Block Heater Comparison Defa vs. Calix

This article is about two block heaters I have installed on my Yaris Hybrid 1.5l engine. The first 300W Defa block contact heater was installed by dealer before delivery, and second Calix 400W block heater later by myself. The reason for adding a second heater element was the first one was not doing very good job in my opinion.

Test data was measured from car OBDII bus with Android application Torque Pro, and uploaded to server for further analysis. 3 different tests were performed; Defa heater alone, Calix heater alone and finally both heaters together. Weather conditions were quite identical, and the small ambient temperature differencies were eliminated by normalising the data so that the initial coolant temperature was the zero level for all measurements.

The test

Block heater(s) on at 0 second, engine on at 3600 second and engine automatically off at 3660 second. No extra thermal isolation in engine bay, normally there is some from October to May.

Unfortunately I think I forgotten the heater(s) on when I started the engine on doing the "Both" and "Calix" tests. In "Defa" test I remember I unplugged the power from heater. That might describe the coolant temperature rise after engine stop in those two tests. I will likely redo these tests one day to get the graphs right, if there were inconsistencies as I think. The graphs can still be used up to 3660 seconds.

The graphs do favor Calix. But if we have a look what happens after the engine is started we will see that when Calix is connected, the coolant temperature will quickly drop 8°C. On the other hand if only Defa is connected, the temperature will raise about 2°C. This is due to different mounting locations of heating elements relative to temperature sensor.

Real effect after 1 hour of heating in calm conditions with Defa 300W heater is +12°C, Calix 400W +19°C and both together +26°C.

Daily results

Below are the normalised results from daily block heater use. Major variations are caused by wind conditions and grid voltage, and minor by measurement inaccuracies. The grid voltage can be 5-10% lower at cold mornings leading to 10-20% lower heating power. The final normalised temperature values are gotten by reducing the ambient temperature from OBDII coolant temperature readings. Calix heater cause false high coolant reading at first and Defa false low, so the temperature readings are taken after the water pump has rotated for few second to even out the temperature differencies in the engine block. The temperature drop/jump can be seen in the graphs above.

I have added some isolation on top and front of the engine to reduce heat loss.

Published on  January 27th, 2014

Yaris Hybrid: Yaris 1.33VVT-i MMT: (ex) Urban Cruiser 1.33VVT-i