Does oil expand when hot?

[John in Leeds]

I seem to have problems accurately checking the oil levels in both the Guzzi and the Highland. The existing wisdom seems to be that in a cold engine left standing all oil would drain into the sump area and give the highest possible reading. This always supposing the bike was set on a centering stand and not moved.

 

My experience is that when the oil is hot I seem to get the highest readings. Does anyone have similar experience? And if oil does expend appreciably then by how much?

 

Could of course just be the onset of senility

[docc]

No question hot oil readings will be higher. Someone here can probably give us a coefficient of expansion.

 

Checking hot is the preferred method, yes?

[Guest Mattress]

Density (T) = Density (15 C) - beta*(T-15) where T is the temperature in °C, and beta is approx 0.0006 g/cubic cm/°C.”

The source of this information from Shell is:

R. Larsson, P.O. Larsson, E. Eriksson, M. Sjöberg & E. Höglund, "Lubricant Properties for Input to Hydrodynamic and Elastohydrodynamic Lubrication Analyses", Proc. Instn Mech Engrs, Vol 214, Part J, pp 17-27

Earlier investigation led me use a 15.5°C (60°F) specific gravity of about 0.890 which is still consistent with this information. Using that yields:

Temperature, °F 5 32 68 104 140 176 212 248 284

Temperature, °C -15 0 20 40 60 80 100 120 140

Density kg/m3 908 899 887 875 863 851 839 827 815

Density, lbs/ft3 56.68 56.12 55.37 54.62 53.87 53.13 52.38 51.63 50.88

[Guest ratchethack]

Interesting, Mattress. But it seems a density change from 0°C to 100°C of -60 kg/m3 (or -3.74 lbs/ft3) would be imperceptibly small, (let alone a normal operating range for a Guzzi motor of perhaps 20°C to 80°C) relative to a oil volume of 3.5 liters, especially read on a dipstick.

 

As Docc pointed out, the more indicative measure would be CoE (coefficient of expansion), a property of materials that's a direct measure of volume change with temperature. CoE takes the weight, and therefore the density of the material out of consideration. I found CoE to be impossible to find published anywhere when researching the CoE of brake fluid. I'd mostly lost a small disagreement with Pete on this, maintaining that brake fluid (like hydraulic oil) is engineered NOT to expand with heat, and that the CoE would be miniscule relative to operating temps and volumes on Guzzi's. As it happened, my "secret mountain laboratory" experiment with industrial thermometer and finely-graduated pipette failed when the thermometer failed, but not before showing the CoE of brake fluid was higher than I'd predicted (yet still relatively small).

 

The question for our purposes in response to John's question is, "What's a SIGNIFICANT amount of thermal expansion??"

 

In the case of Guzzi engine oil, I'd say if the oil expansion by volume from 20°C to 80°C isn't enough to read on a dipstick in the sump of a 3.5 liter (total oil capacity) V11, it ain't significant.

 

Using density, you've got to calculate the weight of 3.5 liters of engine oil and back this out of the considerations so you can deal directly with temp and volume. Somebody can no doubt do the calculations and conversions, but I don't think -60 kg/m3 density change in 3.5 liters translates to a volume change that would amount to much at all on a dipstick.

 

'Nother words, IMHO it doesn't make enough of a difference to be concerned about whether you read it hot or cold. If there's a tiny difference and it bothers you, always read it at the closest thing you'll get to a base temp -- that being ambient.

 

BAA, TJM & YMMV

[dlaing]

Does anyone have similar experience? And if oil does expend appreciably then by how much?

I have had similar experience and was surprised because I thought that when hot more oil would be trapped in the galleys, etc.

I agree with the others that I don't think the expansion coefficient would be "significant" until you reached the boiling point, that we are nowhere near.

In the brake fluid thread, we discussed how contaminants such as water and air made the expansion much more "significant".

Of course if you have negative freeplay on your brake pedal or a stiction problem, and it expands just a little, the release of pressure will push the pads to the rotors. This possibly creates more heat, and more pressure, and more heat and more pressure and more heat, and then the brakes lock and you can kiss your behind good-bye.

As Ratchet made the point in that thread, Clean fluid is a good thing, but I recall Pete and others pointed out that it still expands significantly, and that if the return valve on the master cylinder is shut, the expansion, even of clean fluid is significant and potentially catastrophic.

Some of us argued that some significant contamination of the brake fluid was inevitable, short of changing the fluid every month.

Also we argued that a little brake pedal freeplay is a good thing as it ensures there is no negative freeplay and thus less chance of the return valve becoming shut.

As for the oil, I suspect that contaminants such as air and moisture also play a significant roll.

[Guest ratchethack]

. . .

As for the oil, I suspect that contaminants such as air and moisture also play a significant roll.

What IS a very significant difference between brake fluid and motor oil in the context of any discussion of CoE is that (as previously discussed at length) brake fluid has the property of being powerfully hygroscopic -- that is, it draws water molecules out of the air and puts water directly into solution. Over time, this alters the CoE of brake fluid very significantly, (not to mention the oxidation effects on brake components) and in fact, since water changes state from liquid to gas within the operating temperatures of brake fluid, the very dramatic unwanted effects of liquid-to-gas expansion of water contamination on CoE of brake fluid is the main reason clutch and brake fluid must be changed regularly to ensure safe operation.

 

Motor oil, OTOH, is NOT hygroscopic whatsoever. Not only does water not even mix with oil, but at normal operating temps, any condensation water in the oil very quickly vaporizes and leaves the oil thru the breather and condensor. So water contamination has ZIP to do with thermal expansion of oil under normal conditions.

[dlaing]

I thought detergent combined with high engine temperatures, made it somewhat hygroscopic.

The milk shake effect is from the blending of water and oil.

But maybe that is only at the surface

Perhaps you are correct.

What then do you suppose causes the significant difference in readings? Senility?

I certainly have not accurately measured the difference.

To determine whether contamination had an effect we would need alot of dipstick data.

[Guest ratchethack]

I thought detergent combined with high engine temperatures, made it somewhat hygroscopic.

The milk shake effect is from the blending of water and oil.

While our friends in Old Blighty and other cooler, wetter climates can suffer from the "mayonnaise" accumulation syndrome inside rocker covers and other places , this only happens in cases where the motors aren't reaching normal operating temperature. Under these kinds of low temp & high humidity conditions, water doesn't vaporize significantly enough to be expelled thru the breather and condensor, so it remains behind -- not in solution with oil (water cannot go into solution chemically in oil under any circumstances), but captured as a loosely bonded hydroxide surfactant as "foam" that condenses in cooler parts of the motor (please excuse the likely innacurate application of terms, it's been a long long time since Organic Chemistry). The solution -- scrape it out or run the motor up to operating temp and cook off the water.

 

I can't account for, nor would I speculate on any reason for disparity in oil level readings on dipsticks. I've never noticed any variations at all -- warm or cold. But then, I generally don't have any reason to take a read when hot.

[docc]

I have always found a hot engine runs the oil up the stick significantly. Can't say I've ever checked this on the Guzzi though. I'll put that on my 'more-things-to-do list.'

[Guest Nogbad]

Just to be awkward, on both my bikes I find the hot level to be LOWER than the cold level. This I have always taken to be the result of the burden of oil trapped in the heads right after running that later drains down back to the sump / oil tank. The Buell being a dry sump engine does not vary that much at all.

[badmotogoozer]

Well if you insist on putting the "anal" back into "analysis" don't forget that you must also calculate how much the sump has also expanded due to heat if you really must have a comparison of hot level vs. cold level.

 

Rj

[richard100t]

I suppose someone could take some used motor oil, put it in a pan on the stove cold. Then measure the level before heating, then after hot....Voila

[Guest ratchethack]

OK, did a search. Enquiring mind. Just HAD TO . . .

 

The CoE of typical automotive-type lubricants is .00045 per degree F @ 60°F. (source: Lubricants USA, finalube.com)

 

So at 60°F, 3.5 liters total V11 sump oil volume expands by .001575 liters (1.575 ml) per °F.

 

From 60°F to 180°F then, 3.5 liters would expand by 0.189 liters, or 189 ml.

 

The inside of my sump spacer (where the dipstick marks are) measures roughly 20.5 x 22.5 cm.

 

Is it possible to detect a rise in oil volume of 189 ml on a surface area of ~461 cm^2 on a dipstick?

 

IMHO, only if you look very very carefully.

 

Keep in mind this represents a delta in oil temp of 120°F.

 

Now this is just me, but I don't monitor oil level close enough to notice, and I don't check it hot anyway.

[mike wilson]

In the case of Guzzi engine oil, I'd say if the oil expansion by volume from 20°C to 80°C isn't enough to read on a dipstick in the sump of a 3.5 liter V11, it ain't significant.

 

Certainly nowhere near the change in dimensions over temperature of the container of said oil.

[mike wilson]

I thought detergent combined with high engine temperatures, made it somewhat hygroscopic.

 

Hygroscopic specifically means that a substance binds moisture from the atmosphere. If it is not separated from the air, it will continue to absorb moisture until it either reaches equilibrium in some way (if a liquid) or dissolves itself in its absorbed water (if originally a solid - then the first parameter comes into play).