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Old 02-24-2013, 04:52 PM   #1 (permalink)
Blue Angel
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Location: Ottawa, ON, Canada
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Cruze Eco MT - '12 Chevrolet Cruze Eco MT
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DIY: Bypass GM Block Heater Thermostat

I have a 2012 Cruze Eco and I ordere the oil pan heater as an option. I was under the impression it was actually a block heater when I ordered it, but it is nothing more than a small 200W steel heating elememt pressed to the side of the oil pan. It was only a $65 option, so I can't complain too much.

This oil pan heater does exactly what it is supposed to do and nothing more; it keeps the oil warm during extreme temperatures.

GM has installed an in-line thermostat switch that only allows the heater to work below -18C (0F). This is done to avoid confusing the cold start diagnostic tests, one of which compares the readings of the IAT and ECT sensors at start-up. If certain conditions/discrepancies are present, a DTC is set.

I wanted to use the heater at any temperature, so I bypassed the thermostat switch. Here's how if you're interested in doing the same.


1. This may result in setting a P0116 code. Read up about this condition here, post 36 and 42:

5.3L engine block heater - Page 3 - Ask the GM Technician - - Page 3

2. Your oil pan heater cord is expensive to replace and this is a permanent modification requiring soldering to get it functional once the thermostat is removed.

3. You are modifying a 120V electrical circuit. Electric shock, short circuits, damage to your vehicle's electrical system, and FIRE are allrisks you need to fully understand before doing this yourself. Do not proceed with this unless you are comfortable. Do not blame me if this doesn't work out. YOU HAVE BEEN WARNED.

Step 1, pull the round plastic thermostat cap off using pliers and a back and forth rotating motion. I used a rag to keep from marking up the plastic. You will see the top of the thermostat. Using your pliers, gently pull the thermostat out while twisting back and forth. Doing this will permenently pull apart the crimped connections on the thermostat, so go slow and be patient, twisting and pulling gently until the contacts pull apart. You should have something like this when done:

Now bend up the little tabs and solder a piece of 16ga (minimum) wire across the terminals:

Now push the cap back on using the pliers and rag. This will take a little effort and patience, just keep pushing and twisting, and you might have to push the rubber plug material up a bit also:

Once you're done it helps to check your work by plugging into a power meter to make sure everything is working OK:

This process will work for the Cruze and any other vehicles that use the same plug with the integrated thermostat switch. HOWEVER, the heater on the Cruze is only 200W and so far has not caused any issues with start up diagnostics. I would strongly reccomend finding out how powerful the OEM heater is on other GM vehicles before performing this modification. A more powerful heater, or an actual block heater that directly warms the coolant, may pose a higher risk to messing with the start-up diags.

2012 Cruze Eco 6MT
If it's slow, it might as well be efficient!

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