Coolant Loss and White Smoke on a 2014 Power Stroke
A 2014 Ford 6.7L Power Stroke has been losing coolant with no visible external leaks. The customer reports white smoke from the exhaust, especially after a cold start, and a sweet smell. The coolant level in the degas bottle drops about 1 quart every 500 miles. A pressure test of the cooling system at 16 psi shows a slow pressure drop, but no external leaks are found. A combustion gas test (block tester) on the degas bottle shows a color change indicating the presence of combustion gases. A relative compression test with a scan tool shows all cylinders within 5% of each other. A cylinder balance test shows no significant imbalance. The EGR cooler was replaced 10,000 miles ago. The oil looks normal, with no signs of coolant contamination. A visual inspection of the engine shows no external coolant leaks, and the water pump weep hole is dry.
1. What is the most likely cause of the coolant loss and white smoke?
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The most likely cause is a failed EGR cooler or a cracked cylinder head. The positive block tester indicates combustion gases in the cooling system. Since the EGR cooler was recently replaced, it could be defective or improperly installed, but a cracked cylinder head is also possible. The white smoke and sweet smell are consistent with coolant entering the exhaust stream, which can happen if the EGR cooler internally leaks coolant into the exhaust or intake. A cracked cylinder head could also allow coolant into the combustion chamber, but that would typically cause misfire and may show up in a cylinder balance test. Since the balance test is normal, the leak is likely not into a cylinder but into the exhaust via the EGR cooler. However, a cylinder head crack between the coolant jacket and exhaust port could also cause this without affecting compression. The lack of oil contamination suggests the leak is not into the oil galleries.
2. How would you differentiate between a failed EGR cooler and a cracked cylinder head?
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To differentiate, first perform a cooling system pressure test while watching for coolant in the EGR cooler outlet or intake. Remove the EGR cooler and pressure test it separately; if it leaks internally, it is the culprit. If the EGR cooler holds pressure, remove the cylinder heads and pressure test the cooling passages, or use a borescope to inspect the cylinders and exhaust ports for coolant residue. Another method is to pressurize the cooling system and remove the glow plugs or injectors to see if coolant enters the cylinders. Also, check for coolant in the EGR passages. Since the EGR cooler was recently replaced, check for proper installation and torque of the mounting bolts, which could cause a leak. If the EGR cooler is ruled out, a cracked head is likely, especially if the engine has been overheated.