Saab 900 Heater Bypass Valve: Improved For Longevity


Owning an obscure aging classic like a Saab 900 can be a daunting task, especially as more parts suppliers dry up their existing inventory and end a part.  Most Saab enthusiasts are familiar with the term NLA, and we really hate to hit those three letters.  Luckily, there are several suppliers that manufacture parts that would be otherwise unavailable, continuing the flow of new parts to the market where otherwise there would be none.  A specific example of this is the Saab 900 heater bypass valve, a plastic valve housing that diverts hot coolant from the main coolant stream through the heater core on the C900.

Saab 900It’s been a bit of a bumpy road unfortunately because of the strange design and nature of this part.  With original designs and tooling long gone, ProParts designed their own to keep cars with bad valves from going to the crusher over such a simple thing, since used bypass valves are generally trashed and nobody wants to drive a car meant for the winter without any heat.  Early versions of the valves had a few issues, which could cause the valves to fail and most certainly ruin your day.  There was an update which was considerably better, but still had weakness appear in real world conditions.

We’ve recently sent back the last of the old stock that we had on the shelf and just got some information from Professional Parts Sweden on their new valve, which features some significant changes in order to solve the problem of failing replacement parts.  If you are a member of the community and have heard the stories of people having failed Saab 900 heater bypass valves, rest assured that this saga should be at its end.  The newest updated valve has been shipping from the eEuroparts warehouse since the beginning of 2018, and is clearly labeled HD10 on one of the pipes.

Saab 900 Heater Bypass Valve

The amount of different Saab 900 Heater Control Valves is numerous. Photo Credit John Collins

The message we got from ProParts is translated from Swedish (displayed below), so we will do my best to usefully interpret their roughly translated message:

The new batch of Saab 900 heater bypass valves has revisions to correct leakage.  When initially revised, the updated valve had another problem with sealing in another section of the valve.  Basically a new weakest link was formed revealing further issues with the design.  The most recent design (Batch HD10, which is printed directly onto the part) changes both the dimensions and the materials of the o-rings and gaskets in the main flange.  Additionally, the shaft position has been altered to counteract axial load, specifically on the o-ring seals.  Here’s a list of the most significant modifications the HD10 valve features:

  • Revision of the flange joint construction
  • Redesign of the main gasket to provide a better seal on the flange surface
  • The O-rings and gaskets on the shaft have been updated
  • The axis of the shaft has been revised to reduce axial load against the flange
  • Specific quality control adjustments made during assembly of the plastic housing
  • Re-calibration of the tooling for controlled torque tightening of the assembly screws

That’s all we have for right now, these comprehensive changes should drastically improve the reliability of these valves, and keep your Classic Swede warm and cozy inside, just like it was meant to be.

Saab 900 Heater Bypass Valve: Shop Now

For you Swedish speakers, we have included the original message below.


Vi har gjort mindre justeringar för att korrigera läckage. När vi löste problemet med förpackningen hittade vattnet andra sätt att komma ut, den svagaste länken. De senaste åtgärderna var att ändra dimensioner och material på o-ringar och packningar på axeln. Också axelpositionen har justerats för att motverka axiell belastning på o-ringarna. Men om du skulle påpeka några av de stora modifieringarna skulle det vara så.

  • Byggarbetsplats i foget
  • Packningens utformning för att ge bättre passform för växtytan
  • O-ringar och packningar i axeln. Axelns position
  • Mer kontrollerad montering av de två delarna, styrt vridmoment för åtdragning av skruvarna.
  • Kalibrering av verktyget för plasten.

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