Observing and recording the engine coolant level may be more valuable that many service personnel realize. One service manager's recent experience illustrates how important coolant level can be to solving a potentially difficult diagnosis. My pal Joe is a service shop owner/operator. One of his regular customers drives a Chrysler that developed a mild but noticeable misfire. The symptom only occurred when the engine was cold and didn't last long enough to set any trouble codes. The engine just seemed to run rougher than nor-mal until it reached operating temperature. Then it ran smoothly again. The first time the customer came in for this symptom, Joe and a technician performed a careful visual inspection. They noticed that the fluid level inside the coolant reservoir was low. According to shop records, the coolant level had been checked within the last year and was normal at that time. So Joe added enough to bring the coolant within the normal range. Then he gave the Chrysler a road test. Afterward, he used a felt-tipped pen to mark the coolant level on the side of the coolant reservoir to eliminate any potential guesswork later on. Joe and his technician were justifiably suspicious. When an engine's losing coolant, it may be leaking fluid internally or externally. Of course, an internal leak usually means major repairs such as a head-gasket job. At this point, their visual inspection showed no traces of external leakage. Plus, the customer stressed that the car never dripped fluids onto the garage floor. Joe wanted the customer to leave the car overnight so that his tech could run a test when the engine was stone cold in the morning. He urged the customer to schedule this visit as soon as practically possible and to watch for any other signs of trouble. He described common symptoms of additional coolant loss and overheating. If it was an internal leak, it would likely worsen and worsen gradually—but there were no guarantees. The customer's appointment was only several days away. He insisted he only would be driving locally and promised to shut the engine off at the first hint of trouble. A local towing charge is insignificant compared with the cost of a new engine. The mild misfiring during cold operation continued. But no other symptoms had appeared by the time the customer returned to the shop. However, the fluid level inside the coolant reservoir had dropped significantly below Joe's mark on the reservoir. Since there still weren't any signs of external leakage, he decided to test the coolant for combustion gases. There are several ways to do this. Combustion gases in the coolant indicate trouble such as a blown head gasket and possibly a warped or cracked cylinder head. Indeed, there was combustion vapor in the coolant. Additional tests confirmed a leaking head gasket. A thorough head gasket job cured the condition. Many people associate a blown head gasket with symptoms such as clouds of white exhaust smoke, a sweet odor in the exhaust, severe misfire at operating temperature and no heat or inadequate heat. However, experience shows that the earliest stages of head gasket failure may cause the condition Joe encountered on this Chrysler. Admittedly, some techs may have approached this diagnosis differently. Yet when all was said and done, the path to success here began with good record keeping and an accurate vehicle history. Beyond those things, the key clue was the telltale drop in the coolant reservoir fluid level—a very basic but meaningful observation. Some managers have conditioned their technicians to check, correct and observe coolant levels faithfully. In other service departments, techs tend to overlook it. Be sure your crew always checks it. Ultimately, they'll be glad they did.
Coolant level overlooked diagnostic clue
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