640 temp sensor replacement:how do you get the new one 2 sea

[William Fissell]

HI,

glass broken on my 640 temp gauge

bought new one off this site

got a nice faceful of hot anbtifreeze when I removed the old one :)

I cannot seem to get the new one to seat completely in the block. I removed the #4 spark pug to get me better access to the hex head, but it still doesn't seem to want to go in more than 1 turn past finger tight,a nd the temp prob is still loose.

What did I forget?

thanks!

bill
 

[awhtx]

The only way you will ever get the nut tight enough to completely seat the sensing bulb is to use a flare nut wrench (tubing wrench, line wrench, whatever you call it) to tighten it. You will surely round off the corners of the nut if you use a open end wrench. I have had to remove the battery box in order to get a good grip on the nut.
I have contemplated taking a 5/8" deep impact socket and cutting a slot in the side of it for the capillary tube to pass through and trying to tighten the nut with that but I've never got around to making it.
 

[souNdguy]

wonder if an O2 sensor socket would fit?
 

[Greg1959]

I went to Harbor Freight and bought the assorted size "O" rings. Found one that fit and snugged it up. No leaks and no problems. Wrench tightened it up just fine.


It worked for me. Has anyone else tried this?
 

[William Fissell]

OK, so its not a slam dunk....
 

[john in la]

I think a O2 socket is 7/8 he needs 5/8.
Finding a injector socket in 5/8 would be a task also.

I would think a flare nut crows foot in 6 point would work.


 

[36 Coupe]

You forgot that a 640 has a pressure cap.You forgot to drain the coolant down a bit.You for got you never mess with a hot system.
 

[Blindhawg]

I did something similar, gasket or shim? Chinese gauge?
 

[671DKS]

I used a cutoff blade and cut a slot on a old 6 point socket. worked great, just have to leave the cable in the groove a little. good luck, Kent
 

[William Fissell]

Yes, I forgot it was pressurized. The AF was about 100 degrees - I had just started it cold and moved it. If it had been running any longer than that, I wouldna tried it
 

[souNdguy]

yep.. yer right.

I have a 7 pc sender changer kit and was thinking it had 1 other size in it.. .. and it does.. it's a bigger size for some oil senders. it has a couple pieces that essentially look like a crows foot socket adapeter versio of a flare wrench.. so you may be on to something there.