Date: Mon, 26 Apr 2010 00:18:16 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Water Cooler System Design Flaw Workaround?
In-Reply-To: <4bd4a0be.9753f10a.4118.61da@mx.google.com>
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The numbers and theory not quite right. The engine is rated for 70 kw/hr.
Gasoline now has an energy content of ~115,000 btu/gallon. So at 20 mpg and
60 mph the cooling system has to deal with ~ 345,000 btu/hr.
The cooling system moves the water fast, gallons per minute. That is why
proper circulation is so important. The Vanagon cooling system especially
considering the size of the engine is massive, extremely oversized. Nothing
else with a 2.1L engine carries over 4 gallons of coolant. Most 4 cylinder
cars have a single row radiator with now where near the surface area of air
flow we benefit from.
It is normal for coolant temperatures to rise under certain conditions.
Extended loads, high ambient temperatures, and low speeds waiting for the
fan to turn on. There is even a spread between the t-stat barely opening and
being full open. A properly working cooling system should be able to handle
230 or so without incident.
Under load at speeds low enough or outside temps to be high enough the fan
may come on, even without AC. If temps continue to climb at some point the
fan may go into high speed. This is still OK. During high speed on engine
temp, (not AC pressure) the AC should be cut off. If temps continue to climb
at this point some action should be taken.
If the cooling system is not right such as air in the system, fans and stuff
will not help. Gasses in the cooling system cause the grief not by getting
into the radiator but by vapor locking the pump. The pump does a poor job
pushing air.
The system has to maintain pressure, (test that cap) to prevent flashing and
keeping the coolant in contact with parts of the engine hotter than the
vapor point.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
David Beierl
Sent: Sunday, April 25, 2010 4:01 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Water Cooler System Design Flaw Workaround?
At 01:22 PM 4/25/2010, Jake de Villiers wrote:
>When approaching the long (15 - 30 minute) second and third gear
>grades through Eastern Washington and Idaho you'd turn on the fan
>before the rad got too hot.
Ok, I see the idea. But do the numbers make sense?
Lessee... at 75 horsepower output and 1/3 efficiency the engine's
going to be putting out something like 200 kw of waste heat, or 3.4
kWh per minute.
18 quarts of 50/50 coolant weighs around 36 lb and has a specific
heat capacity of roughly 0.85 BTU per lb per deg F at working
temperature. So changing the entire coolant by 20F would get you
0.85 x 20 x 36 = ~600 BTU, about what a sedentary human throws off in an
hour.
600 BTU = ~0.18 kWh. 3.4 kWh x 0.18 x 60 = ~32
So a twenty-degree change in the entire coolant would absorb the
waste heat of the engine for about thirty two seconds. I think this
is conservative since the coolant inside the engine won't be
participating in this, and because 75 hp may be conservative for
climbing a steep hill.
Somebody check my numbers. If this number is anywhere near correct I
don't think it's worth the hassle.
Yours,
David