Oil Pan Heater Thermostat Bypass

[Maddmatts]

Kudos to Blue Angel on the Cruzetalk forum for this DIY:
DIY - Oil Pan Heater Thermostat Removal

I came across this while trying to figure out why the oil pan heater has a thermostat that only allows it to operate when ambient temp reaches -18C/0F or lower.

The bypass basically involves:
1) Remove the black circular cap on the heater plug. The cap is easier to remove/install if the rubber surround on the plug is warm and pliable.
2) Remove the little metal thermostat switch.
3) Pull up the two tabs and solder a 16ga or larger wire from one tab to the other.
4) Reinstall black plastic cover.

More detailed instructions with pics are in the link above.

It turns out the reason for the thermostat wasn't entirely arbitrary or due to liability concerns like I would have thought. The ECM compares the readings from the IAT and ECT sensors during cold starts to check for faults. Engineers wanted to keep the heater from causing the ECT sensor to read too high compared to the IAT causing false positives.

The thermostat's setting is fairly conservative and you can get away with using it on warmer days. Not that I suggest using it in the summer, but I've always felt that -18C was a little late to start using it.

 

[Papasonic]

Good find! I have never used mine because we seldom see 0 degree temps here, or not for extended periods of time; but I would like to be able to use it for temperatures below 20 degrees, as I believe it may contribute to less engine wear caused by cold starts.
Many years ago, I used a device called a thermo-pump that installed in a heater hose. I would plug it in at bedtime, and in the morning, no matter how cold it was, the car started as if it were a summer day. Even the windshield was free of frost or ice, and there was heat available as soon as it was started. Using such a device on modern cars would be difficult to accomplish because of electronic and vacuum operated heater control valves, and electronic thermostats that are controlled by control modules. Even access to a heater hose that would accommodate such a device is challenging. Sometimes I miss when times and vehicles were more simple.

 

[wpgsonic]

My Sonic does not have the thermostat on the plug and the dealer confirmed mine works whenever it is plugged in regardless of temp,so I assume not all Sonics have the heater with the thermostat on it.

 

[Maddmatts]

My Sonic does not have the thermostat on the plug and the dealer confirmed mine works whenever it is plugged in regardless of temp,so I assume not all Sonics have the heater with the thermostat on it.

I think our heater uses the exact same cord connector at the element as every other block heater GM has used for quite awhile. It's possible yours could have been replaced at the dealership with whatever cord they had on hand before you received the car.

That makes 2 options to lose the thermostat.