Liquid cooling
DOWFROST LC 25 vs LC 55: Freeze Point
Use LC 25 when the freeze point is 14°F. Use LC 55 when the freeze point is -40°F. Both documents print those two points.
On this page
Use DOWFROST LC 25 when the loop's freeze point is 14°F (-10°C). Use DOWFROST LC 55 when the loop's freeze point is -40°F (-40°C). Dow's LC 25 product page, opened October 22, 2026, prints both freeze points and calls LC 25 PG25 in this application. Table 1 of Dow's DOWFROST LC engineering and operating guide prints the same two freeze points, with propylene glycol at 25 volume percent for LC 25 and 55 volume percent for LC 55. The product page's maximum operating temperature is 195°F (90°C), and its use range ends at 194°F (90°C). The guide's maximum recommended bulk fluid temperature is 90°C (194°F). The Celsius high end on both documents is 90°C.
The freeze point is the split
The product page marks each freeze point with an asterisk. The page opened on October 22, 2026 did not include the footnote text, so the freeze points here are the numbers in the table, not an unread note. Table 1 of the engineering guide prints LC 25 at 14°F and -10°C, and LC 55 at -40°F and -40°C. A footnote on that table says the values are typical properties, not specifications. The product page states the same freeze points in its properties table, which is why the request can name them.
The guide says to use a concentration no higher than the freeze protection requires, because more glycol hurts heat transfer and raises pressure drop. It also says the lowest operating temperature is normally considered 0°F (-20°C) because viscosity rises, and that freeze protection down to -40°F (-40°C) can be achieved with LC 55. Zero degrees Fahrenheit is below LC 25's freeze point of 14°F. A loop that has to sit at 0°F is past LC 25's freeze point and inside the freeze point LC 55 prints. The 0°F sentence is the guide's viscosity caution. LC 25's freeze point on both documents remains 14°F.
90°C is the high end both documents print
The product page prints a maximum operating temperature of 195°F (90°C) and a temperature use range of 14°F (-10°C) to 194°F (90°C). The engineering guide prints a maximum recommended bulk fluid temperature of 90°C (194°F) and says operation above that limit may accelerate fluid degradation. Both documents use 90°C. The Fahrenheit figures on those lines are 195°F and 194°F. Copy 90°C, and copy the Fahrenheit number from the line you are citing: 195°F on the product page's maximum operating line, or 194°F on the use-range line and in the guide.
The use range on the LC 25 product page starts at 14°F, which matches the LC 25 freeze point. LC 55's low end on these two documents is the freeze point of -40°F. The guide says LC 55 provides freeze protection to -40°F.
What Table 1 adds, under the typical-properties note
Table 1, opened October 22, 2026, is labeled typical product specifications and then footnoted as typical properties, not specifications. Specific heat, viscosity, and conductivity below are that table. They are not repeated on the LC 25 product page. At 50°C the guide lists thermal conductivity of 0.485 W/mK for LC 25 and 0.336 W/mK for LC 55. Specific heat at 50°C is 3.94 kJ/kg-K for LC 25 and 3.43 kJ/kg-K for LC 55. Viscosity is 2.8 mPa·s at 20°C and 1.3 mPa·s at 50°C for LC 25, and 8.8 mPa·s at 20°C and 2.9 mPa·s at 50°C for LC 55. Volume expansion from -40°C to 90°C is 5.2 percent for LC 25 and 7.7 percent for LC 55. Boiling point at 760 mmHg is 101.4°C for LC 25 and 105°C for LC 55. Electrical conductivity is greater than 2,000 micromho/cm for both. pH is 8.0 to 10.5 for both, and reserve alkalinity is greater than 6.0 mL for both.
| Fluid | Freeze point | Glycol in Table 1 | Specific heat at 50°C | Viscosity at 20°C |
|---|---|---|---|---|
| DOWFROST LC 25 | 14°F (-10°C) | 25 volume percent | 3.94 kJ/kg-K | 2.8 mPa·s |
| DOWFROST LC 55 | -40°F (-40°C) | 55 volume percent | 3.43 kJ/kg-K | 8.8 mPa·s |
The nameplate percent and the in-use window are different columns
Table 1 lists 25 and 55 volume percent. A later paragraph in the guide says LC 25 is between 24 and 27 percent propylene glycol by volume. Table 8, the in-use quality table, lists LC 25 as 24 to 28 percent propylene glycol by weight and LC 55 as 53 to 57 percent by weight, tested to ASTM D3321. Those are three different statements. The fluid to name on the request is LC 25 or LC 55. The weight window is the maintenance check in Table 8. It is not a replacement for the 25 and 55 volume percent cells.
Table 8 also lists an in-use reserve alkalinity greater than 4 mL of 0.1N HCl, to ASTM D1121. Table 1's reserve alkalinity for the fluid as supplied is greater than 6.0 mL. Keep the new-fluid line and the in-use line separate. Appearance in Table 8 is yellow, clear, and free of particulates. The product page says LC 25 is dyed fluorescent yellow for leak detection.
What the fluid line on a hose or coupling request should say
The hose assembly page already asks for the approved fluid. This page is the choice between these two Dow fluids. Seal material for a named coolant is still a separate line. The coupling pages name EPDM and FKM as options and do not assign one seal to LC 25 or LC 55.
- Fluid name: DOWFROST LC 25 or DOWFROST LC 55.
- Freeze point from the page you used: 14°F (-10°C) or -40°F (-40°C).
- High end: 90°C, and the Fahrenheit figure from the line you cited.
- Volume percent from Table 1 if the request asks for concentration: 25 or 55.
- In-use weight window only if the request is a maintenance sample, from Table 8.
- The hose or coupling part number, on its own line.
Questions the two Dow documents answer
Is PG25 the same fluid as LC 25?
The LC 25 product page says DOWFROST LC 25 is commonly referred to as PG25 in this application. Table 1 lists 25 volume percent propylene glycol for LC 25. A maintenance band of 24 to 28 percent by weight is Table 8. Write LC 25 when that is the product, and write PG25 only as the name the product page uses for it.
Does the freeze point mean the loop should run at that temperature?
The freeze point is the protection temperature those documents print. The guide treats 0°F as a viscosity concern and points to LC 55 for freeze protection at -40°F. LC 25's product-page use range starts at 14°F. The documents here give the freeze point and the 90°C high end.
Can the two fluids be blended to a freeze point in between?
The guide says to use the concentration required for freeze protection and no higher, and it points to Table 1 for the freeze points of the two fluids. Order LC 25 or LC 55.
Sources
Freeze points on the product page and in Table 1, the 90°C lines, the volume and weight percentages, and the Table 1 properties are from the Dow product page and the Dow engineering and operating guide opened October 22, 2026. The guide PDF was the file at the Glycol Sales URL in the source list.