exhaust plug leaking |
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bthorsen
Newbie Joined: May-16-2019 Location: MI Status: Offline Points: 15 |
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Posted: May-16-2019 at 9:31pm |
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I have a Ford 351 PCM engine in my ski boat. There is a drip from the plug on the backside (the coolant hose is on the frontside)... I'm thinking I should be able to seal it with some high temp RTV of some sort, but figured I'd see if there is a specific product anyone recommends from having this issue themselves. ....go!
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Ben,
Is the leak at a threaded drain plug? If so, I'd remove it, chase the threads lightly with a pipe tap and then install a new plug with some thread tape of thread compound. No on the RTV. |
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gt40KS
Gold Member Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 946 |
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I'd say it depends on what has caused the leak. If your manifold has rusted bad enough it is leaking through the threads of the plug you may have bigger problems than just plugging a leak. But first, what is the plug made from - Steel, brass or plastic? if it is steel you may have a heck of a time getting it out of there anyway. If it's brass I'd expect internal rust issues that you may want to address first. Then again, it may be as simple as the plug never got tightened enough when drained last for winterization. But as a general rule, if the plug and manifold are both in good shape all that I've ever used is a few wraps with teflon tape. Since the plug is tapered, with the teflon you should be able to tighten it enough to stop the leak. If not, clean the threads out with the correct size tap, wash out the area to eliminate debris and install a NEW brass plug with teflon.
Still leaking? Might have an issue other than the plug ... such as a crack in your manifold that just makes it appear to be leaking from the plug. |
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JCCI
1995 Ski Nautique GT40 |
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bthorsen
Newbie Joined: May-16-2019 Location: MI Status: Offline Points: 15 |
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I've pulled the plug and it's in good shape. I tried some teflon tape on it (in a red container), which helped for a minute but then it started leaking again. This, along with pictures during that trial, have me thinking that it is the plug, not the manifold itself. I'm certainly going to try "everything" before I go to replacing the manifolds.
Why do you say no on the RTV? They make high temp stuff for exhaust leaks and head gaskets on a car... and I'm pretty sure the temp on my boat exhaust are lower than a car. |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Ben, RTV is great on flat surfaces but I've found to be difficult to get completely into threads such as pipe threads. What's the problem with Teflon tape? The normal tape you find is rated for 260 F. and you are no where near that on a water cooled manifold. Even pipe thread compound will handle the temp. There are time when I actually use both tape and compound. I prefer Blue Monster compound. RectorSeal Tru-Blu is a close second. Did you lightly chase the threads with a tap yet? Have you taken a real close look at the manifold around the threaded hole to make sure it's not cracked? |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11061 |
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You seem to be contradicting yourself here. You say the plug is in good shape but them you say you think the plug seems to be the problem. Why not try a new plug? It's a 3/4-14 pipe plug on PCM manifolds Use a brass one with external flats for a wrench and a little can of plumber's dope, goop it up and screw it in. and see what happens. You don't exactly need to use gorilla strength when tightening or you can crack the manifold around the threads like Pete and gt40KS mentioned. |
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GottaSki
Grand Poobah Joined: April-21-2005 Location: NE CT Status: Offline Points: 3359 |
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No room for a tap with the pcm riser in place I suspect
However you can make a makeshift tap from an iron plug by cutting some grooves in it with a cutting wheel |
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"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."
River Rat to Mole |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11061 |
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You're right about that, unless you have a real stubby shorty. |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Tom, Great idea. I've used it several times in a pinch and it does work. The alternate for tight spaces: |
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11061 |
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Nice generic picture of an O2 sensor thread chaser Pete Maybe a part number for what he needs would be useful |
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bthorsen
Newbie Joined: May-16-2019 Location: MI Status: Offline Points: 15 |
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I installed a new 3/4 plug this weekend and that appears to have resolved the issue. After looking at the other side (I was going to swap the plugs to see if the problem moved to the other side) I realized how much material had degraded over the nearly 25 year (1996 Tige). I installed a galvanized 3/4 plug, not "black steel" from HD.
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gt40KS
Gold Member Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 946 |
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Galvanized, better. Brass would have been the best. But glad you seem to have gotten the issue resolved.
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JCCI
1995 Ski Nautique GT40 |
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MrMcD
Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3735 |
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Pipe threads seal on the points of the threads. They are tapered so tightening can fix a leak but sometimes tightening a taper can crack the housing.
A new plug gave you new threads with sharp points on those threads which will help seal your leak. Old used plugs have the points flattened out a little and take more torque to make them seal. In a strong base that works fine, in a cast steel manifold you made a great choice to install a new plug. Brass would be better as already mentioned. How many old galvanized pipes have you seen rotted out in your lifetime. I have seen plenty. Brass, not so much, it holds up. |
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gt40KS
Gold Member Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 946 |
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Galvanizing is a very hard coating as well. If you are having sealing problems anyway the hard coating won't help much if the threads are worn or rough.
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JCCI
1995 Ski Nautique GT40 |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Joe, I hate to tell you but pipe and pipe fittings are galvanized and THEN the threads are cut so, there's no zinc on the threads. Also, you may what to look up the Rockwell hardness of zinc. |
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