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I have a 2003 Jeep Grand Cherokee 4.7litre petrol that has travelled 270,000km which is used predoiminatly for highway trips of 100-400km distance. It has been serviced regularly at the recommended intervals since I purcahsed it new. In March 2013 a new radiator was fitted by my normal service agent as a result of the original radiator found to be leaking. The system was flushed and new coolant & antifreeze added. Just over 6 mths later in early Nov, an overheating problem developed after driving a 350km journey at normal speeds . I arranged for a check/repair by the AA Repair agent in New Plymouth before my return. They advised the radiator was leaking and unrepairable, hence a new radiator was fitted. I have since returned the original radiator that was fitted in March to the supplier because it was provided with a 12mth warranty when installed. He now claims that the radiator failed as a result of corrosion, and that the 12mth warranty does not cover corrosion failure. He advised that he was aware that Jeeps are known for premature failure of radators and that we should have flushed the system every few months. He also indicated that stray electical currents in a vehicle could also cause rapid corrosion of the radiator and that we should get an auto electricial to check for this. Hence the supplier has offered no compensation for the repeated expense of around $1000 for parts and labour.
Can you advise if there is any validity in the radiator supplier's assertions.
If you believe the need for regular flushing or stray currents in the vehicle may have caused the problem, what do you recommend to ensure I don't incurr a $1000 repair bill every 6 mths.

This is a most unusual occurance, however is not beyond the realms of possibility. Essentially, the radiator is rubber mounted and not earthed to the body so electrolysis can cause corrosion in the aluminium radiator core.
To check if this is the problem, using a multimeter set on a low voltage setting, measure between the radiator and the vehicle frame/earth. It should read 0v. If there is a reading, this may be the problem. The remedy is to fit a simple earth strap to the radiator, earthing the radiator to the vehicle.
As I said, it is not common, but is possible.
Obviously, the correct coolant concentration mix is important, as is the importance of using the recommended coolant additive - and not mixing different types of coolant, and changing the coolant regularly (say, every 2 years).

Thanks for your response Andrew. I have had the radiator voltage checked by my service agent and they found a voltage of 0.07V. As per your recommendation they have fitted an earth strap. I sent a response to the original radiator supplier and have received the following response:

Thank you for all the info supplied. I cannot make assumptions for others' work but can only comment on the facts I find before me.

1. Radiator has been stripped to assess reason of failure. The header plate of the radiator has been discoloured (black) around the inlet pipe, which is a sign of electrolysis. I am very pleased that you have found current in the system and that it is over the acceptable level. Current as low as 0.05v can destroy a radiator in a very short period of time. (Literature available from Denso Manufacturing and NRMA, copy can be supplied on request)

2. The inside of the radiator is filthy dirty, indicating a lack of correct flushing procedure. Furthermore, someone, prior to us receiving the radiator back for assessment, has tried to clean the inlet tank by shoving a cloth down it to wipe away dirt accumulated on the plastic.

3. By earthing the radiator to the vehicle is the worst possible thing to do. This can actually increase the amount of current. The radiator cannot become part of the electrical circuit. The stray current needs to be found and that component needs to be earthed correctly. I suggest the earth strap that has been fitted is removed promptly before further damage is done.

4. Electrolysis is by no means an unusual occurrence. It is a lot more prevalent than some may think.

5. On every new radiator we supply, we place a sticker on it stating that the cooling system be flushed before installing the radiator. This sticker has been removed.

Our invitation for you to come and inspect the radiator still stands.

If there is anything else we can help you with please let us know.

Andrew, the recommendation from Auto Radiators is in direct contradiction to your advice. Should we remove the earth strap as they recommend, or do you believe your solution to the probem is better?

We certainly don't wish to go against the advice from the radiator supplier. Electrolysis is a very complex issue and one of my colleagues here in the AA Motoring Advice team had a similar issue a few years ago with another brand of vehicle, with the advice from the manufacturer eventually being to earth the radiator and the problem went away.
The opinion of radiator specialists we've discussed this with is varied, but the common advice is that the 0.05v you mention is the maximum allowable.
Going back to square 1, definitely, the cooling system must be thoroughly flushed as any mineral impurities in the coolant can be a problem and carry current.
It is also vitally important that once meticulaously flushed, the correct coolant is used. It may be preferable to use pre-mixed coolant rather than using tap water with an additive, as pre-mixes are generally mixed using distilled water.
After that, ensure there are no stray electrical issues. We're told that some after-market accessories such as bluetooth systems, reversing cameras etc have also been known to cause problems.
I think it is best to follow the advice of the radiator manufacturer, and perhaps get him or his agent involved in this process.
Apologies that our advice went against that of the radiator manufacturer. As I said, we're aware of this solving one particular issue, but it is advisable to heed the advice of the manufacturer in order to ensure any warranty issues are not contravened.