Safe to mix engine coolants?

TheVoice · 28 Oct 2014 at 11:48

Probably a dumb question here but I'd rather ask it than not. Just checked my car over ahead of its MOT tomorrow and noticed the coolant level has dipped below the minimum line. There's a bottle of old-ish coolant/anti-freeze in the garage, am I safe to just top it up with that? I can go and buy a new bottle if that's better, or just ask the garage to do it tomorrow if its safer to have it flushed and replaced.

Cheers.

pepsilol · 28 Oct 2014 at 11:54

Just top it up with water.

Haggisman · 28 Oct 2014 at 12:02

You shouldn't really mix coolants as they can form a sludge if you end up mixing the wrong kinds together.

Topping it up with water is a quick and easy way to get it through the MOT - just bear in mind with the cold weather approaching, that if it gets too diluted it won't have as low temperature threshold, so may be worth having it flushed and replaced anyway.

Akagi · 28 Oct 2014 at 12:05

Top it up with rainwater. Seriously.

Apparently it is a better idea than using tap water. Tis what my mechanic told me at least... Something to do with the additives and rubbish in tap water maybe? I dont know.

Just make sure it isnt full of crap.

Diagro · 28 Oct 2014 at 12:07

I recently topped mine up with Distilled water. Yup 100% Pure distilled water.

Still have 5 gallons in the garage from when i used to rebuild my pc every week lol

TheVoice · 28 Oct 2014 at 12:08

Thanks guys, water it is. It's due a service soon so I'll get them to flush it and check the system over anyway, bit concerned as to why it's dropped.

sovietspybob · 28 Oct 2014 at 12:09

Best is water from a dehumidifier as that's nice and pure, depending where you live the chlorine and stuff can mess up coolant systems.

TheVoice · 28 Oct 2014 at 15:02

How about deionised water? Might have some of that.

lemonade · 28 Oct 2014 at 15:10

No don't mix and wouldn't recommend just adding water, why not just get it properly drained and refilled? Hardly a difficult job and you shouldn't really be losing coolant.

pepsilol · 28 Oct 2014 at 15:14

lemonade said:
No don't mix and wouldn't recommend just adding water, why not just get it properly drained and refilled? Hardly a difficult job and you shouldn't really be losing coolant.

Don't spout nonsense please. Topping up with water will do nothing.

lemonade · 28 Oct 2014 at 15:29

Short term no, long term yes. Why bother topping up with water when a drain and refill only takes 30 mins.

scratch · 28 Oct 2014 at 15:32

pepsilol said:
Don't spout nonsense please. Topping up with water will do nothing.

A tad harsh! Adding water will reduce the concentration of the coolant and thus raise its freezing point. As long as it's only a small amount then it shouldn't matter but the OP should make sure he gets it properly sorted as soon as possible.

Armageus · 28 Oct 2014 at 15:34

lemonade said:
No don't mix and wouldn't recommend just adding water, why not just get it properly drained and refilled? Hardly a difficult job and you shouldn't really be losing coolant.

As already mentioned topping up with Water will not cause any problems.

Mixing coolant can also be done in some cases, but requires you to know what the existing coolant is, and only certain combinations e.g.

for vw/audi etc:
G12++ can be mixed with everything, but G12 cannot be mixed with G11

http://www.opieoils.co.uk/c-1551-vw-coolant-and-antifreeze.aspx

TheVoice · 28 Oct 2014 at 15:47

Topped it up with deionised water. Didn't actually take as much as I expected, 250ml or so maybe. In any case I'll get it sorted properly during servicing.

Thanks all.

lemonade · 28 Oct 2014 at 15:49

Armageus said:
As already mentioned topping up with Water will not cause any problems.

Mixing coolant can also be done in some cases, but requires you to know what the existing coolant is, and only certain combinations e.g.

for vw/audi etc:
G12++ can be mixed with everything, but G12 cannot be mixed with G11

http://www.opieoils.co.uk/c-1551-vw-coolant-and-antifreeze.aspx

That is an ambiguous statement, depends how much water you are topping up with, what kind of water and for how long, it certainly will cause problems if certain conditions are met, otherwise manufacturers would just tell you to top up your radiators with water :rolleyes:

darael · 28 Oct 2014 at 15:53

Acme said:
Top it up with rainwater. Seriously.

I'm not sure rainwater is a good idea these days, with acid rain and all that. :eek:

Akagi · 28 Oct 2014 at 15:57

That explains why the Polo exploded then.

Haggisman · 28 Oct 2014 at 16:02

Armageus said:
As already mentioned topping up with Water will not cause any problems.

Depends what you class as "causing problems".

It won't cause immediate problems, but if he dilutes the coolant too much and then we have a cold spell, it may freeze, rendering the car un-driveable, or worse, causing damage to the radiator and hoses (or even cracking the engine, although unlikely)

Armageus · 28 Oct 2014 at 16:14

TheVoice said:
Topped it up with deionised water. Didn't actually take as much as I expected, 250ml or so maybe. In any case I'll get it sorted properly during servicing.

Thanks all.

Haggisman said:
Depends what you class as "causing problems".

It won't cause immediate problems, but if he dilutes the coolant too much and then we have a cold spell, it may freeze, rendering the car un-driveable, or worse, causing damage to the radiator and hoses (or even cracking the engine, although unlikely)

a "top-up" in my head, was a couple of hundred ml, i.e. the 250ml that the op has added - 250ml in what 5 litres? is not going to make a huge difference.

Haggisman · 28 Oct 2014 at 16:31

Armageus said:
a "top-up" in my head, was a couple of hundred ml, i.e. the 250ml that the op has added - 250ml in what 5 litres? is not going to make a huge difference.

Well no, not in a one off, but if it gets "topped up" 10 times, then that 50/50 mix of coolant/water becomes more like 25/75, which is a bit more of a difference

, hence why I said "if it gets diluted too much" in my post.

Topping it up for the MOT is fine, as long as he remembers it's been topped up, and doesn't come to a couple of months time when he notices it's low and tops it up again, and repeat...