Question for Cooling Engineers

[Jeff]

removing a thermostat is a BAD idea.

If you're gonna do that, just gut the thermostat or buy/build a restrictor plate.  You want the flow restricted or there will be no heat difference in the coolant.

Likewise, I don't think it's necessarily a problem in the honda, it's just the way it was engineered.  There is no real ill effect from it on a whole model basis.

[Jason748]

Interesting question.... & 

In my past expericence both must be considered, but (just to over add to the overanalyzing) you also have to factor in the effect it is having on combustion chamber tempature.  This then trickles down to chamber shape & design, actual composition of the alloy used to cast the head (thermal coefficient), piston crown design, piston tempature differential, etc.....
Some engines are designed to run "hotter" and may actually have more efficient combustion at a coolant temp of around say 230ish, than if they are run at a lower temp, say 180ish.

I suspect that the CBR600RR's run hotter than average becuase they were designed to.  But without actually knowing the effect the coolant temp is having on combustion there is no way to be sure.

So.... for a short anwers, I have no idea which is better, without knowing & analyzing the rest of the variables.


Hey..... quit analyzing your cooling system and write up the lastest BHF race report.

[Jeff]

Hey..... quit analyzing your cooling system and write up the lastest BHF race report.

I've actually got it written, I just need to sort out a few pics and get it up online.  Should be able to complete it tonight.

[EX_#76]

Jeff,
   Please explain your theory on how increased pressure stops coolant flow.

Guy

[Jeff]

Guy, I looked for data to support the theory I had in my head, but ran out of time before I could find any.  I don't know this to be certain, hence my request for those "in the know" to reply.

[EX_#76]

I do not think pressure effects the coolant flow.  The entire cooling system is under the same pressure (give or take a little, I'll explane later).  Because the radiator cap is essentialy the pressure control mechanism for the cooling system, both the inflow and the outflow sides of the water pump have that pressure exserted on them because they are connected directly or indirectly connected to the radiator.   There is a small differential pressure generated by the water pump to move the coolant.  On the outflow side of the pump the pressure would be the cooling system pressure + the pressure generated by the pump.  On the inflow side of the pump the pressure would be the cooling system pressure - the pressure generated by the pump.


So when you stated that you use coolant without pressure, how are you accomplishing this?  Are you removing the spring on the radiator cap?

Guy

[Jeff]

The pressure created in a water system is caused by 2 factors.
1.  Expansion
2.  (the big one) boiling point

Remove the boiling point (or raise it dramatically) and you have only to contend with expansion.  PG coolant expands roughly 15% at 250 degrees F which creates like 4 point some-odd PSI.  Water, however, is at a much higher pressure due to it boiling within the cooling jacket of the cylinder.

[EX_#76]

Jeff,
     here is something I found on the internet referring to boiling point.  I am sure you know this but I though it was interesting trivia

water boils at 212 F at atmospheric pressure, at sea level. If we put the water in a sealed container and increase air pressure to 15 psi above atmospheric pressure, we can raise the boiling point to about 250F. Then, if we trade the plain water for a mixture of half water and half ethylene glycol and put it in the same container with 15 psi of air pressure, we raise the boiling point even higher-to about 265F.

Here is what I found out about Propylene Glycol

Boiling Point (sea level):
219° F at 40 percent concentration
222° F at 50 percent
225° F at 60 percent
increase by 40° to 45° F if a 15 psi radiator cap is used



So if we assume the above to be true, your bike should not be boiling at the temperatures you reported.  Which indicates to me that if you were to run a 60/40 mixture of distilled water and propylene glycol and your cooling system pressure is correct, you should not boil over.

In order to blow a properly installed radiator hose of it would seem that your cooling system pressure would need to be higher than the 15 to 20psi that your cooling system should be under. 

These things make me wonder what might elevate your cooling system pressure above normal.

Two things come to mind. 
1)   Your radiator cap is malfunctioning allowing excessive pressure to build up until the hoses blow off.
2)   You have combustion pressure gasses getting into your cooling system causing abnormally high cooling system pressure.

[Jeff]

Guy, you misunderstood my first post.  I'm talking about 2 separate bikes.

First the bike with the water & water/wetter in it...  This was the first weekend out with this bike.  It is our belief that the hoses were not properly clamped.  Additionally, it popped the hoses after stopped in the pits, when the heat raises to the highest point.

Second, the bike with the NPG.  It's mine and I've been running it all year with this motor build.  It is running 100% NPG coolant.  There is no water or EG in the system at all.  NPG boiling point is 369 deg F at 0 PSI.

After having this discussion here and other places as well as with several thermo-dynamic engineers, I am not really as concerned as I initially was...  The PG coolant is recording hotter at the temp probe because it is still absorbing heat from the motor, whereas the water may very likely be maxed out on its heat transfer ability.

[HAWK]

Jeff,

I'm not an engineer but as I see it your concern is the engine temp not the coolant temp.  If you really want the answer then you can get rather inexpensive cylinder head temp sensors that mount under the sparkplug. If you were to fit one of these then you could compare the actual engine temp to the temp reported by your coolant temp probe. This would then tell you if the NPG is not transfering heat effectively to the radiator or the water is not picking up heat from the engine.

Just my .02

[Protein Filled]

This is not related to your original question here, Jeff, but I think that Guy may be onto something here. When I have had bikes overheat before, the fluid came out of the radiator overflow hose way before it would pop off any of the coolant hoses. Maybe the radiator cap is not working properly, or like you mentioned, the hoses were WAAAAY loose. I kind of doubt that all of the hoses would be loose though. Whoever the owner is may want to have the radiator cap of that other bike checked.

[Jeff]

Edgar, we'll check the cap as well, but the bike was JUST put back together like the day before the hose blew off.  We should have gone through the bike beforehand but just didn't...  But in any event, we're looking at it.

thanks guys.