Leak from thermostat connection into block

[03PlatinumTDI]

Hello TDI experts. Got a little situation here. Car is a 2003 Jetta TDI.

The last time that I changed the timing belt (about 45K miles ago), I also replaced the thermostat. I mistakenly torqued (didn't check torque setting before) the two bolts that hold the plastic coolant pipe and thermostat to the block too tight. I knew that one day I would have a problem there and I now have a leak there.

What's the best route to remedy this? Should I just source some slightly larger bolts and torque them in? Or do it properly and tap out the holes and then use larger bolts?

I just ordered some replacement coolant, amongst other things from IDParts so I should be ready to take action this weekend.

Thank you for any help you can give. I'm sure I'm not the first person to do this.

Thanks!

 

[Vince Waldon]

The bolts are there to hold the flange in place but have no actual sealing function of their own... so unless you stripped them in their holes you are probably OK, bolts-wise.

Always hard to tell over the interwebs, but what's more likely is that the plastic flange cracked when tightened, the flange has warped, or the o-ring is leaking...and coolant is now appearing at the bolt holes. All of those are reasonably common... it's a pretty cheap plastic part under both pressure and temperature.

A new flange and o-ring are probably what's needed... and luckily, one of the better deals, as VW parts pricing goes.

 

[03PlatinumTDI]

The bolts are there to hold the flange in place but have no actual sealing function of their own... so unless you stripped them in their holes you are probably OK, bolts-wise.

Always hard to tell over the interwebs, but what's more likely is that the plastic flange cracked when tightened, the flange has warped, or the o-ring is leaking...and coolant is now appearing at the bolt holes. All of those are reasonably common... it's a pretty cheap plastic part under both pressure and temperature.

A new flange and o-ring are probably what's needed... and luckily, one of the better deals, as VW parts pricing goes.

That's interesting. I remember it being a pain to replace that silly piece of plastic when I replaced the thermostat a while back. I'll order one and give that a go. Thank you for the input.

 

[CopaMundial]

There are two O-rings in that area that can leak.
One is on the T-stat housing to block. The other is a small o-ring that seals the end of the hard coolant pipe to the flange.

Here is a video showing a little about both.
http://www.youtube.com/watch?v=eEak8EM4KDM

 

[aNUT]

I'd spring for the dealer T-stat housing. It's $11. I don't pay around with Chinesium cooling system components. The currently circulating edict is that the bolts are single use, which is utter BS.

 

[AndyBees]

I agree with Vince's assessment.

aNut, I agree that those bolts can be re-used!........ just snug them down tight!

As Vince said, the "seal" is from the O-ring, not the bolts. But, they can be not tight enough and later develop a leak. That happened to me because I was concerned about busting the plastic housing. I found the leak and just add a little more tightening to them... leak stopped!

 

[03PlatinumTDI]

There are two O-rings in that area that can leak.
One is on the T-stat housing to block. The other is a small o-ring that seals the end of the hard coolant pipe to the flange.

Here is a video showing a little about both.
http://www.youtube.com/watch?v=eEak8EM4KDM

I'd spring for the dealer T-stat housing. It's $11. I don't pay around with Chinesium cooling system components. The currently circulating edict is that the bolts are single use, which is utter BS.

I agree with Vince's assessment.

aNut, I agree that those bolts can be re-used!........ just snug them down tight!

As Vince said, the "seal" is from the O-ring, not the bolts. But, they can be not tight enough and later develop a leak. That happened to me because I was concerned about busting the plastic housing. I found the leak and just add a little more tightening to them... leak stopped!

Thank you all for the great advice. I'll let you all know how it turns out.

 

[RacerTodd]

I had a slow leak crop up several months after installing a new thermostat, o-ring and housing.

What I did to stop it was to clean the block with some green Scotchbrite before re-installing the thermostat with a new o-ring. Note that the o-ring seals on the sides (not the bottom) of the round opening in the block so that's where you want to clean.

 

[Quanger]

Yep. Clean the surface well. Replace both Tstat and Housing is the best bet. I had this problem which actually led to my alternator failing (or coincidence) from coolant slowly trickling on the alternator.

 

[runonbeer]

Use dealer parts. aNUT and I have learned this lesson 100 times. Tstat, housing and seal.

 

[runonbeer]

I am so tired of learning this lesson!

 

[vwdieseling]

I'd spring for the dealer T-stat housing. It's $11. I don't pay around with Chinesium cooling system components. The currently circulating edict is that the bolts are single use, which is utter BS.

OE's are better. They last longer.

 

[03PlatinumTDI]

I had a slow leak crop up several months after installing a new thermostat, o-ring and housing.

What I did to stop it was to clean the block with some green Scotchbrite before re-installing the thermostat with a new o-ring. Note that the o-ring seals on the sides (not the bottom) of the round opening in the block so that's where you want to clean.

Yep. Clean the surface well. Replace both Tstat and Housing is the best bet. I had this problem which actually led to my alternator failing (or coincidence) from coolant slowly trickling on the alternator.

Use dealer parts. aNUT and I have learned this lesson 100 times. Tstat, housing and seal.

I am so tired of learning this lesson!

OE's are better. They last longer.

Thank you all. Message well received on the OE parts. These parts that failed are chinese parts so lesson learned.

 

[03PlatinumTDI]

I had a slow leak crop up several months after installing a new thermostat, o-ring and housing.

What I did to stop it was to clean the block with some green Scotchbrite before re-installing the thermostat with a new o-ring. Note that the o-ring seals on the sides (not the bottom) of the round opening in the block so that's where you want to clean.

This was the fix. Scotchbrite and a wire wheel attached to a dremel for the really nasty stuff. It was tedious and time consuming, but after about an hour it was shiny clean. New OEM thermostat and o-ring (flange is a year old OEM unit) were installed and the leaks are gone.

Many thanks to everyone as that was a frustrating problem, but a relatively easy and cheap fix. The 11 year old TDI continues on......