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My Holden Cruze/Trax/Barina Is Leaking Coolant

Picture of a Holden Barina, Holden Trax and Holden Cruze opposite a plastic thermostat housing and plastic radiator expansion tank. In the middle and over a pink background is the text vs.

It's very much a sad thing that Holden no longer exists. The Commodore was one of the great Australian-made cars and (even though most of them are owned by bogans or pensioners) they have really stood up to the test of time quite well.

However, while Holden itself was a great brand, one of the main reasons their time card got punched might have been the meddling of their American overlords at GM (General Motors) in what could have been a great company.

See, Holden was (almost) always a GM product; Throughout their life, they had special license to create cars that they thought would sell well in the Australian market. However, with the globalisation of GM throughout the late 90's, 00's and 10's, there seemed to be (from a ground level at least) a lot more influence from the American puppeteers.

Be it for profit margins or just because the Americans "thought they could do it better", the late 00's and 10's saw a raft of "new" models which struggled to sell and which helped put the final nail in the ironbark coffin.

So, where did these new models come from? Where did the Holden Cruze, Holden Trax and Holden Barina originate?

Seeing as GM is such a big company, it stands to reason that they have a number of these small, Holden-like brands around the world. A lot of these new models for the Australian market were discovered either through GM's design studios or through one of these secondary brands.

South Korea's Daewoo and Germany's Opel were often the main culprits, and the cause of the common coolant leaks all stem from a singular origin point.

In fact, all of these platforms were originally products of Daewoo which utilised Opel's engines. Otherwise known as the singularity.

Where does coolant leak from on the Holden Barina, Holden Cruze and Holden Trax?

Well, the main culprits for most of these it the plastic thermostat housing, the plastic coolant pipes, the plastic expansion tank (or coolant bottle) and the water pump (though this isn't as common).

Why do the thermostats, coolant pipes and expansion tank all leak so bad on the Holden Barina, Holden Cruze and Holden Trax?

It's hard to deterministically point at one thing, but if we had to, it would be the overwhelming use of hard plastic in the cooling system.

While there are some definite benefits for manufacturers using plastic for cooling system components (it's cheaper), it does have a couple of massive pitfalls.

See, as plastic ages and is exposed to repetitive heat cycles, it suffers from a combination of polymer degradation and oxidation. This is the first source of problems as it causes plastics to become exceedingly hard (brittle) and weakened with age.

The second problem with plastics in particular is a susceptibility to thermal deflection and deformity. This might not mean a lot to you as a technical term, but it just means that when plastic gets hot, it bends and stays that way.

One of the solutions to heat deformity is the use of glass-fibre-reinforced plastics (GFRP) like PPA-GF30, HDPE-GF10, PP-Td20, PA66-GF35 and Bio-PE-GF30, which are all fancy ways of saying plastic with something else added.

It took 30 minutes to figure out what half of those acronyms mean and that is time that will never be recovered.

However, while a lot of plastic manufacturing companies will try to say that these GFRPs are stronger, lighter and more durable than their metal counterparts, in the field it appears to mostly be horse hockey.

Taking all this into consideration, the failure method for these plastic thermostat housings, coolant pipes and expansion tanks is obvious. Plastics, with age, exposed to moderate pressures and temperatures with high rates of heat cycling are prone to deformation and brittle failure.

So, why would manufacturers use plastic for thermostats, coolant pipes and expansion tanks?

It comes down to cost. See, an all-metal thermostat might cost 5c-10c more per vehicle and, across 1,000,000 cars, that's an added cost of $50,000.

The use of these parts might not be malicious either. Most of these manufacturers do an immense amount of testing, often putting thousands or millions of KM's on a chassis before it's released to the public.

However, all of this testing is done over a period of months, not years. This testing involves brand new cars, doing massive amounts of KM's at a time, often without the relentless heat cycling suffered by cars that drive 15 minutes to work and back for 15 years.

So what is the fix for a leaking thermostat, coolant pipe or expansion tank on a Holden Barina, Holden Cruze or Holden Trax.

GIF of robot from Robots movie saying "Upgrades, people. Upgrades".

The first (and best) option is an upgraded thermostat housing. In fact, the failing thermostat housings are such a problem that multiple aftermarket suppliers offer a complete metal replacement. After that, observation and early replacement is the best option.

Being plastic, at least most of these components are fairly cheap. Though, it's more a question as to how long replacement parts will be available now that Holden is gone.


If you have any questions about this blog post, would like a second opinion from a mechanic or would like to find an honest mechanic in Brisbane, check out Kashy here.

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