Weldable EPTFE Vent For Coolant / Washer Fluid Reservoir Tanks

The weldable ePTFE vent for coolant and washer fluid reservoir tanks is a cost-effective, durable pressure equalization solution engineered for the high-volume, wet-environment fluid containers within the vehicle. It combines a chemically resistant thermoplastic body with a high-performance ePTFE waterproof breathable membrane, designed for direct ultrasonic or heat-stake welding into the tank wall or cap. This vent provides continuous pressure equalization as the reservoir fluid volume changes—during thermal expansion of hot coolant, as washer fluid is consumed and replenished, and during altitude changes—preventing the vacuum that can collapse thin-walled tanks and the pressure that can cause leakage. It maintains an absolute barrier against external water, dust, and contaminants that could foul the fluid or clog the washer nozzles. The vent is engineered for chemical compatibility with glycol-based coolants, methanol/ethanol-based washer fluids, and the various additives and detergents these fluids contain.

Coolant expansion tanks (overflow bottles, degas tanks) and windshield washer fluid reservoirs are subjected to continuous, sometimes rapid, internal volume changes. The coolant expansion tank receives hot, expanding coolant from the engine; as the engine cools, the coolant contracts and the tank must draw in external air to prevent vacuum collapse. The washer fluid reservoir is emptied in pulses as the driver washes the windshield, then sits partially empty, breathing with ambient temperature changes. Without proper venting, the coolant tank can collapse under vacuum or burst under pressure—both failures that compromise the cooling system and can lead to engine overheating. The washer reservoir can become deformed, causing the pump to cavitate or the level sensor to give false readings. Additionally, both reservoirs are often mounted in dirty, wet areas—the wheel arch, behind the bumper, or low in the engine bay—where they are exposed to road spray, mud, salt, and dust. A simple open vent allows these contaminants direct access to the fluid, clogging washer nozzles with debris or introducing silt and salt into the cooling system. The tank material—typically polypropylene or polyethylene—is chemically susceptible to certain washer fluid alcohols if not properly vented, as concentrated vapors can accumulate.

The weldable ePTFE vent provides a reliable, permanent breathing pathway that becomes part of the tank assembly. The vent body is molded from a polypropylene or polyethylene material that matches the tank polymer, ensuring a perfect, homogeneous weld. The ePTFE membrane allows the necessary bidirectional airflow: as the tank volume changes, air freely enters or exits through the membrane's billions of nanopores. This prevents vacuum and pressure buildup. The membrane is completely waterproof and dustproof, blocking road spray, mud, and debris. The oleophobic and chemically resistant treatment ensures the membrane does not degrade or wet out from the glycol, methanol, ethanol, surfactants, and detergents present in the respective fluids. The weldable format integrates cleanly into the tank blow-molding or injection-molding process, providing a low-cost, high-reliability vent that requires no additional assembly steps, fasteners, or adhesives.

• Engine coolant expansion tank (overflow bottle, degas tank)

• Windshield and rear window washer fluid reservoirs

• Headlamp washer fluid reservoirs

• Intercooler coolant reservoirs

• Battery thermal management coolant reservoirs (EV, PHEV)

• Power steering fluid reservoirs

• Heavy truck and bus large-volume fluid reservoirs

The weldable vent is integrated into the tank during the manufacturing process. A vent port is designed into the tank wall or cap at a high point, away from maximum fluid level and slosh zones. The vent body, made from the same polymer as the tank, is positioned and welded in place using ultrasonic or heat-stake equipment. The welding process creates a permanent, leak-tight molecular bond. As the engine coolant expands with heat, the rising fluid level in the expansion tank displaces air, which exits through the ePTFE membrane. When the engine cools and the coolant contracts, ambient air is drawn back in through the membrane to fill the increasing headspace. Similarly, as washer fluid is consumed, air enters through the membrane to replace the dispensed volume. The membrane's microporous structure blocks all external water, dust, and debris, keeping the fluids clean and the washer system nozzles free of clogs.

1. Identify the tank polymer (PP or PE) to select a matching vent body material for optimal weld compatibility.

2. Determine the tank's function (coolant or washer) and the expected thermal and chemical exposure to select the appropriate membrane treatment.

3. Calculate the maximum air exchange rate: for coolant tanks, size for the thermal expansion volume; for washer tanks, size for the maximum pump draw rate.

4. Select the vent body size and profile to fit the available tank wall space and to accommodate the tank's wall thickness.

5. Test with complete tank assemblies: thermal cycle the coolant tank from -40°C to +110°C; cycle the washer tank through fill, dispense, and environmental exposure.

• Q: Can the same vent model be used for both coolant and washer fluid tanks?
  A: While the vent body and membrane base are similar, we recommend different membrane treatments: glycol-optimized for coolant tanks to handle hot, pressurized coolant vapor; alcohol-optimized for washer tanks to handle methanol/ethanol and surfactant exposure.

• Q: Will the washer fluid's methanol content eventually degrade the ePTFE membrane?
  A: No, ePTFE is completely chemically inert to methanol and ethanol. The membrane will not swell, soften, or lose its waterproof properties over years of exposure to washer fluid vapors.

• Q: Is the vent compatible with the blow-molding process used to manufacture most fluid reservoirs?
  A: The vent is typically welded into the tank after blow molding, as a secondary operation. We can work with your process engineers to design the port geometry for optimal post-mold welding.

• Q: Can the vent be integrated into the tank cap instead of the tank wall?
  A: Yes, we can provide vent inserts that weld into the tank cap, providing the same pressure equalization function in a cap-mounted format.

• Q: Does the vent prevent the "coolant smell" that sometimes occurs when the engine is hot?
  A: The membrane allows air exchange necessary for pressure equalization, so a minimal amount of coolant vapor may pass through. However, the controlled venting significantly reduces odor compared to an open vent or a leaking cap seal.