The 50-tonne tank, which used to call Cowra War Museum home, is going under the hammer this week.

Pickles Tamworth branch manager Brendan Shoemark said he couldn't reveal who the owner was.

However, the Leader understands it is the same tank purchased by a Tamworth local in 2017, who promised to restore it, "back to its glory days".

Mr Shoemark said the 1955 Centurion Mark 5/1 tank was "purchased as a non-goer", but the owner made good on his promise, installing a state-of-the-art engine.

"It had sat around for too long," Mr Shoemark said.

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"The owner sourced a tank specialist, who then went out and found a new engine, which had been rebuilt by Rolls Royce.

"That engine was a surplus one left over from the Gulf War, shipped from the United Kingdom and installed last year."

The tank has also been stripped back to its original design.

"There were a number of extra modifications that were put on the Mark 5s for the Vietnam War," Mr Shoemark said.

"They've taken it back to the original specs, so it's the way it was originally delivered to the Australian Defence Force."

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Don't expect it to be fuel efficient - the vehicle uses about a litre of petrol for every 100 metres.

The main gun is a 20-pounder cannon and it also has three machine guns, one 50-calibre machine gun and two 30-calibre machine guns.

Mr Shoemark estimates the auction will finish around the "$100,000 to $120,000 mark".

The tank is up for grabs because the owners have sold their farm and no longer have anywhere to store the military vehicle.

The online auction starts on Wednesday.

The tank can be view at the Tamworth Pickles car yard, at 37-39 Armstrong St, Westdale, from 8.30am to 5pm, Monday to Friday.