Tape or dope

[gpd955]

Don,

Would you recommend teflon tape or pipe dope for the hot section of the exhaust?

Jack Manning

[Administrator]

I've got a running debate going with the best tech guy within a hundred miles (ABYC, etc.) regarding whether yellow Teflon tape is for "gas" fittings or "gasoline" fittings. The few Google hits I've looked at are ambiguous on the subject. Anybody know for sure?

Bill

[timday5]

The William H Harvey manufacturing company makes the yellow gas line tape they sell at Home Depot. Here's what their web site states:

Yellow Gas Line PTFE Thread Seal Tape is an extra heavy, full density PTFE tape especially for gas lines. Recommended leakproof sealant for lines carrying natural gas, propane, butane; and water, oil and chemical installations. Use on pipe, conduit, valves, bolts, anything with a thread. Permits easy disassembly. Use on plastic, stainless steel, aluminum and all metals, ceramic, synthetic rubber, monel and carbon pipe. Pressure rating 10,000 PSI; .0035 mil thick, tolerates -450°F. to +500°F. Suitable for use on oxygen systems. Meets Federal Specification T-27730A. UL listed.

As far as using it on the hot section... I'm curious about that as well. A max rating of 500F seems low to me for the hot section (anyone know what the exhaust temp coming out of the manifold at max blast is?).

I was introduced to yellow gas line tape a few years ago when I could not get black iron pipe (for natural gas under my house) to hold pressure using pipe dope, regardless of pipe wrench torque. Finally one of the help (a licensed plumber) recommended the yellow tape. Worked the first time...

[gpd955]

Found this on Wikipedia

Thread seal tape is most commonly a white film (the natural color of PTFE) and is used in plumbing applications, but it is also available in various colors. While pigmented thread seal tape is not materially different from the natural white tape it is often used to correspond to color coded pipelines (yellow for natural gas, green for oxygen, etc.).

However, manufacturers vary the thickness of the tape, white being .003" thick and yellow being about .004" or more. I think that the manufacturer makes the tape more or less permeable by varying the thickness, not the chemical make-up of the Teflon. DuPont's website only has one chemical formula for Teflon.

I got this info from looking up the UL specifications for the different brands of Teflon (or PTFE as it is really called by other manufacturers) and the only differences I found on the different colors was the thickness.

Disclaimer- I am not a chemist. Failed it in high school and barely passed it in college!! Still trying to figure out why I took it again!!

[Don Moyer]

Jack,

I would definitely NOT recommend Teflon tape or pipe dope for the hot section. I replaced the hot section on each of our three sail boats over the past years and all I ever used was Never-Seize simply as a lubricant to be sure the tapered pipe threaded fittings were tight, and I never had any leakage. Having said that, I do hear of a heat resistant dope that some folks have been using, but I can't recall the brand or where they got it.

Don

[HerbertFriedman]

There is actually a mil spec for tape. It states that you must start the tape after the first thread (to prevent pieces from being cut loose and flowing downstream) and two overlapping turns, etc. Also Teflon good to about 400 degrees C which is why is is used as the "non stick" surface on cooking pans.

There is endless confusion as to the word "gas" for the yellow tape. Gas is gas, as in air not gasoline. And Teflon's superior resistance to corrosive liquids and gases makes it ideal as a sealant.

[timday5]

Just heard back from the manufacturer of the yellow tape sold at Home Depot. Here's the response:

Q: Can gas line tape be used on gasoline lines?

A: Yes. Our yellow gas tape is safe for this purpose.

The web site with their contact info is here: http://www.wmharvey.com/

So anyway, now you know what the manufacturer claims about using it on gasoline lines...

[gpd955]

Put everything back together on Friday with only a few cuts/bruises. Had an issue with water dripping from the nipple on the flange and I assumed that water wasn't supposed to be there, so I added a street elbow to raise the pipes up a little, now I have to modify the engine cover since it touches the pipes now! ('79 Catalina 30)

I have two other issues though...1) Had "smoke" coming from the pipes. Enough to set off the smoke alarms but not the CO2 alarm. It smelled strange but not like something burning. I am thinking that it may be the anti-seize compound I put on the threads. After running the engine for a while, the amt. of smoke decreased to the poitn of not setting the alarms off. Does that normally happen with Never-Seize (I used a different brand)?? and.....

2) When reattaching the new manifold to the engine, very little of the three studs were protruding through the manifold. I managed to secure the aft-most and center one but when I put the last one on, it turned a few times and came off. I can't get in on tight enough and have a minor exhaust leak that I can hear. Is there a fix for this without taking the manifold off again?? I would hate going through the process of taking those pipes off again!