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MG MGA - Crystallisation of Antifreeze

I have just started to bring back to life my MGA.
First job to renew the antifreeze.
Removing the top hose showed a build up of whiteish deposits in the aluminium thermostat housing, and on the thermostat. The engine block where the thermostat sits, has no deposits.
As a trial I tried soaking the housing and thermostat in hot water with rad flush. The deposits showed very little sign of softening.
I then tried soaking in vinegar. This did soften the deposits and allow removal.
My question is, is this due to the additives in the antifreeze evaporating, allowing the antifreeze to crystalise.
Or is it due to a reaction between the antifreeze and aluminium/bronze, after the additives have become ineffective. There are no deposits in the thermostat cast steel bowl in the block.
I believe I would have used an antifreeze suitable for aluminium. But some years ago now.
I now use a blue ethylene glycol with distilled water.
And will continue to look for white deposits as I remove/replace all the hoses. The water pump spins freely so not blocked up.


H BUCKELDEE

I had a similar problem with my B, a couple of years ago.

I stayed with my brother the night before MGB60 and in the morning, the temp was only about 5°C and the windows were misted. I put the heater on, but only got cold air.

Anyway, when I got it home, I investigated. The heater tap was furred up with crystals, as were the hoses. I did a cooling system flush with either Radflush or Barrs, then replaced the heater tap, which wasn't actually that old.

The antifreeze which was in there was from Euro Car Parts, but I didn't fancy using that brand again. I bought some from my local MG specialist, which I think was Millers.
Dave O'Neill 2

That does remind me to check the heater valve.
I think as the antifreeze solution weakens, or it is a weak solution to begin with, it is more likely to crystalise. Or attack aluminium.
I have not used my car for a few years and did not replace the antifreeze.
The deposits are hard to remove. A quick test with rad flush and hot water did not remove them. Perhaps a prolonged test would.
H BUCKELDEE

Coolant will crystalize if the engine sits for a long time without being started and having the opportunity to heat up and mix within the cooling system: its basically caused by additives/chemicals in the coolant dropping out of suspension and solidifying. It can also be caused by mixing different, incompatible coolants, and while there are some coolants specifically recommended for aluminum radiators, any of the modern "green" or "yellow" coolants do have additives to protect against corrosion with aluminum engine components.
Nick Kopernik

I’ve found some photos of the deposits.

The heater valve was quite badly corroded, despite only being fitted for four years.




Dave O'Neill 2

I wonder if aluminium or copper/brass (thermostat) acts a catalyst for the crystals to form. As its seems to be in those areas.
Yes Dave they are the crystals, in various colours.
I don't recall mixing antifreeze types.
Only use IAT blue ethylene glycol with distilled water now. Following advise from FBHVC in GB, for historic vehicles.
H BUCKELDEE

This thread was discussed between 09/06/2025 and 10/06/2025

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