Water temp drop through radiator

[Greg Lindahl]

Yes, this question was posed in the Shifter Kart section, to no avail.
Have any of you measured the in and out temperatures of water through your radiator to log the actual temperature drop of the coolant?
I've measured cooling air temperature at front and back of my radiator and found that it varies between 10 - 25 F depending upon air speed; high air speed = ~10 F and ~25 F at low air speed.
Does anyone know temperature drop numbers?

[Ian Harrison]

Hi Greg

We did this many years ago now and much as you say the results were very variable depending on speeds, ambient temperatures, track design, speed of water flow, etc., etc.

The conclusion we came to was that it dosen't matter in the slightest (unless perhaps you are actualy specifying a bespoke radiator).

What is important is that the water leaving the top of the cylinder head remains in the range of 40-55 degrees Celsius, except perhaps in real extremes, when from 55-60 deg is just acceptable and above 60 deg is a no-no with regard to power production.

As long as your rad/water speed (it can be too fast) provides sufficient cooling for the harshest conditions then control can be effected with race tape, etc.

Best Regards

Ian
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[Greg Lindahl]

Thanks Ian.
I follow your logic on this but I have a plan to cool something else with radiator return water, if it is cool enough. I'm set up to gather the in and out temp's at the next race. However, I'd like to add the load for that race; thus the question.

[Robert Daniel]

With the typical water/air heat exchanger it is impossible to get the water speed too high. I have tested many heat exchangers on the dyno and the faster the water flows the lower the engine temp.

[Greg Lindahl]

Now, that's an interesting piece of info!
Have you every measured the incoming verses outgoing temperatures from an air to water heat exchanger?

[Robert Daniel]

I have measured the in and out but don't have the data in front of me.
High flow rates have a small delta T and the converse.

[Ian Harrison]

Hi Guys

I have found the reverse to be true with regard to the 2001 CR250.

I have also been led to believe that this is also true with regard to air speed through the radiator itself, which is why the air inlet duct size of 1/3rd of radiator face area is most popular.

If anyone looks at an '01 headgasket, the water flow holes are only about 8mm dia, whereas the casting slots either side are perhaps 7 or 8 times bigger. When the gasket is removed and the head is 'O'-ringed, the speed of water flow increases and yet the operational temperature also increases for a given set of circumstances.

If a restrictor is then introduced into the top hose, the operational temperature falls again. Some people even weld up the channels in the cylinder/head and just drill holes that replicate the gasket.

In our UK climate, this is not too critical and we just tend to run with the standard channels.

I can't say whether this effect is due to heat transfer speed out of the cylinder into the water or out of the water into the air (i.e. through the rad), but is is an observeable and easily repeatable fact in an Anderson/'01 Honda package fitted with just a side rad.

Interestingly enough, the '02 - '07 heads already have only the small 8mm holes as per the gasket.

Best Regards

Ian
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[Robert Daniel]

Hi Ian,
It would seem in the case you describe the issue is the engine side of the situation, rather than the heat exchanger. Possibly the change to the o-ring head allows laminar water flow around the cylinder and therefore changes the delta T. I don't know.

[Ian Harrison]

[Andy Kiker]

[Andy Kiker]

[Sam Moss]

Has anyone measured the flow rate from the pump?

Possibly the flow rate out of the cylinder head is slower than through the holes on the bottom of the head so an increase of hole diameter would make the head less efficient as the water is passing through too quickly reducing heat transfer and just getting blocked when it tries to exit the cylinder head.

The water can only flow as fast as the smallest diameter pipe will allow it to as you know. Which is why I often wonder why we can have 22mm ID water pipes when the exit from the cylinder head is only 19mm ID?

[Allan Litten]

I suspect that you also have a reasonable amount of aeration in there too as the water pump impeller has an efficient curve which would drop off considerable on such a large RPM range.
Food for thought?

This might have more to do with slowing the water flow down than the thermal transfer in itself.

Maybe modifying the impeller to reduce cavitation at high RPM? - any pump engineers out there that can help?

[Ian Harrison]

[Greg Lindahl]

Restriction as the water leaves the head is used to reduce the surface boiling by raising water pressure in the head, which has the hottest surfaces in the engine.
Laminar flow is not the goal, tumbling action is best for heat conduction from surface to fluid.
Have tested with variable flow valves on head water outlet and results are interesting. Test conditions were wide open with o-rings, therefore free flow: Wide open temp is warmer than restricted and highly restricted stays cool until a surprisingly high level of restriction before the temperature rises again.
Thought there might be HP to gain with restricted flow because the pump is NOT positive displacement and will spin through the water (cavitatation?, don't know). Less pumping = less HP loss. Not measurable in lap times, which was my only measurement capability. HP to drive the pump IS quite low however and not what you might think (~2 - 4% and you MUST have a pump for cooling).