A4 thermostat change How-To

Not that I am aware of. You will have to switch back and forth between controllers.

just wanted to thank the op for helping me id the hose that is under the ip. The thermostat hose. I didnt knwo which hose that was and recently i had it spring a leak and i temporarily fixed it by stretching the hose over it. I will now go get the proper hose and fix it permanently.

thanks,
Steve

DanG144 said:

That is correct. Sorry I have no references to the right measuring block number in the INSTRUMENT controller, but if you open the INSTRUMENT controller and just page through the blocks you will find it clearly labeled.

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Update- got the Vcds hooked up today, and the measurements are very different. The engine controller temp holds steady at 70-80c, but the instrument reading in #17 jumps wildly between 5c and back to normal.

I am also throwing a code as follows, which is odd, as I have replaced the coolant temp sensor.

1 Fault Found:

01039 - Coolant Temperature Sensor (G2)
30-10 - Open or Short to Plus - Intermittent

So, my question is, as my CTS is new, what is this telling me? The behavior in the gauge is the same before and after the new CTS. My heater works fine, and the car seems to run fine.

Sorry for taking this thread OT, as I don't think that I have a thermostat issue now.

Any comments welcome.

You seem to have a bad wire or connection to your coolant thermostat.

I had a 99.5 jetta doing the same thing, reading the same fault. Changed the coolant sensor, fixed. Was the new sensor OEM or Chinese? The sensor has 2 switches in 1. Hope this helps. Thanks Steve

It is a brand new OEM part. I don't know what else to do, taking to a shop today.

DanG144 said:

You seem to have a bad wire or connection to your coolant thermostat.

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Dan- you were right on the money. Bad wire between the sensor and the harness under the battery. Well beyond my expertise, the local VW independent shop got it fixed and all is working perfectly now. Thanks for your help.

I can't believe I said "coolant thermostat" instead of "coolant temperature sensor". Must have been in a rush.

Dan

DanG144 said:

I can't believe I said "coolant thermostat" instead of "coolant temperature sensor". Must have been in a rush.

Dan

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hey, it's Thanksgiving weekend , maybe you had an early start with the wine

to drain engine of coolent

Has anyone ever pulled the bottom hose off the oil cooler to drain the engine of coolent. Thats what may bently tells me but I hanen't read any thing like that on here and was wandering if it works good. I gota change may t-stat tomorrow.

I want to change the engine coolant and thermostat. Reading the post look like will be an easy task. But I have questions?
The 2 pins on the flange is just to hold the thermostat for installation?
I have used too many times aftermarket thermostat on other cars with out any issue, any important comments you want to add If I decide to use an aftermarket thermostat?

Regards
El Serch

The two pins are simply for holding the thermostat for ease of installation. If you need to, you can use a piece of string or a wire hook through the thermostat, with the string going out the other end of the housing, to hold it in place for installation.

I've done both cars in the last 2 days and, for the newb's out there, some things:

(1) find some way to drain the coolant out of the block rather than pulling the t-stat out and having it gush out. It's a real mess. I suppose with a big catch pan and some cardboard, it would be fine, but it would really be better to use the return line method or some other method of getting more coolant out.

(2) using needle nose or whatever on the hose clamps is a major PITA. Make life easier: buy some hose clamp pliers.

(3) if you want to save a few $, drain the radiator coolant into a *clean* catch pan and then strain it while pouring it back into the system. I used a fine mesh paint strainer. I've seen this done by pro's, so others can correct me if this in error.

(4) i saw another thread on refilling the system which talked about disconnecting the upper radiator hose by the battery and pouring coolant into each end (fills radiator and engine). that seemed to work better for me than just pouring into the reservoir and waiting.

YMMV.

I have really good results filling the system while pulling a vacuum with my mityvac on the coolant vent line that goes into the top of the coolant reservoir. Once I have pulled just an ounce or so out, then when running and getting the thermostat open, I only have to add a few ounces.

It looks to me as if the pump and thermostat are the two lowest points on the block. If anyone knows a good place to drain the block, I am all ears.

I use my Pela to pull a vacuum on that return line at the top of the reservoir...

As for emptying the block... good luck... I'd love to hear a good option... (I pulled the lower oil cooler hose after draining the radiator via the spigot at the bottom and putting pressurized air into that return line, and still, when I removed the thermostat (and water pump), quite a bit more coolant came out...)

Yuri

Yuri,
Try alternating air to the coolant ball vent line hose, with your finger over the ball connection, then putting air to the ball connection for the vent line while plugging the vent line hose with your finger.

I use 20 psi air pressure.

This will get you almost a half gallon more of coolant out.

But you still will have some coolant in the bottom of the block.

Dan

I think I did that as well... There also was a small quantity of coolant by the temperature sensor after all this... (I replaced everything as long as I was in there...)

I hope not to be doing this sort of thing too often...

All the best,

Yuri

mchabot said:

Bump for a great procedure. Instructions were easy to follow. When I was done it took about a 1.25 gallons to get the cooling system filled back up. I know lots of people on here think thermostats don't fail but at 175,000 miles mine was definitely toast. The car wouldn't get up to temp in 50 degree weather. After a quick thermostat change and a test drive it heats right up. Just a heads up for everyone my local dealer had G12 for $24 a gallon. Thats actually a bit cheaper than some of the trusted vendors.

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Does the G12 need to be diluted 50/50 or does it already come at that strength, or do you just use it straight?

"Regular" G12/G12+/G12++ needs to be mixed with demineralized/distilled water at a concentration of between 50% and 70%...

However, there are some suppliers who sell pre-mixed G12 that's already diluted to 50%...

You need to read the label...

Yuri

okie dokie~~ thanks

First if all thanks very much to Frugality for the excellent write up.

Also, thanks to Paramedick for the tip on emptying/refilling the coolant into the system. Worked like a champ. Still had about 1/2L of coolant come out once I removed the thermostat, but I had a catch pan underneath for that reason.

Car used to never go over 79.8C now it will get to 92C with the usual highway drive.

Also found out that my torque wrench does not "click" anymore, so off to see about a warranty claim on that now.

paramedick said:

If you have compressed air, you can get nearly a gallon of coolant out.

Remove the return hose from the coolant bottle. Pressurize it slightly with compressed air via blow tip. Coolant will come up into bottle, then drain into radiator. Repeat until very little coolant comes into bottle. Then put cap onto coolant bottle, and pressure the return nipple.

When it's time to refill the sytem, connect a mityvac to the return hose and pull vacuum. Refill bottle as needed. When you get a splash of coolant into the mityvac tubing disconnect it and reconnect return hose to bottle. It will take another bottleful of coolant after car is started to refill system.

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Finally R&R'd the tstat and reservoir after ignoring it for over a year and it was painless with minimal coolant loss.
I had built it up to a big job in my head but after I actually located the tstat I realized that it was a piece of cake.
Great info and help from the forum.
Now I hope to see better mpg's and no return of the dreaded flashing coolant temp light

I just replaced the thermostat with the instructions posted here and
so far, success!

I managed to get about 5 liters out of her, by following the steps,
such as squeezing the hoses, and such, and a lot came out of the
block. On the refill, after filling the overflow tank I also disconnected
the hose on the right and poured as much as I could into the radiator
and the other side into the head.

Now, the temp is rock solid at 190. Before, even after replacing
the coolant temp sensor, it was struggling to maintain 190, and more
often than not well below that.

Thanks again for the instructions. This place is great!

Bump for a great how-to. I managed to get the thermostat to come out still attached to the flange without breaking the pins. I used a Stant Superstat #45379 ($10 at Advance Auto) and it fit onto the pins perfectly.

My only difficulty was the giant aluminum intercooler pipes directly in the way.

Great Write Up

.I completed this today with a bunch of other things. My thermostat was original at 227,500 miles and I found that my water temperature would not exceed 76ºC. After replacement with an Volkswagen thermostat, 95ºC

I went all Volkswagen parts from 1stvwparts. Thermostat for $31, flange for $6, bolts for a buck or two. Don't forget to order the o-ring!; I thought the VW stats came with one but they do not and made a mad dash to the dealer yesterday.

Bruce (post #7) and Dan's (post #76 explains best) tips for getting coolant out using pressurized air are excellent. If you follow their instructions, you will lose almost nothing when you pull the radiator hose from the flange and about 1.25 liters from the block when you pull the t-stat Position a catch pan near the far edge of the oil pan to collect most of the fluid

I had a liter of ELF coolant from ages ago that I mixed 50/50 and had plenty left over. Interestingly, VW no longer sells coolant 1 liter at a time. You have to get something like a half gallon. My total time for this job was on the order of 1.5 hours.

Thanks for the writeup! just changed out mine this weekend, I was able to get it done in an hour and 50 min (not counting test drives and cleanup). First time i did it, if I did it a second time, bet it would be about 45 min. Used the compressed air suggestions above, that really helped, almost got 3L out. only lost a little. To get it back in, I filled up the tank and broke the line at the top of the radiator until coolant came out. then gently used my oil extractor (dont have a mityvac) to suck the return hose until a bit of coolant showed up in the tube. Took it for a run and all was good, the tank was just slightly below min at that point, perfect. was operating at a steady 170F, now seems to be a perfect 190F.... will keep an eye out for leaks. Was at 53mpg, excited to see what I end up getting!

Just did mine as well, following OP instructions & tips on draining with compressed air. Worked perfectly. Temp guage is now steady at 190, and plenty of heat in the cabin. Previously could not get the temp guage above 160-170, thermostat was stuck partially open. Great " how to" and great additional comments. Thanks to all.

arne487 said:

Bump for a great how-to. I managed to get the thermostat to come out still attached to the flange without breaking the pins. I used a Stant Superstat #45379 ($10 at Advance Auto) and it fit onto the pins perfectly.

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I used a coat hanger and made a small hook on the end to hook onto the thermostat. I had to pull pretty hard to get the thermostat out, but it all came out and the flange was not damaged! I used the Stant Superstat as well. I was getting 77*C with VCDS, now I'm getting 98*C. that converts to 208*F. A little high, I hope this is OK?

I think 208 F as an operating number is fine. That is the number out of the head, and runs a bit higher than the thermostat.

Thanks, I think it's ok or else the temp light would come on.