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THE CAR DOCTOR

Get past the gauge to fix oil pressure drop

Plus: Help for Opel driver, clogged radiator

By John Paul
Boston.com Columnist / February 9, 2009

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Q. I own a 2002 Buick LeSabre Limited. I recently noticed that the oil pressure gauge is now reading 25 at idle and 45 or so while driving. In the past it normally read in the 50-65 range. The car has 99,000 miles. Is it the gauge or is this a sign of more serious problems?

A. The specification calls for 60 pounds of oil pressure at 1,850 r.p.m. using 10W-30 oil. If the pressure is less than this it could be the result of a worn oil pump, engine wear, faulty oil sender switch or even low oil. The first thing you should do is check the oil level and the condition of the oil itself. If the oil is diluted it will cause the oil pressure to fluctuate. If the oil looks good, most technicians will remove the factory switch and install a mechanical gauge to measure the actual oil pressure. If the oil pressure still reads normal they will replace the oil pressure sending unit. If the oil pressure still reads low then they will look for other problems.

Q. My car doesn't seem to be heating up the way it used to. The heater gauge only goes up two lines, when in the past it would go up at least halfway on the gauge. What could be the problem?

A. The very first place to start is looking at engine temperature. The engine temperature is controlled by the thermostat in the cooling system. If the thermostat is opening prematurely, the engine will not get up to operating temperature. Replacing the thermostat should solve the problem. At the same time, the garage may recommend flushing out the cooling system. This will wash away any rust or scale that is in the radiator and engine.

Q. I own a 2004 Opel Zafira with the 1.8 liter engine. The engine vibrates at 2500 r.p.m. and at idle. What causes this? The sensors read okay, and the engine runs smoothly, even going uphill. I know this is a long shot that you will answer me from the States, but I need your help.

A. Using the theory that basic diagnostics are the same even on vehicles that I'm not familiar with, there are a few areas that you may want to examine. I would look first at the engine mounts. The motor mounts hold the engine in place, but in many vehicles also counter engine vibration. This is especially true with a diesel engine such as the one in your Opel. Since there are no codes present and the engine runs well, then the motor mounts could be starting to fail.

Q. I have a 2000 Civic Si and the engine seems to be running hot. The temperature gauge in the cluster goes past the middle mark. The car has overheated twice, once this winter. I am not new to cars but am kind of stumped. Could the radiator be the major cause?

A. It is possible the radiator is starting to clog. You can test the radiator with an infrared non-contact thermometer and look for cold spots. These cold spots would indicate a clog in the radiator. You could remove the radiator and perform a flow test to check for blockage. At this time you could also look at the radiator hoses and thermostat. My other concern is that Honda vehicles, as well as many others, don't fare well when they overheat. It is possible that when the engine overheated in the past it may have caused a problem with the cylinder head gasket.

Q. My 2002 Town & Country Chrysler with a 3.3 liter engine and 4-speed transmission is having a problem. During deceleration it shifts hard between third and second gear. I replaced the front transmission mount and axles, but the problem continues. Any ideas?

A. The problem may be in the transmission itself. Have a technician look at the values of the transmission with a computer scanner. It is possible the CVI (clutch volume index) is of specification. Using a specialized scanner, a technician should be able to perform a relearn procedure and perhaps cure the problem.

John Paul is the public affairs manager for AAA Southern New England. He can be reached at jpaul@aaasne.com.