Re-engineering the Grand California 680 – from OEM compromise to a coherent, integrated system

[MarioRS]

Dear Razvan,

 

definitely amazing! Congratulation to the reconstruction and the documentation! Looking forward to the next episode 🙂 

 

Best regards, Mario

[Bizzaru]

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Hey,

thank you, I appreciate that!

That’s actually a very fair question — and to be honest, I asked myself the same thing after your post 😄
I already checked with the guys who helped during the installation, and unfortunately no one took dedicated photos of the exact Starlink mounting position.

The project started purely out of passion and curiosity, not with the intention of documenting every single step in detail. Many of the photos I posted are more “work-in-progress” shots, taken to validate specific technical aspects rather than for full documentation.

Regarding the installation itself:

• it’s a Starlink Mini
• it’s mounted inside the vehicle
• the exact position is at the joint between the two textile ceiling panels
• the fiberglass roof does not noticeably affect reception in real-world use

I’ll dig a bit deeper and see if I can find any usable photos, but I can’t promise anything. If I do, I’ll post them.

 

Best regards,
Razvan

[Bizzaru]

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Hi Mario,

thank you very much, I really appreciate the kind words 🙂

And please don’t hesitate to challenge the project with questions, that’s actually what makes this interesting for me. I’m much more motivated by good questions and discussions than by simply posting updates.

If there’s any part you’d like to see explained in more detail or something you’d approach differently, I’d be very curious to hear your thoughts.

Best regards,
Razvan

[Bizzaru]

I managed to find one photo of the step controller.

 

The controller is custom-made by us and is designed to fully simulate the original Thule step behavior.
From the vehicle’s perspective, the system behaves exactly like the OEM step — no errors, no altered logic, no compromises in usability.

 

The controller is housed in a custom 3D-printed, sealed enclosure and is mounted inside the vehicle’s B-pillar.
This location keeps it protected, discreet and close to the original wiring paths.

 

This allowed the new step to integrate seamlessly with the existing controls and KFG logic, while keeping everything transparent for the vehicle.

 

I’ll add more details later if there’s interest.

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[Thorbonator]

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Wow, what a project you put yourself through! Massive respect for all the passion you have for the details and for questioning the complete van

 

Especially the heating system caugth my interest. Are there some useful modifications to the system, which we normal users can do? I am guessing, that replacing the hose to the rear could be a possible task. What ideas do you have?

 

[Bizzaru]

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Hi Thorbonator,

 

thank you very much for the kind words, I really appreciate it 🙂

 

Regarding the heating system: for me it was relatively easy to work on it because I had almost the entire bathroom removed. At one point there was only a single wall left, I even removed the shower tray. That gave me a full overview of the routing and made it much easier to run a larger diameter hose to the rear.

 

As a general tip, things vary quite a lot between the GC 600 and GC 680, so there isn’t one single modification that fits all cases perfectly.

One improvement that works for both models is definitely better insulation.

If the van is better insulated, the Truma heater runs less often, cycles more efficiently and overall comfort improves significantly.

Replacing the hose to the rear can help, but there’s an important detail to keep in mind:

• if you increase the hose diameter to the rear, you also need to add or adapt rear air outlets
• otherwise the hot air will still take the path of least resistance and escape mainly through the front

What helped us a lot during development was using proper measuring and visualization tools:

• an anemometer to measure airflow at each outlet
• a smoke machine to visualize the airflow paths and detect unnecessary losses in the system

We ran the Truma fan, measured airflow at all outlets, and then used smoke to see where air was actually going — and where it shouldn’t. This made a huge difference.

 

Honestly, this was by far the most frustrating and delicate part of the entire project, and it took a lot of time and iteration to get right.

Even the smallest change in angle had a noticeable impact on airflow. Connections and reductions from larger to smaller duct diameters turned out to be especially critical. To handle this, we designed internal “flaps” inside the connectors to guide the air with as little turbulence as possible.

Initially, we copied Truma’s own connector design and simply adapted it to the diameters we needed. After several tests, however, it became clear that this approach did not work well for the airflow characteristics of this specific vehicle. The geometry had to be rethought and adjusted specifically for the GC layout.

I don’t want to discourage you, just be prepared mentally for what’s involved if you decide to go down this path 🙂

If you want to discuss specific ideas or constraints, I’m happy to exchange thoughts.

 

If the OEM installation had followed Truma’s installation manual and a bit more attention had been paid to airflow fundamentals, a properly working solution could have been implemented from the factory.
Unfortunately, that wasn’t the case, and most of the issues we see are a direct consequence of ignoring those basics.

 

Best regards,
Razvan