The previous owner ran tap water in the cooling system for few years, and we have very heavy, mineral rich water locally. When I bought the car about six months ago, I drained the water, and put a standard pre-mixed "green" glycol based coolant in as per the manuals recommendations.
Recently, I replaced the thermostat ( actually there was no thermostat -- eeck ! ) and upon peeking into the engine blocks coolant passages I saw the following:
I had to re-fill with tap water yesterday as one of my hoses sprung a leak ( replaced the hose today ) and I was wondering if one it's worth trying to clean out the system, and two is it even possible.
I've heard of using distilled water and vinegar to get out the mineral deposits, although I'm worried that might react with any remnants of coolant in the system or maybe attack the head gasket.
Search under my name...Ive done the citrus flush twice and both times other components have been taken out, like the radiator, water pump etc. Im not saying dont do it, just be ready - anything that is on the edge of failure will be pushed over. Have your credit card warmed up and parts supplier ready forewarned :-)
In my opinion, if your cooling system is functioning properly, I would not do the citrus flush.
Is it safe, and is it worth doing, or should I just drain the water and fill back up with my normal "green" coolant?
POSTSCRIPT Oct. 6th, 2016
Before I did a vinegar flush my water pump fins looked like this:
Afterwards it looked like this:
All the fins were melted off the impeller! Of course, this may be partially my fault for getting busy and leaving the vinegar in overnight, but you should definitely be careful as there is a real risk!