VW Fox Cooling System Shows Conflicting Issues

I experienced nearly identical cooling system issues with my 2006 VW Polo diesel last year. I have moderate experience working on VAG diesel engines, though I leave complex repairs to professionals. The symptoms you describe match exactly what happened with mine, slow warm-up combined with occasional overheating. After monitoring the coolant system behavior for a few weeks, I took it to a workshop. They diagnosed a faulty map thermostat in the thermostat housing, which was causing erratic temperature regulation. The repair involved: Replacing the map thermostat, Flushing the cooling system, Installing fresh coolant, Testing the water pump operation, Verifying the cooling fan functioned properly Total cost was 350€ including parts and labor. Since the repair, the engine temperature has remained perfectly stable. To provide more specific guidance: What cooling system maintenance has been done previously? Are you noticing any coolant loss? Does the cooling fan activate normally? This information would help determine if your Fox has the same underlying issue mine had. Would strongly recommend having this checked soon, as irregular temperature control can lead to more severe engine problems if left unaddressed.

Last service was at 125000km and no cooling system issues were found back then. Since your message, I have carefully monitored the temperature sensor readings and discovered a small coolant leak near the thermostat housing. The cooling fan seems to activate normally though. I appreciate your detailed feedback on the thermostat replacement. Good to know the repair fixed similar temperature control problems in your case. Will schedule a workshop appointment to have the thermostat housing checked and the cooling system properly inspected before any major damage occurs.

Thanks for the update about the coolant leak near the thermostat housing. This actually validates my initial suspicion, as these housings are known weak points in our VAG engines. The leak you discovered is likely contributing to the temperature regulation issues. In my case, the workshop found the thermostat housing had developed hairline cracks, causing similar seepage. The temperature sensor was also showing inconsistent readings due to the compromised housing assembly. This explained both the delayed warm-up and overheating symptoms. Since having the complete thermostat housing unit replaced along with the cooling system flush, my engine has maintained consistent operating temperatures. Getting this fixed prevented potential engine damage from chronic overheating. Smart move scheduling a workshop appointment. Make sure they pressure test the entire coolant system while they have it open. In my experience, these leaks rarely come alone, and its worth checking all cooling system components while accessing the thermostat housing. Curious to hear what they find during the inspection. Keep monitoring those coolant levels until the repair.

A quick update, just had the workshop inspect the car. You were absolutely right about the thermostat housing being the main issue. They found multiple hairline cracks causing the coolant leak. The diagnostic also revealed that the temperature sensor was giving incorrect readings due to the damaged housing. They completed the full repair package you mentioned, new thermostat housing, cooling system flush, fresh coolant and a thorough pressure test of all components. Total came to 380€, slightly more than your repair but included some additional hose replacements they recommended while the system was open. The engine temperature now behaves exactly as it should, quick warm-up to operating temperature and stays perfectly stable during driving. No more overheating issues. Really glad I addressed this before any serious engine damage occurred. Thanks again for sharing your experience. The similarities between our cases helped me understand the problem and get the right fix done promptly.