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302 | Electric Water Pump Control - PWM Strategies

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This question is around setting up the Duty Cycle table when the EWP is controlled by PWM.

So my setup

Honda K20a, Davies Craig EWP 115 controlled by Link ECU (G4x) via PWM (Solid State relay) at 100hz.

Full ducting into radiator and out bonnet.

No coolant restrictor, 32mm pipes, no themrostat.

Original Duty Table:


Original Logs:


It was all carefully set up on dyno with air flow just from the fan and worked well, but out on track it's not working very well.

On a 11 to 14c day it took ages to warm up, and on track I initially struggled to get the car to stay over 70 degrees before my radiator ducting collapsed which then allowed the car to get up over 80c.


So I've added an 18mm restrictor before the coolant goes back into radiator to slow the flow down and hopefully widen the operating band of the pump.

But I've also tweaked the duty cycle table, and that's what I'm really interested in feedback on for cars where the cooling capacity is higher then required.

So my first thought (untested on track) was to keep the flow of the pump low until the car is up to 80c.

Increase flow slightly with RPM just to make sure the temp sensor is getting an accurate temp quickly.


But then you still have this target at 85c for the pump duty cycle

where if the days colder/hotter then you expect,

or the cooling flow through the radiator is more/less then you expect

then that target doesn't match the conditions and you end up cycling the ewp up and down a lot.

So I'm not sure if that's that useful, but while testing it I noticed the interpolation between cells that link does, and that gave me an idea.

Why not set the duty cycle at 84c to 1% and at 86 to 98% and let the ecu interpolation between the cells,

i.e every .1 degree change is going to increase/decrease pump speed and it should naturally settle itself at some point appropriate to the conditions of the day.


Is something that would actually work? Or is there risks involved with this approach?

I've typed out a response 3 times now then click one of the links above and loose it haha. So i've add your DC images below..

Original Duty Table:

New table 1

New table 2

If you scale the ET, do the peaks and troughs of the line up (peaks match DC peaks etc)? I wonder if there was some lag in the system.

The ramping doesn't matter too much provided it holds the temp where you want it. I've always thought EWP control would be similar to idle control, where you might have an aim and feed forward table and some PID settings, but I suppose the system reacts more slowly.

I wonder if you need a bit more of a band for hysteresis around the operating temp? Because I wonder if you'll find it doing something similar to previous with new table 2.

There is some lag in the system depending on speed of pump.

It's all very frustrating, I just want to set a target temp and let the ECU work out what it needs to do to get there (within parameters).

I managed to get out on track again, ultimately I ended up with half the ducting taped off and a range from 80 to 95 in the ecu, once the engine got up over 83 degrees it tended to settle in between 85 and 88.

The issue was getting it from 75 to 83, it tended to react too aggressively and overcool, then bounce back and forth before finally getting up to temp.

But it took a lap or too, which just isn't going to work, so I'm just going to put a thermostat in and have like a 6mm hole to always bleed some water through. I might end up setting pump to 50% duty cycle (30% is enough to cool engine now) up to 90 degrees then jump to 100% over that to at least limit the current draw most of the time.

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