Smoke signals

Motor,  Jul 2003  by Marinucci, Dan

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In fact, the smoke machine will detect the smallest exhaust leaks early on-before you or the driver can even hear them. Show these leaks to the vehicle owner and note them on the work order.

The smoke technique also makes quick work of diagnosing those dastardly cracked exhaust manifolds. Occasionally, you may need a mirror to distinguish between a leaking manifold gasket and a cracked manifold, and some leaks show up more readily when the exhaust is cold. But the point is that smoke signals won't lie when you're chasing down exhaust noises.

Many smoke machine users routinely diagnose oil leaks with it. To be entirely fair, the technique isn't 100% effective for tills task. But as one longtime user put it, "The smoke machine identifies three or four out of every five oil leaks. To me, that's a good batting average. Also, it reduces the amount of fluorescent dye we're using to find leaks," he said.

To do an oil leak check, you must effectively seal off the crankcase so the smoke machine can pressurize the engine properly. This means plugging or sealing off items such as the PCV hose, crankcase breather hose, etc. Sometimes plastic kitchen wrap is all you need to do this. Then remove the dipstick and oil filler cap and begin pumping smoke into the dipstick tube. When you see a healthy stream of smoke coming from the oil filler opening, reinstall the oil filler cap and let the smoke machine pressurize the crankcase. Next, watch closely for clues such as a definite smoke signal or oil dripping and/or bubbling out of the leak. If your machine is equipped with UV dye, the dye gives you a third way to spot the oil leak.

We've all battled oil leaks that began on the left side, ran along the engine and dripped off the right side-or something similar. A smoke signal is a timesaver because it flags the origin of the leak instead of the place where it finally drips off. A quick smoke test is also a great quality-control check on a seal or gasket replacement.

At Fadely's Automasters in York, Pennsylvania, Tom Fadely encountered an earlier Corvette that seemed to be spewing oil everywhere. The 'Vettes owner told him he was apprehensive because other shops wouldn't commit to what it would actually cost to cure the leaks. During the routine smoke check, smoke came out of the timing cover, the vent hole in the mechanical fuel pump and the bellhousing (rear main seal leak). Fadely told me that as soon as the owner saw the results of the smoke check, he readily authorized the repairs. Furthermore, the smoke signals were dead accurate, Fadely said.

Today's engines seem to have plumbing everywhere, including those pesky plastic or steel coolant pipes. The smoke machine may not be 100% effective on coolant leaks, either, but many users rave about its ability to quickly flag routine leaks. They drain the system, pump smoke into the radiator neck and look for smoke signals among the myriad of hoses and connections under the hood. One tech even uses smoke to leak-check intercoolers on turbocharged engines.