OUR VERDICT
Flexfab 5521 is Flexfab's premium green silicone heater hose, with a heavier wall than standard heater hose for coolant and heated-water lines. It stays flexible from -65°F to 350°F and meets SAE J20R3 Class A. Buy it for heater cores, coolant transfer, and bypass lines where rubber hardens and cracks. Skip it for fuel or oil; silicone isn't rated for petroleum.
The boxed length suits shops and fleets that keep a size on the shelf.
WHAT WE LIKE
- Stays flexible from -65°F to 350°F
- SAE J20R3 Class A coolant rated
- Heavier wall than standard heater hose
WORTH NOTING
- Not for fuel, oil, or solvent service
- Softer than rubber, so use lined or constant-tension clamps
Specifications
| Hose series | 5521 |
|---|---|
| Inner diameter | 3/4" (19mm) |
| Construction | 1-ply nylon reinforced silicone |
| Use | Heater / Coolant |
| Format | Boxed |
| Fuel rated | No |
| Temperature range | -65°F to 350°F |