Temperature gauge

Is it normal that my temperature gauge is a bit below the middle when I'm cruising at 2000 RPM and below, or should it always be in the middle regardless of the RPM and load, once the engine is warmed? I think my thermostat might be going bad.

should always be straight up and down at 90 degrees C. Thats what the thermostat and coolant are for.

Mine stays at 175f unless I'm climbing hills.

The instrument cluster computer will display 90 C or 190 degrees over a wide range of temperatures, intended to hide all the small normal variations in temperature that you actually get on any car.
If your A4 is not reading straight up and down, then it is too cool or too hot. I would work on mine to get it fixed, get my mileage right, and ensure my engine was properly protected.

The fans are also run by a dumb temperature switch on the left side of the radiator, through the fan controller module. It has two setpoints.

Bentley fan operating points:
low speed
on - 197-206 F (92-97 C)
off - 183-195 F (84-91 C)

Fast speed
on - 210-221 F (99-105 C)
off - 195 - 208 (91-98 C)

The coolant temperature gauge will indicate 90C (194F), if the actual coolant temperature varies between approx. 75C (167F) and 107C (225F)."

The only way to know for sure what the actual operating temp of the TDI is is with an aftermarket (such as Scan Gauge) installed gauge. The factory cluster gauge reads 190 anywhere from 165 to over 200F. The gurus say it is that way on purpose so as not to confuse the operator. And thats OK, as long as it does go up when it actually does start to overheat-which would be rare and a failure of WP or loss of coolant, etc.
My temp wanders around a lot depending on ambient temp, load, speed, setting of cabin temp, etc. Anything between 173 and 181 is typical after several miles. Once I get over 165 on the SG the cluster shows normal 190. Only once has it ever exceeded 200F ('01 "Silver One") and the cluster gauge did start to move up then.

and I would add to the great info in this thread, you want to rule out wiring or a bad coolant temperature gauge before you attack that thermostat

BobnOH said:

and I would add to the great info in this thread, you want to rule out wiring or a bad coolant temperature gauge before you attack that thermostat

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Yes, if an actual check of the coolant tant temp differs much from the indicated, then a faulty coolant temp sensor (common) or cluster gauge (not common) is possible. If you continue with accurate low temps indicated, then very possible the thermostat is shot. If you end up replacing the stat most reccommend getting the flange with it, as often they break getting changed. Both parts are on my "to do" list for the '01.

Thanks for the replies. I did a test yesterday. After being parked in around 10 degrees celcius for a good 5 hours, I started the car and got to the highway within a minute. On the highway it took the arrow a good 3-4 minutes to move out of the last 3 bars, driving at 2000 rpm in 5th (around 90km/h). Then the arrow reached the line before the middle before it started moving at a snail pace, never reaching vertical completely, in 25 km.

Is it normal for the arrow to stay in the lower 3 bars for that long (3-4 minutes)?

My Jetta does not get out of the first three bars until 3 or 4 miles down the gravel road. In the city, it takes a few blocks in rush hour going home. I would say your temperature guage is normal.

Your car would heat up faster if you travelled at 90 kph in sixth gear. The higher rpm in 5th gear causes the engine to consume more air and that cools it more internally. That is a characteristic of diesels. When it gets colder, I would block the grill as well to have the car warm up.

Jack Frost said:

My Jetta does not get out of the first three bars until 3 or 4 miles down the gravel road. In the city, it takes a few blocks in rush hour going home. I would say your temperature guage is normal.

Your car would heat up faster if you travelled at 90 kph in sixth gear. The higher rpm in 5th gear causes the engine to consume more air and that cools it more internally. That is a characteristic of diesels. When it gets colder, I would block the grill as well to have the car warm up.

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I would question the second part, especially since the OP probably does't have a sixth gear-unless there's been some mods done.

Warm up time is real variable depending on lots of things-ambient temps, cabin heat/fan choice, driving habits, etc.

I discovered (could have found out sooner had I read a little on the subject) that "warming" the car up by starting in the morning and leaving it run for 5 to 10 minutes did virtually nothing to heat up the cabin. Best to just put it down the road. Usually takes a couple of miles, at 55mph, to get it to operating temp (190 on the gauge).

Mark

skidoorider600 said:

I discovered (could have found out sooner had I read a little on the subject) that "warming" the car up by starting in the morning and leaving it run for 5 to 10 minutes did virtually nothing to heat up the cabin. Best to just put it down the road. Usually takes a couple of miles, at 55mph, to get it to operating temp (190 on the gauge).

Mark

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Couple of miles? Mine takes longer than that... a lot longer.

Btw it says in the manual to not idle the car, but to start driving it as soon as you start it.

snakeye said:

Couple of miles? Mine takes longer than that... a lot longer.

Btw it says in the manual to not idle the car, but to start driving it as soon as you start it.

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I think he's using the word "couple" in a loose manor. It's a couple like 5-10 (an orgy of miles)

BobnOH said:

I think he's using the word "couple" in a loose manor. It's a couple like 5-10 (an orgy of miles)

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lol I keep forgetting that a lot of people think couple means a few. I used to think that too until the old angry Greek guy in the fast food restaurant screamed at me for making myself three hot dogs when he clearly told me to make a couple.

I just changed my coolant temperature sensor -- but the car does not seem to get above what I estimate to be ~175 F of the gauge. Is this acceptable or should I consider a thermostat change ?

I ordered a VAG-COM -- will this tell me the actual reading for the sensor ?

sundownz said:

I just changed my coolant temperature sensor -- but the car does not seem to get above what I estimate to be ~175 F of the gauge. Is this acceptable or should I consider a thermostat change ?

I ordered a VAG-COM -- will this tell me the actual reading for the sensor ?

Click to expand...

Yes, the vag-com will be able to reading the coolant sensor and I would consider the thermostat is probably bad. 175 on the gauge is not acceptable unless is is really really cold.

r72gsaol said:

Yes, the vag-com will be able to reading the coolant sensor and I would consider the thermostat is probably bad. 175 on the gauge is not acceptable unless is is really really cold.

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Thanks for the information -- it is a pretty nice day today so if the gauge on my dash is accurate sounds like I will need a thermostat.

My VAG-COM is due on Thursday so I'll report back!

The temperature gauge is not very accurate. My car says it is 90 C when it is actually 75C.

I would take out your old thermostat and put it in a pot of water with a new thermostat. Bring it to a boil slowwwly. The old thermostat will probably open before the new one. If you have a thermometer, great! Put it in there to. You will find out how much cooler the old thermostat opens at. To me, 5 degrees is significantly cooler. It only gets worse with time.

If you can't be bothered with being that scientific about it, just change the thermostat. I always changed mine in my old car every three years whether it needed it or not.

No need for a vag-com.

I changed the thermostat and took it out for a short drive -- first time I've ever seen the temperature get to ~190 on the gauge and stay there. Hoping to see some MPG gain from this