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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old April 27th, 2011, 14:57   #1
jjcsnlynn
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Default New Thermostat running a lot hotter

I've had this car for 4 years now and the temp gauge always ran about 180 ish. When I had the new exhaust put on last year it seemed to cool down to just under 180. Lately it started fluctuating more between 160 going down hills to 200 when in light traffic.

I had my son replace the thermostat yesterday and now its at about 195 and seems to be holding steady. The thermostat that was installed was a Stant 13378 which is a 180 degree temp rated thermostate. The one that came out was a 87 degree Celcius rated (184 degree) thermostat.

Is this normal that a 180 t-stat will run the enging at 195?
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Old April 27th, 2011, 16:12   #2
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It's widely been reported that the cluster coolant temp gauge is not to be trusted. It is filtered by software and likes to park itself at 195F, even if the actual coolant temp is different. What does VCDS say the coolant temp is? I'd trust that reading more.
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Old April 27th, 2011, 17:51   #3
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It's widely been reported that the cluster coolant temp gauge is not to be trusted. It is filtered by software and likes to park itself at 195F, even if the actual coolant temp is different. What does VCDS say the coolant temp is? I'd trust that reading more.
I've heard that on the A4's, but not the prior ones. It might be worth seeing VCDS info, but I suspect the t-stat is opening hotter than it should.
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Old April 27th, 2011, 18:45   #4
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I've been seeing more and more thermostat issues. I think I had an issue with one and mine was less than 1 year old and was purchased new from VW. I've opted for the 92*C thermostat and fan switch from www.germanautoparts.com to help out with the mpg.
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Old April 27th, 2011, 19:31   #5
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It's widely been reported that the cluster coolant temp gauge is not to be trusted. It is filtered by software and likes to park itself at 195F, even if the actual coolant temp is different. What does VCDS say the coolant temp is? I'd trust that reading more.
I'll check with the VCDS tomorrow and let you know.
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Old April 28th, 2011, 14:16   #6
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I put the VCDS on and in Group 1 my coolant temp is about 82 (around 180). That's good, but why all of a sudden does my gauge read 195? where does VCDS take the reading from?

Also, I found out injector #4 does not read in Group 13, idle speed . Is this a problem? It seams to be running OK.

Lastly, I have a code 00575 for intermitant MAP. What's the cause of this? Should I clean my MAF?
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Old April 28th, 2011, 14:30   #7
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Quote:
Originally Posted by jjcsnlynn View Post
I put the VCDS on and in Group 1 my coolant temp is about 82 (around 180). That's good, but why all of a sudden does my gauge read 195? where does VCDS take the reading from?

Also, I found out injector #4 does not read in Group 13, idle speed . Is this a problem? It seams to be running OK.

Lastly, I have a code 00575 for intermitant MAP. What's the cause of this? Should I clean my MAF?
I thought the gauge got the data from the same place as the ecu gets it. But don't take that as a real knowledge, just a belief currently that will change as others with real knowledge chime in.

MAP is not MAF. Map is the sensor inside of the ecu - you know the spot that the "little hose" goes to? Might swap out that hose, or look at the longer one that goes from the pressure tubing to the ecu.

Three injectors is all you'll read in group 13. I've been told it's actually 1,2 and 4 being compared with 3 - can't confirm that. However, readings for only 3 is normal.
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Old April 28th, 2011, 16:42   #8
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Quote:
Originally Posted by jjcsnlynn View Post
I put the VCDS on and in Group 1 my coolant temp is about 82 (around 180). That's good, but why all of a sudden does my gauge read 195? where does VCDS take the reading from?

Also, I found out injector #4 does not read in Group 13, idle speed . Is this a problem? It seams to be running OK.

Lastly, I have a code 00575 for intermitant MAP. What's the cause of this? Should I clean my MAF?
The ECU gets the signal from the same sensor as VCDS but the ECU applies a smoothing algorithm before display it on the gauge to make it "rock steady" in order to calm those who are bothered by fluctuating coolant temps.

Go here and search for 00575 to trouble shoot MAP issues.

http://forums.tdiclub.com/showthread...ighlight=00575
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Old April 30th, 2011, 08:27   #9
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I just boiled my old thermostat and used my trusty Harbour Freight infrared thermometer. I don't know the error using this method, but the old t-stat started to open about 155 and was fully open at 168. I shut off the heat and it was still open when I got tired of watching at 147.

This tells me I have error in the dash gauge and the new T-stat is working fine. Agree?

Two questions: How does VCDS read 180 and the gauge read 195? ( I know some have already answered).

And is this better for my fuel mileage or worse (the higher temp)?
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Old May 1st, 2011, 07:52   #10
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Quote:
Originally Posted by jjcsnlynn View Post
I just boiled my old thermostat and used my trusty Harbour Freight infrared thermometer. I don't know the error using this method, but the old t-stat started to open about 155 and was fully open at 168. I shut off the heat and it was still open when I got tired of watching at 147.
Sounds like your old thermostat was BAD. I would expect the t-stat to start opening about 170 and be fully open by 190.

Infrared temp sensors won't be too accurate on shiny parts like a pan of boiling water, but the error would be closer to ~5f

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Originally Posted by jjcsnlynn View Post
This tells me I have error in the dash gauge and the new T-stat is working fine. Agree?
Yup!

Quote:
Originally Posted by jjcsnlynn View Post
Two questions: How does VCDS read 180 and the gauge read 195? ( I know some have already answered).
1) There are 2 independent temp sensors in the temp sensor assembly, hence the 4 wires. One sensor could be starting to fail, which is why you see the 180 Vs. 195 temps.
2) One sensor is for the dash gauge and the other sensor is for the ECM.

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And is this better for my fuel mileage or worse (the higher temp)?
I don't think you will see too much difference in fuel economy. If it was 100F vs. 190F operating temp, you might see an improvement when returning to the normal operating temp.

Tony
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Old May 1st, 2011, 16:44   #11
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Great. Thanks Tony. Always a pleasure to get help on this forum.
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Old May 2nd, 2011, 05:45   #12
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Before condeming and replacing the sensor, I'd suggest testing it with an ohmmeter first. On mine, they were very close to each other at a given temp. Mine was 29k and 29.1K ohms at around 50F as I recall.
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Old May 2nd, 2011, 06:04   #13
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Great. Thanks Tony. Always a pleasure to get help on this forum.
Glad to help!

Tony
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Old May 3rd, 2011, 14:37   #14
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Before condeming and replacing the sensor, I'd suggest testing it with an ohmmeter first. On mine, they were very close to each other at a given temp. Mine was 29k and 29.1K ohms at around 50F as I recall.
I measured mine today after work. The gauge read 160 degrees and the sensors read 529 ohms and 260 ohms. I'll try to read them when it's cold, but I may have a bad sensor.

Is it worth changing the sensor or just let her ride?
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Old May 3rd, 2011, 18:26   #15
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Is it worth changing the sensor or just let her ride?
If you can afford the $15 and ~1qt of coolant, replace the sensor.

Tony
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