Loss of Methanol Antifreeze in
Automobile Cooling Systems
H.C. DUUS, E. H.KELLER, AND H. M. ChDOT "Zerone" Division, Ammonia Department,
E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
thr liquid in the cooling system is maintained a t a minimum temperature of 140' F. by means of thermostats. This temperature was therefore chosen as the standard for the practical tests, and the data are limited to this operating condition. The boiling point of methanol (149' F. or 65" C.) is lower than that of other antifreeze materials such as denatured alcohol (172O F., 77.8" C.), isopropanol (180' F., 82.2' C.), ethyleneglycol (387.3' F., 197.4" C.), or glycerol (555.8' F., 291' C.). Nevertheless, because of its low molecular weight, appmximately 20 to 25 per cent less volume of methanol is re quired to effect a given lowering of the freezing point than of glycol or denatured alcohol; this is an economic advantage. From the purely physico-chemical standpoint, the boiling Doint of the straizht antifreeze is an inadeanate criterion of
OST of the automobiles in the United States are operated in territories where atmospheric temperatures are low enough to permit freezingof the cooling water during the winter months. Materials added to the water to prevent freezingare called "antifreezes." From the consumer's standpoint, the most important consideration is the rate of loss of the antifreeze. As a result, antifreeze materials are classified into the two general types, "volatile" which have boiling points below that of water, and "nonvolatile," which have boiling points above that of water. According to a current conception, shared aIike by experts and the general public, volatile antifreeze is supposed to evaporate and leave a less concentrated solution; nonvolatile antifreeze is supposed to remain permanently in the cooling system ( & 5 , 4). When synthetic methanol became available, this conception proved a serious obstacle to its introduction as an antifreeze. In order to determine the validity of this idea, the Ammonia Department of E. I. du Pont de Nemours & Company, Inc., initiated a series of practical tests in automobiles under average driving conditions several years ago. Laboratory tests such as can be made by setting aside open beakers or evaporating dishes and noting the change in concentration or liquid level are inconclusive because they give no means of evaluating the importance of numerous mechailical factors. Although the practical tests are being continued to keep abreast of developments in automotive design, the results on present-day engines are completed and are sufficiently interesting to report. In practically all such engines
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181" F Y (82.8'' C.),'respectiveiy (1). Both ofthese boiling points are well above the operating temperature of modem automobile engines equipped with thermostats opening a t 140' F. Common experience demonstrates that there must be losses, even though operating temperatures are below the boiling point of the solutions, since i t is necessary to add water to the cooling system in summer driving when no antifreeze is present even though operating temperatures never reach 212" F.(100" C.), Such iosses a t temperatures below the boiling point cannot be due to evaporation. On the basis of this every-day experience, i t was felt that 142
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tests and every two weeks later. Records were kept of the the losses from methanol antifreeze solutions, which are usumileage, specific gravities, and amounts of replacement, ally assumed to indicate separation of methanol, might be For control pur oses it was desirable t o use both a volatile and due to other causes. For want of a better term, losses other a nonvolatile antigeeze. The two chosen for the majority of the than those which result in separation by volatilization are cars were proprietary brands of methanol antifreeze1 and of ethyleneglycol antifreeze. The boiling points of the straight classified as mechanical losses. They are due to leaks, therantifreezes and their solutions are as follows: mal expansion, ''afterboil," forward surges of the liquid on sudden stopping, or to the carrying over of fine spray through B. P. of Soln. Freezing a-:t the overflow by the violent agitation in the cooling system. B.,P. of +20" F. ' 0 F. -20' F. If it could be shown by practical tests that losses are mainly Antifreeze Antifreeze (-6.7' C.) (-17.8' C.) (-28.9O C.) due to these mechanical causes, the low boiling point of methaO F. (" (7.) F. ( O C.) ' F . (" '2.1 F. ( O C.) nol would be no serious objection to its use as an antifreeze. 178 81 1) Methanol 149 (65.0) 196 (91.1) 184 (84.4) 215 (101.7) 218 (103.3) 221 llOi.0) Glyool 343 (172.8) The principle involved in such tests is relatively simple. If the losses result in separation of the antifreeze and lower the concentration, they must be replaced by straight antifreeze. Losses from the radiator through the overflow were measured by attaching to the overflow pipe of the radiator, small cans of 1If, however, they are due to mechanical causes, the concenor 2-quart capacity (0.946 or 1.892 liters) called "catch-pots." tration may be maintained by making replacements with Care was taken t o install the catch-pots in such a way that the solution of the same concentration as was first put into the liquid spilled over during running could not be sucked back when cooling system. The test procedure followed was to make the engine cooled. Concentrations of all samples were determined by measuring replacements with solution rather than with straight antithe specific gravity on four-place hydrometers, but the reprofreeze. If the results showed that freezing points could be ducibility of measurement was usually not greater than one in the maintained by this procedure, it would follow that losses were third place. When the volume available was too small for these mainly mechanical. hydrometers (as was often the case with the catch-pot samples), a WestphaI balance was used. The cars used in the tests were privately owned and operated in order to approach average conditions as nearly as possible. Information obtained from various sources inResults dicated that the average mileage would be about 400 to 600 The results of two series of tests conducted between Nomiles per month. No effort was made to regulate operation vember 15 and April 15 during the two seasons of 1935-36 to this figure but, as it happened, the results confirmed its and 1936-37 are summarized in accuracy. In a few special tests Table I. The tests of 1935-36 the monthly a v e r a g e ran up to were conducted w i t h s o l u t i o n s about 1800 miles. The tests were freezing a t -4.0" F. (-20.0" C.). always run for at least one month Antifreeze materials added This degree of protection was or more in order t o e l i m i n a t e lowered to -16" F. (-26.7" C.) in to w a t e r in automobile variations due to special driving the tests of 1936-37. Atmospheric conditions. All the engines were engine cooling systems to temperatures in the locality where equipped with thermostats opening prevent f r e e z i n g in cold the tests were run seldom reached a t 140" F. weather a r e c o m m o n l y 0" F. (-17.8' C.). Although the principle of testclassified into two typesWith the methanol a n t i f r e e z e ing was simple, the great number there was only a slight loss of convolatile and nonvolatile. By of variables in conditions of operacentration and freezing point in tion made it necessary to run about a series of practical tests in either series of tests. This result three hundred cars a t all seasons, three hundred cars over the confirms those obtained in all previthough mainly under winter condipast seven years it has been ous tests and shows that the largest tions, over a period of seven years shown that losses in engines proportion of the losses are meand in several different territories, chanical in character. In the earlier equipped with 140"F. (60"C.) before conclusions could be contests the magnitude of the replaces i d e r e d final. It would be imthermostats supplied by the ments was somewhat larger-3.0 possible in the space limitations of m o t o r manufacturers are quarts (2.84 liters) per 1000 milesthis paper to present all the data. mainly due to mechanical doubtless because cooling systems Moreover, cooling systems have causes with both types of were less perfect. With the nonbeen markedly improved during v o l a t i l e antifreeze there was a the period covered by the tests antifreeze. Losses due to slight increase of concentration in (6), and some of the earlier results evaporation are so slight as the 1935-36 tests but a small deare now obsolete. The data reto have no significant praccrease in the 1936-37 tests. The ported are t h e r e f o r e limited t o tical effect, and f r e e z i n g change in freezing point with either typical test series of the last two points may therefore be antifreeze was so slight as to be of years. no practical significance; it has maintained by replacing Driving Tests been shown that, e v e n t h o u g h losses with methanol solusmall amounts of ice may form in At the beginning of the tests, cooltions of the same concening s y s t e m s w e r e repaired and the solution, the point a t which tration as was originally put tightened and then serviced with a enough ice is present to stop the stock antifreeze solution protecting flow lies about 10" F. (5.5' C.) into the cooling s y s t e m OOor -2OOF. to approximat:l below the freezing point (6). The ( - 1 7 . 8 O or -28.9 During the The average replacement losses of freezing point noted in season replacements were made as needed, is approximately 2 needed from this same stock solution. Table I with the v o l a t i l e antiWarning tags were placed on the cars quarts (1.892 liters) of solufreeze were well below this marto avoid having unauthorized replacetion per 1000 miles of driving. 1 This product is approximately 99 per ments made by the owner or by cent synthetio methanol: the remainder is service stations. Samples were taken corrosion inhibitor and dye. every week at the beginning of the
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gin of safety. The h a 1 concentrations and freezing points listed were taken in the early spring after the passing of cold weather when there was no need for maximum protection. Comparison of the replacements with the amounts recovered through the overflow pipe in the catch-pots shows that replacements are several times larger than recoveries. The difference between recoveries and replacements represents losses due to leakage. POINTCHANQES IN AUTOMOTABLE I. LOSSESAND FREEZING BILE ENQINES EQUIPPEDWITH 140' F. THERMOSTATS No. of cars Av. mileage per car: Total Per mo. Re lacement per 1000 mi.: &arts Liters Recoverv in catch-Dots Der
Av. concn. % by vol.: Initial Final Of replacements
-1935-36-Methanol 36
Glycol 21
-1936-37Methanol 34
2200 450
2285 457
3016 603
Glycol 26 2792 558
1.516 1.434
1.705 1.612
1.914 1.812
2.138 2.021
0,430 0.417
0.217 0.205
0.399 0.378
0.285 0.270
-4.0 -20.0
-4.0 -20.0
-16.0 -26.7
-13.8 -25.5
0 -17.8
-4.6 -20.3
-10.8 -23.8
-12.5 -24.7
35.0 35.5 35.0
35.7 32.8 36.0
40.6 39.9 40.0
29.2 27.0 30.0
Leakage losses obviously cannot effect any separation between antifreeze and water; but even in the losses through the overflow pipe and recovered in the catch-pots, separation of antifreeze and water is by no means complete. I n the case of methanol these losses, if due to evaporation only, should have consisted mainly of methanol. Actually the average concentration of the catch-pot samples was only 55.5 per cent. Because of the small volume of the catch-pot losses, the slight separation which did take place had little effect on the freezing point. With glycol the average concentration of the catch-pot losses was 24.4 per cent. TABLE11. LOSSESAND FREEZING POINT CHANGES WITH METHANOL IN VARIOUS TERRITORIES (SEPTEMBER 1TO OCTOBER 1, 1935) No. of cars in test Av. total mileaae Der car
Mein Max. Min.
12 1852 1852 1.10 (1.04) +11 3 11 5) +8:1 [--12:8) 19.5 21.8 31.0 65.8 (18.8) 90.0 (32.2) 40.0 ( 4.4)
I n addition to the results summarized in Table I, the results in two other series of tests will be of interest. The &st was carried out in the early fall of 1935 by a number of operators using their cars for business purposes in each of the following metropolitan areas : Boston, New York, Baltimore, Buffalo, Detroit, Chicago, Des Moines, Kansas City, and Salt Lake City. The operators made the initial servicing and subsequent replacements, and returned weekly samples for accurate laboratory analysis. It was impracticable to install catch-pots in these tests; the tests were limited to methanol but were more severe since the monthly mileage was above average and the atmospheric temperatures much higher than in winter driving. The results are summarized in Table 11.
VOL. 30, NO. 2
This series shows that the concentration increased during the course of the tests because the operators were making replacements with a solution of greater average concentration than the original. I n spite of the greater average mileage per month, the losses per 1000 miles are less in these tests than in those with a lower monthly mileage. The result is probably explained by the fact that a certain proportion of the losses is due to minor leaks or seepage through hose and gaskets which go on regardless of whether the car is running or standing idle. The other series of tests was carried out a t Denver (altitude, 5000 feet) in the late winter of 1937 to test the practical effect of lowering the boiling point with altitude. All records and analyses were made in a temporary laboratory set u p in a local service station. The results of this series are shown in Table 111. Comparison of Table 111 with Table I shows no essential differences. The total replacements in Table I11 are a little higher for both volatile and nonvolatile antifreeze, but catchpot losses are approximately the same. It is interesting that the average monthly mileage is about the same in Denver as in the other tests. TABLE111. LOSSESAND FREEZING POINTCHANGES AT HIQR ALTITUDE (FEBRUARY 9 TO MARCH 8,1937) No. of cars in test Av. total mileage per car Av. mileage per car per month Re lacement per 1000 mi., quarts (Eters) Recovery in catch-pots per 1000 mi quart (lite9 AV. Gitial F. P . ~F. ( 0 c.) Av. final F. P., F. C.) Av. initial concn., voi. % Av. final concn., vol. % Concn. of replacements, vol. %
Methanol 10 602 602
aiycoi 10 438 438
2.556 (2.418) 0.35 (0.33) -16.0 (-26.7) -13.2 (-25.1) 35.6 34.3 35.0
l.g90 (1.883) 0.32 (0.30) 9 9 23.3) -l0:2 1123.4) 38.4 38.6 38.0
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Reasons for Losses In order to understand why there should be losses through the overflow even though the average operating temperatures are well below the boiling points of the cooling solutions, it is necessary to examine the operation of cooling systems in more detail. The amount of heat dissipated to the cooling air by the radiator of an ordinary automobile engine under full load a t high speed is equivalent to that necessary to warm a 6-room house to 70" F. (21.1" C.) on a day with 0" F. (- 17.8"C.) atmospheric temperature. In rating radiators, the standard condition is that they shall dissipate this heat with the engine running and the car moving through air at a temperature 100" F. (55.5" C.) below the boiling point of water. In practice this means that air temperatures must be up to 112" F. (44.4" C.) before water boils in an average radiator. When running on the road, this rating provides an ample margin of safety for water in summer and for antifreeze in winter. However, when the engine is shut off after a run, circulation of the cooling liquid stops. The residual heat in the mass of metal in the engine is a t a considerably higher temperature than the cooling liquid and may cause local boiling a t hot spots in the engine bloc. The expanding vapors from this local boiling will then force liquid through the overflow pipe. Such a condition is called "afterboil" and is responsible for most of the overflow losses. Since the cooling system is not designed to serve either as a still or fractionating column, separation of antifreeze and water during the afterboil can take place only to a limited extent. The results given in Tables I to I11 show that afterboil is of relatively slight magnitude with 140" F. thermostats. Reverting to the original problem presented by the popular acceptance that methanol antifreeze would rapidly be vola-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
tilized from the cooling system, it is evident that the controlled tests have shown the fallacv of this conceDtion. The losses are general, and antifreeze and water disappear in approximately the same proportions. If such losses are replaced with water only, the antifreeze will be diluted, and freezing points will be raised. It may be that the popular misconception concerning methanol antifreeze arises from an improper appreciation of this fact. Again it is possible that by acting on that misconceDtion. redacenients have often been made with straight antiheezej Gith a resultant lowering of the boiling point and large losses* It is hoped that these data may correct this misconception and promote a more rational method of servicing by making replacements with
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solution rather than with straight water or with straight antifreeze.
Literature Cited CHEM., 23,708 (1931). (1) Aldrich and Querfeld, IND.ENGI. (2) Bur. Standards, Letter Circ. 28, Dec. 9, 1921 (revised Dec. 1. 1925). (3) Currne’and Young, IND.ENQ.CHEM.,17,1117 (1925). (4)Keyes, Ibid., 19, 1119 (1927). 15) Olsen. Brunjes, and Olsen, Ibid., 22, 1316 (1930). (6) Saunders, S. A . E. Journal, 39,496 (1936). .-I
RECEIVED August 31, 1937. Presented before the Division of Industrial and Engineering Chemistry a t the 94th Meeting of the American Chemical Society, Rochester, N. Y., September 6 to IO, 1937.
I n this painting, No. 86 in t h e Berolzheimer series of Alchemical and Historical Reproductions, this prominent Dutch artist has again turned t o the early apothecary’s “kitchen” for his inspiration. The original, painted in 1818, is in t h e Rijksmuseum in Amsterdam. While some of t h e apparatus are clearly children of the alchemical age, others show a decided improvement over the latter--for example, the boxed condenser at the left. T h e enormous scale-beam, suspended from the ceiling, is also of interest. This is t h e second reproduction in the series by this artist; the first, No. 48, appeared in our issue of December, 1934, page 1279. D. D. Berolzheimer 50 E a s t 41st St., New York, N. Y.
A list of Reproductions Nos. 1 to 60 appeared in our issue of January 1936, page 129. the list of Nos. 61 to 72 appeareh in our issue of JLnuary, 1937. page 74: snd Nos. 73 to 84 are listed on page 70 of our issue of January, 1938.
