Coolant Leak from Capillary Tube/Bulb

[Bmartin]

I had my coolant gauge rebuilt and finally added coolant to the engine today.  It was leaking out of the hole that the capillary tube comes out of.  Is there any kind of gasket that is supposed to be between the bulb and the retaining nut?  I had silicone tape on the threads. Anything else that I need to do?

 

 

It is leaking along the capillary tube right where my index finger is. 

 

 

Strangely the back of the bulb is a flat face, but the nut is concave like it should accept something that is cone shaped.  Could the rebuilder have put it together incorrectly?

Edited July 9, 2016 by Bmartin

[TodFitch]

It could be that the tape you used is the problem.

 

There is a brass fitting that screws into the head. That has pipe threads on the outside which, when replaced might need some sealant (I prefer pipe dope over tape). You probably did not remove that fitting but you also may not have verified that the seat in the bottom of it is clean and smooth.

 

The bulb slides into that fitting and the ring around the bulb should seal against the seat within the fitting. Dirt, debris or damage to the bulb or seat can cause a leak.

 

The gland nut, where you have some leaking, presses the bulb against the seat to make the seal. The machine threads on the gland nut need no sealant and use of it there might keep the nut from properly pressing the bulb shoulder against the seat.

 

I'd verify that the seat the bulb presses against is clean and smooth. If not, clean, repair or replace. And I'd remove that tape from the gland nut, so it is free to do its job.

[Bmartin]

OK, that makes more sense.  I was not quite sure how it was supposed to seal.  I'll give that a shot. Thanks. 

[Dartgame]

You might want to use some quad 0 steel wool to polish the mating/sealing surfaces and then use some Teflon pipe dope as suggested above. Be generous with the pipe dope and wipe off excess after tightening. I would also guard against coolant being on the surfaces while reinstalling.

[Jerry Roberts]

Also when you inspect the gland nut note that there is a taper to the seat that matches the taper of the brass bulb . That tapered seat can rust away . It wouldn't hurt to use a little thick pipe joint compound on this area . 

[Bmartin]

I'd like to hear any opinions on the condition of this bulb.  The original bulb was used in the rebuild and it looks a bit rough.  Is this at the point where it need to be replaced?

 

Jerry - have you had luck sealing up the bulb by putting pipe dope on the bulb itself, right at the sealing area?

 

 

 

 

Edited July 8, 2016 by Bmartin

[Reg Evans]

A little clear silicon adhesive might be the best cause it's not water soluable when dry like pipe dope might be.

[Don Coatney]

Read everything in the resources section of this webpage. There is an article on how to replace the bulb and capillary tube. Look in the technical tips section.

[Jerry Roberts]

" Jerry - have you had luck sealing up the bulb by putting pipe dope on the bulb itself, right at the sealing area? "   YES . 

[Bmartin]

I found new replacement gland nuts at Oreilly.  They are in a packet and manufactured by iEquus Performance, part #9851.  $10.

 

Installed the one that fits, only one in the packet is correct.  We'll see if it holds.

 

 

[Dartgame]

Wow the repair works looks kind of rough. Hopefully you can get it to work. Note - if u use silicone sealant, allow 24 hrs for it cure before exposing it to coolant and pressure. Silicone cures with moisture, but if not cured before being put under stress it can and often will fail. There is a special grade of silicone for thermostat flanges - gray in color. I'd try that.

[Bmartin]

The new gland nut and some pipe dope has worked so far.