After doing head gaskets (and lots of new cooling system parts) exactly 12 months ago, after which the cooling system in my Anny was well behaved without fail, I went to buy gas a few days ago, 80° out, and sat in line for a short while waiting my turn w/the engine running, A/C off. Noticed the coolant temp climbing higher than it should, past M (usually not past O|R)...fan finally came on, no drama, but not good. Got home, noted the coolant level in the expansion tank was past HOT and started checking why.
No fail w/the fan, just that it was coming on late. No leaks, no bubbles in the expansion tank, no codes, radiator cap/IRCM/thermostat/both fan speeds all checked good...hoped it wasn't another head gasket so did a combustion-gas-in-the-coolant test which came up negative.
Volts in/out at the ECT seemed off given the heat that it took before the fan came on, but it's connector was clean and a new sensor didn't help. I moved up the harness to the large grey main harness multi-wire connector (C172?) back near the self-test connector & ABS relays (while wondering if maybe the ECU was borked) to check ref. signal at the connector with it open so I could lay eyes on pins. Bingo...green means stop.
Cleaned everything up, reconnected, problem solved, signals dead on specs at ECT. Looks like the signal was off enough to cause late lo speed turn-on, but not enough to throw a code. Time to start checking every connector I can reach that I know hasn't been opened/inspected in the last few years...or more.
No fail w/the fan, just that it was coming on late. No leaks, no bubbles in the expansion tank, no codes, radiator cap/IRCM/thermostat/both fan speeds all checked good...hoped it wasn't another head gasket so did a combustion-gas-in-the-coolant test which came up negative.
Volts in/out at the ECT seemed off given the heat that it took before the fan came on, but it's connector was clean and a new sensor didn't help. I moved up the harness to the large grey main harness multi-wire connector (C172?) back near the self-test connector & ABS relays (while wondering if maybe the ECU was borked) to check ref. signal at the connector with it open so I could lay eyes on pins. Bingo...green means stop.
Cleaned everything up, reconnected, problem solved, signals dead on specs at ECT. Looks like the signal was off enough to cause late lo speed turn-on, but not enough to throw a code. Time to start checking every connector I can reach that I know hasn't been opened/inspected in the last few years...or more.
Last edited: