Curious Heater Problem

First I will wear gloves when I drive and expect to be in stop and go traffic. Second I will hand my glove and heavy sweater when she complains. Did I tell you that the heated seats don't work either so I have been catching it for that too.

Happy New Year and Stay well.

Good plan.

Well worth fixing imho.

And to you too.

You are right about the venturi effect. That's a different concept. But I still think that 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.

As the manual says" the valve closes off the heater core reducing the flow" obviously the valve is not working correctly if it shuts the heater core off completely. Swedes would have had this corrected long ago with temps below zero degrees in Scandinavia.

Only partially. If Bernoulli's principle is the only thing that makes airplanes fly, they could never fly upside down...

What gives lift to an airplane wing is its angle of attack with the relative wind and Newtons third law (action = reaction - if you stick your flat hand out of the window of a driving car, at an angle with the wind, it will push your hand up or downward, regardless of Bernoulli's principle or the venturi effect.

Saab content? They build aircraft...

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.

The thermostat is likely blocking the flow to the heater core more than it should, due to its being out of calibration. This is only noticeable when low RPMs cause reduced circulation through the core.

This clever feature is designed to heat up the passenger compartment first. (BMW, naturally, suggests you sacrifice your comfort and allow the engine to warm first :-)

I think there is a consensus here. Saab intentionally designed the system to provide more heat flow to the heater core during warm up.

However....

This particular car has a diverting valve that is not working correctly thereby freezing the passengers during periods of idle engine running.

Must be really cold in the Winter there for the engineers to go to this extreme. The electric heated seats are silly enough but this.......

You get the gold star beets

According to Saab those thermostats were meant only for realy hot countries, middle east & such.

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

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

Any ideas?

ACE

WOOFER wrote:

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.

Velocity pressure goes up, static pressure goes down, total pressure remains constant when flow passes through a veturi (i.e. a narrowed portion of the tube or pipe. this is how the detergent is sucked into the wash water in a washing "wand". The lower static pressure at the restriction which is causing the velocity pressure to rise sucks in the "soap".

Malcolm