Heater Pipes 2

Partial failure of alluminium underfloor heater pipes.

I fitted MS alluminium underfloor heater pipes in March 2003, because of visible corrosion to the original Rover steel pipes - see Heater Pipes - underfloor.

Now, 3 years later and I have a problem. As to the cause, it's not fully clear, and I was lucky to have a Coolant Level Alarm fitted - see Coolant Alarm - which tripped before I even got out of the driveway.

A quick inspection underneath revealed that one of the hoses attached to the pipes at the engine end was weeping and that the pipe clip needed a little tightening. It was while doing this that I discovered that the rear mounting bracket on the underfloor pipes had sheared.

Both pipes were now clearly unsupported at the engine end, though the 2 other support bracket further forward were undamaged. Moving the heater hoses by hand resulted in movement of the pipes adjacent to the broken bracket.

Removing the bolt, spacer tube and broken section, allowed for a closer look at the damaged bracket.

As to possible causes.....

Hitting a speed bump or similar. This would tend to leave visible damage to either the bolt or pipes themselves or the car underbody. There are no obvious signs of this having happened.

Excessive vibration of the engine being transmitted via the rubber hoses to the pipes themselves. I couldn't find any obvious vibrations in the static tests I did, (a bit more difficult when moving and changing gear!) and the engine mounts seem to be okay. Besides which, part of the function of rubber hoses is to allow for flexing and movement within the system.

The 2 photographs of the broken bracket, both showing the upper face, clearly show the indent marks left by the steel tubular spacer pillar in the soft aluminium bracket, and that the spacer was offset from the centre line of the bracket hole. Tolerances are clearly large enough to allow one side of the pillar to be inside the diameter of the bracket hole, thereby not supporting it on that side and allowing the bracket to be twisted.

If the flat surface of the bracket becomes distorted due to the support of the pillar being mis-aligned, then the weld / plate interface is placed under a lot more strain, and will become far more susceptable to any flexing.

Some flexing is inevitable but I would expect, under normal conditions, the rubber hoses to absorb most of it, which is one of the main reasons for their use. I agree that if the engine is shifting dramatically then the flexing would become a problem, but if the original steel pipes were still in use, then I would expect the hoses to break down before the pipes

To ensure the pipes are supported enough, I fashioned a simple plate that would hold the pipes firmly, surrounding each pipe in rubber insulation (not shown here) between the new bracket and the underfloor of the car to ensure that vibration would not cause the parts to become loose again, and also to prevent corrosion.

Advice? If you have similar pipes, get underneath and check them.