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An overheating engine has long list of possible suspects

  • Article by: PAUL BRAND
  • April 20, 2012 - 4:08 PM
Q My daughter drives a 1998 Dodge Stratus ES with more than 120,000 miles. Recently, the engine started overheating. At highway speeds, the engine operates within the normal temperature range. At city speeds, however, the engine quickly overheats.

No steam appears when the engine is overheating, so I assume the radiator cap and hoses are not leaking. What tests I can do to rule out the simple problems like a worn radiator cap, malfunctioning thermostat, plugged radiator, or air in the cooling system? Your advice is greatly appreciated.

A Is the car actually overheating? True overheating occurs when the coolant reaches its boiling point, creating bubbles in the coolant that hamper the coolant's flow from the water pump. This leads to increasing and ultimately out-of-control coolant temperatures. Excess pressure will force open the cap and drive boiling fluid into the recovery tank. There may also be bubbling and boiling felt and heard in the upper radiator hose -- be careful to wear gloves and never loosen or open the radiator cap when the coolant is hot!

Here are the "ifs." Overheating can occur if the radiator cap does not hold pressure in the system. Normal coolant temperatures can exceed 212 degrees, so if the cap can't hold pressure, the coolant can boil at normal temperatures.

Is the electric fan operating? The fan should come on when coolant temperature reaches a certain level or when the air conditioner is on. Test by turning on the A/C.

Are the front of the A/C condenser and the front of the radiator clear of leaves, bugs and debris? You may have to remove the upper radiator cover to check the front of the radiator. Flush from the rear forward with compressed air or water.

If the thermostat is not fully opening at the proper temperature (typically 195 to 205 degrees), engine operating temperatures may be too high. Coolant coming from the thermostat outlet should be at full operating temperature. If the water pump is not pumping adequately due to a slipping belt or worn impeller, coolant will not circulate properly.

And finally, if you start the engine from dead cold with the radiator cap off, does coolant bubble out of the filler neck? If so, combustion pressure may be getting into the coolant from a head gasket leak.

Q I asked my Dodge dealer about servicing the four-speed automatic transmission on my 2004 Dodge Ram 3500 diesel. He said that they drop the pan, drain the fluid, adjust the bands, replace the filters and put new fluid in. I also asked an independent shop and they said about the same thing as the dealer with the exception of adjusting the bands -- they said that the bands are not adjustable on that transmission. Who is right?

A The dealer. The 48RE four-speed transmission has two bands -- the front kickdown band and the rear low/reverse band. Routine transmission service suggested by Chrysler should include this: "Check the adjustment of the front and rear bands; adjust as necessary."

Q I've got a 2005 Toyota Sienna with about 65,000 miles on it. Recently, when I make a 90-degree right turn or accelerate quickly, the parking brake warning light flashes on momentarily. Left turns and braking do not prompt the same problem. I have disabled the anti-skid system and saw no change. Of course I have set and released the parking brake itself as well, with no change. Could this be something like a rear disk brake/parking brake wear sensor or a loose micro-switch?

A Remember the "KISS" (Keep It Simple, Stupid) principle. In automotive vernacular, it means look for the simple answers first. Check the fluid level in the brake master cylinder. If it's low, it can create exactly the symptoms you describe. When accelerating or cornering, the fluid moves away from the level sensor, momentarily triggering the warning light. Inspect brake system wiring harnesses for shorts. A scan tool can identify issues with the brake or traction control systems.

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