Which caulking to use for exhaust hoses?

[bwindrope]

Thanks for the input Halekai36, although I think my application needs are different than what you thought. In this case I do not need any caulking for pipe to pipe connections, and so the thread tape won't be useful. All my junctions are exhaust hose to male fitting of some sort: smooth metal or the high temp Centek fiberglass or plastic muffler with the exhaust hose attaching to it.

So as I explain in my blog, the original system is all 1 5/8 and the only reason I need the Centek reducing coupling is that Universal/Westerbeke no longer makes their exhaust risers with anything but a 2" exit. I would certainly know not to reduce exhaust flow from what is spec'd! In fact, the Universal exhaust flange requires a 1.25 NPT pipe to feed into the new exhaust riser, so even stepping up to 2" and then back down to 1.63 is still larger than what is at the manifold. Back in my days hot rodding cars, I learned all about freeing up the exhaust gases...

I'll look into that Real Tuff thread sealant, although I am still hot on the trail of the mysterious white sealant used on my hose connections that the boatyard used!

Thanks again.

[halekai36]

Originally Posted by bwindrope

Thanks for the input Halekai36, although I think my application needs are different than what you thought. In this case I do not need any caulking for pipe to pipe connections, and so the thread tape won't be useful. All my junctions are exhaust hose to male fitting of some sort: smooth metal or the high temp Centek fiberglass or plastic muffler with the exhaust hose attaching to it.

So as I explain in my blog, the original system is all 1 5/8 and the only reason I need the Centek reducing coupling is that Universal/Westerbeke no longer makes their exhaust risers with anything but a 2" exit. I would certainly know not to reduce exhaust flow from what is spec'd! In fact, the Universal exhaust flange requires a 1.25 NPT pipe to feed into the new exhaust riser, so even stepping up to 2" and then back down to 1.63 is still larger than what is at the manifold. Back in my days hot rodding cars, I learned all about freeing up the exhaust gases...

I'll look into that Real Tuff thread sealant, although I am still hot on the trail of the mysterious white sealant used on my hose connections that the boatyard used!

Thanks again.

Sorry I though you were talking about the threaded fittings...


If you are "hose clamping" rubber exhaust hose to fiberglass or metal use nothing. I have never seen anyone use a sealant on a rubber exhaust hose on either a tail piece or barb type fitting. I've replaced many exhaust hoses, some connected to fiberglass, some to metal and never once used anything but good quality "T-Bolt" hose clamps.. No leaks either!!

Every single water lift muffler on new Catalina's, since at least the mid 90's, is made of fiberglass. I have never heard reports of them leaking at the hose to fiberglass junction and they too use nothing but hose clamps.

[rocinante33]

Originally Posted by bwindrope

All my junctions are exhaust hose to male fitting of some sort: smooth metal or the high temp Centek fiberglass or plastic muffler with the exhaust hose attaching to it.

So as I explain in my blog, the original system is all 1 5/8 and the only reason I need the Centek reducing coupling is that Universal/Westerbeke no longer makes their exhaust risers with anything but a 2" exit. I would certainly know not to reduce exhaust flow from what is spec'd! In fact, the Universal exhaust flange requires a 1.25 NPT pipe to feed into the new exhaust riser, so even stepping up to 2" and then back down to 1.63 is still larger than what is at the manifold.

On my Universal (M25) with the same Westerbeke exhaust elbow that you describe, the 2" exhaust hose runs down to the Vetus muffler (with no sealant, only double hose clamps at both ends). At the inlet flange to the muffler, there is a short (~3") piece of 1 5/8" hose on the barbed muffler inlet. The large 2" hose is a perfect fit over the outside of the smaller diameter hose. The two clamps constrict it adequately as there has never been any hint of a leak, nor backpressure evidenced. AFAIK, it came from the factory with that configuration. It is simple, with no hose adapter needed, though maybe not perfect, as it is an abrupt constriction point in the flow of exhaust gases. It wouldn't be ideal for a hotrod, but it's OK for a small diesel.

[bwindrope]

Great input guys, I appreciate it very much.

From halekai36 I appreciate the reassurance that no caulking should be needed. I had thought that before because it is only a fairly low pressure environment and the rubber of the hose clamped firmly down on something should bite enough to prevent leakage. It's weird that all my junctions had caulking, because I always thought: "Why would you need that? They must know something I don't..." I'm comfortable not using caulking at all based on your recommendation because it jives with all my experience with hoses and clamps and such.

From rocinante33 I really get a kick out of that idea. Exactly the sort of left field "wouldn't have thought of it myself" solution that makes idea sharing on forums like this so valuable. In my case, I have the $20 reducing coupling already arriving tomorrow, and so I'll use it, both to not bother returning it and because it may be a smoother flow like you say. But, in a pinch it's good to know your solution.

BTW, what came in the Gulf 32 is a Universal 5432/M40. It's crazy really, because Universal says they stopped making the 5432 in like 1982, and yet my Gulf is a 1988 and the block is stamped as a 5432. I've read that builders would sometimes buy a load of engines and then use them as they did production, perhaps getting them for cheaper because they were discontinued. In any case, the parts on the 5432 are in almost every case identical to the M40, and so it hasn't mattered. She's been a great engine: easy to service, reliable and easy to find parts.

[sailaway21]

bwindrope,
After looking at your blog it appears to me there are a couple of questions here.

For those hose connections I'd use the black version of the permatex sealant which you can get in an economical sized tube at your auto parts store for about $7.95.

Halekai's suggestions on good pipe dope for the NPT threads is exactly what you want. The dope works better than the teflon in my opinion but most plumbers these days actually use both in conjunction. Note that the advantage to either, particularly the dope, is that they will allow you to get a good seal without resorting to 24" pipe wrenches (g) and, more importantly, they'll allow you to get that seal and still be able to take the assembly apart at a later date. That will be of particular interest to you if you're combining dissimilar metals such as aluminum and steel.

I'd also give heed to Halekai's question on reduction in discharge size. I realise that the part has changed for the same engine and the old one worked but it might be worth a couple of calls to find out why it has gone up to 2" discharge from 1-1/4". Backpressure from gases are much more easily ignored than those from liquids but the consequences are just as severe. generally speaking, any exhaust gas system should expand in size downstream.

I'm not sure about your choice of sked 80 black pipe over sked 40 galvinized either. Black pipe is negligibly corrosion resistent and the sked 80 rating is achieved by a smaller internal diameter while maintaining the same OD. the purpose of sked 80 is strength and not high flow per se. And you can buy three galv nipples in sked 40 for the price of one in sked 80 black.

Sounds like you're having fun. (g)

[bwindrope]

Hey sailaway21. Good stuff and thanks for the input. Hear you folks are having nasty storms out there. Been 10-15 degrees below normal in the NW for some time...

As for the decision about schedule 80, I based that primarily on the strength factor. My old nipple was black schedule 80. I actually went and bought a schedule 40 galvanized at first and connected the flange to the riser and felt it was too risky.

In a bouncy seaway I fear that the weight of the riser with water in it will have enough f=ma to possibly crack a slightly corroded schedule 40 nipple. We do some violent unavoidable bouncing sometimes around the Straits of Juan de Puca and I don't want to worry about that darn pipe. As you know, it's pretty thin stuff after the threads are cut into it.

My diesel has always run so smoothly and strongly, reaching rated RPM when it should, running at the proper operating temp, no smoke, good fuel economy, that I have never had reason to question the flow of exhaust gases. I do hear your point though, and it won't hurt to call Universal and see if they have changed the specs for the M40 for some reason.

Many brains better than one...

[JimsCAL]

The exhaust manifold on my Universal 5411 was made up using standard 1.25 inch NPT pipe fittings and nipples . A short length of exhaust hose connects the last nipple to the Vetus muffler. Some of the fittings are still fine after 25+ years. I carry a set of extra nipples, elbows, etc. just in case. A complete set for the entire manifold was about $25. Has to be a lot less than what Westerbeke charges for a manifold.