THERMO CONTROLLER SWITCH

[artyfartymarty]

I got myself a thermo fan and it came with a temp sensor controller, threaded brass unit that screws into the manifold type...it is 3/8 thread and came with a bushing/ adapter to to adapt it to 1/2 thread. as per link
http://www.ebay.com.au/itm/THERMO-FAN-C ... 3a7ed9bff5

i wanted to install it into the thermostat lower housing as i had a dead temp sensor there just plugging the hole and doing little else....having spent 3 days trying to crack the old, dead one out , i finally succeeded by soaking it overnight in a hydrochloric acid solution to clear the rust seized thread and then overnight again in WD40, (heat did not help!) i clamped the bugger to the workbench and with all my weight on a 1m long bar finally cracked the frozen thread...all good! or so i thought. when it came time to install the new thermo switch i found that it leaked, so i put on some thread tape and proceeded to reinstall and make it nice and tight, but this time it kept going in until the nut hit the housing...bigger leak! damn! upon close inspection i found that the thermostat housing base had 2 split lines at the point where the hermo switch screws in, cracked the casting! so a new one has been ordered...anyway, to the point, did i split it by using the adapter with incorrect hread size (its 1/2 NPT) or overtightening? or did i crack it trying to get the old one out?. i have noticed that the whole of the first half of the male thread of the adapter has the thread stripped off (did i possibly cross thread?) but the top half is OK so makes me assume it wasn't crossed but incorrect size???

so that i dont crack the new one, can someone please advise if you think the adaptor i'm using may be the culprit or if it would be ok to get a new brass adapter (stripped thread halfway in on the current one) or if i should turf the switch and get a tridon unit made for the hole (without any adaptors). should i be using thread seal of any kind or is this designed for a tapering thread? anyone know what would be the correct part number for one made for Holden red (normally open type closed when hot).

[Mick]

i wouldn't say you cracked it with the adapter (being brass and much softer) probly while trying to get the old one out, i would think with the correct adapter you should have no problems with it

[Harv]

Agree with Mick - unlikely to crack the thread in a cast fitting by screwing in a brass adapter. Probably did it with the bar trying to ge the old one out.

The stripped fitting sounds like you are trying to screw a BSP thread into an NPT hole (or vice versa) - the threads are very similar, and will screw into each other... but will not be gas tight.

Cheers,
Harv.

[artyfartymarty]

After I realised it had cracked, at first I thought it may have been because its one of those tapering threads that gets bigger the further it goes in but like you guys say, I can't imagine a brass fitting cracking a cast part like the thermostat base while only using a socket wrench.

Harv, Is there a way of telling whether a thread is NPT or BSP?

As the adapter is longer than required, could I simply remove the now useless non threaded leading part and install it with thread tape? Or should I start again with new adapter?

Marty,

[Harv]

Marty,

If the thread is longer than you need, you can cutt off and go again, though it is likely to strip out again. A good idea to get the right size fitting, or have your local hose fitter (eg Pirtek) to run the correct die down the incorrect part to at least "smooth the way" for the wrong threadform.

Best way to identify BSP vs NPT is to break out the verniers - check the dimensions below, or look for thread taper (thinner at one end than the other).



Cheers,
Harv

[artyfartymarty]

Ill cut off the dud part of the adapter and have another go (gently with caution) for a short term fix but will chase down the correct size temp switch from local parts supply. Ill check the threads tonight on the old one and the new adapter... If you check my link, the seller advertised as universal 1/2 NPT / BSP , but looking at your post Harv, I can now see it can't be both NPT and BSP.

As they say in a nearby land..."same, same... But different".

[artyfartymarty]

Sorted the issues with threads with new 1/2 NPT adaptor and new thermostat housing....sorted
The switch was a bit of an issue though, thermo fan came with a switch that is 85 on 75 off and that was never going to work properly with my thermostat opening at 82. So got a tridon switch which was supposed to be 92 on 85 off but turns out its was the wrong one and was turning on too hot. Got a replacement Tridon 92 on 85 off, works a treat, comes on in traffic turns off when moving....the alloy 3 core radiator seems to be doing its job well. Now to just get around to installing that temp gauge!