Hello all, As some of you may know I have been building a ETW Sealion engine for a while and am now in the final assembly stage, hoping to see the engine running by the end of the year. The building of the engine involved the building of a radiator and I used the Jerry Howell radiator design as the inspiration to build my radiator with some modifications to Jerry's design. My modifications were as follows: - The radiator top and bottom part is build up and can be disassembled if needed. - It is designed to operate as a single tube / single pass heat exchanger resulting in a cooling pass length of 24 inches (2 feet) - It uses brass for the upper and lower radiator body and the side straps - It uses aluminum for the 6 finned tubes of 4 inch length each for improved heat transfer - It uses O-rings as the sealing element between the tube ends and the brass upper / lower radiator body. - The aluminum finned tubes are spray painted black - It incorporates temperature sensors in the radiator inlet and outlet because I am curious about the cooling efficiency of the radiator as build. - The temperature sensors were made using Honeywell Thermistor elements rated for up to 280 degree F paired with a Lascar EMT 1900 Temp display unit. During the assembly process and upon the radiator assembly, I tested the radiator for leaks because I was not happy with the soft soldering job I did of the upper radiator part. It looked suspicious as if the solder did not flow completely - I remembered that I did not tin the two mating surfaces thoroughly and completely and it left minute cracks in the joints. My suspicion was confirmed because upon pressurization with air and submerging in water it leaked. I had two ways to solve the leak problem: one was to use an anaerobic sealant to fill the cracks - the other was to make a new upper part. I decided to do both. The anaerobic I had on hand was a Loctite 609 retaining compound, reasonably thin enough to flow into the cracks. By internally air pressurizing the part after application of the Loctite I could see the Loctite oozing out of the cracks to the outside, indicating that the cracks had been flooded. After letting the Loctite cure for 24 hours, the part was again pressure tested under water with up to 60 PSIG air and showed no leaks. Good, but I still went ahead and made a new radiator part and the way I went about it is shown in the following pictures and description associated with each picture. 1 - To build the radiator, which has a thickness of 1/2 inch, I am using two 1/4 inch brass flats, which, when folded upon each other will make up the 1/2 inch thickness. Picture shows the two flats in my milling fixture ready for milling the cooling channel halves. 2- After milling the cooling channels at half depth 3 - The two halves being folded onto each other after milling, showing the coolant ports prior to soldering. 4 - The tinned two halves interior surfaces prior to soft soldering 5 - The two halves fixated and held loosely together. Ready for soft soldering 6 - Countersinking the cooling channels to size for the finned segments at dia. 3/8 inch 7 - Cooling fin segments with ends turned to dia. 3/8 with 1/16 O-ring groove 8 - Close up of finned tube turned end with O-ring grove. 9 - Finned tube end with O-ring installed 10 - Depiction of first installed cooling finned tube. Upon inserting the tube segment into the upper and lower radiator parts, grease is applied to both ends and the tube hole so as not to damage the O-ring. 11 - Assembled radiator with outlet elbow into expansion tank, radiator front shown 12 - Assembled radiator with fan shroud installed, radiator rear shown. 13 - Installed radiator attached to engine base plate with outlet temperature sensor installed at bottom of expansion tank. Inlet temperature sensor installed at left in picture. 14 - Close up of temp sensor in expansion tank and expansion tank 15 - Radiator rear view with cooling fan / expansion tank and inlet / outlet temperature sensors The post continues in Part 2 Thanks for watching. Peter J.