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Old 09-19-2018, 09:26 AM   #1
xathor
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Default 200Tdi thermostat housing repair

I'd like to record this somewhere just in case it helps someone else out in the future.

Yesterday I was swapping out my thermostat and while hand tightening the three screws into the thermostat housing, the threads pulled out of two of the screws holes.

The thermostat housing is ERR1499 and looks to be around $300 for a replacement.

The bolts that hold the thermostat housing on are M6x1.0-40mm bolts and the housing has a considerable amount of material around the threads.

I chose to drill and tap the housing for larger bolts, specifically M8x1.25 because it is a very common thread pitch and size found readily pretty much anywhere.

A M8 tap requires a 17/64th drill bit. Drilling out the hole is very easy as the aluminum is soft and there is room to plunge through the housing. The hole will guide your drill bit to some extent, but you should try to get this as straight as possible. You should stuff some rags behind the water pump pulley so chips do not get behind the waterpump pulley. I left the old thermostat in the housing as I drilled to prevent chips from getting into the coolant.

Once the holes are drilled out, use the tap to make the threads. There is plenty of room to run the tap nearly all the way down.

The top housing, ETC5967 needs to have its bolt holes drilled out to 5/16ths or marginally larger. 5/16ths is the OD of the M8x1.25 threads. 21/64ths or 11/32nd would probably be a better choice as it will allow for easier installation of the cover. I would recommend doing this on a drill press of some sort as the holes are quite long and the soft aluminum is likely to grab the drill bit and break it if drilled by hand.

You'll need to replace the bolts with M8x1.25-40mm, which can be found at Lowes or Home Depot easily. If you cannot find a flanged head bolt, you can use a standard bolt with a washer.

An added benefit of this procedure is that you no longer need to have a 8mm socket to remove the housing as M8 bolts use a 13mm head.
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Old 09-19-2018, 09:26 PM   #2
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Why not just fit helicoils? In the middle of nowhere I had to do this. Sorry Mr Farmer but my needs was more than yours at the time.
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Old 09-20-2018, 06:49 AM   #3
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Nice write-up. This was and issue for me as well when doing the 200 swap. We lucked out and was able to chase the threads and get enough bite but if I ever need to replace my stat I will be doing this procedure as well. Nice Job!
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Old 09-23-2018, 03:16 PM   #4
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Quote:
Originally Posted by Roverman2010 View Post
Why not just fit helicoils? In the middle of nowhere I had to do this. Sorry Mr Farmer but my needs was more than yours at the time.
Helicoils are expensive and I can't imagine a scenario where I'd rather have a helicoil than a slightly larger drilled and tapped hole.
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Old 09-23-2018, 04:31 PM   #5
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Quote:
Originally Posted by xathor View Post
Helicoils are expensive and I can't imagine a scenario where I'd rather have a helicoil than a slightly larger drilled and tapped hole.
The soft metal alloy in the casting means that a helicoil will allow the use of the standard size hardware, improve the holding power, and last longer than new oversized threads drilled and tapped. Standard cut threads at 80% or so will hav the leading (initial) ~3 threads carrying 75% of the load - whereas a helicoil will distribute that force across 4-5 threads.
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Old 09-23-2018, 06:44 PM   #6
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Jesus. It is just a thermostat housing. It is not a demanding application.
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Old 09-24-2018, 11:06 AM   #7
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I think you guys are confused as to why helicoils exist.

The only time I would recommend helicoils is if you need to put a bolt of the same thread as the one that came out. You cut the next size up threads, then fill the gap with the helicoil.

If I needed a permanent repair of the same thread size and pitch, I'd skip the helicoils all together and use a timesert. Helicoils can roll inside the threads from being over torqued, a timesert cannot.

In this case the helicoils are totally irrelevant as there is plenty of area to cut two sizes up from the original bolt. In this case, the repair is stronger than the original as there is more thread engaged surface area on a M10x1.25 bolt than an M6x1.0 bolt.
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Old 09-24-2018, 11:17 AM   #8
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Helicoils are.made for exactly this issue . not everyone has Taps up to next size that's the point of helicoils comes in a kit has everything you need to put it in when you're done.

Time sert is great if you need ultra strength ot if the hole is oblong or ruined . They are also expensive as heck!
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Old 09-24-2018, 11:34 AM   #9
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Buying a tap is cheaper than a helicoil.

https://www.amazon.com/Helicoil-5546.../dp/B0002KKPXK
https://www.amazon.com/Performance-T...eywords=m8+tap
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Old 09-24-2018, 11:36 AM   #10
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Thanks for the shopping tip, I'll never keep that in mind
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