Heater problems

You can flush it with tap water which is free.

A lot of people don't bother using distilled water, but if corrosion is becoming an issue my advice would be to fill it with coolant and distilled water; its not so expensive.

Surely tapwater is distilled in a tank or reservoir before you turn the tap on, making it distilled water anyway? LOL!

I've never heard of distilled water being used in cooling systems before and I done my apprenticeship with the Romans! If there is corrosion in the cooling system it is 100% caused by Oxygen getting into the cooling system via a leak or allowing the coolant level or anti freeze content to fall.

If you allow the coolant level to drop, air (which has oxygen in it) will fill the space the coolant took up. Leading to corrosion. If the coolant level has dropped it means a leak.

Anti freeze has corrosion inhibitors in it so low anti freeze content means corrosion. A drop in anti freeze content is caused by neglect or someone having to top up the coolant with water. Indicating a leak.

That said, your car is 16 years old so I would expect there to be a bit of corrosion in the cooling system.

If one heater pipe is hot and the other cold, the water is either not circulating well (which is probably caused by a dodgy thermostat) or a drop in the water level (leak).

You could fire the parts shotgun at it and just fit a new thermostat but if you remove it and check it first you will know it is faulty. A thermostat is pretty cheap but fitting parts you dont need is expensive. What will you do if you fit a new thermostat and it isnt any different?

If you check for leaks, check the thermostat works and try bleeding the cooling system (the bit where you leave it running with the heater fan and radiator cap off) it will increase your chance of fixing it first time.

The worst job on any car is redoing the job you have just finished!

I know its not that critical particularly in a modern car where there must be only a few litres of coolant anyway.
I'm in an extremely hard water area and avoid using tap water in anything other than my tea.
We use gallons of distilled water in aircraft cooling systems as distillation removes minerals and organic material so is more pure.
There is a lot of discussion about this in many vintage car forums as many early cars dont have water pumps and rely on the sole efficiency of thermo-syphon. Moreover on an 80 or 90 year old system there is an obviously greater need to reduce any chances of corrosion than ever on an already internally corroded (through age) engine . Its on this that I base my reasoning

This is all very true, Max.
In modern engines the only time people usually talk about distilled water is for the battery. You would need around 6 litres of distilled water and anti freeze to fill a Jimnys cooling system from empty. The Jimny has a lot less ferrous metal in its cooling system than your typical vintage car, so like the Mrs. at the pub, tap water is fine, LOL!

I think the point I was trying to make is, rather than read too much into how to stop the water looking rusty the OP should concentrate on establishing whether there is a fault or not.

If you top up the cooling system, turn the heater fan off, set the temp to hot and run the car at idle with the raiator cap off you can ensure the cooling system is bled properly and monitor whether the thermostat is working or not, establish whether the water is circulating thru the heater matrix or not and determine whether you have an obvious leak or not. It costs nothing, its easy, it does not involve breaking out the toolbox, it does not involve spending any cash and you can even have a cup of tea whilst doing it.

To me, it seems madness anyone would not do this as a 1st step with any problem concerning the cooling system. You have to test the system to see what works and what doesnt!

I am sure you would agree, regardless of whether you are working on a plane, vintage car or Jimny you should start with the easiest and most obvious?

Absolutely! Always do the easiest solutions first [smiley thumbs up needed here].

I didn't replace the coolant on my Jimny myself when I first got it almost 12 months ago - I just threw it at my local Suzuki dealership along with a full service and a myriad of other jobs - simply for speed of getting it back quickly otherwise I would have done it all myself, so I'm not that familar with the Jimny. the coolant weas black!
I think however that on mine (M13A) the thermostat is an utter pig to get at; during the summer I had a small coolant leak from an area around the top right side of the engine. I'm told it was the pipe between the block and thermostat housing that had began to leak; it had corroded. Again, I had to throw it at a local workshop as I didn't have the tools (or time) to do it myself, so my knowledge of the cooling arrangment for the Jimny is sparse but it does seem a bizarre place to put a thermostat.
My modern (1979) Midget is an utter nightmare to bleed; it seems to have air pockets in all sorts of places in the system and takes ages to properly sort out.
The old Midget (1932) is still in a million pieces so I have no first-hand experience of that yet. The radiator is made of lead and brass and weighs a ton without any water in it!

I think in these circumstances, putting new parts on it will be worth it and it's not a case of throwing new parts at it in the hope of fixing it.

Yes, making sure the system has no air locks in it and getting it working properly by just doing that, if possible, might save the cost of a thermostat.

Is it worth it though? The coolant sounds grim and needs replacing. What damage has the corrosion in it caused already?

You don't want to keep working on it, wishing you'd done a bit of preventative maintenance in the first place. To this end I might be tempted to throw a new water pump on too if it were mine.

Testing a thermostat is all well and good but you need a new gasket to put it back in with, just like the one that comes with the cheap to buy new thermostat.

Maybe I'm a bit too anal but I like to remove future problems before they occur.

If I'd done this on my blessed BMW as I knew I should have, I'd not have had to change the thermostat, radiator/expansion tank and water pump in three separate jobs. They are known failure points on that model though, whilst Jimny's are quite good. It just sounds like this one in question needs a bit more TLC.

Modern anti-freeze has anti-corrosion properties in it, so tap water should be fine. Use more anti-freeze if you're worried, it won't harm the engine.

Kirkynut