Yet ANOTHER thermostat thread

Joester

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So there was like 2 other threads about thermostats but I thought I would start my own to document my problem and the results.

Here is my 22 minute drive to work this morning. it was about 45 degrees F out this morning. My commute is mostly highway (with stoplights as you can see by the vehicle speed)






As you can see, my coolant temp never went over 75 degrees Celcius, but of course the idiot dash gauge displays 190F (which is 88C).

Is this normal? I've been fighting bad gas mileage for the past year or so. I already have a new thermostat on the way from the IDparts, so we will see if that fixes it and I will be reporting back to this thread. I've never replaced it, and I've owned the car for 55k miles since 2009.

The coolant temp sensor was new 25k miles ago, so I'm pretty sure its not that.


It was about 70 degrees F when I got out of work, and I didn't log it, but I went on a very spirited 35+ minute backroad run and when I got home, my coolant temp was at 77 degrees Celcius.
 
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Joester

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I just looked at logs from 5 months ago and none of them have any coolant temp value over 75. This means that when I set my IQ and my injection timing, it was all probably done at 75C. All of those things contribute to gas mileage. I don't know how I didn't notice this. This could explain everything.
 

FUCHT

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That's why its good to replace the tstat with every timing belt change. I believe "whaler" is the oe tstat for vw. But please correct if im wrong.
 

Joester

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like I said I've already got a new one on the way from IDparts. Its the Wahler one, not the OEM VW one, so I hope that works. I've seen different opinions on them.
 

RacerTodd

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I replaced my thermostat on my last timing belt change, about 10K ago. Original thermostat had 360K on it, I replaced it with an OEM VW item.

After completing the timing belt, I did a quick test drive. Once back home, I hooked up VCDS to check timing. I noticed that the coolant temp in VCDS was reading 90C. In the past a similar test drive would only produce around 80C temp. The thermostat is supposed to be fully open at 87C, so the old one was clearly opening too early and keeping the engine colder than normal.

On cool mornings (40-50F) I've noticed that when I leave for work I get usable heat much quicker than before the change.

And, I've picked up 1-1.5MPG so far. The thermostat most definitely can impact MPG.
 

BleachedBora

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That's why its good to replace the tstat with every timing belt change. I believe "whaler" is the oe tstat for vw. But please correct if im wrong.
Nope. Made in Germany and a great thermostat though. Some gurus refuse to install them because they don't have the locking tabs for the thermostat housing. I've heard of horror stories of 30-60 minutes to install from more than one person. Oldpoopie for example will only install OEM thermostats...
 

FUCHT

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Nope. Made in Germany and a great thermostat though. Some gurus refuse to install them because they don't have the locking tabs for the thermostat housing. I've heard of horror stories of 30-60 minutes to install from more than one person. Oldpoopie for example will only install OEM thermostats...
what's the name of the one VW sells? I can't remember the manufacturer name, just for reference:D and also when people are buying them.
 
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oldpoopie

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Nope. Made in Germany and a great thermostat though. Some gurus refuse to install them because they don't have the locking tabs for the thermostat housing. I've heard of horror stories of 30-60 minutes to install from more than one person. Oldpoopie for example will only install OEM thermostats...
Yep.... Oem with tabs and a new neck every time. The instalation hassle of the non OE one is too much to bother with.
 

fruitcakesa

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I replaced my thermostat on my last timing belt change, about 10K ago. Original thermostat had 360K on it, I replaced it with an OEM VW item.

After completing the timing belt, I did a quick test drive. Once back home, I hooked up VCDS to check timing. I noticed that the coolant temp in VCDS was reading 90C. In the past a similar test drive would only produce around 80C temp. The thermostat is supposed to be fully open at 87C, so the old one was clearly opening too early and keeping the engine colder than normal.

On cool mornings (40-50F) I've noticed that when I leave for work I get usable heat much quicker than before the change.

And, I've picked up 1-1.5MPG so far. The thermostat most definitely can impact MPG.
I picked up 4 mpg when I finally replaced mine with oem
 

Powder Hound

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You should be able to use the string trick. Just insert a piece of string under the hoop at the top, run the threads out the thermostat pipe, and use tension on the string to keep the thermostat and o-ring in place while you position it. I'll bet even I could do it.
 

oilhammer

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There are just too many to list....
I will only install OEM ones, too. Not only do they fit properly, they seem to do a better job holding temps. Behr is who makes them, not Whaler. They say "BTU" on them. You can sometimes find Behr boxed ones a little cheaper than VW ones. And I also always use a new OEM water neck and o-ring.

We are doing lots of these this time of year.
 

FUCHT

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I will only install OEM ones, too. Not only do they fit properly, they seem to do a better job holding temps. Behr is who makes them, not Whaler. They say "BTU" on them. You can sometimes find Behr boxed ones a little cheaper than VW ones. And I also always use a new OEM water neck and o-ring.

We are doing lots of these this time of year.
Thanks for the info.
 

Joester

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I guess I should've bought OEM but oh well. I guess I'll just install the Wahler I have on the way and then do OEM next time.
 

kiva822

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the non OEM install is pretty easy, but does double the install time, at least...but that's only up to about 30min or so.

I would have just got an OE one from Aaron and did it that way, but I had it all apart and bought one locally...we'll see if it lasts.
 

Joester

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I've never done a thermostat before so I don't understand what the difference is between the 2, but I'm assuming it will be pretty self explanatory once I get in there.
 

oilhammer

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There are just too many to list....
The OEM/Behr ones twist-lock on to the new neck, with the o-ring inbetween, so you just stick it against the block and put the 2 bolts in place. Makes it really, really easy.

Some of the others require you to break the tabs off the neck, then try and position the 'stat and o-ring in the block while you put the neck on. Which is not a huge deal, VAG gas engines (which use a different 'stat on EA113 engines) are like that. But trust me, every time I do one of those I tend to curse under my breath and think "why can't these just be like the diesels? SO much easier!" Especially on some of the 1.8t engines stuffed in cars like the TT and NB.
 

RacerTodd

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I've never done a thermostat before so I don't understand what the difference is between the 2, but I'm assuming it will be pretty self explanatory once I get in there.

This thread: forums.tdiclub.com/showthread.php?t=148452 , shows how to install a non-OEM thermostat. You can see the two tabs that are made to hold the OEM thermostat into the housing. The thermostat gets really stuck in the block and when you pull on the housing, those tabs break off.

Another thing I noticed when doing mine is that the two bolts on the housing are down in kinda of well and it's real easy to have them drop down behind the accessory bracket when you loosen them. Yes, one of my bolts is patiently waiting behind the bracket. I'm sure it'll be waiting for me when I rebuild the motor 5 or 10 years down the road.

Here's an old mechanics trick to deal with this situation. Tear off a piece of paper towel about 1" square. Before you put your socket on the bolt, take the square of paper towel and hold it over end of your socket. Place the socket over the bolt, with the piece of paper towel jammed in between the socket and bolt. The paper towel fills up the space between the socket and bolt. Loosen the bolt. When you pull the socket back, the bolt will come with it.

The same technique can be used to install the bolt. Place a small piece of paper towel over the socket end then insert the bolt into the socket and it will stay there while you guide the bolt into the hole.
 

Jettadoor

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This thread: forums.tdiclub.com/showthread.php?t=148452 , shows how to install a non-OEM thermostat. You can see the two tabs that are made to hold the OEM thermostat into the housing. The thermostat gets really stuck in the block and when you pull on the housing, those tabs break off.
I have a new housing on the way too, but i guess that doesnt matter cause the thermostat i ordered doesnt have the clips.. D'OH!

Thanks for that link. It is very helpful.
 

Joester

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I've replaced my thermostat and it seems to come up to temperature much quicker. Friday should be about 45F in the morning so I am going to do another log on the way to work and compare it to the log i took in post #1 and see how it compares. I want to wait until then to try to duplicate the outside temperature as closely as i can to my original pre-thermostat-replacement log in order to get comparable results.

More to come on Friday.
 
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nicklockard

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I'm surprised more threads and "is my T-stat bad" posts aren't popping up. It is that time of year.

My t-stat is in that marginal period of its performance lifetime envelope: it regulates well once up to temp, but leaks and flows too much as it warms. I'm too lazy to change it, so I put a radiator grill block on. With the cold rainy days we get here, engines need all the help they can get warming up.
 

VeeDubTDI

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Hopefully more people are searching and not starting duplicate threads.
 

Joester

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When I started this thread there were at least 2 other active thermostat threads. I started another one to post graphs, fuel mileage, and other information before and after thermostat replacement. Hopefully people with similar symptoms will be able to find this thread later and benefit from the info contained within.
 

JB05

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Now I'm confused. I replaced my t-stat last year that I bought from idparts and could have sworn it is a wahler. It did have the locking tabs IIRC, because I did not have to use any special trick to line it up. I thing I don't like about this replacement is that it never seems to open according to my SG. Temperatures average 197 while driving, and when I stop and open the hood, the lower radiator hose is stone cold; but after sitting for 5 or 10 minutes the upper part of the hose will get warm, but not hot.
 

Joester

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my Wahler did not have the locking tabs and i used the string trick and it was easy as pie. Mine seems to be functioning normally. I am going to check coolant temp when i get home tonight but its a really warm day today so that wont really prove anything.
 

xreyuk

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Just a quick question from me..

If the coolant was only actually reaching 75c due to a failling thermostat, why would the dash still display 90c? Is that possibly a broken coolant sensor too?
 

Joester

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Just a quick question from me..

If the coolant was only actually reaching 75c due to a failling thermostat, why would the dash still display 90c? Is that possibly a broken coolant sensor too?


Probably not. The dash gauge is just a dummy gauge.

The only thing that you should infer from it is if you car is completely cold, operating at reasonable temperature, or way too hot.

It should NOT be used to infer exact temperatures.

Just like you said, In my original graph in post #1 of this thread VCDS tells me that my coolant temp never got higher than 75C while my dash gauge read 90C almost the whole trip. This is normal coolant temp sensor operation and dash gauge operation, but it is NOT normal thermostat operation as far as I understand.
 

VeeDubTDI

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Just a quick question from me..

If the coolant was only actually reaching 75c due to a failling thermostat, why would the dash still display 90c? Is that possibly a broken coolant sensor too?
Because the dash display is buffered to display "190" any time the temp is between 165 and 225. It prevents stupid people from going to the dealer about nonexistent problems that they don't understand. It also prevents smart people from realizing that there may actually be a problem with their cars. *shrug*
 
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