Coolant Contamination We all know that neglected coolant can lead to a clogged cooling system and a loss of cooling system efficiency, but it can also cause other less obvious problems. The buildup of coolant scale and deposits can coat or corrode the exposed surfaces of engine temperature sensors, affecting their accuracy. Inaccurate sensors may send incorrect information to the computer, and temperature controlled vacuum or electrical switches may fail to function properly. Any of these may cause drivability problems. If the coolant's age or condition can't be easily determined, there is a quick check for coolant contamination using a Digital Volt-Ohm Meter (DVOM). Attach the positive DVOM lead to the radiator, then dip the negative lead into the coolant at the filler neck. A voltage reading of 0.2 volts or less is very good. A reading of 0.5 volts should be considered borderline and anything over 0.7 volts is unacceptable. If the coolant fails this test, the cooling system should be thoroughly flushed and cleaned. Remove any engine temperature sensors and inspect them for contamination or other damage. Repair as necessary. Always check to make sure that the ground straps are in place and complete connections are made. Visit our Resource Library for available downloads