New Thermostat running a lot hotter

jjcsnlynn

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02 & 03 Jetta TDI,99 Beetle TDI, 04 Chevy Duramax 2500HD 4x4
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?
 

dieseljunkie

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96 Passat TDI wagon
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.
 

rdkern

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Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
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.
 

G60ING

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MD
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No TDIs Currently, I have an R36 Corrado. I've had an ALH Corrado swap, AHU Corrado swap and 2003 TDI Jetta
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.
 

jjcsnlynn

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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.
 

jjcsnlynn

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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?
 

rdkern

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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?
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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dieseljunkie

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New England USA
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96 Passat TDI wagon
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.php?t=75959&highlight=00575
 

jjcsnlynn

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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)?
 

TonyJetta

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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.
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

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

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.

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
 

jjcsnlynn

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Great. Thanks Tony. Always a pleasure to get help on this forum.
 

dieseljunkie

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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.
 

jjcsnlynn

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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?:confused:
 

jjcsnlynn

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That's not too bad. I expected it to be at least $40 for the sensor.
 

dieseljunkie

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96 Passat TDI wagon
Out of curioisity, I measured my coolant temp sesor resistances again and I think I measured it wrong the first time (by measuring vertical sets of contacts instead of horizontal). At 90C coolant temp, the top set of contacts (left to right) was 145 ohms. Bottom set was 290 ohms, consistent with yours (one is double of the other). I would clean the ground connection at the sensor (br gr wire pigtail to a lug) and see if that fixes your problem, BEFORE replacing your sensor.
 

jjcsnlynn

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Tony, Thanks for the link. I was In IDParts earlier and could only find the green 4-wire sensor for the A4s. I was going to ask if it would work.

Dieseljunkie, I'll try cleaning the grounds.
 

dieseljunkie

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I measured coolant temps sensors again at around 55 F and also jotted down the wire color codes.Top contacts 1.179 k ohms br/gn yel/red bottom contacts 3.368 k ohms br/bl bl/brDoes anyone have a W/D handy and look up which goes to the cluster and which goes to the ECU?You said you put in a 180F Stant Tstat? That is not an OEM brand I don't think? 180 F sounds too low. What does the shop manual recommend?
 

UFO

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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
I saw a 6mpg improvement changing out my old thermostat that was open at 160F.
 

jjcsnlynn

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I measured coolant temps sensors again at around 55 F and also jotted down the wire color codes.Top contacts 1.179 k ohms br/gn yel/red bottom contacts 3.368 k ohms br/bl bl/brDoes anyone have a W/D handy and look up which goes to the cluster and which goes to the ECU?You said you put in a 180F Stant Tstat? That is not an OEM brand I don't think? 180 F sounds too low. What does the shop manual recommend?
I remeasured mine at 180F. I get 185 across the top two ( Green/Brown and Yellow/Red) and 390 ohms across the bottom contacts (Brown and Blue and Blue/Brown). Why are we so far out on measurements? I"m sure mine is in Ohms not K Ohms.

I looked on the wiring diagram and the color of wires are completely different from our wires. Not sure what's going on. I don't know how to post a picture here, but the wd I have shows them as the G20 and G172 with br/bl and ge/sw (G20) and br/bl and li/br (G172). I'm confused.
 

dieseljunkie

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Yours seem fine and close to mine in resistance. The k ohms was at 55F. See post #19 for my measurements w a hot engine, those numbers are similar to yours. Higher the temp, lower the resistance. Your sensor seems fine and your gauge is fine also. I bet if you put in a a 190 F stat, your gauge will read 195 F because VW applies a smoothing algorithm to it.
I remeasured mine at 180F. I get 185 across the top two ( Green/Brown and Yellow/Red) and 390 ohms across the bottom contacts (Brown and Blue and Blue/Brown). Why are we so far out on measurements? I"m sure mine is in Ohms not K Ohms.

I looked on the wiring diagram and the color of wires are completely different from our wires. Not sure what's going on. I don't know how to post a picture here, but the wd I have shows them as the G20 and G172 with br/bl and ge/sw (G20) and br/bl and li/br (G172). I'm confused.
 

slam

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1996 Passat TDI B4V Wagon
My gauge also started suddenly reading 195 instead of 180 where it used to sit steady for 2 years. My problem seemed to coincide with a coolant loss issue I was having.

In pursuit of that coolant loss I replaced the thermostat and the temp sending sensor. The dash still reads 195.

The coolant loss issue ended up being my coolant cap not holding any pressure at all.
 

jjcsnlynn

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I'll check that out. My son did the work (he's in a technical school for autotech). He might have messed up the cap.

Dieseljunkie, where are the grounds you talked about cleaning? I couldn't find it. I didn't see the pigtail. The wire went straight into a plastic sheath.
 

slam

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In case it wasn't clear, replacing the cap didn't fix my higher reading either. It has, however, stopped me from losing coolant. =)

On the other hand something else blew up within 200 miles of the new cap installation and now the car doesn't start at all. Arg.
 

dieseljunkie

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...

Dieseljunkie, where are the grounds you talked about cleaning? I couldn't find it. I didn't see the pigtail. The wire went straight into a plastic sheath.

In post #18, I wrote: "I would clean the ground connection at the sensor (br gr wire pigtail to a lug)"

On my car, if I follow the brown green wire from the connector for about 6 inches (that's what I call a pigtail, not a real pig's tail:D), it goes to a copper lug ground. Is yours different?:confused:

Actually, I wouldn't bother cleaning it, if your only complaint is the gauge reads 195 when VCDS says it is 180. That is normal from all I've read.
 
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jjcsnlynn

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I'll look further up the harness, but I agree. It seems normal and I may not touch it.
 

slam

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Actually, I wouldn't bother cleaning it, if your only complaint is the gauge reads 195 when VCDS says it is 180. That is normal from all I've read.
Well, it might be normal for some people, but it causes me significant concern when my used to stick firmly at 180 and now sticks at 195. Obviously *something* changed somewhere. And given that this is a VW it usually means something *expensive* is about to rapidly change for the worse.:(
 

jjcsnlynn

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Well, it might be normal for some people, but it causes me significant concern when my used to stick firmly at 180 and now sticks at 195. Obviously *something* changed somewhere. And given that this is a VW it usually means something *expensive* is about to rapidly change for the worse.:(
It sounds like you might have a head gasket going. Extra heat, loosing coolant. Have you tried changing your t-stat? Maybe it's sticking.
 
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