Build a junkyard heat exchanger!

How do you take advantage of the waste heat from your generator?

Disclaimer: Modifying a pressure vessel of any type can be dangerous and could result in the loss of life, always fit proper pressure relief. If you cut or weld a tank, have it pressure tested and certified for your use. What you read here is for educational purposes only. 

I've been experimenting with the use of cooling tanks versus radiators for stationary use.  My biggest concern with these tanks is the lack of rust protection and antifreeze in the engine block.  Running an open system with hard water can be a real problem, If you're attempting to use the generator on a regular basis; proper coolant in the engine block is a nice thing to have.

Making an inexpensive heat exchanger, allows for the use of a proper coolant AND you can harness the energy to heat domestic water as well. There is a reasonably safe glycol based antifreeze that won't Poison you if your exchanger develops a  leak (so they say).  I guess a cautious person could add a generous amount of red dye to the coolant as an indicator as well.

There are basic rules for thermal siphon systems, the most basic, is have everything move upwards from the engine, any low spots in your coil or hoses could cause your setup to malfunction and damage your engine.  A basic understanding of what is happening in a thermal siphon system will help a bunch. As water gets warmer, the molecules expand and it become less dense. This causes it to rise to the top of the system. Gravity acts on the heavier and cooler water forcing it to the lowest point in the system. If you were to accidentally create a lower point in your hoses between the engine and the tank, you'd have cooler water trying to migrate from both sides interrupting the flow. Picture a nice straight angle upwards from the engine to the tank on both runs. Maintain this, and keep the size of the hoses adequate and the thermal system will work.

If you plan to make use of such a system, make sure you place a temp gauge of some type in the block prior to the thermostat (if used) where you can see the real coolant temp. Thermostats are a concern for some of the Older than dirt folks that have been around cooling tanks, they explain that a sticking thermostat can cause overheating and may not be worth the risk of a failure. With this in mind, a person has to weigh the benefits versus the risks of a particular cooling system design. Personally, I think thermostats have proved themselves in Autos, and I make use of them.

I start my DIY project with a FREE water heater!  I exploit the two standard one inch NPT (National Pipe Thread) holes in the side that were used to hold the heating elements. These become the lower and upper ends of the wound coil placed inside the tank. Most water heaters have been lined with a material to prevent the tank from rusting, it is important to try and preserve this barrier as much as possible.

the first thing I did was 'chuck up' a thin kerf cut off composite blade in my air tool. I cut a fraction below the weld on top of the tank. Watch your depth, you want to cut through one layer only, go all the way around and then find yourself an old screw driver or chisel point to use as a wedge, place it in the cut, and tap it in lightly all the way around to lift the top free.

If you do things right, you'll be able to lift off the tank top.   Wipe it dry and take 200 grit (or so) sand paper and clean up the area you cut loose. Notice that the wedge you used broke the glass lining in a neat little crack.

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If you look closely, you can see that there is a slip joint that fits inside of the one inch copper tubing. I found a copper piece that screwed into the pipe threads. I used a rat tail file to open up the hole just enough for this slip piece to pass through and then sweat soldered all the joints. Notice that everything moves upwards, even the last piece at the top moves slightly upwards as it exits out the side. Winding this coil; and soldering it in place will take a little patience, just keep pushing and prodding slowly till you have it. If you are going to be banging around your exchanger, consider making some support for the coil on the inside, I bonded the copper coil in several spots to the side of the tank with epoxy, if you try this, use the 200 grit sandpaper to scratch up the area you bond to.


Once you solder everything good, place the tank up right and fill it with water to test your work. If you like, use a rag and air hose to elevate the pressure in the coil and look for bubbles inside.

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I screwed in these copper adapters TIGHT into the threads before soldering.

Once this work is complete, you can have the top refitted, and welded. The use of wire feed keeps the heat localized and does less damage to the glass lining.

IT is very important that you fit the domestic water side with a proper pressure relief valve! 


If you wish to use it for a cooling tank only, leave the top off,   fill it with water, and start your engine.

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I removed the neck off a junk radiator and grafted it onto a one inch tee on the top end of the coil. this becomes the fill point and high point in the system. Use the same caution you use around an automobile when checking coolant, steam burns can be serious! Use a proper radiator pressure relief cap! 

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Here you can see the lower end of the coil, below that is the stock drain valve which I've fitted with an adapter to receive the male coupling of the hose for charging the tank.


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Above is a picture of the shake down test site.


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Here you can see the windshield washer bottle and modified mounting off a 74 Chev PU being used as an expansion tank for the engine side cooling loop.

6/2003 Note, there are external heat exchangers that can be mounted to the side of the cooling tank externally. I highly recommend this approach. If you go to all the work of placing a coil inside the tank, and you end up with a leak, it would be a bunch of work to fix it. I will post such a set up time permitting.





George B.