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Intercooler Monitor

Real time monitoring of intercooler efficiency

by Julian Edgar

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At a glance...

  • Directly monitors intercooler efficiency
  • Easily configured to drive flashing warning light or pulsing alarm
  • Can be used to control an intercooler water spray
  • Uses cheap and mostly prebuilt electronic control module
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It’s not uncommon for people with turbo or supercharged cars to fit intake air temperature gauges. As the name suggests, these measure intake air temp, usually by means of a remote probe digital temp module.

But what if you don’t want to clutter your dash with another gauge? Instead you want just a single light to show when there’s a problem with the intake air temp?

Sounds fine – but what does “when there’s a problem with the intake air temp” really mean? Usually, it means that the intercooler has become heat-soaked and is no longer working properly. Let’s take a look at that concept.

Intercooler Efficiency

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An intercooler works by exchanging heat with an external cooling medium – that’s usually air but in some systems it can be water.

When an intercooler is working effectively, the intake air arrives hot and leaves a lot colder. Therefore, there’s a temperature drop across the core.

A perfectly efficient intercooler would drag the temperature of the compressed air down to ambient. But no intercooler is perfectly efficient, so the temperature drop across the core is always much less than this. For example, when a car first comes on boost, the temp drop across the intercooler might be 40 degrees C – the air coming from the turbo or supercharger is at 90 degrees C but after the intercooler it is decreased to 50 degrees C... a 40 degree drop.

However, stay on boost for a longer period and the intercooler will start to heat-soak, its efficiency (and so the temperature drop across the core) getting less and less. With some intercoolers, after being on boost for a while, the temp drop across the core can end up being only about 10 degrees C!

So to measure the effectiveness of the intercooler, we can use two temp sensors – one on the inlet and one on the outlet. If the temperature difference is high, the intercooler is doing a good job. But if the temperature difference is low, the intercooler isn’t working very well. And that means you should back off (or turn on a water spray).

Therefore, by using two temp sensors placed appropriately, we can directly measure intercooler efficiency and indicate to the driver when efficiency is falling away. The driver can then be alerted to the problem by a flashing light or pulsing buzzer.

Sounds good – but how do we do it? Pretty easily in fact.

The eLabtronics Pulser

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The heart of the system is the eLabtronics Pulser - see eLabtronics Pulser Part 1, for our introductory story on the design. This pre-built electronic module costs only AUD$59 and is available at the AutoSpeed Shop - eLabtronics Pulser Module - Pre Built. In this Intercooler Over-Temp Warning application, you’ll need four extra components – two temperature sensors, a resistor and a pot, the latter allowing the switch-on point to be adjusted. But don’t panic – these extra components cost only AUD$12.95 (see Performance Modules Accessory Pack ) and are easy to wire into place.

With the system you can set the threshold at which it triggers (that is, how much difference there is between the outlet and inlet temps), and also the pulsing behaviour - how quickly the light or buzzer pulses. (If you want, you can also use the module to directly drive a pump to operate an intercooler water spray – more on this in a moment.)

Putting the System Together

We suggest that you first assemble the system on the bench so that you can test its functionality.

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The Pulser module has a high current output transistor called a MOSFET, a fuse, four wiring connections, an option switch (not used in Pulser configuration) and two user-adjustable multi-turn pots.

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As can be seen in this picture, one pot controls frequency and the other pot, duty cycle. These controls are used to adjust the output of the Pulser – whether it flashes the warning light fast or slow (frequency), and for how long the pulse is on each time (duty cycle).

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The warning light (or pump or buzzer) is wired between the output of the Pulser and ground. If the load has a polarity, positive goes to the Pulser.

To test the system, connect the load (light, buzzer, etc), 12V power and ground.

Adjust the Frequency pot half a turn anticlockwise from the fully clockwise position. (Note: These pots are multi-turn so don’t expect to make only one rotation when setting them. Multi-turn pots also don’t have clear end-stops [although they can sometimes be heard clicking when they’ve reached the end of their adjustment] ).

Set the Duty Cycle pot to roughly the middle position.

Temporarily connect a wire from the 12V feed to the Input terminal. This turns the Pulser on.

Your light or buzzer should then pulse. Adjust the duty cycle and frequency pots to give you the behaviour you want.

Now that you have the Pulser working correctly, disconnect power.


The next step is to mount the sensors. The two sensors are called thermistors – they are components that change in resistance with temperature.

The thermistors come as bare electronic components. To wire them into place, you’ll need to do two things: solder them to extension cables and mount them.

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Here’s a bare thermistor.

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Shorten the leads and then solder two long insulted wires to the leads. Give yourself plenty of length to work with – you don’t want to later have to extend these cables.

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Use tape or good quality heatshrink to insulate the connections, both from each other and also from anything they could touch.

The sensors can be pushed down in the fins of the intercooler and if required, held in place with a dob of silicone sealant. But don’t do that yet – you still haven’t tested the full system on the bench.


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This diagram shows the wiring, minus the load (light, buzzer, etc) and power and ground feeds to the module. (A complete diagram will be shown in a moment.)

(Note that this circuit is a little different to the one presented in Part 2 of the Pulser series. Note also that the pot wiring is shown from below.)

The required components are:

  • 1 x 200 kilo-ohm resistor

  • 2 x 100 kilo-ohm thermistors

  • 1 x 1 meg-ohm potentiometer (“pot ”)

The wiring is carried out as shown here.

  • The ‘cold thermistor’ is placed on the outlet of the intercooler.

  • The ‘hot thermistor’ is placed on the inlet to the intercooler.

When the cold thermistor is (say) less than 15 degrees C lower in temp than the hot thermistor, the Pulser will be switched on. This temp difference can be set by the pot. Make sure you label the outlet and inlet sensors so that you know which is which!

In this circuit, turning the pot clockwise increases the temp difference at which the Pulser turns off. With the depicted components, the selectable temp difference is from about 0 degrees C to about 100 degrees C.

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This diagram adds the load, and power and ground connections. We recommend that you also set this circuit up to test on the bench. Click on any of the diagrams or photos to enlarge them.

When complete, adjust the pot anti-clockwise until the warning (light or buzzer) goes off. Then adjust this pot a little clockwise until the warning goes on. This indicates that there is not sufficient temp difference between the sensors. Heat the inlet sensor (or cool the outlet sensor!) and the warning should go off. You can use a soldering iron to apply heat to the hot sensor and/or ice to cool the cold sensor.

Using a multimeter to measure the voltage on the Input will let you quickly see what heating and cooling the sensors does to the input sense voltage. Depending on the individual module, the turn-on point is about 2.6V and the turn-off point about 2.4V.

If all is working correctly, you can install the system in the car. If there is a problem on the bench (and the Pulser worked correctly when manually triggered by connecting the Input to 12V), check your wiring of the pot, thermistors and resistors. Don’t forget the required values – 100 kilo-ohm thermistors, 200 kilo-ohm for the resistor and 1 meg-ohm for the pot.

Understanding the Warning

This system detects the temp drop across the intercooler. When you first start the car, the inlet and the outlet temps of the intercooler will be the same – so there will be no temp drop and so the monitor will trigger.

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To an extent that’s OK – it shows the intercooler is yet to start functioning – but if it bothers you, put a load switch (boost or throttle position) in the Input lead so that the system comes alive only when the car is on boost or at high loads. Even if the Pulser is powering a big load, this switch carries only a very small current.

Triggering a Spray

If you set the duty cycle pot on the Pulser to 100 per cent, the output will be continuously on whenever the temp drop across the intercooler is too small. You can directly drive an intercooler water spray pump with this output. Match this with a boost or throttle switch (as described above) and this approach can work very well.

You can also adjust the Pulser’s duty cycle and frequency controls so that the intercooler spray pulses, something we’ve found in the past very effective at reducing water consumption without reducing the cooling affect. A good starting point is the pump flowing for 2 seconds every 5 seconds. Check this timing with the pump, reservoir and nozzle actually connected - some pumps take a moment to get into their stride.

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The pump can be wired directly between the Outlet terminal and ground. If you are using a very high powered pump, you may need to fit a heatsink to the MOSFET. (See eLabtronics Pulser Part 1) for more on required heatsinks. None will be needed to drive a warning light or buzzer).


Either used to trigger a simple flashing alarm light, or in conjunction with a boost pressure or throttle position switch to control an intercooler water spray, the Intercooler Monitor achieves the unique outcome of directly and in real time measuring actual intercooling efficiency.

The Pulser is available fully built and tested from the AutoSpeed Shop

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