One of our loyal customers—and fellow Fanatics Forum member—brought in his G20 330d, which had recently come off motorplan.
The main concern: an “Engine Temperature Too Hot” warning appearing on the iDrive, but only after highway pulls in higher gears. The strange part? Absolutely no coolant loss.
Once the vehicle was dropped off, we ran a full diagnostic to check for any DTCs (Diagnostic Trouble Codes) stored on the ECU (Engine Control Unit).
For all BMWs, especially G-series models, we rely on ISTA—the official BMW diagnostic software. Keeping our ISTA licenses up to date ensures precise and efficient diagnosis for G Series cars.
First Surprise: The Tune
First up, was the motor-plan killer code S 0777 - Engine Tuning Detected. The owner had no idea that he purchased a tuned car! Knowing full well that this code can sometimes pop up for several other reasons we proceeded to check the Sport Displays on the car to check for calibration changes, no surprise it was not factory stock either. The owner granted us permission to dig deeper since he did not want an unknown tune on the car and mentioned he was not entirely happy with the power delivery on the road.
Cooling System Faults
Without detracting from the main issue at hand we analysed the remaining DTC's which included:
1. Engine too hot! Drive with care
2. Engine overheated! Stop carefully
3. Bottom Radiator Blind – plausibility: Blocking
4. Bottom Radiator Blind – position control: Control Deviation
5. Top Radiator Blind – position control: Control Deviation
Next point of order was to clear all the DTC's and road test the vehicle to determine under what conditions the issue would present itself and also to see which DTC's would re-appear.
Driving around on the smaller roads in lower gears we noticed the Radiator Fan would kick in which was certainly not normal. A quick sprint in 4th and 5th gear and we noticed the coolant temperature gauge climb a little above the half way mark followed by the "Engine Temperature Too Hot" message on the I-Drive.
Running ISTA again revealed:
1. Engine too hot! Drive with care
2. Engine overheated! Stop carefully
3. Bottom Radiator Blind – plausibility: Blocking
The Bottom Radiator Blind fault was investigated where we ran a few test plans on ISTA, activating both the Top and Bottom Radiator Blinds both of which were found to be operating manually. The Bottom Blind was opening a few milliseconds slower when locking and unlocking the vehicle most like due to the Power Management DTC on the car (Old and Worn Battery).
Digging Deeper: Coolant Pump Suspicion
We then followed ISTA’s test plan for the overheating DTCs. With no coolant loss, and understanding how the mechanical coolant pump works in these B57 engines, we suspected the coolant circulation valve inside the pump might be the culprit—especially since overheating occurred only under high engine load.
We shared our diagnosis with the owner and was granted permission to remove the coolant pump for inspection. Upon removal and inspected our suspicion was correct with the faulty valve being visible and OEM replacement was ordered.
Replacement Pump, Cooling System re-fill and bleeding procedure along with a V-belt inspection carried out. It was time to test the car again.
Immediately we noticed the Radiator Fan was no longer kicking in on the short sprints. Onto the highway we proceeded and decided to Data Log the car to monitor all the parameters. Everything was back to normal with No Engine Temperature Messages. Findings were shared with the owner who sighed with relief.
ECU Tune Analysis & Re-Tune
Having collected data from the road data logs we shared our finding on the current unknown ECU Tune which had an odd boost pattern under light load and raised fuel rail pressure which is not required on the B57 since these already 2500 bar pressure on the factory tune.
After getting the car on the dyno the numbers were fairly good not weak at all. Power was not the goal with this car.
The goal was re-tune the car with the following in mind:
1. Minimal smoke
2. Factory fuel rail pressure
3. Consistent, linear boost across all load cells
After two revisions on the dyno of our Custom ECU tune we were happy with the data logs and numbers on the dyno.
Permission granted from the owner for us to road test the vehicle, data log & adjust the tune, as the real-life power delivery experience on the road was of utmost importance to him.
⸻
The result?
This 330d now runs smoother and cooler than ever, with torque on tap throughout the rev range—and as an added bonus, improved fuel economy.
Previous tune on the right vs our Custom tune on the left. 243kw & 792nm on the wheels at altitude makes this one of the strongest stock turbo 330d's around!
This is now one super strong 330d running hassle free.
Sent from my iPhone using Tapatalk
The main concern: an “Engine Temperature Too Hot” warning appearing on the iDrive, but only after highway pulls in higher gears. The strange part? Absolutely no coolant loss.
Once the vehicle was dropped off, we ran a full diagnostic to check for any DTCs (Diagnostic Trouble Codes) stored on the ECU (Engine Control Unit).
For all BMWs, especially G-series models, we rely on ISTA—the official BMW diagnostic software. Keeping our ISTA licenses up to date ensures precise and efficient diagnosis for G Series cars.
First Surprise: The Tune
First up, was the motor-plan killer code S 0777 - Engine Tuning Detected. The owner had no idea that he purchased a tuned car! Knowing full well that this code can sometimes pop up for several other reasons we proceeded to check the Sport Displays on the car to check for calibration changes, no surprise it was not factory stock either. The owner granted us permission to dig deeper since he did not want an unknown tune on the car and mentioned he was not entirely happy with the power delivery on the road.
Cooling System Faults
Without detracting from the main issue at hand we analysed the remaining DTC's which included:
1. Engine too hot! Drive with care
2. Engine overheated! Stop carefully
3. Bottom Radiator Blind – plausibility: Blocking
4. Bottom Radiator Blind – position control: Control Deviation
5. Top Radiator Blind – position control: Control Deviation
Next point of order was to clear all the DTC's and road test the vehicle to determine under what conditions the issue would present itself and also to see which DTC's would re-appear.
Driving around on the smaller roads in lower gears we noticed the Radiator Fan would kick in which was certainly not normal. A quick sprint in 4th and 5th gear and we noticed the coolant temperature gauge climb a little above the half way mark followed by the "Engine Temperature Too Hot" message on the I-Drive.
Running ISTA again revealed:
1. Engine too hot! Drive with care
2. Engine overheated! Stop carefully
3. Bottom Radiator Blind – plausibility: Blocking
The Bottom Radiator Blind fault was investigated where we ran a few test plans on ISTA, activating both the Top and Bottom Radiator Blinds both of which were found to be operating manually. The Bottom Blind was opening a few milliseconds slower when locking and unlocking the vehicle most like due to the Power Management DTC on the car (Old and Worn Battery).
Digging Deeper: Coolant Pump Suspicion
We then followed ISTA’s test plan for the overheating DTCs. With no coolant loss, and understanding how the mechanical coolant pump works in these B57 engines, we suspected the coolant circulation valve inside the pump might be the culprit—especially since overheating occurred only under high engine load.
We shared our diagnosis with the owner and was granted permission to remove the coolant pump for inspection. Upon removal and inspected our suspicion was correct with the faulty valve being visible and OEM replacement was ordered.
Replacement Pump, Cooling System re-fill and bleeding procedure along with a V-belt inspection carried out. It was time to test the car again.
Immediately we noticed the Radiator Fan was no longer kicking in on the short sprints. Onto the highway we proceeded and decided to Data Log the car to monitor all the parameters. Everything was back to normal with No Engine Temperature Messages. Findings were shared with the owner who sighed with relief.
ECU Tune Analysis & Re-Tune
Having collected data from the road data logs we shared our finding on the current unknown ECU Tune which had an odd boost pattern under light load and raised fuel rail pressure which is not required on the B57 since these already 2500 bar pressure on the factory tune.
After getting the car on the dyno the numbers were fairly good not weak at all. Power was not the goal with this car.
The goal was re-tune the car with the following in mind:
1. Minimal smoke
2. Factory fuel rail pressure
3. Consistent, linear boost across all load cells
After two revisions on the dyno of our Custom ECU tune we were happy with the data logs and numbers on the dyno.
Permission granted from the owner for us to road test the vehicle, data log & adjust the tune, as the real-life power delivery experience on the road was of utmost importance to him.
⸻
The result?
This 330d now runs smoother and cooler than ever, with torque on tap throughout the rev range—and as an added bonus, improved fuel economy.
Previous tune on the right vs our Custom tune on the left. 243kw & 792nm on the wheels at altitude makes this one of the strongest stock turbo 330d's around!
This is now one super strong 330d running hassle free.
Sent from my iPhone using Tapatalk
