Model G overheats

I've got two Model G tractors.  Both running.  One of them runs at a normal temperature, but the other one, the subject of this post, seems to run hot.  I topped off the antifreeze/water mix to the overflow spout at the top of the radiator (it had been low).  I ran it for a few minutes, and water began leaking out the overflow spout.  The top tank in the radiator felt quite hot to the touch.  I saw some steam, but not sure exactly where it was coming from.

JayB

If I thought the rad had sediment in it, I would first go to your fav auto parts store and buy some radiator flush. Drain the rad, and maybe flush it out a bit with a garden hose. Then add the chemical, and fill to the top of the fins. Operate the engine till fully warmed, maybe let it cool off and do it again.
 There should be easy directions to follow on the bottle. NAPA has such a product.

I 'm not sure about the G, but most systems like that are not pressurized so , shouldn't run that hot. If you don't have a good oven thermometer to "borrow" get a $30 infrared gun.

Check the timing and the fuel mixture. Late timing or a lean mixture will make any gas engine run warm.

The standard half and half permanent antifreeze mixture boils at about 225 F at atmospheric pressure, higher with a pressurized system depending on the pressure.

Even with the gravity flow system there should be a thermostat otherwise it won't ever warm up and an engine stuck at less than 135 will not be efficient because of the loss of heat energy from combustion to the cold block and head.

I have G owner's manual and a multi tractor shop manual that includes the G on line at:http://www.geraldj.networkiowa.com/Trees/

Gerald J.

We fill ours to the top of the radiator fill. If you don't keep it filled the water will not circulate and engine will overheat. If the radiator is full and it still overheats (assuming fan is working) then the system needs to be flushed.

I second Gerald J's advice. Check your timing. Retarded or late timing will definitely cause an engine to run hot. Just had a Farmall Cub in the shop that would overheat in less than 10 minutes of starting. Customer said he's seen the manifold glow red. Timing was too late (retarded). Was set at about 5 degrees After Top Dead Center at high rpm. Should have been 16 degrees BTDC at high rpm.

Just clarification- The radiator cap IS a pressure-type cap. Not very high pressure, but just a few PSI is sufficient to do the job.

These are called 'passive' cooling systems, because they don't have a forced circulation system... instead, they use gravity and density to cause circulation. There are two types of gravity/density cooking circulation systems- there's Evaporation/Condensation, and Thermosyphon. Understanding them, makes it much easier to solve cooling system problems for 'passive' cooling systems.

Evap/Condensing early- it's also referred to as 'hopper' cooling... and it's very simple, and you'll see it on hit-and-miss and throttle governed slow-speed engines. The engine block and head are encased with a cooling jacket, and there's a hopper or tank above the cylinder. As the engine warms, heat is conducted into the cooling water, which evaporates off (where block contact surface is below boiling) or it boils off (cylinder/head areas are above boiling). Regardless of what happens, as long as there's sufficient water in the hopper, the engine will NEVER get over 212F at sea level, or over 193F at 10,000ft.

The open hopper is considered 'total loss' cooling, because the cooling medium (water) is allowed to either evaporate or boil off. Recovery requires just putting more water back in the hopper.

An enclosed 'radiator' can also be used, so that any water that boils off, rises up the radiator's cooling fins, and since there's airflow over the cooling fins, heat passes out, and the steam condenses, precipitating back down into the hopper below.

The third type, 'active' cooling systems... use a pump to circulate.

Of course, the flow character of each system are entirely different... the passive system must have low restriction to flow, and it must be such that steam bubbles naturally want to pass uphill through the plumbing. Hot cooling liquid needs to want to flow too, so blocks designed for thermosyphon have lots of available space in the jacket for good flow... or at least, we hope they do... it may be plugged a bit.

In a coolant-pump -based system, the flow restriction is not nearly as critical, and in some ways, having some restriction (and that pressure cap) means the centrifugal pump has a little more head-pressure, and as a result, high temperature areas are less likely to boil... so it absorbs more heat, and sheds it quicker at the radiator.

IF you pull the radiator to flush, I recommend you pull the coolant neck(s) from the engine, pull the cylinder head, and flush the block out really good, shove a rod down through every passage of the block and the head, then blast water through it every which way you can. Having a clear radiator is important, but having a clear flowing block, and one that isn't insulated by large deposits of crud, is absolutely positively mandatory.