Cooling off

© By: Dwight Smith, MOG NORTHWEST

Formatted for the Morgan Web page by: John T. Blair (WA4OHZ)

Originally written: circa 1995

Last update: June 16, 2009 - Reformatted page and corrected my email address.

(Thanks to Ben Hodgkiss ( for submitting the following.)

Freightliner Truck Manufacturer's engineers take a hard look at the Morgan and Dwight Smith of Northwest Morgan Group draws some conclusions that might make your summer a bit happier!
Backround dot_clear
For many Morgan Owners, the first stop after filling the radiator on a warm summer's day results in an annoying and embarrassing flood of hot, steaming coolant pouring out of the overflow tube and on to the ground. By all the physical signs, the car is overheating, and it may well be. However, at the request of the Northwest Morgan Owners Group, Freightliner truck manufacturers took a diagnostic look at a Morgan and came up with some most interesting findings.

Freightliner builds its large semi-, over-the-road trucks in Portland, Oregon, trucks made to withstand something like a million miles of the hardest year-round driving possible, while pulling a 70M cargo. Their cooling systems must be able to stand up to the extreme heat of the desert and then, two days later, cope with the ice and snow of the frozen north. Presumably, Freightliner engineers know a bit about engines and their cooling systems! At the request of a MOG NW member who worked there, the engineers took a close look at a '72 Plus 8, analyzing the radiator size, number of tubes and vanes and the system capacity. Most important, they also studied just how air flows through the radiator and engine compartment when the car is on the road. Surprisingly, their first conclusion was that the radiator, while not excessively large, was big enough to cool the engine, if working properly. This conclusion is backed up by another MOG NW member who has been building radiators for the last twenty years, even though most Morgan owners think first of recoring their radiator and increasing its capacity as the first remedy to overheating to attempt! But if in fact the radiators capacity is sufficient, what is the problem?
Freightliner's Conclusion dot_clear
Freightliner's conclusion is that there are two problems with the Morgan cooling system. And, if you can tackle the comparatively simple work yourself, it shouldn't cost you much more that S20 to lick them!

The problems?

  1. The inability of air to flow smoothly in sufficient quantity through the radiator when the car is traveling (which could account for the perplexing habit of the Morgan to cool off when idling in traffic and then to heat up on the road, when it should be cooling off).

  2. The inability of trapped air to escape from the radiator.
Solving Problem No. 2 dot_clear
The trapping of air in the radiator. Take a close look at your radiator from the side, as it is in place in your car. If you have a level, use it to see for yourself how the radiator shapes up. Note first that the radiator cap has a rubber gasket on the bottom and that it fits! down about 1 1/2 inches into the neck of the radiator filler. The level of water in the radiator will be right at the level at which this gasket seals. Now, use your level or another straight edge to draw a line parallel with the ground, from the bottom of this gasket seat across the radiator top tank. Not all Mogs are the same, a bit of news which will astonish you, I'm sure!, but if yours is typical, there will be a 1 or 2 inch space above the water level at the top of the tank. This area, unless you found a way to stand the car up on its grill, rather inconvenient at the local gas station, will never fill with water, but will remain a trapped bubble of air. Since air expands faster than water, as your engine warms up, this air bubble will pressurize and inevitably displace some of the water below it in the red. When you stop, the last bit of engine heat rises quickly into the radiator. Its temperature will quickly rise, the air will expand further, and up to a pint of coolant blows out the overflow tube like Old Faithful. Nature here is working the same way as does an Expresso coffee maker, but not at the time you want it to and against the efficiency of the system.
Retaining The Water dot_clear
The cure is quite simple. Fit a recovery bottle. Most auto supply stores carry them, and a particularly compact one is carried by Volvo parts dealers, about the size and shape of a thermos bottle, an important consideration in the crowded engine compartment of a Morgan. Simply mount the plastic recovery bottle to the engine compartment wall and run the overflow tube (which is attached to an outlet next to the filler neck and runs down along the side of the radiator) to the inlet/outlet at the bottom of the bottle. You most likely will have to replace the rubber tube with one of the same diameter but longer, in order to reach to where you have mounted the bottle.

You now fill the system through the recovery bottle; the cap on the original filler opening remains in place at all times. You have created a sealed cooling system, which many contemporary cars are now fitted with. If you have trouble finding the right cap for such a sealed system, any cap will do if fitted with an additional rubber gasket on its inside where it seals on the mouth of the filler opening. Radiator shops can supply such a gasket. Do not exceed a 4-pound pressure cap; with more pressure than that, Morgan radiators will spring a leak. Be sure also to buy a cap for the recovery bottle, and remember, it is through this opening that you fill your system with coolant.

Not only will this addition increase your system's capacity, it will also allow the system to eliminate that trapped air bubble that was causing you overflow problems. Now when the engine heats up, the air will expand and be forced through the tube into the recovery bottle, where sufficient space is left for it to fill. After two or three trips in the car, water will have replaced the air in the radiator top tank, effectively making your systems capacity one pint larger. (You have eliminated the annoying run off, sealed the system to prevent the almost constant loss of coolant and increased the system's capacity and hence efficiency, all at the expenditure of comparatively little time and money).
Solving Problem No. 1 dot_clear
Now for your second problem, the impeded flow of air through your radiator and engine compartment. What the Freightliner engineers found was that the configuration of the Morgan forces a strong current of air directly under the radiator, a flow which does not simply pass under the car but flows up into the engine compartment where it collides with the firewall, causing the air to back up in the compartment and create a relatively high air pressure inside it. If air inside the bonnet is exerting even the slightest back pressure, it will inhibit the flow of air through the radiator. The higher the speed, the more pressure and more impedance, and at high speed, this can be substantial.
The Answer dot_clear
Block the area directly beneath the radiator down to the bottom edge of the frame with an air dam, preventing that unwanted flow of air into the engine compartment and thus greatly increasing the efficiency of the flow of air through the radiator at speed.

The best design for this simple air dam we've been able to come up with uses a 12" x 27" piece of rubber floor matting available at most hardware stores. This is fixed in place with bolts that hold the radiator to the frame beneath it. The rubber matting, after it is bolted on, can be draped over the steering rods, and will not interfere with their operation. It must be long enough to extend the bottom of the frame; 12 inches should do the trick, and 27 inches should be sufficient horizontally. As the air hits this dam, it will force it into place in front of the suspension frame just behind the radiator. Above 25 m.p.h., this system will really work. The relatively low pressure inside the engine compartment pulls air through the radiator and down and under the car. Side benefits include:

  1. Reduced engine fumes inside car.
  2. Cleaner firewall and engine.
  3. Some improvement in cooling by the engine fan, as it can no longer pull air from beneath the radiator.
One Final Modification dot_clear
One other additional change is a good idea: a plastic fan. For example, Ford Cortina engines which can, and most likely should, switch to a Capri 1600 water pump, of higher capacity than the one installed, requires a Capri 1600 pulley and plastic fan, available at many junk yards for under $10. The plastic fan came along some 15 years ago, when the price of copper, used extensively in radiators, was going up. While looking for a cheaper way to make radiators, firms took a hard look at the total system. The plastic fan is one result. It is light, unbreakable and can be set at a higher pitch, which will pull more air through the radiator at slow speed. Due to the flexibility of the plastic, the fan's pitch will be reduced as engine speed increases, lessening the drag on the fan and increasing gas mirage. Above 35-40 m.p.h. there is enough air blasting through the radiator most radiators that is! - that the fan does not really contribute that much. So the plastic fan pulls more air at slow speed when it is really needed, then bends out of the way when it is not! I have mentioned the Ford engine, but I'm sure that a plastic fan can be adapted to the Plus 4s and Plus 8s. In fact, the Factory should be able to supply a plastic fan, as I would think the new Plus 8s would come with one, as do most new cars, including the 4/4.

If you are looking into this, the important things to remember are: distance between pulley and the frame behind the radiator; the bolt pattern and center locating hub of the pulley itself; diameter of the fan being considered. It can only be as large as the hoses and engine parts in the vicinity will allow. It might surprise many 4/4 owners to find that they can fit as large as 12 inches. With the many plastic fans fitted to British cars in the 70s, most of which followed similar design patterns, you should be able to find one suitable to your Morgan. A good wrecking yard can help.
The Temperature Gauge dot_clear
You might find it valuable to have your temperature gauge checked as well. To check, a thin candy or meat thermometer is best; it must be immersed into the coolant and be accurate. If your radiator's construction prevents this, common sense can help you determine if you're overheating. For example, if after fitting the recovery bottle the coolant fills and overflows the recovery bottle, you have a problem. If the level in the recovery bottle goes up and then down two or three inches, then the system is working as it should. If the needle is still bending on 'Hot,' the gauge is most likely not reading correctly. Sometimes corrosion attacks the sender, inside the radiator or block. Try using a fine grade of sandpaper to clean the sender and make it shiny bright. If it is necessary to replace it, it might be worth the postage to send a letter to the Factory or the Morgan Sports Car Club England's spares department. By the way, it might help to know the senders are made by Smiths, not Lucas. You should have no trouble finding senders for 4/4s nor for Plus 8s, with their early 60s Buick engines.
Thermostats - Fact or Fiction dot_clear
As for thermostats, changing them for the seasons can be more confusing than helpful. Some come in three temperature ranges, some just winter and summer. This should be easy for Morgans, since almost all driving is done in the summer. With big American cars in years gone by, there was enough capacity in the radiator that the different thermostats meant something. With Morgans, however, a 180 thermostat should be good all year round. A 160 thermostat opens at this lower indicated temperature, and is called a summer thermostat. But with a Morgan, the temperature will rise to 180 anyway, and this lets the head warm up a little faster, which is good for engine combustion and should hold the temperature within the narrowest range possible. The only reason for a 190 thermostat is to provide extra heat for the car heater in winter; with the Morgan's smaller cooling system heating to 190 sooner than they have to just doesn't make sense. A 180 thermostat will provide plenty of heat in a Morgan and would seem to be the best all-round, as I see it.
The Last Component - Coolant dot_clear
Finally, there is the coolant for the system. Anti-freeze obviously will not freeze, but it also transmits heat better than plain water. (ED. (8/99) I don't believe that this last statement is true - I believe water is the best coolant. If you opt to use streight water in the summer, you should at least add a water pump lubricant. (6/09) Better yet is to add "Water Wetter" which can reduce the temperature by as much as 30 degrees F. and contains a water pump lubricant.) Most companies now sell Summer/Winter coolant, Anti-Freeze, Anti-Boil. These protect the metal inside the radiator and engine and many claim they contribute lubrication to your water pump. About half the fluid in your system should be anti-freeze, half water. It should be changed at least every other year as it's PH can change and it will become corrosive. If in doubt as to your system's capacity drain the radiator completely, add one U.S. gallon of coolant (a little more than half its capacity) and fill with water. If you need to add to the recovery bottle after running, add straight H20. And Happy Morganing next summer!

dot_clear Dwight Smith, MOG NORTHWEST

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