The hotter an MG engine runs, within limits, the better. And the colder the air and fuel it has, within limits, the better. "Hot inside" gives good carburation, promotes good lubrication (we use 76°C oil cooler thermostats) and promotes healthy wear inside the cylinder bores. One of our "cool running" cars still had the cross-hatched hone marks on the cylinder walls after 35,000 miles when we took the motor apart for other reasons. This is not good.

Hot on the inside: Our MGBs use 196°F thermostats, which gives a circulating coolant temperature of 90 - 92°C with a laboratory-type thermometer inserted in the radiator filler. Our MGBs are chrome bumper cars which have a filler cap, and the later sealed radiator would be harder to check. Naturally, the radiator is not always this hot because the thermostat only opens as the engine produces excess heat. Generally, the temperature needle only registers a good, healthy "N" on warm days.

Cool on the outside: Not all the extra heat goes into the water jacket. A lot of it radiates from the engine itself, especially from the exhaust manifold. On the MGB, the carburetters are fitted above the exhaust manifold, which causes two bad things to happen on really hot days. The first bad thing is that the air going into the engine is pre-heated by being sucked from around the exhaust manifold. A rough check on the temperature is that working around the rear carburetter is only possible for a minute or so, even with a vinyl glove giving some thermal protection. The second bad thing is that the fuel boils in the fuel lines.

A condition sometimes referred to as "vapor lock" occurs when the fuel boils at some hot spot fast enough to keep liquid fuel out of the lines. The vapor simply does not contain enough energy to sustain combustion, and the engine sputters and stops. The most common time for this to happen to one of our cars is after stopping for fuel following a long run on an expressway on a hot summer day. Everything gets a lot hotter when the car is stopped during a fuel and cold-drink stop, and the first half-mile back on the expressway can be a little slow, as there is not enough fuel getting to the float bowls for normal engine operation due to fuel boiling in the lines. A temporary solution we actually used on one car that took care of most of the fuel-boiling was to tie a sock near the fuel line inside the engine bay. This easily held a handful of ice cubes or, in an emergency, a can of frozen lemonade from the grocery store. Functional, but not at all elegant.

A better solution to eliminate overheated air and boiling fuel is to reduce the amount of heat escaping from the exhaust manifold. There is insulating material that can be wrapped around the exhaust manifold sections and secured with stainless steel bands. The work does require that the carburetters, heat shield, and intake manifold be removed, but the whole job can be done in a few hours. The photographs illustrate the installation process. We purchased the insulation at a price of about $75 from Pegasus Auto Racing Supplies (1-800-688-6946). There is enough insulation to take care of two manifolds, following the directions with the supplies. If you only have one MG, here is the reason to acquire another, or install a V-8.

Wrapping in process, above. Finished, below. Notice the band clamps.