Rad plastic inlet failure mode

[Doyt W. Echelberger]

Lots of posts indicate that the plastic inlet on the upper tank breaks off,
leaving a stub which can in some cases be used to re-attach the upper hose
and get you home. Such failure can be catastrophic, giving the driver only
a few minutes of driving time as the coolant gushes out and the engine
temps rapidly zoom far past the red zone. At best, there is somewhere
around three minutes of driving remaining, to get off the road and stopped
without engine damage. Having synthetic oil in the engine is helpful as the
temps go up past 400 degrees F.

In my experience, plastic tank radiators have a useful working life of
between 7 and 9 years before the described failure of the plastic upper inlet.

I think it will be useful to describe the condition of that upper inlet,
prior to failure, so that owners of radiators in over 6 years old can
predict failure and replace the radiator before it lets them down in a very
difficult or dangerous and certainly inconvenient manner. There may be
other failure modes for this part, but this is how mine failed.

A month before my plastic rad inlet dumped all my coolant, I had the upper
hose off for another reason and was able to inspect the condition of the
plastic. Normally, the plastic is rigid and unyielding to attempts to
deform it by pressing on it with fingers or by gripping it with pliers. As
it nears the end of its useful life, the plastic becomes sort of punky,
softer and more rubbery and easily deformed with pressure from the pliers.
In the final stages of failure, one can grab the end of the inlet with
one's fingers and twist off a piece almost the same as tearing the corner
off of an asphalt roof shingle. The plastic has lost it's rigidity. All
this is taking place under the covering of the rubber of the upper inlet
radiator hose, which hides the deterioration from casual inspection. I
suspect that the act of tightening the radiator hose clamp at this stage
would accelerate the speed at which the system is moving toward
catastrophic failure.

The part of the inlet that had become punky was the part inside the rubber
upper hose. Beyond the end of the hose and toward the plastic tank, the
inlet was in much better condition. I suspect that the contact with the
rubber hose and the clamping pressure had something to do with the failure
of the distal section of the inlet.

The stub that remained after failure wasn't punky and was solid enough to
accept a short grip on the hose, long enough to get me home and to a mechanic.

I also suspect that prior to the total failure mode, it would be possible
to extend the working life of the system by inserting an aluminum tube of
the correct diameter for a loose fit (about 2.5 inches long) into the inlet
and fixing it there with a coating of waterproof epoxy. It would probably
be necessary to clean and dry the inlet, perhaps with a hair dryer, and
maybe swab it out a few times with alcohol, to prepare it for the epoxy
bond. And at that point, I would order another radiator and set aside a few
hours of downtime to install it.

So, I am encouraging listers who drive older Audis with plastic radiator
tanks to courageously and assertively examine the condition of their upper
rad plastic inlets, and take action to prevent the catastrophic failure
that can be so inconvenient and risky, and expensive. When that failure
occurs on a turnpike 20 miles from an exit, in a howling blizzard, at 3am
on a weekend, you are going to remember this suggestion and maybe write
something like this yourself.

Doyt Echelberger
87 5ktq  now on its 3d new plastic tank radiator.