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Discussion Starter #1
can someone tell me what this part is called? This is where the main leak is. coolant is coming from that rust coloured area on the "T" junction part. I need to know what it's called so I can get a new one.



this photo is taken a little lower because I'm sure there is another leak coming from the lowest hose as you can see spatter way down on that red thingy there.



the coolant resevoir is nearly empty but I never have overheating problems but I am going to drive to Melbourne soon and I don't like the idea of driving 10,000 kms with the leak.

thx for your help. :D
 

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From Sydney to Melbounre is 800km, 10,000 is like 1/4 of the way round the plannet!

Sorry cant help you with your specific problem tho :confused:
 

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Hi there,
The part in question is a Bypass valve for the heater water.
Not quite sure of its' operation other than to say that I was told (from a dealer ...!) that it is designed to bypass the heater circuit if the temp becomes too high, so as to ease the stress on the cooling system. I was confused when I was told this and am still not totally happy with this description to date.
However, a leak is still a leak that needs to be rectified.
Soon, I will need to change the hose that goes from the bypass valve to the throttle body and the back of the water pump.........$100 trade, just for the F*****g hose.:evil: Sadly, one just cannot rock up to Repco or Super Cheap and buy a generic.

Good Luck

Cheers


15 mins later.
P.S. Having thought some more, I'm willing to accept that the bypass valve does the opposite to what I was told, that is, bypasses the heater to speed up the heating of the engine from cold to reduce warm up phase time of the engine. But whenever I've felt the hoses when doing checks and tests, they all felt like they heated up at the same rate. :confused: So, as Kent Brockman says, "That's my Two Cents".;)
 

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Discussion Starter #4
Lloyd said:
From Sydney to Melbounre is 800km, 10,000 is like 1/4 of the way round the plannet!

Sorry cant help you with your specific problem tho :confused:
whoop too many zeros. I mean 1000 kms but 800 is even better
 

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Im not entirly sure you are right Rodentmaster as the heater bypass is controled via the thermostat, cutting out the heater when the engine gets too hot, to divert all water to the radiator.
 

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Discussion Starter #6
I took a few extra pics just to clarify the area.





see trhat lowest hose? I think there's a leak coming from there also. But how the hell do you get at it? :confused:
 

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Doesn't look familar to me... IIRC

You have one hose from the cross-pipe under the manifold goes to the heater matrix
one from the coolant reservoir to the coolant pump and one from the pump to the heater matrix. I don't think I've ever saw that T-fitting you have there.
 

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Discussion Starter #8
all your cars are "turbos".

maybe it's an "injected engine" thing?
 

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Nope my injection B202 900 S was (well, still is) the same as my turbo cars.
 

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My '90 900i has no such valve. The hoses just run to water pump and to thermostat. The '92 LPT has the valve and it seeps too. AIUI, you can just bypass it.
 

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Discussion Starter #12
900t said:
Nope my injection B202 900 S was (well, still is) the same as my turbo cars.
sorry I thought the 900S was a turbo.

what does "S" stand for?

now I am a little confused as to why that part is there.
 

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On many later cars the bypass hose was fitted to prevent the usual problem of the coolant being diverted when the engine needs cooling causing the cabin heater to go cold. With the bypass in place you shouldn't get the cold spots from the cabin airflow when the heater is on.
 

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Discussion Starter #14
so if I was to look for that part, what is the official name for it?
 

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Jezzadee said:
On many later cars the bypass hose was fitted to prevent the usual problem of the coolant being diverted when the engine needs cooling causing the cabin heater to go cold. With the bypass in place you shouldn't get the cold spots from the cabin airflow when the heater is on.
So the bypass valve prevents the cabin airflow going cold when the thermostat diverts all coolant to the radiator? How does the valve achieve that?

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I'm not entirely sure, but would guess it keeps an additional flow of coolant into the heater control valve avoiding the existing valve bypass. A bypass bypass. I found this on another site, but cannot confirm its source as it was just a quote:

BYPASS VALVE FOR THE HEATER SYSTEM
Model 1985-on Saab 900 wi 16-Valve Engines Group Heating System Bulletin No. 11/90-0072
Symptom Poor Cooling/Heating

On certain cars with plastic heater valves the flow of heat from the heater core may fluctuate depending on driving conditions. The heater control valve has a constant bypass which may result in insufficient coolant flow at low engine speeds to provide a comfortable level of heat during certain situations, such as stop-and- go driving.

An auxiliary bypass valve has been developed to help remedy complaints of fluctuating heater output. The service kit is designed for use on cars with 16-valve engines, with or without ABS brakes. The previously-released kit containing the circulation pump (see PSI 03/90-1221) should henceforth only be installed on cars with 8-valve engines, -M88. To further assist the operation of the bypass valve kit a 890 C thermostat, PIN 88 17 298, may be installed in place of the standard 820 C thermostat, PIN 8817 538.

Before installing the bypass kit, investigate and remedy all other potential sources of insufficient heat output such as a blocked heater core, low coolant level, faulty thermostat, etc.

NOTE: This kit will not remedy complaints of insufficient heat during highway driving or driving conditions other than stop- and-go traffic. There is sufficient coolant flow through the heater core at any engine speed above approximately 1500 rpm and the bypass valve will not improve a complaint of poor heat at speeds above this level.
And from Townsend:

92 and newer cars may have a problem with the bypass valve located in the heater hoses in the engine compartment, above the alternator. This valve can block flow to the heater core or develop leaks. It is there to prevent loss of cabin heat at idle,something we do not see a need for if the rest of the cooling system is up to par. See the Cooling System Section for more on this. When we see a problem with this bypass valve, we simply remove it from the car. You can splice in connectors in its place or better yet replace the heater hoses and it with heater hoses from a earlier car without the valve.
 

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The heater control valve has a constant bypass which may result in insufficient coolant flow at low engine speeds
Yep. This is how the heater valve works. The valve is a sliding affair which either recirculates coolant out the return hose (on 'cold') or entirely through the heater core (on 'hot'). At intermediate positions, some coolant is recirculated. Quite how the auxiliary bypass valve is supposed to keep a consistent level of heat, I'm not sure. Unless it artificially restricts the coolant flow at higher engine speeds to keep the heat down...
 

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Discussion Starter #18
thanks for that info Jezz, it makes things a lot clearer. So what's the prognosis doc, should I kiss it goodbye?
 

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I dunno if my engine was about to over heat I would throw the heater on full blast!!! even in summer...wait...about 5 years ago the theromstat was in dire need of replacement and it finally died,my mother was driveing and I was ridding shotgun and my "future car" started overheating,so I told her to put the heater on full blast,we drove for twenty miles and the heater kept the engine from entering the red(before it was creeping into the red...
 

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GearHead said:
I dunno if my engine was about to over heat I would throw the heater on full blast!
That will work on most cars to bring the temperature down, but not a C900 if it has a genuine Saab thermostat, since as soon as it became hot enough to overheat, coolant would be diverted away from heating the cabin to instead cool the engine.
 
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