Saab TSB # 03/90-1221 - Saab 900 Bulletin Board - Saabnet.com
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Saab TSB # 03/90-1221
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Posted by Brad Herrick (more from Brad Herrick) on Thu, 22 Feb 2001 11:48:37 Share Post by Email
In Reply to: dismal heater output, Jason, Thu, 22 Feb 2001 11:02:08
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Flow of Heat from the Heater core May Fluctuate.

Subject: Circulation pump for the Heater System

Application: 1986-89 900 models

On certain cars with plastic heater control valves, the flow of heat from the heater core may fluctuate depending on driving conditions. These heater control valves have a constant by-pass flow and the heater core may not receive sufficient flow at low engine RPM to provide constant, comfortable heat during certain situations, such as extensive stop and go driving in cold weather.

To remedy this problem a circulation pump (P/N 41 18 063) may be installed. The pump starts when the ignition is turned on and supplies the heater control valve and heater core a constant flow of water that is not dependent on engine RPM.

There is suffecient coolant flow at any engine speed above 1500 RPM, and the pump will not solve customer complaints of poor heat above this level.

Before installing a circulation pump, investigate and remedy all other potential problems - blocked heater core, faulty thermostat, etc.

--------
That's the TSB on this, Jason. Since you say the engine is running in the normal range, I think I would try a higher engine speed, (and perhaps 1500 rpm in neutral at the stoplights) to see if this makes a difference.

If still no heat, then you should disconnect the heater hoses in the engine bay and do a flow test through the core and valve assembly.

Good Luck!

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