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Date: Thu, 05 Jan 2006 03:05:54 GMT
From: "WOOFER" <Woofernospamo.com>
Subject: Re: Curious Heater Problem


I really think a water pump replacement (SAAB original part) would be a good gamble. The thermosat replacement (SAAB original) would be smart too. Maybe start with the thermostat. Cheaper and you'll have to replace it someday anyway. Woof. "ACE" <allansnospamd9.net> wrote in message news:4Z_uf.3712$DY3.1502nospam.lga... > Dear Woofer , > > A concise and I believe accurate analysis. But what does one do with this > problem or how does one deal with it ? ( Within reason of course) . When > engine is at idle it warms up and the two stage thermostat progressively > diverts more hot coolant to the radiator and away from the heater core. > The cabin temp drops and passenger complaining begins. Before air flow > through the radiator is the answer of course , but not always possible > when in stop and go traffic. > > The car is a 900 cs and has a single ( two stage thermostat) unlike the 99 > which had a summer and winter model . > > Any ideas? > > ACE > > WOOFER wrote: >> Fellow Travelers, >> >> This has been a most enjoyable thread but it's time to dispel all the >> myths with the introduction of some real wisdom.....mine, of course. ; ) >> >> Simple water flow models are easily analyzed with Joule's Law...Power = >> Current x Volts. This axiom, together with Ohm's law, shows us that if >> you have enough Voltage (Pressure), small changes in the Resistance >> (Passageway options) will make no meaningful difference in the Power >> (Heat) delivered to the Loads (Radiators) because the Current (Available >> Flow Volume) part of the equation becomes insignificant to the Voltage >> (Pressure) part. As pointed out in a parallel thread, it's only a >> problem at low RPMs. Low pressure. Low Voltage. We have a classic >> Voltage sag resulting in inadequate Power delivery to the Load with the >> higher Resistance. The bathroom light goes dim when your wife turns on >> the hair dryer. With triple the Voltage there would be no problem. >> >> So...Is the water pump developing enough pressure (Voltage) to avoid >> these problems? A worn/defective impeller could do all these things. >> >> Does noone remember changing the thermostats in a SAAB 93 from a "Summer" >> thermostat to a "Winter" thermostat? It's the same problem. An >> inadequate (or malfunctioning) heat exchange system being asked to >> operate beyond it's abilities to perform at the extremes. >> >> Let's also remember that the divergence of coolant flow through the >> heater core on a hot summer day is unlikely to be a problem in a vehicle >> that controls its heat with a water valve!! >> >> Thanks to everyone for their input on this one! I've enjoyed the ride. >> >> Samhot >> >> "MH" <nonospamo> wrote in message >> news:dp9tuk$k3t$1nospam3.zwoll1.ov.home.nl... >>>> .. if you reduce the parrallel paths from 2 to one, and >>>> maintain the same pump pressure, the amount of flow through the >>>> remaining path will be increased. >>> I do not know how you define 'amount of flow', but flow rate Q is >>> defined as a volume passing throug a surface area in a certain time; >>> e.g. litres/sec or m3/hr. >>> With the same pump at same rpm and the same flow rate, if you close one >>> leg of the parallel path, the same flow Q will go through a smaller >>> area, at higher speed; if you half the area, the _speed_ will double. >>> >>> If hot water flows through a radiator at higher speed, its retention >>> time in the radiator is less, and it will release less heat to the >>> passing air. For the flow speed to be as slow as possible, you would >>> want the radiator to have an as large as possible flow through area (for >>> both water and air). >>> >>> The thermostat changes nothing to the pump's flow rate, it just opens to >>> divert part of the flow out of the block to the radiator, instead of >>> directly back to the pump. >>> >>> -- >>> MH >>> '72 97 '77 96 '78 95 '79 96 >>> '91 900i >>

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