thermostatic switch 12338599 variations?

[aguas]

Troubleshooted my 998a1 last week, found thermostatic switch was not closing after the truck reached cooler temps (verified with a continuity meter test on the switch after it opened, engine cooled, and i unplugged the leads).

ordered the replacement which is in all my TMs (A0-A2 parts manual, as well as m1113/4 parts manual) as 12338599. finally got a minute to replace the switch and the old switch is the same diameter, thread size, and length as the new. both are marked as 12338599, but the new version has 150% as many threads down its length.

crossover must have fewer threads because new switch tightens with three full threads still sticking out of the crossover. i applied some hi temp thread sealer and got the switch tight, so i assume im good to go. this means the body of the switch isnt inserted as deep as the old one by a good 5/16s. i hope that doesnt affect the ability of the switch to detect the temp correctly.

the amount sticking out reflects the amount of extra threads on the new unit, btw.

the crossover is the same part number in the later m1113 so i dont think that this is a switch meant for a newer version with more threads cut into it. its like they simply redesigned the part and kept the same part number.

anybody ever seen this? im waiting a few days per the sealant to test it out.

[Kurt Lesser]

Probably just supplied by a different vendor. If it's got the same NSN it should be OK.

[dilvoy]

Nothing to worry about. There are pipe threads and are tapered so the seal is made when they tighten up and not when a flat surface on the sender touches the manifold. Some sealant that is glycol proof is all that you need and don't tighten it super tight. Many do because the hex size is large, but it just needs to be put in to lets say 35 lb ft and not with a big ratchet with a long pipe put over the handle.

[aguas]

thanks for the replies. im pretty handy with houses and im a professional with 120v/240v AC but automotive mechanical stuff (and lets throw DC stuff) is still new to me.

ive learned how to navigate the TMs pretty well and that seems to have made all the difference, but i dont have the experience to tell me whats passable and whats not.

large future projects include paint and a 6.5t/4l80e swap so im going to have some questions!

[JuanPrado]

ditto on everything said.

Standard white teflon tape or liquid sealer you might use on home plumbing fixtures already is all you would need for automotive pipe threads.

[aguas]

thought id add an update. i cant stand it when i find threads that help but there never is resolution of the problem.

new switch fixed it right up. difference in position doesnt cause issues. new switch is more consistent and also comes on alot hotter than the other one did, but i read the new ranges are the correct ones. probably comes on (switch opens and fan clutches) at 215-220. my truck stays from 210-220 degrees in this hot part of the year during 55 mph highway driving.

again. thanks for the help.