Product Description
The QUINTON HAZELL Thermostat, coolant (QTH105) is an original-equipment-quality mechanical thermal regulation valve manufactured by Quinton Hazell. Positioned inside the coolant distribution flange or water pump housing, its primary operational function is to regulate the flow of coolant fluid between the engine block and the radiator based on real-time operating temperatures. When the engine is cold, the thermostat remains tightly closed, routing coolant through a bypass loop to accelerate warm-up, minimize mechanical wear, and rapidly bring the cabin heater online. Once the engine reaches its optimum calibrated thermal threshold, the internal wax element expands, forcing the valve to open and allow hot fluid into the radiator for cooling. Over years of service, thermal fatigue can cause the internal return spring or wax capsule to fail, leaving the thermostat stuck open (causing the engine to run cold and kill fuel economy) or stuck closed (inducing instant, catastrophic engine overheating).
Product Specifications
- Manufacturer: QUINTON HAZELL
- Item Number: QTH105
- Product Condition: New
- Component Classification: Mechanical Coolant Thermostat / Thermal Control Valve
- Opening Temperature [°C]: 80
- Flange Diameter [mm]: 54
-
Kit Components Included:
- 1x 80°C Mechanical thermostat core unit
- 1x Premium elastomeric sealing O-ring
Vehicle Compatibility
This universal 54mm, 80°C thermal valve configuration is precision-calibrated to regulate the cooling systems of legendary air-cooled, water-boxed (WBX), and water-cooled inline petrol and diesel engine families across the classic Volkswagen Group (VAG) portfolio from the early 1970s through the late 1990s:
| Car Model / Platform | Compatible Engines / Variants | Engine Displacement Range | Year of Manufacture |
|---|---|---|---|
| VW Transporter T3 (Bus / Box / Platform) | 1.6 D / 1.6 TD / 1.7 D / 1.9 WBX / 2.1 WBX (Critical for managing water-boxed rear engine loops) |
1588 - 2110 cc | 1979 - 1992 |
| VW Golf II (19E, 1G1) / Jetta II (19E) | 1.6 / 1.8 / 1.8 GTI / 1.8 GTI 16V / 1.6 D / 1.6 TD (Standard EA827 external water pump blocks) |
1595 - 1781 cc | 1983 - 1992 |
| VW Golf I (17) / Jetta I (16) / Golf 1 Convertible (155) | 1.5 / 1.6 / 1.6 GTI / 1.8 / 1.8 GTI / 1.5 D / 1.6 D | 1471 - 1781 cc | 1974 - 1993 |
| VW Golf III (1H1) / Vento (1H2) / Passat B3 & B4 | 1.6 / 1.8 / 2.0 / 2.0 GTI / 1.9 D / 1.9 TD / 1.9 TDI | 1595 - 1984 cc | 1988 - 1997 |
| Audi 80 (81, 85, 89, 8A, B2, B3, B4) / Audi 100 (4A, C4) | Longitudinal inline 4-cylinder petrol and diesel models | 1.6 / 1.8 / 2.0 / 1.6 TD / 1.9 TDI | 1978 - 1996 |
⚠️ Opening Temperature Calibration Warning: This specific thermostat has an opening temperature specification of **80°C**. This is a cooler thermal threshold than the standard 87°C factory thermostats typically specified for modern passenger cars. It is highly sought after for classic setups, high-load configurations, towing, and hot-climate regions (such as rear-engine Transporter T3 water-boxer platforms) to give the cooling circuit an earlier cooling buffer against overheating. Always check your workshop manual to confirm if your vehicle thrives on an 80°C or 87°C baseline. When performing an overhaul, never reuse the old sealing ring, and always orient the bleed pin/jiggle valve (if equipped) to the 12 o'clock position to allow trapped air bubbles to bleed out smoothly during coolant system refilling.
Original Equipment Manufacturer (OEM) Reference Numbers
This premium replacement coolant regulation valve directly cross-references with, or acts as a factory-correct swap for, the following original factory equipment codes:
- VAG (VW / AUDI / SEAT / SKODA): 025 121 113C, 025121113C, 056 121 113D, 056121113D, 068 121 113, 068121113
- FEBI BILSTEIN (Interchange Reference): 17888
- BEHR (Interchange Reference): TX 13 80, TX1380
- VALEO (Interchange Reference): 819932