Vehicle: Skoda Octavia 2012

Engine: 1.6 TDI CAYA

I have been experiencing an intermittent engine cooling problem.

I replaced the radiator, water pump, and thermostat housing. I first tried a Mahle thermostat, then installed an OSSCA 87°C thermostat. The coolant was properly bled, the cooling fan works, and there is a steady coolant return flow to the expansion tank. There is no coolant loss.

During normal driving, the engine temperature usually stays at 90°C on the dashboard. However, after longer drives or sometimes even during short trips, the temperature gauge fluctuates slightly above 90°C and then returns to normal.

The radiator fan often runs at high speed and continues for about 30 seconds after the engine is switched off, even after relatively short trips and without using the A/C.

VCDS readings while idling show:

Engine coolant temperature: 98°C

Radiator outlet coolant temperature: 58-67°C

The coolant temperature sometimes fluctuates slowly between 95°C and 98°C.

I also replaced the radiator outlet temperature sensor, but the problem remained unchanged.

At one point, I had fault code P2122, but it appears to have been caused by a loose accelerator pedal connector and is no longer present.

My questions are:

1. Is the thermostat opening correctly?

2. Could the G62 coolant temperature sensor or its wiring be causing this issue?

3. Could there still be air trapped in the cooling system?

4. What is the most likely cause based on these symptoms?

There are no bubbles in the expansion tank, there are no coolant leaks, and the oil and coolant are not mixing. The water pump is working. However, when checking the diagnostics, we found that the coolant temperature at the radiator outlet is 67°C, while the engine coolant temperature is 98°C. As the engine temperature increases, the temperature continues to rise, and the radiator fan starts running at maximum speed.

We purchased a MAHLE thermostat, but it did not work properly, so it was removed and replaced with an OSSCА thermostat. The OSSCA thermostat is currently working.

Welcome to the forum.

Personally, I wouldn't be too concerned with those small increases in coolant temperature - 98deg.C is still a fair way off boiling temperature at pressure and the cooling system appears to be controlling the temperature increases correctly.

Is the engine possibly doing a DPF regen when these temperature rises occur?

No, I don't think so. It is not during a DPF regeneration. The temperature can also rise by another one or two bars and then drop again. This happens even when there is no DPF regeneration.

1 hour ago, Warrior193 said:

Welcome to the forum.

Personally, I wouldn't be too concerned with those small increases in coolant temperature - 98deg.C is still a fair way off boiling temperature at pressure and the cooling system appears to be controlling the temperature increases correctly.

Is the engine possibly doing a DPF regen when these temperature rises occur?

No, I don't think so. It is not during a DPF regeneration. The temperature can also rise by another one or two bars and then drop again. This happens even when there is no DPF regeneration.

What does the temperature gauge indicate on a hard climb uphill?

Not sure on the MK3 but my 2012 mk2 FL CAYC I think has an auxiliary water pump. From memory its electric. If it has failed or blown a fuse it may explain slight temp rise. The rad fan running after stopping car is on mine due to short runs and failed DPF regen. On mine the idle speed is around 950rpm when regen and drops to 750rpm once completed. If I do a short run and notice the increased idle speed I try to keep going for a longer one till revs drop to normal. If I cant the rad fan comes on after car switched off.

Alasdair

Edited 10 hours ago10 hr by Alasdair1

@mdureadi If you check most cars the actual coolant temp will be higher than the cars temp gauge shows. Is it nice new Summer Coolant / Anti Freeze / Rust inhibitor you have filled up the Coolant system, with?