Coolant Leak / Temp Sensor in the block

[Jim_Gruber]

Discovered where coolant has been going on Bugsy my '68 Sprite when I noticed that temp sensor appears to be leaking around the inside where the sensor fits inside the nut. This is an in the block sensor on a 1098. Who's got some good tips other than being careful not to damage the tube and letting the ether out in terms of tightening this up and preventing a leak.

Teflon Tape

Plumber's Putty

How do I go about cleaning up and stopping the leak.

Got a Dremel tool and mini wire brush as one of the tool I figure I'll be using to clean things up. Sandpaper to clean contact surfaces on the sensor.

Amazing the times you'll find once you pull the hood, valence, and fenders off to start installing a Bugeye Bonnet. Now that Bugsy is naked up front I've just added another dozen things to fix to my list before June.

 

[Hap Waldrop]

Teflon tape or paste ought to the job, I used both with positive results. Yes be careful with the tube, don't bend it. I'm not sure about your quaestion about cleaning the sensors, I assuming you're asking about the probe that goes inside the cylinder head, no real reason to clean it, just wipe it off, I wouldn't get a dremmel tool near any of the tube or sensor. As for the treads, a little brake clean a shop rag/towel and a god wipe off.

 

[Jim_Gruber]

Hap,

This is leaking around the inside of the nut where the tube goes through the center of the nut. As I recall when I installed that sensor, there is simply a compression fitting in there that the nut squeezes down. I cleaned off when I installed originaly but that was 6+ years ago. I'll need to get into it and see if I can remove without breaking the tube. Looks like I've had a leak here but not enough to see it or smell it. Coolant has been disappearing recently and I'm hoping this is where it has been going. Oil is the right color, no white smoke, and car has never, ever overheated.

 

[DrEntropy]

The coolant can propagate past the "bulb" taper and leak thru the threaded collar as you describe, Jim. A good cleaning of the tapered seat and bulb should result in a good seal. You could consider a VERY light film of hylomar on the bulb taper, too.

 

[Jim_Gruber]

Hap,

Probably hylomar on the taper after a cleanup would likely be all I need. Trying to get teflon tape in there might be problematical. I'll give that a try.

 

[Bugeye58]

The seal isn't on the threads it's on the bulp taper. Make sure you carefully clean the bulb taper. I use a very fine Scotch Brite pad. Clean up the seat in the head using the same pad and a dowel of some sort.
Don't attempt to overtighten it to stop a leak. If it's caused by a piece of schmutz on the seat or the taper, you'll only make it worse.
I've fixed bunged up seats by making a threaded insert that seals against the head with a washer, and has a new seat on the inside. You may even be able to buy them.
Jeff

 

[Jim_Gruber]

OMG schmutz. Yes I need to pull apart and see if I can do so without wrecking the capillary tube. I've already wrecked one of those a few years ago. If I hadn't pulled hood and fenders I never would have spotted this leak.

 

[cdsmith]

I had the same leaking problem when I moved the sensor to the head from the radiator. I used PERMATEX Black Silicone with good success... No leaks.
cd

 

[Jim_Gruber]

Thanks everyone. I'll have a chance to see if I can resolve later this evening. I'll give a full report.

 

[Hap Waldrop]

I've been putting teflon tape on them for 20 years, considering with the race cars, this is something you would do several times a season, it's worked for me.

 

[DrEntropy]

OH! And use a LITTLE anti-seize on the threads and the surface where the bulb & the collar contact. That'll help keep you from tweaking the capillary tube the NEXT time ya gotta remove it. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif