18 replies to this topic

[Rubbershorts]

Hi everyone. My temperature sensor on the head leaks after a run. It doesn't leak whilst hot, but after it has cooled down. I used ptf tape when I first fit it and this was fine. I removed it for head work and have been unable to seal it since. I've tried re-wrapping it twice. I've just read the tape may not be the correct way to do it as this can affect the grounding. Any ideas guys? Thanks, Daz.

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[Chris1275gt]

PTFE tape would never affect the grounding it’s used on gas pipe threads and the pipe is used as an earth for a house. You’ve probably not wound enough on the thread. Are you using the thin PTFE or the one wrap thicker stuff?

[68+86auto]

Try it without the tape. It is supposed to seal by itself, it doesn't seal on the thread. IF that doesn't work, I'd use a liquid type sealant.

[Rubbershorts]

PTFE tape would never affect the grounding it’s used on gas pipe threads and the pipe is used as an earth for a house. You’ve probably not wound enough on the thread. Are you using the thin PTFE or the one wrap thicker stuff?

The thin stuff Chris.

[Rubbershorts]

Try it without the tape. It is supposed to seal by itself, it doesn't seal on the thread. IF that doesn't work, I'd use a liquid type sealant.

Hi Auto. What type exactly?

[68+86auto]

 

Try it without the tape. It is supposed to seal by itself, it doesn't seal on the thread. IF that doesn't work, I'd use a liquid type sealant.

Hi Auto. What type exactly?

 

 

I haven't had to seal one of these with sealant before but if I did, I would use Loctite 577 because that's what I've got on the shelf.

[mpialan]

Try liquid PTFE

[weef]

PTFE tape is used extensively to assist the sealing of threaded joints, usually giving good results.

To give it it's best chance of success there are a few guidelines to follow. 

The threads in the cylinder should be as clean as possible so run a tap down the thread removing any traces of corrosion and old sealant.

Similarly wire brush the threads of the sensor to clean it.

Let the threads dry out completely before assembly, usually two or three turns of tape are enough overlapping each turn, you should always see the origional thread form.

Start at the bottom of the thread leaving the bottom thread of the sensor without tape and wrap the tape round the sensor in the direction that it screws in.

Screw the sensor into the cylinder head, no need to overtighten.

[mab01uk]

'Loctite 55' sealing cord is a bit like dental floss and works really well, you can even re-adjust position or back off the fitting and it does not leak. Especially useful in plumbing when a tapered thread fitting has to end up facing in a particular direction or position.

 

 

 

[Rubbershorts]

Thanks everyone. Just ordered a tube of this. See how I get on.

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[Mr Piggy]

The temp sender should seat on a shoulder at the end of the threaded hole. If the hole has been drilled and tapped all the way though then you will have to seal the thread but be careful with liquid sealers as they can work like loctite and it's not to difficult to shear the head off.

[Ethel]

As Mr P says it shouldn't seal on the thread it has a tapered shoulder, similar to an inlet/exhaust valve.  Some of them even have a separate threaded sleeve, that works like a brake pipe union. Take it out  & give it a good clean up, if it looks dubious a smear of rtv, or similar, on the conical seat could help

[Rubbershorts]

Thanks fellas. I'm struggling to visualise what Mr Piggy is describing. The sensor is tapered on the end though, I remember that bit. I've had the sensor out of the head and replaced it a few times for various reasons and it has always sealed. That was prior to sending the head off for work though. Since, it won't seal. Was there perhaps a build up of crud in the head that helped it seal, but that has now been flushed out during the work?  Could the sensor I have now be worn on the pointy bit with removing and replacing, so it no longer seals where it should.

 

I do have a new sensor I bought as a back up, but when I removed the one that's in to reseal it all looked okay so I didn't think I needed it. 

 

The Permatex reviews reckon this stuff doesn't go hard so wouldn't lock the sensor into the thread hopefully. It does say "Reposition after application" on the packet too. Do we think this might be okay?

 

Daz. 

[Ethel]

If you noticed the shoulder, there's a female equivalent cut in the head. The thread bushed them to together. I can't imagine whoever did the head would touch it, but if it was dipped to clean it, or masked for painting it could have left something to effect the  seal. It's 5/8unf, not a pipe thread, so getting it to seal on the seat rather than the thread should be the better option. If necessary, you could pop in an O ring.

[Rubbershorts]

Cheers Ethel. Where exactly would the o ring go? One the shoulder end and pressed into female recess?