I wrote the below on coolant, earlier this year. I hope that it is of use. We are all different and 50 years ago, I decided that I would do my own spannering and saved a fortune. If you think that you will need something three times, it may be worth learning to do it yourself. Also, it does not matter how much you pay, it is difficult to find someone to do the job properly.
COOLANT
Do not mix antifreezes. Not just types but even different formulas from the same manufacturer. In addition to not freezing, antifreeze is made to combat corrosion. Manufacturers use different chemicals and recipes. If mixed, some chemicals cancel each other out. The result is reduced protection.
The Deauville engine has been around for more than 30 years. The specified coolant is ‘high quality ethylene glycol antifreeze containing corrosion protection inhibitors’ with the instruction to ‘replace every 2 years, or at the indicated odometer intervals [24,000 miles], whichever comes first’ together with the warning ‘Using coolant with silicate corrosion inhibitors may cause premature wear of water pump seals or blockage of radiator passages. Using tap water may cause engine damage.’
Things change and usually improve. I consider replacing the coolant with a modern one, as they appear to be more stable. The figures of 100,000 miles and ten years are bandied around.
The shelf life of my chosen brew is five years and I buy five litres. The total capacity of the NT700 is 2.28 litres.
Comma Super Longlife Red Antifreeze & Coolant - Ready To Use - 5 Litre
https://www.ebay.co.uk/itm/Comma-Super-Longlife-Red-Antifreeze-Coolant-Ready-To-Use-5-Litre/184480640043
https://www.commaoil.com/productsguide/file/fa6d4abcc12f45c5f882ad60d6da267c
Do buy the ‘ready to use’ type, as it is already diluted with the most compatible water.
The system is repeatedly flushed with tap water until it runs clear, followed by condensate from my clothes drier. It took a lot of water. After at least 1,000 miles, I intend to change the fluid again. The idea being that by then, anything foreign will be neutralised and corrosion protection will be bolstered. It will be a simple drain and refill with no flush. In any case, the coolant will just go off in the container.
Do not run the engine without coolant, or at least water. For sealing the input shaft, the pump uses ceramic seals, also known as mechanical seals, and they are reliant on liquid for cooling. I bought a second hand engine, which I started dry just to see if it would run before I did more work. Ten seconds was enough to overheat and crack the ceramics.
Go to YouTube and search for ‘annealing a copper washer.’ You do not want to lose that new coolant.
Hopefully, there will be nothing to report other than good running and the next change in 2026.
References are specific to the NT700.
