November 7, 2020.  Cooling system.
November 7, 2020.  Cooling system.

November 7, 2020. Cooling system.

I’ve been taking a break from the wiring to focus on the cooling system of the engine.

The original connections to the engine for coolant have an internal diameter of 32mm, which is an area of 804mm2, splitting that in two for the dual radiators (402mm2) it should be possible to go down to a internal diameter of 22.6mm. The radiators came with 32mm OD (1 1/4″) connections which give an ID of 29mm or 660mm2 which is 64% bigger than what should theoretically be required. This is big simplification of the issue but enough to let me think that the 32mm OD tube used is not undersized for the task.

32mm OD x 1.6mm thick seamless aluminium tube is A$20 for a 6.5m length, so I could afford to do some experiments with different processes. Below is what worked skipping all the efforts that didn’t.

To do any forming work with the tube it needs to be annealed (softened) to get rid of the temper the tube is supplied with. As the melting point of Aluminium is low it is possible to melt it easily with home equipment and the material doesn’t glow or give other indications its about to melt, so a method is needed to see that you’ve got it to the correct temperature. The method I used to do this is mark the tube with a Sharpie then as the tube is heated when the correct temperature is reached the marks will fade to nothing. After being heated the tube needs to be left to cool slowly.

Before heating.
After heating

With the tube softened it can now be worked with.


The pressure that will build up in the cooling system will attempt to push the various fittings apart in the system, this is why there are beads on the fittings so that the hose clamps can trap the hose behind the bead on the fitting and prevent it being forced off. To make the beads on the ends of the tubes I made the simple device below. The tube is trapped between the two rollers, pressure is exerted from upper bolt and the lower roller is turned to from the bead.

The result of this looks like this on the tube end.


The other major process in doing this is was tube bending, to get this done I wanted a predictable process without too much artisan requirement as I’d fail at that. After some experiments 3D printed forms to work in the press, this is the final version.

This is built to a 3x diameter bend radius, which is quite large, but this helped with minimizing the wrinkling that can occur on the inside of the bend in theory the forms if pushed all the way would create a 120 degree bend. In practice it is less than that as there is some spring back when the force is realeased.

To try and prevent dents being pushed into the tubes at the far ends of the form some extra saddles were used as shown above, that part of the form was also has a radius, but that on its own was not enough to stop the issue.

Also when being bent the tubes need to be filled with sand to prevent their collapse, most of the tubes I did were filled with dry sand, which I believe was a mistake, dry sand has to be used if you are hot bending tube, but this process is cold and damp sand has a higher strength.

It is essential that the sand be packed in tightly to the tube, I used a steel bar to ram it down repeatedly when filling the tubes. The longer the tubes are the more important it is to make sure the sand is packed in tight. The tubes are then plugged to keep it all in place.

with a process that I knew should work, I then went back and adjusted the design to used the bend radius’s I could make, which thankfully I could make fit like this:

Then it was on to creating each tube, by the end of the 10 tubes required this is the most effective process I’d developed.

  1. Create a dimensioned drawing of the part from the 3D model.
  2. Create a wire model from the drawing using welding rod.
  3. Check the rod for fit on the car and adjust if required.
  4. Prep the tube for bending. Often one or both ends of the tube will need to be left longer than the final requirement to fit in the bending form.
  5. Bend the tube using the wire model as a guide.
  6. After bending Empty the tube then use the wire model as a guide to trim the ends of the tube.
  7. Check it fits.
  8. Clean up the ends of the tube and then bead them.

Repeat the above and this is the finished job…

One thing that did not occur to me until late in the process with this design is the sheer number of hose clamps involved at 46 in total, 24 of these are due to the external thermostats. I’ll use the permanent ear type clamps similar to the one shown below on most of these as they should not need regular attention.

Other parts in the system that still need work…

These are the tees for the radiator bypasses to feed back into the inlet side of the system, which need welding and one of them need another branch added for the expansion tank d connection.

At the rear of the engine there are connections that need to be completed to form part of the air venting system from the engine.

A vent also needs to go at the discharge tee on the front of the engine.

The pressure relief in the radiators is not going to be used, instead the pressure relief in the expansion tank will provide this, so the vent points from the radiators have been blocked. I was hoping to find a threaded bung to fit these but the thread was unidentifiable so they were tapped out to M8 and bolted up.

The expansion tank proved to be too close to the cooling piping to be able to sensibly connect the two, so the coolant tank was raised 30mm.

Next is back to more wiring and testing the fuel system.