# Engine takes too long to warm up(Not thermostat)



## Andy Macca (May 20, 2015)

Does anyone know where there may be a detailed schematic of the cooling circuit(2006 Passat 2.0t FSI) I have a strange cooling issue that goes beyond thermostat and temp sensors.

Right now its fairly cold here in Ottawa -10C but the engine should still warm up to 90C fairly quickly once running. The last few weeks its been taking double the driving distance to attain operating temp of 90C and same for air coming through the vents(cool for a long time but hot eventually ) Once it reaches operating temp 90C it stays there rock solid. Ive owned the car for 5 years and know when it normally reaches temp, its definitely very slow right now. I also have another Passat that warms up way quicker.

My first suspicion was the thermostat, which I replaced last weekend with OEM part but no improvement.(also tested the one I removed and it closes/opens just fine) I've also verified the temp sensors with my temp gun.

At this point I need to get a full understanding of the whole cooling circuit and a schematic. I know there is a secondary water pump that runs the coolant in reverse once the engine is turned off. I'm wondering if there are any non return valves in that pump that may be jammed open allowing coolant to bypass thermostat when running normally? 

Any other thoughts/ideas would be welcome.

Thanks


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## jetta_2.slow (Feb 18, 2008)

I've been noticing the same thing with my A4, slow to warm up but once it's at full temp it stays there. Also noticed that if I let the car sit and idle before the coolant temp gets up to 200 or so that it will drop back down into the 160 range and stay there. Also have a less than 10k mile old OEM Audi thermostat and have verified coolant temp sensors are working properly. 

Car doesn't take what I would consider an unreasonable amount of time to reach full temp though.


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## rommeldawg (May 25, 2009)

you didnt happen to notice/check the wp impeller when you changed the t-stat, when was it last changed and was it plastic or metal. that and air still being in the system would be things to consider. does the interior heat seem better when the car is under load rather then at idle?


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## jetta_2.slow (Feb 18, 2008)

at least with mine heat is consistent, water pump was replaced at the same time as thermostat along with all of the coolant hoses and new coolant (car has been very well taken care of). 

I know there is thermostat mapping in the software and my car does have an APR flash so I may just for grins try putting it into stock mode and see if the behavior is the same. Again not a real concern for me since my heat still works fine, just thought it was odd behavior. Was -15 F when I started the car this morning and let it idle for 15 minutes (omg no not idling) at which point the coolant temp was around 130, within 10 minutes of driving it had reached 200


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## Andy Macca (May 20, 2015)

To be honest I did not look at the water pump impeller, however it never overheats so suspect the mechanical water pump is alright. It is still the original though and will be changed with the timing belt in the near future.

As for cabin temp, its steady hot when warmed up either idle or driving, does not sound like there is any air in the system.

I'm still curious how the electric water pump influences the cooling circuit when the engine is running. I'm convinced it actually does not work as after a hot run it does not seem to turn on(no noise or vibration) when the engine is turned off, (NO CEL though either) I'm wondering if its defective if its allowing coolant to bypass the thermostat when cold.


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## rommeldawg (May 25, 2009)

http://www.golfmkv.com/forums/golfgoodies/mk5golfengine.pdf

on page 18



> To prevent carbon build-up on the turbine
> shaft in the turbocharger, an auxiliary
> coolant pump provides additional coolant
> circulation for a certain time after the
> ...


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## Andy Macca (May 20, 2015)

rommeldawg said:


> http://www.golfmkv.com/forums/golfgoodies/mk5golfengine.pdf
> 
> Thanks
> sure does look like coolant has to flow through that aux pump even when it's turned off, although that illustration is handy it does not show the thermostat.
> think I'll get my lazer heat gun and try and monitor a few hoses as the engine warms up. perhaps I'll be able to see where the coolant is flowing as it warms up.


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## Andy Macca (May 20, 2015)

jetta_2.slow said:


> at least with mine heat is consistent, water pump was replaced at the same time as thermostat along with all of the coolant hoses and new coolant (car has been very well taken care of).
> 
> I know there is thermostat mapping in the software and my car does have an APR flash so I may just for grins try putting it into stock mode and see if the behavior is the same. Again not a real concern for me since my heat still works fine, just thought it was odd behavior. Was -15 F when I started the car this morning and let it idle for 15 minutes (omg no not idling) at which point the coolant temp was around 130, within 10 minutes of driving it had reached 200


How does this thermostat mapping work exactly. My car has a mechanical thermostat. Do some fsi engines have electrical thermostat?


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## jetta_2.slow (Feb 18, 2008)

Andy Macca said:


> How does this thermostat mapping work exactly. My car has a mechanical thermostat. Do some fsi engines have electrical thermostat?


Sorry it is mechanical, I was thinking of the thermostat in the 1.8t B6 chassis cars.


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## xtravbx (May 21, 2005)

Bleed the air from your coolant system.


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## Andy Macca (May 20, 2015)

So I finally figured out this issue.

I had the VW dealer send me a full parts illustration of all the components in the cooling system. There is not just one main thermostat on this engine but 3! there is main thermostat plus two more smaller inline units. I removed mine and found the one going to the oil cooler jammed hard open. Put in a new VW part $38 and fixed the problem right away. Car warms up in 5 mins driving now as opposed to 15 mins.

See illustration below. The inline stats are item #21. Very easy to change and I would recommend checking these before you change the main stat like I did. just pinch hoses and undo clamps, 10 mins for each thermostat.


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## kjr6306 (Sep 12, 2007)

Sorry to revive old thread. I am dealing with an issue where my 2006 Passat is slow to reach operating temp.This post mentions 2 inline thermostats....does any one have any idea where these are located?


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## Andy Macca (May 20, 2015)

Although the illustration showed 2 I only ever found 1 inline, new part fixed the problem. It’s right below the battery, think I removed the battery and tray, it’s inline with a hose that goes to the oil cooler. Just a black round cylinder.


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## kjr6306 (Sep 12, 2007)

This is for a 2006 FSI engine? My oil cooler is in the front of engine.


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## Barn01 (Feb 26, 2011)

Anyone have schematics or part #'s?


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## kjr6306 (Sep 12, 2007)

i think the other poster was full of Sh*t. I can't find any other documentation about other thermostats in an FSI engine.


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## Andy Macca (May 20, 2015)

Sorry you feel that way, I did originally link an illustration showing exactly where it is located to help other members. don’t know why you can’t share/link pictures anymore, I’m out of the forum loop these days


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## Andy Macca (May 20, 2015)

1K0121113A Is the part number. Google it, there are different variants of the FSi so location can vary. Check your VIN with VW


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## Barn01 (Feb 26, 2011)

Andy Macca said:


> 1K0121113A Is the part number. Google it, there are different variants of the FSi so location can vary. Check your VIN with VW


According to ECS that part is an oil cooler t-stat and it doesn't fit my 06 A3 with a BPY. It looks like it's only on VW and not Audi


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## kjr6306 (Sep 12, 2007)

From ECS:

In-line Thermostat
Ensures proper coolant flow to the automatic transmission oil cooler.

Not sure how this would affect the heat but you never know. Going to see if I can find it on my Passat.


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## Andy Macca (May 20, 2015)

Because like your regular thermostat it dumps warm water back to the rad, on cold days it therefore takes much longer for the engine to warm up. That stat needs to stay closed like the regular one for the engine to warm up. Trust me, when I replaced it the car would warm up in 5 mins as opposed to 15(below 0 degrees C)


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## kjr6306 (Sep 12, 2007)

Perfect. I did find one on my Passat by the battery just like what was posted earlier. Going to give this a shot and see if it helps. Funny thing, when its warmer like 35 degrees outside, the car seems to warm up fine. Its only when its really cold out that the car doesn't heat up...

Thanks for the help...


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## Barn01 (Feb 26, 2011)

Andy Macca said:


> Because like your regular thermostat it dumps warm water back to the rad, on cold days it therefore takes much longer for the engine to warm up. That stat needs to stay closed like the regular one for the engine to warm up. Trust me, when I replaced it the car would warm up in 5 mins as opposed to 15(below 0 degrees C)



I do agree that my A3 takes forever to heat up when it's cold. Do you think my car has this or is ECS correct that my car doesn't have that part?


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## reds4biturbo (Dec 31, 2012)

Sorry to bring the thread back to life once again but I'm having a very similar problem and found this searching. I know this thread is for the fsi but does anyone know if they're more then one thermostat for the tsi? I have a 2010 gti and am having the same problem as the original poster with very slow warm-up times. I already replaced the main thermostat and that didn't fix my issue. Any help would be great.


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## GTI's (Nov 27, 2011)

reds4biturbo said:


> Sorry to bring the thread back to life once again but I'm having a very similar problem and found this searching. I know this thread is for the fsi but does anyone know if they're more then one thermostat for the tsi? I have a 2010 gti and am having the same problem as the original poster with very slow warm-up times. I already replaced the main thermostat and that didn't fix my issue. Any help would be great.


What trans type do you have in this '10 GTI, if DSG it has one.


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## reds4biturbo (Dec 31, 2012)

GTI's said:


> What trans type do you have in this '10 GTI, if DSG it has one.


The trans is a DSG.


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## GTI's (Nov 27, 2011)

Bypass thermostat yellow arrow











Included with radiator upper hose and you should be able to find the bypass by itself.












https://parts.vw.com/p/Volkswagen__...-T---connector-Upper/48126076/1K0121087R.html


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## reds4biturbo (Dec 31, 2012)

GTI's said:


> Bypass thermostat yellow arrow
> 
> 
> 
> ...


Thanks for the info! So what you're saying is that there is a thermostat inside of the upper radiator hose? Is just the thermostat serviceable or do I have to replace the entire hose?


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## GTI's (Nov 27, 2011)

reds4biturbo said:


> Thanks for the info! So what you're saying is that there is a thermostat inside of the upper radiator hose? Is just the thermostat serviceable or do I have to replace the entire hose?


Please see more info posted above for just the bypass itself without the rest of the hoses. The bypass thermostat can be removed and tested from the housing, not sure if you can just get the thermostat by itself if it fails or is only available with the housing. If you need to find out how to test let me know.


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## reds4biturbo (Dec 31, 2012)

GTI's said:


> Please see more info posted above for just the bypass itself without the rest of the hoses. The bypass thermostat can be removed and tested from the housing, not sure if you can just get the thermostat by itself if it fails or is only available with the housing. If you need to find out how to test let me know.


Thanks for the info!


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