until the thermostat opens, in any weather. Then as you drive, gradually the oil temperature will slightly exceed the coolant temp. With ‘spirited’ driving on a hot day, the oil will hit about 230, while the coolant will not generally exceed 210, no matter what you do. The coolant also will cool down very rapidly after a hard acceleration, while the oil takes much longer. This is expected I suppose, considering the car has a nice big radiator in front, and that the coolant cools the oil, indirectly…