200Tdi thermostat housing repair

xathor

New member
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.
 

Roverman2010

Well-known member
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.
 

Attachments

  • 20150808_133201.jpg
    20150808_133201.jpg
    774.9 KB · Views: 950

1of40

Well-known member
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!
 

xathor

New member
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.
 

DefendersNW

Well-known member
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.
 

xathor

New member
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.
 

Napalm00

Technical Excellence Contributor
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!
 

Red90

Well-known member
I think you guys are confused as to why helicoils exist.

You need to understand that there are certain people that believe that overkill is the only answer to a problem. They can't just be happy that something has been fixed and will now work forever because the most expensive way to do it was not used. They install 3000 psi plumbing on 5 psi systems. They use $50 wiring connectors for everything. These people slowly go insane working on Land Rover as everything is barely fit for purpose from the factory and they can never be happy until everything is changed. The way you fixed this item was completely fine and will be much stronger than the original, when the original was already fit for the purpose.

Personally, nothing make me happier than going to the junkyard and pulling some next to free stuff off a random vehicle and chucking in on the 90, if only to make these guys cringe.
 

xathor

New member
I buy Irwin branded taps at Lowes all the time, super cheap.

Helicoil kits come with a tap... Just buy the tap, skip the helicoil!
 
Top