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| The JH Cooling System | Rating: 
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| Posted: 04-02-2005 04:48 pm |
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1st Post |
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Mark Rosenbaum Member 
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Originally posted August 2004. My recent water pump studies have led me to a brief study of the JH cooling system, and I've a few comments which may be of interest. As always, I welcome any additional information and/or corrections. Cooling systems that will handle all the waste heat from a high-power engine are large, heavy, and expensive, so most cars are constructed with systems that can handle only smaller amounts of heat. This works only because few cars are called upon to produce their maximum power output for more than a few seconds at a time. Since most engines normally operate at a temperature considerably below their coolant's boiling point, a fair amount of excess heat can be 'stored' in the coolant for a little while (raising its temperature, of course) and dumped at some later time, when the engine's heat output is not exceeding the cooling system's capacity. Gasoline engines are not particularly efficient. As a rough rule of thumb, for every horsepower an engine produces, it dumps a horsepower's worth of heat into its cooling system and a horsepower's worth of heat out the exhaust. This being so, a JH engine at full throttle makes enough waste heat to warm its entire coolant supply by 7^F a second. If this engine normally runs at 180^F and the coolant boils at 230^F when pressurized, then it could run at full throttle for no more than (50^F)/(7^F/sec) or a mere 7 seconds before its coolant turned to steam. In practice, of course, the waste heat warms more than just the coolant, and the cooling system transfers much of the heat to the environment, so the time to boilover would be considerably greater. But for prolonged full throttle operation, boilover is inevitable unless ALL the engine's waste heat can be transferred to the environment. This means more effective heat transfer inside the engine, and more effective heat transfer from the radiator to the air. Assume that the engine is properly filled with coolant. When the engine runs, rotation of the water pump forces coolant present there into the block, and fresh coolant from the lower radiator hose and upper heater hose flow into the void thus created. The coolant moves through the engine and head, then flows (a) into the heater core through the lower heater hose, and (b) through the intake manifold hose back to the water pump. When the engine is cold, the upper section of the dual-action thermostat is closed and prevents the return of coolant to the radiator via the thermostat cover and upper radiator hose. The lower section of the thermostat, essentially a spring-loaded disk, is connected to the upper section, and under these circumstances does not block the bypass passage that feeds the water pump's input. This arrangement avoids hotspots, ensures even engine warmup, and provides at least some heat to warm the cabin when that is desired. The coolant temperature increases as the engine continues to run. When the coolant reaches about 82^C (for the standard thermostat), the upper section of the thermostat starts moving downward, allowing coolant to flow into the radiator. Simultaneously, the disk at the bottom of the thermostat begins move downward and restrict coolant flow through the bypass passage. By the time the upper section has opened about 0.4", the bypass passage has been closed off; further motion of the upper section of the thermostat merely increases the force applied to the disk. Coolant flow through the heater core is probably somewhat reduced as well, but I know of no data to prove or disprove this. It should now be clear that if the proper dual-action thermostat is not used, or if the thermostat's operation is faulty, then the system will not work as intended and most likely the engine will overheat. In an emergency, though, one could use a conventional thermostat -- or none at all -- provided that the bypass passage were blocked. Other than some of the passages between block and head, the most restrictive parts of the cooling system appear to be the passage between water pump and engine, and the water pump spigots for the various hoses. I've made a few measurements and calculations for these. Pump to engine passage: .25" x 1.5" (rough), 0.37 square inches. Upper radiator hose spigot on thermostat housing: 0.93" ID, 0.68 square inches. Manifold hose spigot on pump: 1.06" ID, 0.88 square inches. Lower radiator hose spigot on pump: 1.13" ID, 1.00 square inches. All of the water pump's output flows through the passage between pump and engine. In the examples I've seen, this passage is quite irregular with uneven edges and appears to have been chiseled open (literally!). Enlarging and smoothing this passage, in much the same way as one would port a cylinder head, should significantly increase coolant flow while reducing stress on the water pump. To my eye, the various spigots also appear small enough to be restrictive. System performance might be improved by modifying these passages for improved flow. The only ferrous parts exposed to the coolant are the water pump shaft and impeller, and the cylinder liners. A rusty water pump impeller makes an inefficient pump, and rusty cylinder liners are poor conductors of heat -- both conditions promote overheating. Since the 50-50 antifreeze/water mix suggested by the factory is a fairly good rust preventative, if kept fresh, _any_ rust in the coolant should be taken as a sign of impending problems. Hope this provides food for thought.
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| Posted: 04-02-2005 09:15 pm |
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2nd Post |
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Ron Earp Member 
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Mark Rosenbaum wrote:
Let's hope it is considerably greater! We'll be racing the JH in May and if all goes well it'll do the 30 minute sprint races and the 1.5 hour mini-Enduro. For both of these races it'll be full throttle between 6k-8k only letting off for four braking zones. The only changes I've done to the JH motor for cooling is a four core radiator, and probably more importantly, a larger oil cooler, an Accusump oil pressure system, and a two filter remote mounting oil filtration system. Many times people overlook what oil does in a motor, sure it lubricates, but it takes a lot of heat out an an engine as well. This system will give me me about five additional quarts of oil in the system and greatly increasing the cooling capacity of the entire system. Ron
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| Posted: 04-03-2005 12:46 am |
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3rd Post |
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Mark Rosenbaum Member
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I recall seeing, 40 years ago, dragsters starting a run with 5 or 10 gallons of ice water as coolant. By the end of their run a few seconds later, that water was boiling. Of course the dragsters had no real means of transferring coolant heat into the environment. Any practical cooling system must dump enough heat so that the car doesn't overheat for the duration of its use. This is where the presence of additional coolant and oil provide their benefit: they add mass that can absorb more heat before the engine as a whole overheats. An ideal cooling system would be able to dump all the heat produced by the engine. The extra size, weight, and frontal area requirements of such systems are usually major drawbacks. However, a lot races have been won by slow heavy cars that kept running long after their faster, quicker competition broke down. In most cases, it ends up being a judgement call. If the rules under which you're racing allow, you can see a significant improvement over the stock cooling system without much effort. Basically, this means making certain that as much air as possible flows smoothly through the oil cooler and radiator when the car is at speed. This means (a) a front spoiler to increase the effective area of the air inlet, (b) smoothing the sheet metal and transitions in front of the radiator -- think of this as 'porting' the radiator inlet, (c) sealing all unused openings in the radiator bulkhead, (d) sealing the full width of the gap between the top of the radiator bulkhead and the underside of the hood, and (e) ensuring that the heated air can exit the engine compartment as easily as possible -- in the case of the JH, this will most likely be via the gap between the back of the hood and the windshield. Increasing the air flow over the headers will also be of benefit (though in a LHD car, the driver may cook). You can try placing the heater core in a container of ice and get rid of a fair amount of additional heat as the ice first liquefies, then boils away. If the ice container is sealed save for a single vent, and you put a rocket nozzle on the vent, you gain a tiny bit of thrust that may help a little. No, I'm not joking here -- it's been done, though I don't currently recall when or where. One trick to improve airflow across sheet metal is to replace any protruding hardware with flathead screws. Another is to use a fan to redirect air from rough areas to smoother ones -- technically, the fan itself provides little or no cooling. IMHO, with a bit of experimenting you should come up with all sorts of things that comply with your racing rules and which help. And if ten small improvements equal one big one, it's usually better to go with the small ones -- you'll lose less of the benefit when one quits in mid-race.
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| Posted: 04-03-2005 01:29 pm |
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4th Post |
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Ron Earp Member
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I've made a few of those improvements you mention. Spoiler has been attached to help out with airflow, and of course the radiator gaps have all been plugged to make sure the air goes through it. I'm using a fantastic electric fan with full shroud that will move 2400 cfm of air. Although I cannot enlarge the radiator opening, the radiator is taller than this opening to catch additional airflow on the bottom of the car, and of course get more water in the system. My headers are competely wrapped, and while I know header wrap always brings up a contraversy for various reasons 1) longetivity 2) effectiveness etc, it makes sense for me to keep the heat out of the engine bay and offer me some insulation between the header and floor board. Those things are right beside the footwell! Airflow over the radiator is so very important. Two weeks ago I was racing our rental Z car in a 1:15 race. The race start had a delay and I had to sit on the grid for about 10 minutes idling. In 55F weather the car coolant temp gets to 236F, just idling (I would have loved to shutdown but the carbs are not friendly to warm re-starts). The car has a good electric fan, but the fan setup stinks and has no shroud so it is very ineffective at pulling air. Once the pace lap started the car was down to 170F within about 1.5 minutes - airflow over the radiator takes care of business. And throughout the entire race at WOT temp is 170F. Clearly this weekend I spent a couple of hours and put two shrouded e-fans on the car so we don't see that problem again!!!!! Last edited on 04-03-2005 01:32 pm by Ron Earp |
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