Can't get wiring info to load properly or search at the moment, may be able to have a look tomorrow.

5 minutes ago, Breezy_Pete said:

Can't get wiring info to load properly or search at the moment, may be able to have a look tomorrow.

Thanks for your effort 👍

On 26/08/2025 at 11:59, token_454 said:

Hi, the coolant temperature rises above 110°C, depending on how much I accelerate and press the gas pedal. This mostly happens in summer temperatures, at speeds between 180–200 km/h, or when driving around 150 km/h on a steep highway section. When I reduce the speed to under 130 km/h, the temperature goes back to normal.

I tracked this with VCDS while driving. I also noticed that the cooling fan activates too late. The fan only goes to 100% once the temperature reaches 110°C. Mostly the cooling fan is on 10.2%.

The car doesn’t seem to have the temperature sensor… hmm, that’s a good question. 😅

When the engine is heating up the VCDS (true coolant temp) might look like this, the ECU modifies the temperature Gauge to read exactly exactly 90C until the temperature rises to a (true) ~ 107C, is yours reflecting this, the fan if controlled by a coolant temperature sensor must read the true temperature?.

The basic fan speed control is just a thermoswitch with two sets of contacts and two speeds, (one controlled by a resistor in the fan motor) screwed into the rad header.

VW Polo 02092024

Coolant Temp

VCDS (true temperature)/Car (coolant gauge)

52 /52

53/55

56/58

58/62

60/65

63/69

64/72

66/74

68/78

69/82

71/84

73/86

74/88

75/89

75/89

10 minutes ago, Johngerard said:

When the engine is heating up the VCDS (true coolant temp) might look like this, the ECU modifies the temperature Gauge to read exactly exactly 90C until the temperature rises to a (true) ~ 107C, is yours reflecting this, the fan if controlled by a coolant temperature sensor must read the true temperature?.

The basic fan speed control is just a thermoswitch with two sets of contacts and two speeds, (one controlled by a resistor in the fan motor) screwed into the rad header.

VW Polo 02092024

Coolant Temp

VCDS (true temperature)/Car (coolant gauge)

52 /52

53/55

56/58

58/62

60/65

63/69

64/72

66/74

68/78

69/82

71/84

73/86

74/88

75/89

75/89

But should the ECU use both temperature sensors to control the radiator fan, or only the G62?

In the attachment you’ll find a CSV file with the measurements I took. In the table you can see that when the coolant temperature reaches about 110 °C, the cooling fan only runs at around 10–15%. At 110 °C the coolant gauge on the dashboard already shows a value above 90 °C.

LOG-01-IDE00025_&7.CSV

On 26/08/2025 at 10:56, token_454 said:

I have the 2.0 TDI EA288 engine.

G83 only appears in the 1.4 and 2.0 petrol engine sections of the pdf service manual I've got.

7 minutes ago, D402 said:

G83 only appears in the 1.4 and 2.0 petrol engine sections of the pdf service manual I've got.

Hi, thanks for sharing. Can you share the manual here or in private message maybe?

88 degrees as a choice (by the ecu) sounds off to me because it's not showing any cooling done by the rad. I have logged and graphed the two sensors together on my VW diesel van and as the G62 records the warm up on a drive the G83 stays flat lined until the thermostat opens then it goes up to about 40 degrees and waves around that point according to load on the engine. If I had to chose a fixed value for the G83 it would assume that the radiator is doing some cooling.

This was the log I made with VCDS. The top grey trace is the G62 the lower dark blue trace is the G83. You can see that the G83 line doesn't move until the thermostat opens and normal circulation begins.

Hello everyone, here’s an update on this topic.

I also replaced the thermostat, but that didn’t change the behavior of the problem. I’m starting to think that the issue might be related to the 4x4 (all-wheel drive).Maybe the weight of the car and the 4x4 system could be causing the 150 PS engine to overheat when driving over 200 km/h on warm days. Maybe thats a general problem but most people doesn‘t notice because they not drive so fast.

As the usual modern suspects have been dealt with:-

Back in the day when I tuned engines (Essex V6 etc) radiator contrition was crucial. Just thinking re old fashioned first principals is there a chance the rad is partially blocked - eg has it had the dreaded "Mit Silikat" header tank issue in the past?

How much is a new radiator?

9 hours ago, token_454 said:

Hello everyone, here’s an update on this topic.

I also replaced the thermostat, but that didn’t change the behavior of the problem. I’m starting to think that the issue might be related to the 4x4 (all-wheel drive).Maybe the weight of the car and the 4x4 system could be causing the 150 PS engine to overheat when driving over 200 km/h on warm days. Maybe thats a general problem but most people doesn‘t notice because they not drive so fast.

I doubt the haldex would be engaged at that speed and the weight of the 4x4 system is only similar to an extra passenger so that's not an issue.

At speed drag causes the most load.

Working an engine hard uses fuel. Towing a caravan at 60mph and doing less than 30mpg on the TDi 150 is doing far more work than you are doing and I never had an issue with overheating on any of mine.

On the 1.9 (PD) VW diesels, cylinder head gaskets can leak under load. Sometimes the symptoms are obvious but often more subtle especially in the early stages.

One thing worth checking is to open the coolant cap first thing in the morning before starting the engine. There should be no residual pressure. If you get a definite hiss as you open the cap that means pressure other than the normal pressure caused by heat is still in the system. Any normal pressure should dissipate once the engine is fully cold. The system starts with no pressure and should return to that state if all is normal. So any pressure left in the system must have come from somewhere else.

Edited 26 September, 202526 Sep by Rheumy

12 hours ago, bigjohn said:

radiator contrition was crucial. Just thinking re old fashioned first principals is there a chance the rad is partially blocked

I would 100% think this is the case.

Cools fine under 130....over that the cooling demand is higher, so you see a rise in temp.

Get the radiator refurbished or renewed.

I had a car where anything over 120 or uphill would cause the temp to rise.

Got the radiator rodded and it was all good.

Us oldies remember the seventies when radiators where often blocked after say 50,000 miles or less. (Think mini's or Hillman Minx's) When you held the old and new rads in your hands you could easily feel the weight difference between blocked and clear.. But these days materials and rust inhibitors are much better and you rarely see a modern radiator. I'd be surprised if that was it unless the coolant looks brown and sludgy. Worth checking for any restriction in the cooling fins though. If you have an intercooler in front of the coolant radiator they can get stuff caught in between the two. Usually feathers or leaves.

Edited 26 September, 202526 Sep by Rheumy

Not sure if yours is the manual or DSG, but if it's a DSG could be the secondary thermostat as it was in this case here https://www.briskoda.net/forums/topic/445467-dsg-equipped-cars-second-thermostat/

Hi guys,in the meantime I found a similar situation like mine on the german skoda forum. Underneath are the experience from a person that also contacted skoda to this topic. This is his experience:

I have a 2-liter TDI with 150 hp and DSG, and when driving at speeds over 200 km/h, the oil temperature already exceeds 130°C after just 10 minutes. When towing a 1,800 kg caravan in the mountains, the oil temperature often climbs above 135°C. That seemed too high to me. The workshop just shrugs and can’t find any cause. Therefore, I contacted Skoda and received the following reply:

Thank you for your message.

Under normal operating conditions, the oil temperature is usually between 90°C and 110°C; under load, we allow oil temperatures of up to 150°C.

Load means:

• High ambient temperatures (above 30°C)

• Extreme acceleration

• Driving with a trailer

• Driving with a high payload

• Long uphill drives

One or more of these factors can lead to a higher oil temperature.

The TSI and TDI engines from ŠKODA are designed so that a continuous engine oil temperature of 150°C is not exceeded.

However, modern oils also allow short-term peak temperatures of up to 170°C in extreme situations (unlikely in Central Europe).

It is important to always ensure there is enough oil in the engine.

For all questions regarding ŠKODA, we are of course at your disposal in addition to our authorized dealerships.

Kind regards,

Your ŠKODA Customer Service

The link to the topic is here, but everything is in german:

https://www.skodacommunity.de/threads/superb-iii-ahk-nachgeruestet-125-c-oel-oel-temperatur-senken.133719/page-3

From the experience from the tipps i will first try to build in a bigger oil cooler and then also maybe changing a coolant radiator as you guys write above.

I have a manual car and not a DSG.

On 26/09/2025 at 08:43, logiclee said:

I doubt the haldex would be engaged at that speed and the weight of the 4x4 system is only similar to an extra passenger so that's not an issue.

At speed drag causes the most load.

Working an engine hard uses fuel. Towing a caravan at 60mph and doing less than 30mpg on the TDi 150 is doing far more work than you are doing and I never had an issue with overheating on any of mine.

And what was the outside temperature? This problem never occurs in winter days when we have outside temperatures like 10 Celsius and lower. I can drive then 240 km/h and everything is fine. This occurs when we have 30 Celsius on the highway.

2 hours ago, token_454 said:

From the experience from the tipps i will first try to build in a bigger oil cooler and then also maybe changing a coolant radiator as you guys write above.

I don't think you need a bigger oil cooler.

You need to refurbish the radiator.

Then the coolant will be able to cool the oil more readily

8 hours ago, token_454 said:

And what was the outside temperature? This problem never occurs in winter days when we have outside temperatures like 10 Celsius and lower. I can drive then 240 km/h and everything is fine. This occurs when we have 30 Celsius on the highway.

I usually tow through summer and through Europe so well over 30 degrees at times.

Don't most VAG engines now have two stats?, mine (a 2019 petrol Polo) has, with opening temperatures something like in the attached, if so, should both be tested in the event of a overheating problem?. See (VW SSP 820333 pdf)

Two Stat Photos.docx

Edited 2 October, 20252 Oct by Johngerard

Interesting