BMW Coolant Light

Cotta

The orange coolant light on my BMW has just came on for about 5 seconds. Is it OK to top this up with regular water alone?

forgotmyname

If you top up with water alone you will be reducing the strength of the antifreeze in the coolant.

Its usually the antifreeze that escapes 1st. So the antifreeze / water ratio is probably less than it should be already.

Strider590

Yes, it'll probably be fine.

It's usually about 250ml from max to min, the system will hold over 4 litres, so the change in ratio is minimal at best. If your genuinely concerned then just buy some antifreeze and mix it 50/50 with water.

shaz77_2

Just intruding on this post, this is something I've never really done as my car doesn't use much. Do you need to top up often and does the coolant you buy require mixing?

ChumpusRex

The coolant in the car engine contains 2 main components:
1. Antifreeze, which prevents freezing in cold weather (you don't want the engine to split open in Winter, like a frozen drink can) and also prevents boiling when the engine is running.
2. Anti-corrosion, which prevents all the metal parts of the engine that touch the coolant from rusting, or otherwise corroding.

If you top up with water, you dilute both ingredients. If it's just a 1-off small top-up it won't really matter, but if you are doing it regularly, eventually you'll dilute the antifreeze and anti-corrosion ingredients so they don't work. (Just bear in mind, that some of the very latest coolants - mainly from Japan and Korea, are not compatible with hard water and the anti-corrosion additives will be damaged if topped up with hard water).

In general, cooling systems shouldn't need topping up regularly. Normally, the car manufacturer recommends replacing the coolant periodically (usually every 5 or 10 years) because it gradually goes off. However, because of the way cooling systems are sealed, it is possible to have a temporary leak, which then seals itself. Regular topping up indicates an on-going leak which may be a sign of serious engine problems and should be checked out by a mechanic.

Be aware that there are literally dozens of different coolant formulations on the market, all with different trade secret anti-corrosion formulations, or anti-corrosion recipes specially formulated for the metal alloys used by that car manufacturer.

It's anyone's guess as to what will happen if you mix different formulations. For this reason, it's safest to buy something that has specifically been approved by the manufacturer (e.g. go to a dealer, or check your owners manual for a part number, and buy the correct product online).

There are "universal" top-ups available (most big supermarkets), which are designed not to react with existing formulations, and don't require dilution - you just pour them in. Although the formulation of this type won't exactly match the factory fill, unless you're pouring loads in, these will be close enough for most purposes.

colino

Top it up with enough water to get you to a decent garage. Sealed systems don't need topped up, you have a problem that needs attended to straight away.

Marktheshark

When you remove the cap, clean the rubber seal in the cap with some vinegar, you will see it is quite dirty.
They can let steam escape over time when the seal is dirty and hence a slow loss.
Top up the water and put the cap back.
Worry about soothesayers another time.
Just keep an eye on the level.

colino

OP, if you have a car with a flashing low coolant light, especially a BMW, have it checked straight away, or take the, "manana" approach, "advised" here and cook the engine.

Marktheshark

Checked as in £140 + vat per hour to top up the water expansion reservoir.
Plus a day with no car.
It is an almost weekly routine as the miles mount up.
Just happen to have had a few BMW in my time.
Most required some coolant at some time or other.

colino

Apologies shark if you could only get one of these, very prone to coolant issues, cars at the end of their lives. Perhaps if a more caring owner had actually looked after them in the past you would have enjoyed a decent one. Like any sealed system, if your old BMWs start using water, brake fluid, power steering fluid or automatic transmission fluid and you haven't the skills, knowledge or experience to work out why, get a professional to check it for you.
Clearly you have been stung by dealer maintenance costs in the past, or should I have added on my usual, get your car checked at a friendly, local, recommended garage for you?
If you need a £140+VAT tech to help you in the future, how about getting yourself some car maintenance classes and lay off potentially expensive, "advice" on the internet?

OnanTheBarbarian

I would guess this is either an E36 or E46 3 series?

Common places for coolant to leak is the thermostat housing (especially if it is a plastic one) or the radiator. They tend to bow out at the bottom and you can't see this unless you get the car up in the air and remove the plastic under tray.

I would give it a quick top up when the car is cold and then keep an eye on it. if the light then reappears I would seek advice from a friendly local independent garage to look into the problem further if you are not mechanically savvy.