2010 Jetta Thermostat Change - What a Pain

10mm ratcheting wrench to and an 8mm triple square bit and a very steady hand. Highly recommend always using white rags under your immediate work areas to prevent bits and bolts from falling into the abyss and ruining your entire day. Had to REMOVE the newly installed thermostat because one of the tstat bolts fell into the netherworld just under it - worst feeling in the world when I was so close to finishing the job and probably why my hard pipe o-ring failed on me from having to remove and install the tstat repeatedly.

The same thing happened to me with the lower thermostat bolt, fortunately I was able to remove the belly pan and it was sitting right there underneath the oil filter. Then it happened again, of course. Total deal breaker if you lose one of those and can’t put the whole thing back together.

I got a mini ratchet set at Lowe’s that coincidentally came with a set of triple square bits as well, and thanks to your pointer I was able to remove that screw behind the oil filter housing, move the thermostat around somewhat freely and didn’t have to touch the alternator or the oil filter housing. Kudos to you man.

It took me about 2.5 hours to put everything back together. I was going to flush the whole coolant system with distilled water to clean out any debris (and flush out the remnants of that gross looking orange crap that the PO put into the vehicle), but it was late and we’re having below freezing temperatures overnight. That’ll be my project for tomorrow and there’s a really nice thread here describing how to do it with just a shop vac and a few jugs of distilled water. I paid extra attention to all the hose clamps and the o-ring on the hard pipe (I actually replaced it), tomorrow will be the moment of truth.

Thanks again for your pointers, I’d probably still be trying to figure out how to tip over the alternator or remove the oil filter!

k3ys3r_soz3 how long was your test drive when you noticed that the car was dumping coolant? Was it visible under/behind/around the thermostat that there was a leak? Just asking out of curiosity, I don’t see anything leaking in the vicinity of the thermostat and my test drive was approx. 42 miles / 65 km. The coolant level in the reservoir dropped a tiny bit, which I think was due to an air pocket in the system, as no dripping was visible when I arrived and checked the underbody. Just want to be on the safe side.

My test drive was only 2 or 3 km from my house. The coolant started gushing from the hard pipe when I started testing the heat in the cabin. I guess that's when the thermostat opened and let it all leak out at the failed o-ring at the hard pipe. I could see it dripping significantly on to the block and sizzling from the hard pipe. I think you should be good if you got it up to temp and have heat and still no leaks. I'm gonna re-attempt the job this weekend one last time - just in time for the weather to get freezing... Bought a new hard pipe just in case but not sure if I'm gonna be able to get it off because I couldn't even SEE the other rear bolt that is holding it on to the block!

Just for anyone interested:

when I do these, I take the front of the car off, I take the oil filter housing off, and I always replace the plastic pipe that goes into the thermostat housing and runs around the back of the head to the heater hose. I do not mess with the alternator.



Note that car was also getting a new intake manifold, so that was removed in this picture. I normally would just take the throttle flap loose, and leave the intake and EGR valve in place. Good opportunity to fix any engine harness or A/C+alt harness chaffing too.

Manual cars are a little easier as there is no ATF cooler hoses to mess with. You *can* do this job without discharging the A/C I would think, but it would be a pain because of the very small amount of free play in the hoses to the condenser, but you could probably swing the whole front assembly off to the side, "hinging" on the passenger side where the A/C lines are, to gain better access.

Oilhammer, thank you! Quick question, do you know where in the CJAA the coolant temperature sensor is located and how easy/difficult it is to access?

One is in the coolant flange at the flywheel end of the head, same as earlier cars, and the other is in the radiator hose that comes from the thermostat, down near the oil cooler.

hey oil hammer, my car is due for a new thermostat as it’s only getting up to 140 degrees. I’m waiting to do it with the timing belt. Also have a Cp3 pump I’m going to be installing, do you recommend pulling the car apart like this, if so. Would you happen to have a how to guide ? Thanks. I have a lift and a shop.

oilhammer said:

Just for anyone interested:

when I do these, I take the front of the car off, I take the oil filter housing off, and I always replace the plastic pipe that goes into the thermostat housing and runs around the back of the head to the heater hose. I do not mess with the alternator.

Note that car was also getting a new intake manifold, so that was removed in this picture. I normally would just take the throttle flap loose, and leave the intake and EGR valve in place. Good opportunity to fix any engine harness or A/C+alt harness chaffing too.

Manual cars are a little easier as there is no ATF cooler hoses to mess with. You *can* do this job without discharging the A/C I would think, but it would be a pain because of the very small amount of free play in the hoses to the condenser, but you could probably swing the whole front assembly off to the side, "hinging" on the passenger side where the A/C lines are, to gain better access.

Click to expand...

Would anyone like to post the part numbers for the various tubes / O rings they suggest replacing when doing the thermostat ? Will be tackling mine while I do the timing belt / cp3 conversion. Thanks

03L-121-111-AC thermostat

03L-121-065-T pipe

045-115-441 gasket

I normally reuse these unless something looks amiss with them:

03L-131-547-B seal ring for intake flap

3D0-260-749-C / 4E0-260-749-A o-rings for A/C condenser connections

I just did this repair too, here's what I used:

Thermostat 03L121111AC (I purchased the Mahle Behr version from FCP, it came with a new o-ring installed)
O-ring 06B121687 (for the plastic coolant pipe, I didn't replace the pipe itself)
O-ring N90043201 (for the oil dipstick tube, I removed mine for the job)
Gasket 03L131547B (for the throttle body)
Gasket 03G131547C (for the EGR, I removed mine for the job)
Gasket 069131547D (for the EGR tube)

I didn't remove the oil filter/cooler nor did I tip over the alternator, so I didn't need the 045-115-441 gasket. There seem to be multiple ways to tackle this job so if you want the step-by-step I wrote up, let me know and I'll be happy to share. I didn't remove the front either btw.

you guys are life savers