944 Cooling System — Thermostat, Cap & Bench Checks
Factory cooling-system figures for the 944 — thermostat opening and fully-open temperatures with the water-bath bench check, the radiator-cap pressure-valve settings, and the leak check. Temperatures switch between °C and °F, pressures between bar and psi.
The factory cooling-system figures for the 944, with the bench checks that go with them. These are the numbers behind the repair pages — when a thermostat is replaced or a cooling-system fault is traced, these are the values a known-good part should meet. Temperatures switch between °C and °F and pressures between bar and psi; the thermostat's opening travel is a fixed dimension in millimetres.
Thermostat
| Figure | Value |
|---|---|
| Opening temperature (begins to open) | 81 °C178 °F to 85 °C185 °F |
| Fully open | approximately 90 °C194 °F |
| Opening travel (lift) | at least 7 mm |
The opening band is the same whether you read it as the spec-sheet range of 81 °C178 °F to 85 °C185 °F or as the bench figure of about 83 °C181 °F give or take a couple of degrees — they describe the same thermostat.
Bench check
Test a thermostat in a water bath, not on the car:
- Suspend the thermostat in a container of water so it does not touch the sides or bottom, with a thermometer alongside the valve.
- Heat the water slowly. The valve should begin to open at 81 °C178 °F to 85 °C185 °F.
- Keep heating; the valve should be fully open by about 90 °C194 °F, lifting at least 7 mm.
- A thermostat that opens late, never fully opens, or sticks shut runs the engine hot; one that is stuck open never lets it reach temperature. Replace rather than free off a sticking unit.
Radiator cap
The cap is a two-way valve. The high-pressure valve sets the system pressure so the coolant can run hotter than 100 °C212 °F without boiling; the low-pressure valve lets the expansion tank draw coolant back as the system cools.
| Valve | Opening pressure |
|---|---|
| High-pressure (relief) valve | approximately 1 bar15 psi (0.9 bar13 psi to 1.15 bar17 psi) |
| Low-pressure (vacuum) valve | 0.1 bar1 psi |
A cap that relieves early loses the pressure margin and lets the coolant boil at a lower temperature; one that does not relieve at all over-pressurises the system and can burst a hose or the tank. Test the cap to the 1 bar15 psi figure with a cooling-system pressure tester, and replace it rather than guess — a tired cap is a common cause of unexplained overheating and coolant loss.
Checking the system for leaks
With a pressure tester on the filler neck, and by eye:
- Inspect visually for leaks at the radiator, hoses, water pump and joints.
- Check the hoses for porosity and brittleness — a hose that has gone hard or weeps under pressure is due for replacement.
- Tighten the hose clamps.
- Pressure-test the system to the cap's rated 1 bar15 psi and watch that it holds; a steady drop with no visible leak points to the head gasket or an internal path.