The PT Boat Forum

Forum Category: PT Boats of WWII

Forum Name: PT Boats - General

Topic: Elco exhaust

Were the straight through exhaust pipes on an Elco 80 water cooled? I have heard many folks want to plumb their model cooling water through the transom pipes to 'make it more real' but I didn't know for sure if they did that on the real boats.
Also, what was the differrence in sound between the mufflers and straight pipes? As I get ready to build my giant 60" Elco I started thinking about a sound system. There is a very neat commercial unit that even has startup sounds. But would I need to make a 'muffler' for the speaker system? And how often did the boats switch between the straight pipes and the mufflers?
Sorry for these simple questions, but this kind of insider info is never discussed in the books.



Posted By: boater dave | Posted on: Sep 20, 2011 - 7:46am
Total Posts: 18 | Joined: Jan 6, 2011 - 4:40pm


The cooling system for the engines was both salt water and fresh water. The salt water system , which cooled the fresh water, lubricating oil, exhaust manifold, and exhaust pipes. The fresh water system cooled the engine cylinders, and warmed up the cold mixture of air and gasoline flowing from the carburetor.

There was an anti freeze solution added to the fresh water if operation was below freezing. Mufflers were in the open position when the engines were started, and were open all the time above 1200 rmp. These Mufflers were closed when the boat did not want to be detected and the exhaust was driven below the surface of the water.

Posted By: Frank J Andruss Sr | Posted on: Sep 21, 2011 - 4:09am
Total Posts: 3266 | Joined: Oct 9, 2006 - 6:09am


In my previous post I meant to write RPM. By the way you can purchase Packard Engine Sounds for your boat ( if Radio Controlled) to simulate all types of manuvers for the boat. By the way when they opened the Mufflers, for high speed, the sound was incredible as you could imagine. When normal patrol was going on, the boats usually had the Mufflers closed to avoid detection.

Posted By: Frank J Andruss Sr | Posted on: Sep 21, 2011 - 4:28am
Total Posts: 3266 | Joined: Oct 9, 2006 - 6:09am

Thanks for the reply, but I am still confused as to whether they pumped water through the pipes or not. Both salt water and fresh water systems? The fresh water system would be recirculating, as I could not see carrying all that fresh water only to dump it over the side. The heat exchanger in that system uses seawater for cooling. They could pump seawater over the heat exchanger, then run it into the pipes and out the back. If this is the case then there would be water mixed with exhaust coming out of the pipes.
Thanks again for all the info. This forum is very helpful.



Posted By: boater dave | Posted on: Sep 21, 2011 - 12:42pm
Total Posts: 18 | Joined: Jan 6, 2011 - 4:40pm

Check here Dave, the catalog has some good diagrams of the various systems to go with Franks excellent description:


On early (?) boats the salt water outlet pipes can be seen next to the exhaust pipe outlets above the mufflers at the stern. They dumped into the inboard side of the exhaust outlet, around the outlet jacket, then into water jackets on the outboard side of the mufflers then into the mufflers. Here's a shot of PT 109's mufflers:


Posted By: Jeff D | Posted on: Sep 21, 2011 - 3:13pm
Total Posts: 2023 | Joined: Dec 21, 2006 - 1:30am

I may be reaching, but most marine cooling systems, including the elco's I suspect, were two stage as previously stated. The engine used a closed system of fresh water, with anti-freeze as needed, and it passed thru a heat exchangerthat transferred the heat to the salt water side of the exchanger. The salt water then exited the boat with some ofr all of it passing thru the exhaust system to coo the exhaust. Without this cooling by the salt water the exhaust pipes would become a significant fire hazard.
This arrangement is used to this day on most boatsthat have exhaust systems that run thru to boat hull.
Hope this helps.

Posted By: Jonathan Eno | Posted on: Sep 21, 2011 - 6:29pm
Total Posts: | Joined: Unregistered

Hi shipmates
I am pretty sure we discussed this subject before on this discussion board, maybe about a year ago. I think Dr Al Ross answered the question definitively. I am comparing it to the exhaust pipes on our 78 ft Higgins PT658.
On the 3 Packard engines we have, the engine exhaust manifolds are cooled by the sea water. The sea water then enters the exhaust stack cooling water jackets. The sea water does not actually mix into the exhaust inside the stack. The exhaust stacks, and I believe the Elco boats used a similar arrangement, are literally a "pipe-within-a-pipe". The exhaust gases stay within the inner pipe, and there is a spirally wound flowpath for seawater between the inner pipe and the outer rubber hose. The spiral wound flowpath prevents any hotspots from forming. The outer rubber hose and inner exhaust pipe connect to the "through hull" fitting which connected to the muffler, where the water is mixed into the fitting to keep it from getting too hot and catching the wooden hull in contact with the fitting on fire. We actually caught some of our engine room on fire before we recreated what they originally had in 1945. The fact that the water is not mixed into the exhaust in the inner pipe is important because when the engine is secured, there is the possibility that the water in the pipe will contract and suck seawater back into the engine exhaust valves and cause a lot of problems. It is also very important when starting the engines to ensure seawater is actually flowing inside the stacks soon after starting the engines. It is possible to get a vacuum lock of sorts and if it forms and prevents water flow through the stack you could easily cause them to melt from the intense heat. These engines literally blow flames out of their exhaust at high rpms when burning 100 octane gas, and the temps can easily exceed 850 degrees F. Not good on a wooden PT Boat. I hope this is helpful info. Jerry PT658 Portland OR

Jerry Gilmartin

Posted By: Jerry Gilmartin | Posted on: Sep 21, 2011 - 9:38pm
Total Posts: 1275 | Joined: Oct 8, 2006 - 11:16pm

I went digging through the Elco drawings, it looks like the salt water through-hull jumpers as seen in the above photos were only used on PT's 103-145 and 147-162. The ones on PT's 103-138 were slightly different. The other boats used a water jacketed design to go through the hull as Jerry described. Interior pipes were copper tube within copper tube with a copper coil spacer, again as Jerry described.

Posted By: Jeff D | Posted on: Sep 22, 2011 - 3:27am
Total Posts: 2023 | Joined: Dec 21, 2006 - 1:30am

As always, thanks for the information. This is exactly what I was looking for. Unfortunately, this means that plumbing my ESC/motor cooling water into the model exhaust outlets, although neat, is not accurate. I will incorporate my water cooling into some other through hull fitting. I will also dig back into the forum and review the other posts on the exhaust.
I still have not settled on a specific boat for my big (60") project. I am looking for a boat with two roll-off torpedoes to keep it simple, as I would love to make the torpedos function under electric power. In 1:16 scale those fish should be about 1-1/2 by 12 inches. Big scale gun kits are expensive, so if this boat didn't have a 40mm on the back even better. Although, I did find a very nice unit for about $100.



Posted By: boater dave | Posted on: Sep 22, 2011 - 10:23am
Total Posts: 18 | Joined: Jan 6, 2011 - 4:40pm