Small Engine Water Cooling

[Captain Jerry]

This is just for discussion.  I'm not building anything based on this.

Many of the small engines that are seen on here include a water jacket that surrounds the cylinder for cooling,

For many years on my cruising sailboat, I operated a diesel genset powered by a 6HP single cylinder Farymann Diesel that ran at 1800RPM and was rated at 4.5 KW  The engine was cooled with a freshwater circulation with a seawater heat exchanger and it provided good service for as long as I owned it with normal maintenance issues.

The thing that I thought unusual was that there was no cooling water jacket on the cylinder.  All of the cooling water circulated through the head only.   I asked the factory rep about it and he said that almost all of the heat was generated in the head and that by not passing water flow through a head gasket joint, they eliminated the problems that could come from a head gasket water leak.   It must have worked because the engine was painted white and after about 3000 engine hours, the paint was still white on the cylinder and showed just a little heat discoloration on the valve cover.

My question is, has anyone ever considered this for model engine design?

Jerry

[gbritnell]

Hi Jerry,
I'm sure that the greatest amount of heat is generated in the head area and in some cases the very top of the cylinder bore. I'm guessing that with a full length water jacket it's more a matter of keeping the cylinder under a somewhat of an even temperature for expansion reasons. Another reason might be the type of engine and it's working rpm. With the type of engine you had (slow running) by just cooling the head it was more than adequate. In drag racing they sometimes fill the bottom of the water jacket area  and just cool the top where all the heat is made but then again the engine is only running for several minutes including start-up and making a pass down the track. When I run my engines they make quite a bit of heat after several minutes. Would they run any differently by just cooling the head? I don't know. It would be a major undertaking to rebuild one just to find out.
gbritnell

[Ian S C]

I'm sure that the 15 cc glow plug motor my nephew has in a RC Hydroplanehas a water cooled head, and air cooled barrelon its cylinder.   Ian S C

[Bogstandard]

Ian,

I think all the OS watercooled gloplug i/c engines just had head cooling, no cylinder cooling, plus a little cooling area on the back of the crankcase.

I used to run them for well over an hour at full bore with no signs of overheating.


John