Getting rid of rust in the cooling system

[Cityscape]

So I'm replacing my water pump on my '92 MkII and I do notice a little bit of rust in the engine block's coolant channels. There are faint signs of rust in the coolant hoses too. I don't think my car has a lot of rust, but it does have some. This was probably the result of me running it on water for a couple months. Yeah a friend told me it'd be fine, but I guess they were wrong.

So anyway. Is there a way to get rid of the rust? And how would you recommend doing it? I've read on other car and VW forums about flushing the whole coolant system with vinegar, is that okay to do? Some people say CLR but I'm thinking that's not a good idea.

Also, if I was to get rid of most of the rust and top the car up with actual coolant, would the rust get worse?

[RabbitJockey]

i've just flushed mine with regular water then filled with the proper coolant and the problems gone away, if your coolant keeps becoming discolored you may have a headgasket leak.

[scubagli]

Clr is fine I've done it tins of times.

[vanbcguy]

A CLR flush is definitely a good idea. You can use automatic dishwasher detergent too, though that's better for getting oily residue out rather than rust.

Whatever you use, it's just a flush - fill 'er up, run till it gets warmed up to circulate it through the system, drain it all out, flush with water, fill with proper coolant. 

You can certainly use the cheaper green coolant, but if your whole system is nice and clean I HIGHLY recommend going with one of the G12 variants.  The pink stuff is awesome, it doesn't degrade and it keeps all your hoses and things in great condition.  You can open a system that's been running G12 for years and it all looks brand new inside, plus you basically never have to change it.

[scubagli]

Mkii should be g11, BMW makes a cheaper version.

[RabbitJockey]

i run the green stuff with stilled water in all my older cars, and anything that called for g12 gets g12, if i ever empty the coolant out of my older cars i'd probably switch to g12 though, but with out a reason i will not bother with something like that.  i've never touched g11 though.

[mtrans]

x 2 on vinegar.
to get rid of the rust?
I use fuel filter housing and oil filter from some Peg,I think 104,because it has 16*1.5 mm,just for bypass valve in it.and put on hose from rad to overflow bottle.

[92EcoDiesel Jetta]

A CLR flush is definitely a good idea. You can use automatic dishwasher detergent too, though that's better for getting oily residue out rather than rust.

Whatever you use, it's just a flush - fill 'er up, run till it gets warmed up to circulate it through the system, drain it all out, flush with water, fill with proper coolant. 

You can certainly use the cheaper green coolant, but if your whole system is nice and clean I HIGHLY recommend going with one of the G12 variants.  The pink stuff is awesome, it doesn't degrade and it keeps all your hoses and things in great condition.  You can open a system that's been running G12 for years and it all looks brand new inside, plus you basically never have to change it.

Is that really true with G12? Don't the additives degrade over time?

[vanbcguy]

G12 is considered a 'lifetime fill', with 'lifetime' being about 100,000 miles / 160,000 km in VW's mind.  G12 will outlast your water pump / thermostat anyhow, you won't need to do a coolant flush until one of the other system components is due.

It works fine in all the older cars; there's nothing metallurgically different between say an AHU which spec'd G11 and an ALH which spec'd G12.  It's just one of those things where the science behind making a stable engine coolant has improved significantly since the older stuff was invented.  Just make DAMN sure you don't mix G12 with anything but G12/G12+/G12++/G13; the additives that make it work aren't compatible with G11/Dexcool/green stuff and will form a nasty sludge in your cooling system.

[745 turbogreasel]

There is some  **** in cool-aide  powder that works well on rust too, but you have to flush a  bunch to get rid  of the smell afterward.

[RabbitJockey]

just make sure you don't run dexcool and you'll be fine haha

[Cityscape]

Thanks for all the replies guys! My concern with CLR was if it damages seals or something (whatever the incorrect coolants supposedly damage.)

If there was a bit of rust in there still when I top it up with coolant... would it get worse or would the coolant kill/inhibit the rust?

I've bought myself G13 coolant to fill 'er up with!

[vanbcguy]

The biggest issue with incorrect coolant is really coolant chemistry 'A' coming in contact with coolant chemistry 'B'; engine coolant is a pretty complex chemical soup these days with things like buffers that try and maintain a very specific pH level.  If you mix two different chemistries together they tend to fight to the death to pull the chemistry to the level they are designed for resulting in them completely depleting their additives and often filling everything with sludge.  Worst-case scenario is doing something like a waterpump change where half the coolant is drained but the block/rad/heater core are all still partly full.  Top up with the wrong thing and you've got problems.

CLR shouldn't hurt anything seal-wise or anything else.  It is pretty safe around plastic / metal / rubber.  Obviously it isn't suitable for sustained use.

I wouldn't worry if there is a little rust left at the end.  It'll go inactive once the corrosion inhibitors from the coolant get to it.  Having a clean block and radiator free of scale and debris is the most important part, no sense having your brand new coolant use up 20% of its capacity trying to fix stuff you could have flushed out, right?