VW Jetta TDI coolant temp

[Audiman]

What’s your radiator outlet temp? With the thermostat closed the outlet temp sensor reading should stay at what it started at (matching outside temp) a small increase over a period of time may be acceptable if stationary with revs on but if driving I wouldn’t expect it to increase until the thermostat starts to open.

Your use of both degrees c and fahrenheit make it difficult to follow the readings you have taken.

 

[Marcozi]

OEM thermostat is 190°F right? Wouldn't 212°F be pretty warm while driving?

Great question. Modern cars are designed to run at hotel temps. Why? Fuel efficiency.

 

[wheelman]

What’s your radiator outlet temp? With the thermostat closed the outlet temp sensor reading should stay at what it started at (matching outside temp) a small increase over a period of time may be acceptable if stationary with revs on but if driving I wouldn’t expect it to increase until the thermostat starts to open.

Your use of both degrees c and fahrenheit make it difficult to follow the readings you have taken.

I don't have a pid for that however I can tell you with an infrared thermometer my upper and lower radiator hose around around 45-48°c and and the coolant temp is 73.8°c

 

[wheelman]

Great question. Modern cars are designed to run at hotel temps. Why? Fuel efficiency.

They don't normally run consistently above their thermostat rating though.

 

[Audiman]

I don't have a pid for that however I can tell you with an infrared thermometer my upper and lower radiator hose around around 45-48°c and and the coolant temp is 73.8°c

What is your ambient temp when taking these readings?

 

[wheelman]

What is your ambient temp when taking these readings?

It was about 1 degree Celsius

 

[Audiman]

I would say you have a thermostat that is passing coolant before it should then.

 

[Thermo1223]

Replace the thermostat, it shouldn't even be opening till 87C. Consequently our Tiguan's temp never budges from 194F, the oil temp can fluctuate a bit but coolant never changes.

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[wheelman]

I would say you have a thermostat that is passing coolant before it should then.

What leads you to believe that?

 

[Trav]

Those numbers are fine for that car, leave it in peace. It is not a sketchy thermostat, it is probably beginning to open at the correct temp then gets cooled down quickly when cooled coolant from the radiator filters into the block, it will take a longer time to heat the whole system to operating temp. Your 150+ temp at the vent is plenty hot, it shows a correct functioning cooling system, in mid summer you will see higher numbers.

 

[Audiman]

What leads you to believe that?

Why would your rad pipes be at 45 degrees c if your thermostat was closed? Your not in Dubai! It should not be allowing coolant to pass before 87 degrees c.

 

[wheelman]

Those numbers are fine for that car, leave it in peace. It is not a sketchy thermostat, it is probably beginning to open at the correct temp then gets cooled down quickly when cooled coolant from the radiator filters into the block, it will take a longer time to heat the whole system to operating temp. Your 150+ temp at the vent is plenty hot, it shows a correct functioning cooling system, in mid summer you will see higher numbers.

So I know the factory thermostats are 87°c does that mean thats when it cracks open or when it's fully Opened?

 

[Thermo1223]

So I know the factory thermostats are 87°c does that mean thats when it cracks open or when it's fully Opened?

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[Trav]

Why would your rad pipes be at 45 degrees c if your thermostat was closed? Your not in Dubai! It should not be allowing coolant to pass before 87 degrees c.

It can still has some circulation albeit much less even with a closed thermostat. These engine use a bag of snakes for hoses inc a bypass hose so as the engine warms slowly it is providing heat to the heater core. Note the position if the temp sensor #7.

 

[Audiman]

It can still has some circulation albeit much less even with a closed thermostat. These engine use a bag of snakes for hoses inc a bypass hose so as the engine warms slowly it is providing heat to the heater core. Note the position if the temp sensor #7.

View attachment 142849

I know, I work on these daily.

 

[dumkid]

if it never gets below 170 its fine. diesels don't make much heat. if it runs below the thermostat temp while cruising on the highway then you have problems.

 

[wheelman]

It can still has some circulation albeit much less even with a closed thermostat. These engine use a bag of snakes for hoses inc a bypass hose so as the engine warms slowly it is providing heat to the heater core. Note the position if the temp sensor #7.

View attachment 142849

Wouldn't the temp sensor in that location mean the sensor would read cooler than if it was installed in the block or thermostat housing?

 

[Trav]

Yes it will until all of the coolant in the system was fully up to temp. Your 153f vent temp shows it is getting up to good temp, in fact it is quite good.
This is a mix metal engine, iron block aluminum head and really benefits from slightly lower temps at the cyl head, withough a coolant flow chart to see exactly how it is flowing through the engine I suspect it is moving quite a bit of coolant through the head early in the warm up.

 

[wheelman]

Yes it will until all of the coolant in the system was fully up to temp. Your 153f vent temp shows it is getting up to good temp, in fact it is quite good.
This is a mix metal engine, iron block aluminum head and really benefits from slightly lower temps at the cyl head, withough a coolant flow chart to see exactly how it is flowing through the engine I suspect it is moving quite a bit of coolant through the head early in the warm up.

Well I guess as long as my fuel mileage is good and I'm not getting any codes and the heat is good I should leave it be. I'm averaging close to 40mpg and that's with idling to watch temps driving it like I stole it etc.

 

[Audiman]

I used to get 70 mpg (UK) out of my Audi A4 2.0 TDI so I don’t think your 40 is good. Even when considering the difference between imperial and metric gallon.