At 12:57 AM 10/21/2012, turbowesty wrote: >I'll explore that possibility. I was trying to find a way to get it >as close to the turbo as possible so it would be the temp from all 4 >cylinders and that didn't look straight forward.

Silly me...forgot you had an inline engine, was thinking WBX in which case you've got a couple feet of pipe to pick from.

>Is there a "usual" place to install?

This may be somewhat relevant: http://www.thesamba.com/vw/forum/viewtopic.php?p=4035126

Ok, going on no experience here:

1) Should be upstream of the turbocharger, since that will introduce load-dependent temperature drops as the turbo extracts energy from the gas stream.

2) To get an aggregate temp, has to be somewhat downstream of the manifold collection point. HOWEVER: Aircraft people may have one EGT probe per cylinder. Very commendable, and makes lots of sense if you're worried about falling out of the sky. Given that you're not going to do that, I submit that an aggregate reading has comparatively little advantage over a reading from any single cylinder. If the cylinders are in balance it will make no difference, and if they're not the aggregate reading will only deviate by a quarter of the real difference. So even though it's aesthetically inelegant, I'd be willing to monitor one cylinder and stick the probe wherever it's easiest to get to and best protected, as close to an exhaust port as convenient.

>And I've assumed stainless for the bung as it's easier to weld to >cast, correct?

Welding to cast iron is technically demanding. The *correct* way to involves heating the entire part to about 200C and the weld area to a dull red before welding, and then cooling slowly afterwards buried in ashes or other insulator. Especially for a used casting it's also desirable to remove volatiles contamination by heating the weld area to 475C for fifteen minutes and then wire-brushing. Preheating may be minimized and possibly avoided by using a high-nickel filler metal which is soft and allows deformation while cooling; and peening the weld while hot. Brazing-welding is a more forgiving way of attaching something to cast iron because of lower peak temps. See http://www.esabna.com/EUWeb/oxy_handbook/589oxy15_5.htm et. seq., http://www.brazing.com/techguide/procedures/cast_iron.asp

That said, I've watched a machinist join two pieces of cold cast iron by using stainless-steel electrode wire and tri-mix gas with a MIG welder, making what were essentially glorified tack welds in several places of the vee-grooved junction and continuing using the same short welds in rotation to fill in between them and eventually overweld the entire joint. I cannot remember whether he peened each new weld segment. The part (drill press column about 4-5" diameter, ~3/8" wall thickness, broken clean across) worked in service and did not come apart preferentially when the machine was later broken up with a sledge hammer. The man was technically highly skilled but with a habit of taking shortcuts in both his work and his life...

Anyway - I defer to people who've done it; but my own approach would be to put the probe in a section of pipe instead or if placing the sender on the manifold simply tap it for the proper NPT thread and use no bung.

Only If neither of those is possible would I want to braze or braze-weld it using "bronze" or perhaps nickel silver filler. I wouldn't use silver braze metal unless I could arrange a close-fitting (gap of a few thou) joint because it's very fluid when heated and does not build up a bead (while in a properly fitted joint it will readily flow in by capillary attraction). Bronze rod (really brass) is particularly easy to build up by working torch and filler rod.

Yours, David