Radiator Cap--flow rate through radiator

John Hess JohnH at ixc-comm.net
Wed Oct 15 16:55:13 GMT 1997


Don't forget that the amount of heat transfer (both in and out) are
somewhat dependant on differential temperature.  The greater the
temperature differential between radiator temperature and ambient, the
larger the temperature drop within the radiator.  Water moving too fast
will not sink up as much heat in the heat developing portions of the
engine AND will not cause as high a temperature differential in the
radiator (between radiator and ambient), resulting in higher engine
temperatures, even when the coolant temperature reading is lower.

I once had an MG that ran at it's coolest (per the temperature gauge)
when there was no water in the radiator.  Don't get caught up in coolant
temperature readings as the sole source of information.


> ----------
> From: 	michaels at telerobot.com[SMTP:michaels at telerobot.com]
> Sent: 	Tuesday, October 14, 1997 10:47 AM
> To: 	diy_efi at coulomb.eng.ohio-state.edu
> Subject: 	Re[2]: Radiator Cap--flow rate through radiator
> 
> <<File: RFC822 message headers.txt>>
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> ______________________________ Reply Separator
> _________________________________
> Subject: Re: Radiator Cap
> Author:  diy_efi at coulomb.eng.ohio-state.edu at Internet
> Date:    10/13/97 8:24 PM
> 
> 
> There's a problem with the argument below.  If the water is in contact
> with the 
> block long enough to pick up some thermal energy (and no matter how
> small the 
> time of contact is, there _will_ be a thermal transfer if there is a
> difference 
> in temperature), then it will be in contact with the radiator fins
> long enough 
> to get rid of the same amount of thermal energy, provided the radiator
> is 
> properly designed.  Obviously if the radiator is too small, or
> clogged, or 
> bypassed, or what-have-you, then the temperature of the water will
> continue to 
> rise as time goes by.  
> 
> 
> 
> 
> 
> Not only does it not absorb enough heat from the engine, it goes
> through 
> the rad so fast it doesn't release the heat either. Getting the
> coolant 
> up to a high enough temp  gets the temp difference at the rad higher, 
> allowing the rad to shed more calories or BTUs. This effectively
> removes 
> more heat, even if the operating temp is a bit higher. I know it does 
> not make a lot of sense, but without a restrictor in an engine running
> 
> without a stat, overheating of the valve area, for instance, with 
> resulting head cracks and/or detonation can be a real problem.
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