What's the Octane?
Q: I have a 2002 Sport Trac with 46,000 miles on it. Not long after I bought it used, a noticeable valve clatter began. It mainly happens when the engine's warm, under load, and the A/C is on. Once the heat of the day takes over, the clatter is almost continuous. The dealer says there's nothing he can do to remedy the noise and suggests using higher-octane gas and thicker motor oil.
A: Higher-viscosity motor oil isn't the answer to valve clatter. Your description sounds more like a spark knock, which has always been a temperamental automotive complaint. The noise can be difficult to reproduce, occurring intermittently under specific temperatures, speeds, and load conditions. Adding to the equation, most automakers state that a slight spark knock or ping under light acceleration are normal characteristics of a low-emissions, fuel-efficient engine. Before switching to a higher octane rating, try the recommended fuel from a different company and station. Also be sure that the service department has updated the PCM with the most recent calibration. If the EGR system--which bleeds exhaust gas into the air/fuel mixture to reduce combustion temperature--isn't functioning as designed, that also can cause a spark knock. A worst-case scenario would be an internal condition such as excessive carbon buildup on top of a piston. Ask the dealership to be sure it's not a timing-chain-related noise. Some of Ford's 1999 to 2002 4.0 liter V 6 engines produce a rattling noise that sounds like a spark knock under acceleration between 2000 and 3000 rpm. A modified primary timing-chain tensioner kit corrects the problem. After that, get the vehicle to the dealership when the engine's hot and consistently producing the noise. Ask the service manager or next highest in command to drive the vehicle to confirm the condition.
Losing Your Cool
Q: When I start my 5.7-liter, 1998 GMC Sierra 1500, the oil pressure goes up to 50 psi. After 10 minutes or so, when I come to a stop, it drops down to about 20 psi. Then the pressure returns to 50 psi while I'm driving. Is that normal? I also hear a slight ticking that doesn't sound like a valve. Could it be a lifter? The truck only has 84,000 miles on it. Also, my truck usually runs a 185- to 190-degree water temperature, but now it's running at 145-150 degrees. I recently replaced the water pump, thermostat, and hoses. Could I have done something wrong?
A: The oil pressure sounds perfectly normal. Pressure increases and decreases with engine speed and drops as the oil warms up and thins out. Minimum oil-pressure specifications at normal operating temperature are six psi at 1000 rpm, 18 at 2000, and 24 at 4000. Some 5.7 liters do make noise. There were issues with connecting-rod and main-crankshaft bearings causing knocks, with modified bearings recommended as a designated fix to adjust oil clearances. These engines also can produce a "tick" from a defective valve lifter. And there's a Technical Service Bulletin in effect (number 00-06-04-045) to correct a less-conventional cause of a ticking noise from the engine compartment. This one can sound like valvetrain noise or detonation and usually occurs when the engine's hot and under load. The cause is waves of exhaust pressure traveling by the air injector reactor (AIR) check valves and into the adjoining hose. The AIR system pumps air into the exhaust to help convert carbon monoxide into carbon dioxide and burn hydrocarbons (unburned fuel vapor). Three baffles can be installed in the AIR hose to reduce the noise. Finally, the thermostat should be maintaining the engine's coolant temperature between 188 and 206 degrees. If your coolant temperature has dropped out of range since replacing the thermostat, the new one may be defective, installed incorrectly, or something has affected the accuracy of the coolant-temperature gauge.