Coolant type for Xantia V6 ?

[Paul-R]

There are some blue OAT types on the market.

Are you sure about that or are you just repeating what you've seen written around (as I have). Do you have any names/brands? Any links to such a product?

[CitroJim]

Chris, what's the problem with tap water?

I've always used it with no apparent effects..

My local water is very hard so not sure if that makes a difference? I know some soft tap water can be very acidic and back in the old days of lead piping special internally tin-plated lead pipes had to be used to stop the water dissolving the pipe and causing lead poisoning... I could see using such water in a cooling system might lead to issues..

Hard water does not seem to cause cooling system limescale in a 50/50 mix with glycol antifreeze. Does the antifreeze have some softening effect on the water?

[Mandrake]

Looking at the receipt from 2007 when the radiator was replaced it lists:

C997978 - Antifreeze - 3x £3.90
C1331PR - 026938/RADIAT EXCHA - £163.61.

I tried to look up C997978 on service citroen - no match. If I look it up without the C I get a match, the price is comparable (about £5 now) but the description of the item is "***". Thanks Citroen.

(By the way, how do you replace a radiator and use only £11.70 worth of coolant to fill the system again ?? Seems like they didn't drain and flush the system when the radiator was changed - just replaced what was lost)

I think I'm just going to use the old style Silicate stuff and flush well as a precaution.

[CitroJim]

I think I'm just going to use the old style Silicate stuff and flush well as a precaution.

Just going on the cost of the coolant in 2007 suggests its just common glycol stuff Simon. The post stuff would have been much more expensive...

[Mandrake]

I'm assuming its 3x 1 litre bottles at that price, or maybe 3x 2 litre bottles - either way, not enough to drain and refill the system from scratch. 3x 5 litre bottles would be too much! However you look at it it won't add to 10 litres...

[Mandrake]

Ok I decided to go with the Triple QX Blue, which is an old style Silicate type which is probably what is in the car now. I'll try to flush it out as much as possible as well as a precaution.

I decided to go with readymix so I don't have to faff around trying to get demineralized water as well - 2x 5 litre bottles for the main fill, and 2x 1 litre bottles, one in case I need slightly more than 10 litres or have any spills and another 1 litre bottle to keep on the shelf long term so I always have a bottle of the exact same stuff if any future topups are needed.

£22 including 2 day delivery for 14 litres seems pretty decent, especially to a poor skinflint such as myself!

That means I should be able to get back on the road for £122 all up. The annoying thing is I was about to do a coolant change before the winter anyway...

Thanks for the help everyone, on a very confusing topic!

[Stickyfinger]

Warm engine drain, back flushed with a hose, filled and run with tap water, drained and filled with OAT mixed with distilled water.

[white exec]

Last time I browsed coolant on the hypermarket shelves down here I had to look carefully at exactly what was in the large choice of 5L bottles on offer. It included OAT-type in blue, as well as yellow, pink, and red. Cannot now remember the make.

Tapwater contains dissolved minerals, and bringing it near to boiling will cause these minerals to drop out, leaving sediment or limescale behind, same as your kettle or coffeemaker. One of the functions of a good coolant mix is to act as a softener, and keep these dissolved solids in solution, but it's better not to introduce them into the system to start with, hence the recommendation to used demineralised/distilled/deionised water. None of these are acid, and so will not attack the mixed metals in an engine system. Acidic coolant is capable of operating like a battery electrolyte in such a mixed metal system, causing both metal erosion and generating small amounts of gas. Delicate items such as head gaskets, heater matrixes, and aluminium oil-water heat exchangers are particularly vulnerable.

[Stickyfinger]

I have always been of the thought that the system should NOT hiss when the cap is removed (when stone cold) as this is a sign of the system pressurising above the normal (from heat expansion).

If it does there is something happening to generate additional pressure.

[Mandrake]

It's amazing how dependent on temperature depositing limescale is. See the graph below and article:


http://inspectapedia.com/plumbing/Water ... revent.php

At 80 degrees C limescale deposits about 6x more readily than it does at 60 degrees C.

The moral of that story is don't let the system get hot, ideally not over 50 degrees, when circulating water without suitable inhibitors present. (EG during a flush)

Same applies to central heating systems too - don't run it at normal operating temperatures until the inhibitors have had time to fully mix around the entire system and definitely don't run it without inhibitors, even for a day or two.

I'm about to do a full drain and flush of our heating system in a couple of weeks and I learnt that lesson the hard way last time. (temporarily running at normal temperature without inhibitor, which deposited lots of limescale in the boiler, grr) This time I will be doing all the flushing cold and adding inhibitor and letting the pump circulate the cold water around all radiators for at least half an hour without any heat to allow it to fully mix the inhibitor before letting it get hot. (Thus in theory avoiding the limescale depositing I had last time)

[white exec]

Alasdair,

The hiss could well be air sucking in. As the system cools, it generates a slight vacuum, and opening up the filler cap will relieve this.

If all works well, during normal driving, any pressure in excess of the 1bar or so design will be relieved by the pressure cap valve lifting. The pressure increase is deliberate, so that the boiling point of the water is raised from 100C to something like 130C, to allow very hot running without boiling*. When things cool, pressure inside the system can go negative, hence the hiss when you allow some air back in.

*...and the advice not to open a pressure cap with a very hot engine: a sudden reduction in pressure can bring on immediate boiling and massive loss of coolant.

[Mandrake]

The hiss could well be air sucking in. As the system cools, it generates a slight vacuum, and opening up the filler cap will relieve this. If all works well, any pressure in excess of the 1bar or so design will be relieved by the pressure cap valve lifting.

Aren't most radiator caps supposed to have differential relief valves though to avoid this ? I was under the impression that a cap would resist opening until about 1.3 bars in the outwards direction, thus allowing the system to pressurise when hot, but have a separate and very low threshold (thanks to a one way valve) on the inwards direction, so that any negative pressure is relieved.

Thus over a cycle of operation the level in the expansion chamber finds a natural equilibrium level with no negative pressure when cold.

The pressure increase is deliberate, so that the boiling point of the water is raised from 100C to something like 130C, to allow very hot running without boiling. When things cool, pressure inside the system can go negative, hence the hiss when you allow some air back in.

Indeed, the pressure rise increases the boiling temperature on purpose - the system will boil more easily if you leave the cap loose and thus prevent it pressurising. I don't think it's nearly 30 degrees of increase though, I think RichardW posted a calculation in another thread not long ago and it worked out to something like an extra 10 degrees over atmospheric pressure. You get some significant increase in boiling temperature from the antifreeze as well - even when it is not pressurised.

[white exec]

Simon, you're right, and about the 1.3bar being typical. Modern radiator caps do contain that second valve to allow air back in.

On the 130C front, I was just going by our XM gauge, which has been known to clock 125C (when the injection ECU reduces fuelling to almost nil, and car to walking pace maximum). This sorry state of affairs happened after a front-end collision, years ago in Cadiz, leaving us with a one-fan 2.5 and a heavy caravan. Stand to be corrected on the boiling point elevation figures.

Very informative graph above. Disn't realise the deposition rate was so affected by such a small temp increase.

[CitroJim]

Gosh! This thread has turned out to be very interesting and informative Excellent stuff!

[momag46]

My 1999 v6 coolant was a bit low and like above, the handbook was a no great help.

I rang the main dealer who had serviced the car from new (until I bought the car) and also fitted a new radiator and they checked their records and came back with BLUE.
Because I only needed a small amount I used Carplan Blue Star.

If I was adding much more I may think of a drain, flush and refill.

Thinking on my feet as I sit here - I suppose the system should be changed every 2-4 years

Maurice