overheat and alt not charging

[sunbird3400]

i have a 90 cav 3.1 5 speed i just bought it and it over heats amd the alt is not charging the battery, i changed the cooling fan relay (no difference) and tested the batttery and alternator and advanced auto (both good) i think there related, any ideas im stumped.

[2.8-350TBI]

ummmm is the serpentine belt on???

The water pump and the alternator run off it, so that the first thing that come to my mind lol

[Azrael]

Does the alt charge the battery at all while the engine is cool and stop when it's overheating? That would indicate an internal short of the cooling fan. A multimeter measuring resistance on the fan's terminals will tell you if there's a short. A few ohms is normal while zero = short circuit.

Otherwise, both systems should be electrically independant so it could be two different problems. The voltage regulator circuit could be dead or have a bad connection to the alt. And the impeller in the waterpump could have come off it's driveshaft. If no coolant is flowing then the PCM won't know how hot the coolant is and never start the fan until it's too late.

[pocket-rocket]

The (+) lead from the battery to the alt could be broken internally if it doesn't charge at all and the alt tests out good on the bench at the parts store. Try running a jumper wire from the alt to the battery as a test to see if it will start charging. Also check your grounds.