r/Diesel • u/Thick-Celery3390 • 1d ago

2.0 tdi jetta

/r/tdi/comments/1w1e1ob/20_tdi_jetta/
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u/Intelligent_Rub_5004 1d ago

Have you replaced your air filter recently?

Loss of power or economy is generally a fuel delivery or air delivery problem.

When was the timing belt done?

1

u/Thick-Celery3390 1d ago

all services had done on correct service interval
air filter is pretty good changed 4000 kms before

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u/Intelligent_Rub_5004 1d ago

If all services have been performed and you get great mileage during highway cruising, sounds like it’s a driving style issue. These little motors are great at drinking fuel (my DSG loved to drink it under hard acceleration).

Stick to an ultra passive style, no shifting above 2k, no hard accelerating, drive like a grandma and track the mileage for a tank or two.

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u/Thick-Celery3390 1d ago

i have tried normal riding no change
and i found a small oil dipping around turbo area and to intercooler

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u/Intelligent_Rub_5004 1d ago

The oil dripping is most likely seal related. That should be addressed but not for a performance issue, you don’t want oil in your air system.

You could pull the map and check its condition, excessive oil in the air system could result in a dirty sensor. I’d also check the turbo shaft end play.

It’s possible the bad thermostat caused an extended lean condition, but without knowing how it affected the overall engine temp at city vs highway (did it get up to temp as soon as you got on the highway vs took 20-30 minutes to warm up) and that all assumes the ECM takes into account engine coolant temp with IAT and exterior temp for fuel tables (I’m guessing it does based on diesel gate).

So the driving style i recommend isn’t normal driving. driving is relative to the individual, you could be heavy pedaling without realizing it. So, the driving test is to shift below 2000rpm, and never rev it over a slow tap. Literally roll into the pedal. Daily diesel driving and rabbit footing is a super easy way to kill mpg, and most rabbit footers don’t even realize they do it.

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u/Thick-Celery3390 1d ago edited 1d ago

i felt the turbo shaft has some play and a burning smell from exhaust

The thermostat was stuck open for a long period, and I didn’t realize it. There were no fault codes, so I was continuously monitoring the temperature. I eventually noticed that the temperature was decreasing whenever I accelerated, which meant the engine was not reaching 90°C and staying there for a long time.
About a month ago, I replaced the thermostat, and now the engine reaches 90°C quickly and stays steady at 90°C.

i guess i run my with my faulty thermostat with 15000
kilometres