You of course want to maintain opposing flows thru the heatex to maintain an even delta across the plates for a steady transfer.

Oh no, their may be a problem with my system.  Although I don't know if its fatal.  After rethinking this, with thermosiphoning , I don't think I can satisfy the above requirement. In my sketch, hot water from the primary loop (engine), enters the heatx at the top port (circuit 1), and cool fluid from the secondary loop (tank), enters the heatx from the bottom port (circuit 2). This would seem to allow a large temp gradient across heatx, lowering effficiency. To do it optimally, I think I would need to raise the tank considerable. Tough with 7 1/2 ft ceilings.

Same reason ancient wooden ships were sometimes clad in copper.

Gotta love this forum, ancient history to boot.

Yes, I was talking about the ones between the deck and cylinder. Thanks for the reply.

Ron - Very good point. That settles that.

Doug -

Ditto the other responses. The most reasonable way, is a battery/ inverter system. I'm not an expect, but have recently converted my house over to handle all 120v loads, and lighter 220volt loads.

The inverters these days, are quite flexible.  For instance, when mine detects an AC input, it automatically synchs to it then activates transfer relays to feed loads directly. If the battery bank need charging, it will proportion your available capacity to the charger & load. If your load increases to the point where the total of battery + load is greater then your genset, it will feather down the charge current to prevent overloading the genset.  If the load itself become greater then the genset, it will use the battery bank to aid the genset.  Mine can be programmed to autostart and auto turn off, along with alot of other features (not much good now, but maybe in the future), based on battery bank state or time. In short, as long as I'm their to start and stop the listeroid, everyone else thinks their hooked up to a utility "almost". The battery bank is the key. For my house, a 48V, 800 ah works. If I could have afforted it, I would have gone bigger. Almost, no matter what you get to handle your overall requirements, their will be system limits on peak load, unless you spend alot of money and really overkill it. The batteries will be a major cost. Do a good job in your load demand calcs, plan for the future.

You of course want to maintain opposing flows thru the heatex to maintain an even delta across the plates for a steady transfer.

Ron - This is the part I've been wrestling with. Each loop will counter-flow with respect to the other, and with "enough" flow in each loop, their certainly is sufficient plate area to move the required btu's into the insulated tank. I guess what was causing me to question the whole thing is that both loops rely only on thermo-siphoning. I guess, as long as the flow is not serverly restricted by port openings, hose dia, or "flow resistance" in the heatex, and I keep air out of the system, I should be OK??

Where did you get your monster stainless heatex?

This is the amazing part. Originally, I was going to go with copper coils in the tank, but when I started considering the practical details of doing this, my plan change to using a very big shell and tube, or two smaller units. At this point, I didn't even consider using a plate heatex because of cost, very low volume, "flow resistance", etc... Just before I was about to get my big shell and tube, I happen to notice this thing on ebay, 8 minutes before the auction close, brand new, and going for less then one tenth of its retail price. I had to get it.

After three months of daily runs, I  pulled the heads last night to check for carbon buildup. Since I'm burning wvo, I did expect their would be some, and their was a little more then I expected. I attribute this to having insufficient temps during earlier runs (150- 170 deg. F), but with recent changes, I quicky get temp up to 220 deg F and maintain at injector. Hopefully their will be less  carbon in the future. Today, I'll pull cylinders and pistons and have a complete look at everything else. One observation was the oil, although still black, looked very clean. I guess a bypass filter is a good thing.

Now for the title subject. The major reason why I had to stop running, is the cooling temps. Coolant started to boil in the heads during the last few runs, at which time I had to decrease load significantly. I alwayed believed the "radiator" setup I was using was undersized, and would have to be replace eventually. With the increase in ambient temps, this became obvious. Now, I'd like to do what I wanted to do in the first place, heat exchange to a large, insulated tank of water, then use the collected heat. I know from previous discussions, their are many here who believe, this just isn't worth it. My own observation indicates, that at the load I'm usually carrying, their is a considerable amount of heat that can be captured.

My plane is to thermosiphon thru a very large flat plate heat exchanger (24" x 9 1/2" x 8 1/2", 2 1/2 ports reduced to 1 1/4"). Like before, I am planning to run 1 1/4" ID hose , from the stock coolant manifolds, with a healthy raise, to the heat exchanger ports. As before, 195 deg thermostats will be installed. The upper port coolant connection will contain a tee  just before heat exchanger port, to allow for a 1/4" hose connection to a reservoir above the heat exchanger. The other ports of the heat exchanger will connect to a 80 gal, insulated hot water tank, with the tank raised so connections are above heat exchanger port, to allow for effective thermo-siphoning. To cool the water in the insulated tank, the tanks second upper port will connect to a Taco pump, then to a couple of tees, each having gate valves. One tee connection will connect to a water to air heat exchanger, mounted almost flush to the wall with a louver openning, into my work shop/ wvo bulk storage area. This will help cool down the insullated tank fluid, heat wvo bulk tank when needed, and exhaust heated air into a much larger area. A second connection will connect to insulated pex pipe that will connect to a couple of baseboard radiators iin my house. A third port, when additional cooling is required in summer, will run out to a coil of 3/4" or 1" dia pex tubing, hung underneath the ladder in the pool.

I am planning to start implementing this in a few days,  and I'm definitely hoping for a sanity check before I start. The part of this that bothers me the most, is the low volume of water that will be contained in the primary cooling loop.

All comments are welcomed.