Date: Sun, 01 Jan 2006 10:48:46 -0500
From: Allan Schneider <allansnospamd9.net>
Subject: Re: Curious Heater Problem


Allan Schneider wrote: > > Hello, > > I have a 1993 900 CS ( Non Turbo) with a curious problem. Car starts > and heats up well. When engine is at normal operating temperature there > is plenty , I mean plenty of heat , but as you sit in traffic - not > moving- and the engine temp rises up to the point that the radiator fan > comes on the heater goes cold. But once you start moving and the engine > temp starts to drop back down to normal the heat comes back. > The temp knob seems to have no impact during the no heat period , is > effect again once the operating temperature drops back to normal. The > radiator fan comes at the right time and works well. > > Any ideas? > > Allan Schneider Hello NG, I have learned a lot since my original posting of this question. I cannot say whether or not this is a "good" engineering design, but here is what I have found. On page 261 -1 of the Official Service Manual SAAB 900 (Bently Publications) it says: "When the engine reaches full operating temperature , the thermostat closes off the lower outlet in the thermostat housing to substantially reduce the coolant through the heater core" I am assuming that at the above full operating temperature the cooling fan comes on and the flow is also further diminished. This is consistent with my experience and I wonder if others have seen this as well. As the cooling fan comes on ( or the car begins to move ) the engine temp goes down and the heat comes back on. There are times when I am stuck in traffic and it is also very cold and this feature seems unhelpful at best . Any way to net it all out 1) The SAAB appears to be engineered that way and 2) It is operating in the manner intended. Any ideas ? or just live with it ? (Another thing I have observed is that once the engine is warmed ( not the highest operating temp- the temp needle just moved up a bit) up a LOWERING of the temperature adjustment back to 2/3 increases the amount heat coming out of the vents. Give the discussion in the post following my original post it would suggest a lower coolant flow rate and HIGHER residence time in the heater core . Thus more time for heat transfer to take take place. I may be all wrong about this.)

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