An older but interesting article concerning V6 Ecoboost/Police vehicles.
Durability and Reliability
No American police car has ever been powered by a supercharged or turbocharged engine. In the minds of many police fleet managers, the use of a turbo causes flashbacks to horror of Chrysler’s 2.2L turbo I4 from the 1980s. The mere mention raises all kinds of durability and maintenance questions.
Just as fuel injection and engine controller electronics have drastically improved in the past 30 years, so has turbocharging. And, turbos are not new on Ford passenger car engines. Ford of Australia has used turbos on its gasoline-powered Falcon sedans since 2002. Of course, Ford of Europe has used turbo diesels for ages. Forget the Chrysler 2.2L turbo engines. Turbo problems from the 1980s were solved in the 1990s, a generation ago.
The EcoBoost engine uses two Honeywell GT15 turbochargers with water-cooled bearings. These water-cooled and oil-cooled turbos are quite unlike the turbos from the 1980s that were cooled only by engine oil. The EcoBoost turbo bearings are water-cooled in the same coolant loop as the engine to bring turbo temperatures down.
The EcoBoost engineering design life is 10 years and 150,000 miles. This series of engines uses standard grades of oil; synthetic oil is not required. The EcoBoost engine uses the same 5W-20 engine oil as most Ford gasoline engines. The EcoBoost engine has the same 7,500-mile oil change intervals as other retail Ford engines. It runs on regular grade, 87 Octane fuel; mid-grade and premium are not required. The turbos do not need any separate, different or more frequent scheduled maintenance.
Introduced in 2010, the 3.5L V6 EcoBoost was recognized as one of Ward’s Ten Best Engines. The EcoBoost engine uses the base engine architecture from the Duratec 3.5L V-6, itself one of the previous Ward’s Ten Best Engines. Of course, to handle the extra torque, upgrades were made to the block, crankshaft, connecting rods and exhaust valves. The EcoBoost engine has about 75 new, different or redesigned components to improve reliability and durability compared to the naturally aspirated 3.5L V6. After all, it needs to handle an additional 100 hp!
Engine coolant is responsible for about 60 percent of the engine cooling, while engine oil handles about 40 percent of the cooling. Ford has a unique twist on this. The EcoBoost engine delivers a short spray of oil to the underside of each piston. Squirt jets deliver a 25 psi dose of oil on each piston stroke. This does two things. On a cold start, this helps to quickly warm the oil to operating temperatures, which lowers internal friction and improves fuel economy. Under normal operating conditions, of course, the oil squirt keeps the piston temperatures under cooler.
The EcoBoost engine will see plenty of retail use to get the bugs worked out before police use. The EcoBoost engine is already in retail vehicles like the Lincoln MKS, Ford Flex, Taurus SHO and just introduced for the F-150. Remember the EcoBoost engine has passed all of Ford’s durability standards for a retail vehicle. Remember, too, that some of these retail durability tests are run twice on Ford police package vehicles.
Turbo Durability Testing
The durability testing for the twin turbo, EcoBoost engine included 20 different dynamometer tests run at maximum engine speed and maximum turbo boost under a wide variety of coolant and oil temperatures. For example, cold start and immediately run at Wide Open Throttle. For example, run at Wide Open Throttle and suddenly shut down. In all, the EcoBoost engine has had 12,000 hours (500,000 miles) of dyno testing and the equivalent of 500,000 miles of on-track testing at Ford’s Romeo Proving Grounds, which totals 1 million miles of durability tests.
With the turbos from the 1980s, oil “coking” could occur in the turbo bearings. The oil was essentially baked in the hot bearings, especially the center bearing, when the engine was shut off. The result was coke, which is the solid residue formed on the bearing surface when oil breaks down due to extreme heat. This solid residue damaged bearings and early bearing failure. The bearing operating temperatures were simply too high for conventional oil and passenger car driving habits.
Of course, that was 30 years ago, making those old turbos as different from today’s turbos as the 1981 Ford LTD is from the 2011 Taurus…a 30-year leap in technology. The turbo problems of 25 years ago were solved 15 years ago. The EcoBoost engine does not have to be idled at all before shutting the engine off.
Cooled by Thermal Siphoning
The EcoBoost twin turbos are water cooled. Water cooling the bearings solved the problem. During normal operation, engine coolant is cycled through the center bearing. When the engine shuts off and the water pump stops, the coolant flow reverses and the EcoBoost uses thermal siphoning for water cooling. Coolant near the extremely hot bearing picks up heat, boils and flows away from the bearing water jacket. This pulls fresh, cooler coolant into the bearing water jacket, which picks up heat and cools the bearings. This cooling process continues silently until lower temperatures are reached, providing key-off protection for the turbo bearings.
To test this thermal siphoning process, Ford ran the EcoBoost engine at Wide Open Throttle and maximum boost for 10 minutes. Then the engine and all the cooling was abruptly shut down. The turbos were allowed to “bake” after this high-speed operation. This is exactly the conditions that would “coke” a center turbo bearing from the 1980s. They repeated the test 1,500 times without an oil change. A teardown of the turbo and inspection of the bearings validated the method of water cooling the turbo bearings.
The retail customer might operate the engine at peak power for just a few seconds, while in police use, the engine may run at peak power for a few minutes. The durability testing during Ford’s development was based on operating at peak power for hundreds of hours. The old standard used to be to test at Wide Open Throttle for a tank full of gas. Today’s durability and reliability standards are tougher. For example, a standard engine durability test was to operate the EcoBoost engine at Wide Open Throttle and at maximum turbo boost and at maximum rpm for 362 hours. That is the 24 Hours of LeMans for 15 days straight. The turbos themselves got a separate, hot-cold cycling durability test. For the thermal shock test, the turbos were warmed up to operating temperature (1740 deg F) and run at peak boost, peak power. Then every 10 minutes, the turbo alternated between peak power at maximum exhaust temperature and then at peak power at cold start temperatures. This test went on for 150 hours, about 1,000 hot-cold cycles. During the Road Cycle Durability Test, the EcoBoost engine was started cold then run at peak power and peak torque for an hour.
During the test, the coolant temperature ranged from 50 deg F to 200 deg F, i.e., normal operating temperatures. This cold start-maximum output test was done 1,000 times, for 1,000 hours of engine testing, which represents about 60,000 miles of driving.
In addition to the dynamometer and durability testing conducted at Romeo and Dearborn, Ford conducted high-altitude driving tests in Colorado, where more than 1,000 peaks are over 10,000 feet high. Then they ran extreme hot weather tests at the Arizona Proving Grounds and extreme-cold weather tests at Florida’s Elgin Air Force Base. Using a wide variety of fuels, the engine testing was performed at temperatures from minus 40 deg F to 110 deg F, and at altitudes up to 12,000 feet.
Published in Police Fleet Manager, Sep/Oct 2011
http://www.hendonpub.com/resources/article_archive/results/details?id=1091
As I said, older... but interesting.
