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What techniques could be used for sensing coolant level?


Boss

The news is reporting issues of engine damage from coolant loss in a modern car engine. It would appear that a dashboard warning is either missed by the driver or is too late to prevent damage. Hence the 'drive' behind this idea, which for a few pounds could save the £8k typical engine replacement costs when a piece of tubing fails...

I am thinking of a simple add on that could detect coolant loss sooner than the current method which seems to be sensing the engine block temperature which will rise rapidly BUT after the coolent is lost. Hence the radiator header tank seems a better sensing point..

My aims are:

1. External to the header tank. I simply do not wish to drill holes and introduce other problems!
2. It has to cope with the engine environment temperature extremes.
3. Work on a typical 'plastic' semi transparent header tank.

An example tank is shown below. Unfortunately Min and Max straddle the welded joint, but sensing in the area of the green line would be an example sensing surface and range.

Coolant_header_tank_7d00223107f434c588f2a32c4f00b84462db6c60.jpg

Just for starters my thoughts are:
1. A multi-capacitive type sensor which will detect the change from coolant being present or not. So think of something like a capacitive touch switch sensor strip.
2. Using opto reflective sensors  127-3057 . Could these sense the coolant (which has colour) through the housing?
3. This could be my favourite to try out! A LED shining through the top of the housing and multiple optical sensors700-0776 down the side. This seems to have the advantage that the coolant surface refractive/reflective properties as well as optical density may provide a nice transition to detect. It may be that the sensor colour could be matched to the coolant colour for improved detection?

This is simply just the 'first idea' step and I'm just thinking of the level sensing at the moment, so issues of fluid splashes and slopping around will be thought about in more detail later.
Any thoughts on the problem, suggested solutions or other techniques?

I will not be selling this but if I actually make anything I will publish on DesignSpark as a project.

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