Thermostat failing confirmed by VCDS logging

cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
I finally get my dealership timing belt debacle dealt with, and now I notice the temp gauge dropping at stoplights. It has been cooler so I thought that was the main reason for the temp fluctuation, but during my 2 hr highway commute last night (68F Ambient Temp) the gauge is still behaving the same. Gauge may drop slightly while driving as well as at idle. I had suspected something was amiss on Friday (mid 40s Ambient) so I used VCDS to monitor my coolant temp during part of my drive. It never got above 75.6C (~168F) during that drive. I ended up logging the 2nd half of my trip last night, and the results are in the graph below. I am so NOT looking forward to doing the thermostat on this car from what I've read!

I find it strange that this started after I had the dealer do the timing belt/water pump/coolant service at 120K, but oh well I guess it's time to get dirty! I've looked at the pointers here and on the myturbodiesel.com site so I feel confident going into this repair, but if anyone else has any other pointers please feel free to share. I'll be gathering the parts and post up my progress as I can get to it. Thanks!

PS: I was not using my winter front for either data gathering session. I did encounter a regen around 3/4 of the way through the drive last night, and you will see that peak and drop off in temp on the graph as well. Interesting.

 

Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
In a couple of threads I mentioned my believes that t-stats do degrade with age and heat cycles and it's a good idea to replace them at timing belt time while you are there.

Some people flamed me away but I'm still sticking with my theory.

Is the t-stat on your car the one "with the large flange" like the one described here? http://forums.tdiclub.com/showthread.php?t=371430

If so, then yeah, it's a Royal PITA to do it but it's doable...
 

meerschm

Top Post Dawg
Joined
Apr 18, 2009
Location
Fairfax county VA
TDI
2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
Not to flame, but my theory is that thermostats degrade from corrosive coolant, not age or heat cycles. particulates can also jam the mechanism if allowed to grow in the coolant.

in this case, G62 data says the thermostat has changed, and needs to be replaced.

on my 2009, it worked fine for 205k miles and almost 9 years.

If I had changed the thermostat, it would have been a waste of time and money.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
In a couple of threads I mentioned my believes that t-stats do degrade with age and heat cycles and it's a good idea to replace them at timing belt time while you are there.

Some people flamed me away but I'm still sticking with my theory.

Is the t-stat on your car the one "with the large flange" like the one described here? http://forums.tdiclub.com/showthread.php?t=371430

If so, then yeah, it's a Royal PITA to do it but it's doable...

You got "flamed" because you thought incorrectly that it is an easy thing to change, and it isn't. And it has very little overlap with the timing belt labor anyway.

So no, I would not do it at timing belt time, nor would I expect anyone to do it. They generally last longer than that regardless.

To me as it relates to the timing belt, it is just about as linked as a tail lamp bulb. Other than the coolant, which is hardly any issue, there is no real savings to doing it while a timing belt job is done. I have customers who are coming up on their third timing belt on CR engines with the original and functioning thermostat still in place. When it fails, it gets replaced.

If it were easy to do, like it is on the earlier cars, a preventive measure is certainly not a bad idea. But when it takes as long to do a thermostat on a CJAA engine as it does to replace the clutch on an ALH, it is a different story. How many people replace a clutch "just because", with no reason or symptoms? Not many.
 

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
Yeah, I have to think that VW not including t-stat replacement in the maintenance schedule is a pretty good indicator that they expected most of them to last a long time. 170k miles on mine so far without any problems. Looks like a major PITA to replace, good luck!
 

mishkaya

TDIClub Contributor
Joined
Mar 4, 2005
Location
Iowa
TDI
'06 Jetta 5MT, '10 JSW MT, '14 JSW 6MT
I have not had good luk with thermostats on CJAA engines. I have had to replace two thermostts already, and I have a third car thats needs a replacement when the weather improves. It i dfiniely a PITA, but you don't need to take apart all the stuff in the MTD how to. There is a thread somewhere on this forum with pics showing how to get the thermostat out without removing the hard coolant line. An extra set of hands to install the new thermostat is almost a must if you go this route.
Good luck. :p
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
PITA? Nah....



The PITA comes when the plastic coolant pipe that goes into the t-stat housing cracks. And that seems to be more common than the t-stat failures. So, may as well do them both while it is apart. :)
 

cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
The PITA comes when the plastic coolant pipe that goes into the t-stat housing cracks. And that seems to be more common than the t-stat failures. So, may as well do them both while it is apart. :)
Do you happen to have a part number for that plastic pipe or is it something I can look up on idparts or ecstuning easy enough? Thanks!
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
03L-121-065-T and it comes with the o-ring where it goes into the thermostat assembly. The other end is the heater hose connection, just a spring clamp.

You will also need the oil filter stand gasket 045-115-441 since that has to come off to get the pipe out.

In the picture I was also replacing the intake manifold, you do not need to take that off, and you can do this job just by moving the lock carrier assembly out into service position, but it is just easier to take the whole thing off for me.
 

cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
Thanks oilhammer! I don't think I'll be pulling the radiator/intercooler/ac condenser and all that, but that'd definitely make it easier! :D Should I try to plan to do this around an oil change to minimize oil loss? I'm also guessing I should remove the oil pan insulation in case oil or coolant spills everywhere.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
It for sure helps to remove the lower oil pan sound baffle, yes. I do that with just about anything that may potentially let fluids down in there and ruin it.

You will lose about a liter or so of oil, as the cooler and filter together hold about that much. It helps make less of a mess though if you take the filter out the top as you usually would, and then suck as much oil out from the filter hole as you can, so that when you take the stand off the block there is not much left to drip out. Goes without saying make sure that area stays clean so not only no debris gets into the engine, but that the gasket surface stays good so a proper seal takes place with the new steel gasket.

The turbo oil feed pipe is there, too, so have to take care those threads do not get damaged. Not a hard job, just time consuming.

You will need to slide the lock carrier out, there is simply no room in there otherwise. Do that FIRST, as that makes everything else much, much easier. Just slide it out on long M10 X 1.50 bolts, get it as far out as you can. If you need more room, you can remove the roll mount from the transmission underneath, and "rock" the engine/trans back and forth which can sometimes give you an extra inch or so.
 

Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
cliballe, have you checked the radiator return hose?
Today I checked mine after not too long drive and it was warm. Not hot but not stone cold either.
To me it seems that my t-stat might not be fully closing.
I never see coolant temperatures over 82 *C under normal conditions.
When in a regen it gets to 88-91 *C.
The t-stat in this car is rated for 92 *C
77k miles on the clock but the car is seeing exclusively short trips only and city driving
 
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fastalan

Veteran Member
Joined
Jan 1, 2010
Location
Richmond BC
TDI
2010 Golf TDI Wagon
When my dealer did the thermostat replacement, the following parts were used:

x1 06B-121-687 Washer
x1 069-131-547-D Gasket
x1 03L-131-547-B Seal
x1 03G-131-547-C Gasket
x1 06B-121-119-B Washer
x1 03L-121-111-AC Thermostat
x1 03G-131-547-H Gasket
x1 1K0-253-115-AG Gasket
x1 1K0-253-725-E Clip
x1 AM06B121687 Seal --> I don't know if this is a VAG part or some other general automotive plumbing part

This thermostat replacement, I am glad I didn't try to DIY, and that I didn't send it to a privately owned third party shop without direct VW part resource. It most likely drove the dealer mechanic team and the part guy crazy, having to work on it twice, spend way more than the 3 hours charged on the invoice, and all the parts they had to replace again without charging me. It is probably an usual fix, once in a car's lifetime fix and most dealers more familiar with routine maintenance type job, are simply not familiar with this particular part replacement.

Finally, I don't want to say that it is poorly designed, but the location of the thermostat, when the engine is placed transversely, doesn't make it easy to work. I guess the repair hours/procedures specified by VW may also have been too optimistic, a bit unfair to the dealer service dept.

That picture posted by oilhammer, with the entire front end removed, remind me of a friend's early 2000 Audi A4. I can't remember what part had to be fixed on the 2.8 V6, his car is in Taiwan, but with cheap labour rate in Asia, the shop simply removed the whole front end in order to finish the repair.
 
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Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
In the parts list there's a lot of gaskets for EGR plumbing, EGR valve as well as ASV valve.
Stange enough they also included a Turbo-to-DPF gasket too.
 

cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
cliballe, have you checked the radiator return hose?
Today I checked mine after not too long drive and it was warm. Not hot but not stone cold either.
To me it seems that my t-stat might not be fully closing.
I never see coolant temperatures over 82 *C under normal conditions.
When in a regen it gets to 88-91 *C.
The t-stat in this car is rated for 92 *C
77k miles on the clock but the car is seeing exclusively short trips only and city driving
I haven't done that yet myself. I will check after my evening commute and post back the results. I'm expecting to have the same results as you. Most of my during the week driving is 15 minutes to and from work, but on the weekends I log a several hours of sustained highway driving.

Edit: My coolant hoses were all just warm after driving around for over 30 minutes... not hot. Dash gauge was straight up at "190F."
 
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Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
I haven't done that yet myself. I will check after my evening commute and post back the results. I'm expecting to have the same results as you. Most of my during the week driving is 15 minutes to and from work, but on the weekends I log a several hours of sustained highway driving.
Well, sustained highway driving is not very hard on engine; if the car is unloaded the load isn't high.

What we want to eliminate before getting into that difficult replacement stuff is that your car may not be reaching full operating temperature for t-stat to open (wind from the fron of the car, cabin heater blasting on full power, low engine load). Of course the chances are minimal but still, let's check. These TDI engines are very fuel efficient so they produce not much waste heat.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Well, sustained highway driving is not very hard on engine; if the car is unloaded the load isn't high.
What we want to eliminate before getting into that difficult replacement stuff is that your car may not be reaching full operating temperature for t-stat to open (wind from the fron of the car, cabin heater blasting on full power, low engine load). Of course the chances are minimal but still, let's check. These TDI engines are very fuel efficient so they produce not much waste heat.
The load on the engine is HIGHEST on the highway. You can watch this data in with a scan tool, most every car has this information. It takes more energy to move a car through the air at a higher speed, and the energy required goes up the faster you go. It does not take twice the power to move a car at 80 as it does 40, it takes something like 2.5 times.

The difference is, the load is more sustained, without the strong spikes, so it levels off. You can idle the engine to about 30 or so. After than, you need more fuel and air to push the car through the air.

This is why idling the engine does little to warm them up, and even short trips around town don't do a whole lot. But you jump on the highway and (when everything is in good order) they'll get up to temp quicker.
 

fastalan

Veteran Member
Joined
Jan 1, 2010
Location
Richmond BC
TDI
2010 Golf TDI Wagon
In the parts list there's a lot of gaskets for EGR plumbing, EGR valve as well as ASV valve.
Stange enough they also included a Turbo-to-DPF gasket too.
Copied off from the dealer invoice....

It was leaking all over the front of the block, perhaps they had to take a whole bunch of stuff off to check.
 

Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
OH, thanks for info. I really thought it was the opposite. I remember seeing dealership posters advertising VW LongLife service schedule. It was listed that cars driven lightly, most on the highways are eligible for long-life programme. That's why I assumed the load was minimal there.
 

turbobrick240

Top Post Dawg
Joined
Nov 18, 2014
Location
maine
TDI
2011 vw golf tdi(gone to greener pastures), 2001 ford f250 powerstroke
Cars that do a lot of highway driving go through fewer heating/cooling cycles, spend more time at operating temp., and are generally happier than their short trip counterparts. The extra load is actually good for the engine.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Cars that do a lot of highway driving go through fewer heating/cooling cycles, spend more time at operating temp., and are generally happier than their short trip counterparts. The extra load is actually good for the engine.

Exactly. And it is more of a steady load, which is also easier. Most "wear" happens during warmup, so a 20 mile trip is just as bad as a 200 mile trip. I live in the country, I never short trip my cars, unless I run into town for something locally. And then I try and use one of the gasoline fueled cars since they warm up much quicker anyway. The older diesels are less finicky about short trips though, even though they take longer to warm up.
 

Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
My daily trip is 5 miles one way usually. And this is if I don't stop at a gasoline station, grocery store or somewhere else. Sometimes I take it for a longer spin (as well when I notice regen in progress).
I don't want a gas car - there's no torque, not that fun to drive :)
 

Henrick

Top Post Dawg
Joined
Aug 24, 2010
Location
Ireland
TDI
Golf VI TDI, 77 kW (CAYC)
My daily trip is 5 miles one way usually. And this is if I don't stop at a gasoline station, grocery store or somewhere else. Sometimes I take it for a longer spin (as well when I notice regen in progress).
I don't want a gas car - there's no torque, not that fun to drive :)
 

cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
Okay, here's my parts list. Let me know if you think I'm missing anything:

-2 M10-1.5x180mm bolts to move Hood Lock Carrier to service position

-1 Gallon of G13 Coolant, G0-13A-8J1-G, (in case I am not able to catch/reuse what's in there)

-1 Thermostat, 03L-121-111-AC, (includes new o-ring, 06B-121-119-B)

-1 Plastic Coolant Pipe, 03L-121-065-T, (includes new o-ring, 06B-121-687)

-1 Oil Filter Housing to Engine Block Gasket, 045-115-441

-4 Oil Filter Housing to Engine Block TTY bolts, N-911-494-01, (15N-m or 11lb-ft plus 90 degrees)

-1 EGR Valve Gasket, 03G-131-547-C

-1 "Throttle Body"/ASV Gasket, 03L-131-547-B
 
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nicklockard

Torque Dorque
Joined
Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
In a couple of threads I mentioned my believes that t-stats do degrade with age and heat cycles and it's a good idea to replace them at timing belt time while you are there.

Some people flamed me away but I'm still sticking with my theory.

Is the t-stat on your car the one "with the large flange" like the one described here? http://forums.tdiclub.com/showthread.php?t=371430

If so, then yeah, it's a Royal PITA to do it but it's doable...
They very obviously degrade and should be replaced about every ~40,000 miles or fuel economy suffers. I agree with your hypothesis--I think the wax pellets are degraded by copper ion poisoning from heat cycling.
 
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cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
Well I began to attempt the thermostat replacement this weekend, but I did not allow myself enough time so I had to abort to try again another day (I ended up spraying our 5 acre yard which took most of Saturday as the weather was unexpectedly perfect).

On Friday night I had pre-emptively moved the hood lock carrier out to service position which wasn't too difficult. I had the air box removed, but I was still unsure if there was enough room to be able to find the rear fastener to loosen the coolant pipe so I left it for the night. After I got done with all my spraying late yesterday afternoon I was able to reach way under the boost tube to locate the 12mm Triple Square bolt. At this point I realized it was too late to try and finish the job so I put everything back together and maybe I can try again next weekend.

Question:
Am I going to be able to remove and replace the coolant pipe once I remove the two fasteners/hose clamp? I could feel the heater hose clamp near the firewall, but man it is very tight back there so I am a little concerned over all the coolant hoses, EGR tube, boost tube, etc. in the way. If I wasn't replacing the pipe I would just loosen it, get the thermostat out, and be done, but since I have to remove it the task is a little more daunting to me.

Thanks ahead of time for your input!
 
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oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
You'll need to remove that charge air pipe to gain access to the coolant pipe. I remove the clamp on the heater hose at the pipe you are replacing, not at the firewall. The heater hoses are made together, you'd have to take a bunch more stuff apart to get those out.

The picture I posted shows all the stuff (including that boost pipe) removed. It is the one that goes across the top of the bellhousing area and down past the starter.
 
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cliballe

Well-known member
Joined
Jan 21, 2010
Location
Tennessee
TDI
2010 Jetta
Thanks, oilhammer, I'm going to give it another go this coming weekend with removing the charge air pipe. I'll have plenty of time to dig into it then.

BTW: About how long does this job take you to complete?
 
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oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
BTW: About how long does this job take you to complete?
Ha! That depends as I usually have several things going at once. I suppose start to finish, including complete removal of the front end, maybe 2.5 to 3 hours' worth of actual time. I never really pay much attention to clocks, I pay more attention to detail in getting the job done correctly and completely.
 
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