ROAD AND WORKSHOP by Handyman
Page 47
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Diesel-engine Temperature
DESPITE THE RUSH and bustle of goods-vehicle repair and maintenance, there are odd items of equipment that give exceptional service, and one result of this long life is that the real duty and the importance of such items can be overlooked, or never, questioned, in times of mechanical trouble. I refer particularly now to the thermostat. This small unit in the cooling system is entirely automatic in operation, requires no regular maintenance, and is rarely examined or tested except as a last resort when all else has failed. Yet this important item has a bearing on maximum performance, fuel economy and smoke emission, and can influence to some considerable extent the expectation of engine life.
Where the thermostat can work in conjunction with a temperature gauge on the dashboard, and that gauge and its allimportant and very special pipeline are will cared for, all is well and little can go wrong unnoticed. However, in the main, the thermostat "goes it alone" and is rarely given a thought. Briefly, it is sited in the water outlet from the cylinder-head and the unit itself is a metal bellows held at the bottom by a frame in the housing and at the top end a valve is attached.
This valve, when closed, can completely cut off the passage of water to the radiator, other than tiny holes in the valve or seat, to relieve any steam or pressure. In the closed position with a cold engine, water is trapped in cylinder heads, water pump and cylinder block, this allowing a quick warm up, The valve remains closed until the trapped water reaches around
175° to 185°F. (79° to 85°C.), when the bellows expand and the valve begins to open, continuing to open up to between 190° and 200°F. (87° to 93°C.). Normal lift of this valve is ?, in. From then on the water is in full circulation around radiator and engine, until the temperature falls below 190°F. It therefore follows that 200°F. (93°C.) is the target temperature for the engine, and at that figure it will give its best pefformance if all else is in order.
At 200°F., the lubricant is doing its intended job and combustion should be correct. However, blanking off the radiator, if not carefully controlled, can overheat the engine regardless of the thermostat: also, excessive heat can damage the thermostat bellows to a point at which it will stick open. This is usually noted after a cold start in winter when grey or white vapour is emitted from the exhaust, and persists for several miles. In later life, the thermostat can become stiff or work-hardened and fail to open, and the engine temperature can rise dangerously. If the thermostat is not fully open, the engine will steadily overheat, lubricating oil will thin out and can pass down the inlet valve guides, giving off increasing amounts of blue smoke. Cylinder compression can drop away also, causing bad combustion and black smoke from poorly burnt fuel. This combination could well confound the repair Man, who may concentrate of the fuel-injection side, and on occasions even draw the pistons, without seriously considering that the thermostat may be the cause of the trouble. Therefore, as part of the repairer's test in these circumstances, he should make a habit of checking water temperature first and be guided by his thermometer readings, with 200°F. as the yardstick.
To test the thermostat off the machine, place the unit in a bucket of water and bring the water slowly to 200°F,, checking the point of .first movement and wher fully open against the figures above.
Worcester Winner
THIS week's winning idea comes from 1 Mr. P. W. Prue, a Worcester reader. Mr. Prue refers to the item "Electrical Equipment—and Safety", which appeared in "Road and Workshop" on January 10. To overcome the danger of accidents with starter motors he has, he says, made up a "jump lead" from a line fuse (as used on many Ford cars) and two alligator clips, which is used between the battery and the battery lead. A 15-amp. fuse will allow any electrical tests to be carried out, but will blow before the starter engages or turns, even if the starter is accidentally operated.