Cooling tank height

Good question. It seems to me that the greater the height differential, the greater the speed of flow. At least in theory, the coolant could be less in quantity.

Other things to consider is that heat loss through pipework (better in matt black painted copper than gloss black iron for instance) could be important & the better efficiency of water with a degree of anti-freeze in it could be investigated. Finned pipework would be useful in an out of the way place - perhaps below the tank - and easily obtained from scrap fridges and scrapyards dealing in dairy and pub stuff.

My thought here is to achieve a smaller tank as it seems to me that most engines you see at events are both understressed and overcooled. At least for four stroke engines, it should be possible to weaken off the mixture and run an engine hotter to the considerable improvement of its fuel consumption. Now that should raise a few eyebrows and hopefully lower a few wallets!

I'm going to stop now before me higgorance shows too much, but I bet there are those here who can make much better suggestions than me.

Regards,

Kim Siddorn,

Mark, I would suggest something about the size of a 4.5kg gas bottle - braze or weld the existing bottom fitting (which looks original) into the bottom of the bottle, and then make an inclined top pipe to suit. The position of the bottom of the tank is not too critical, more important is to ensure that the top pipe rises continuously upwards so that a thermo-syphon is induced. Another option would be an old fire extinguisher.

A consideration for the upwards pointing bottom fitting is that the engine may have been fitted with a run-through cooling system - water in the bottom and out the top controlled by a valve - though it's unlikely with an engine this size.

HTH Regards Dan

Cooling of this sort relies on thermo syphon. That produces very little pressure gradient so pipe runs need to be as efficient as possible. That means short and straight or with sweeping bends at most. In theory (a lovely place where everything works and no practical limits exist) the tank has two connections and the engine can be anywhere between them. In practice, most engines have a horizontal bottom water connection and many have a more vertical to one. In order to reduce pipe bends and so losses, a straight pipe from the tank to the bottom of the engine and the upward pipe from engine continuing to the to of tank is the best solution. Your Norman may have been desighned to suit another arrangement out of a practical need. That's not to say it's wrong, perhaps simply not the most efficient.

John

In practice it reduces with increasing height. The benefits of extra "head" reduce once you've adequately separated the hot and cold volumes. The main effect though, same as everything like this, is that pipe losses in long thin pipes soon dominate anything else.

Any extra head will increase the static pressure, but it also increases the pressure the pump is pumping against (assuming it's a thermsyphon assisted pumped system) just as fast as it increases the pressure "driving" the flow. It's the _difference_ between legs that matters, and increasing the head only increases the total. OTOH, for non-sealed and pressurised system this might itself improve pump performance.

Another nice-looking tank is one of those backpack copper tanks for weed spraying. Riveted construction, hemispherical bottom sitting on a perforated copper ring. I picked one up at 1000 Engine Rally for £5.00.

Regards,

J. Kim Siddorn,

Hi Dan,

That pretty well aligns with my inclination. I have made a tank of similar size, perhaps a little taller and narrower. I was just a bit concerned about going against the flow, so to speak, and doing something that clearly Norman (or whoever) thought was OK but others seem to advise against.

Putting the engine inlet into the bottom of the cooling tank may not be the optimum solution (as John M points out) but it was obviously as intended by the engines makers so I guess I can try it whilst monitoring the cylinder temperature.

My thought is that as long as the water outlet at the top of the engine is nicely inclined to avoid air locks etc. (IIRC Lister recommend a minimum slope of 1 in 8) then the thermo-siphon should work and the relative position of the bottom of the tank is not so important.

Hi Mark, It's the differential between the "water inside the cylinder" and the "water in your water tank at cylinder level" that moves the water. So in that regard, the bottom of the tank at cylinder level is best.

But the top of the tank is a bigger consideration. You want the inlet to your water tank to be considerably higher than the outlet from the engine.

On your cylinder outlet pipe, provide a good amount of uphill slope. Level will work, but should be avoided. ANY downhill slope will ruin your thermosiphon.

Make your tank outlet near the bottom of the tank. If you tap the tank half way up, the water in the bottom half will be unused. It won't circulate and will stay cool even if the water on top is hot.

The inlet near the top of your tank should be high, to provide more thermosiphon, but it shouldn't be so near the top that a little bit of evaporation will expose the inlet. As soon as that happens, your thermosiphon is lost. Allow for a "cushion" of water above the inlet.

Keep your tank of adequate size to provide ample cooling. If it gets really hot, say almost as hot as the cylinder, then you'll not get good flow and things will get even hotter.

Excess cooling shouldn't be a big concern. The water doesn't flow until the engine warms up some, and if you DO find that it isn't running hot enough, just obstruct the flow with either a valve or by stuffing something in the pipe.

=-=-=-=-=-=-=-=-=-= Rob Skinner La Habra, CA