Hi, I have a problem. My 86 3.8 keeps overheating, I have replaced the tstat, radiator, temp sending unit, resevior, hoses, water pump, and clutch fan. Took it to a mech who did this test to see if the cylinder that he attached to it turned blue or green to show if it has a hairline crack or needs new head gaskets and it doesn't by what he said. My timing is at 10 deg BTC. After it warms up 10 -15 minutes at the most the gauge shows that it is almost redline, when i get out and lift the hood there is no sound of boiling or anything yet the resivoir is completely full???? Is there a chance that I might need a reverse rotation water pump instead of the regular one? I cant figur this out. All suggestions or input will be greatly appreciated...
start off with a coolant flush then if that doesnt help try the reverse flow waterpump - or standard wichever you dont have.
is your coolant circulating?
Well, the water pump needs to be reverse rotation (counter clockwise) unless you've done a v-belt swap or something. Do you get copious amounts of heat from the heater core? If not, suspect a bad water pump. Another option is a bad replacement t-stat. Pull some water out of the radiator and keep the radiator cap off while warming up. When the thermostat opens, the water should drop a little bit and you'll see flow coming though. Rev the engine to make sure you're getting flow through the thermostat. You can also just remove the t-stat and run it to see if it still overheats. Let us know how it goes. If you suspect a bad sender, pull off the ECT sensor harness and take readings from it while warming up. The EEC will see the open circuit and ignore it...won't hurt anything. Here is a chart of Ohms vs. Temperature (1 (http://www.knology.net/~belchja/ACT-ECT.xls)).
Do you have the digital dash?
in 86, your car should require a reverse rotation water pump, if my memory serves me correctly