The "Low Coolant" indicator light is coming on intermittently, even though there is plenty of coolant in the reservour and the temperature gauge isn't showing unusually high temperatures. I've read of this problem elsewhere here, and generally those postings indicate a faulty "low coolant" sensor. I'm fine with that diagnosis, since my car (a 1996 SSEi) is almost 10 years old and nothing lasts forever. I recently changed the "check oil" sensor and haven't looked back.

:?: The point: I have introduced some non-standard coolant into the system. My wife drives a Mitsubishi montero, which uses a different coolant. Rather than stock two different coolants, I'm using one of those "universal" coolants to top-off both vehicles. Could this non-standard coolant, which would be dillutted anyway by whatever the ordinary coolant is, be causing the sensor to malfunction? Should I flush the whole coolant system and replace it with factory spec coolant before replacing the sensor?

Any informed advice appreciated.

IMHO....I would blame the sensor failure on old age rather than the introduction of some universal coolant. But, if it will make you feel better, after you install the new sensor and find that all is right with the world, you might want to flush the system clean and install new coolant.

While the sensor may be defective, after so many years.....

I would first remove and clean it down to the bright shiny metal.
Years of suspended particles, (Calciums, Oxides, and other Minerals that may be dissolved in water)
have a way of building up on the sensors rendering the electrical properties inert.
( they won't work, or work intermittantly )

The way most coolant level sensors operate is by resistance to a current flowing thru them.
This resistance is low when coolant surrounds them completely, and all is well. (dash lights won't light up ).

When the level drops, there is no easy path for the current to flow thru the sensor,
this sets in motion, the Alarm signal. (Dash light lights behind a transparent wording of "LOW COOLANT")

So clean it first, then decide if it needs replacement.

You might save yourself some time and money.

Then you can follow the other "Ol timer" '* advice...

Yeah, I'm old too....

Thanks. How often should the coolant be flushed anyway?

Well, that depends on whom you talk to....
See:

http://ths.gardenweb.com/forums/load...902087175.html

The real answer is "When the additives wear out"! .....or before there'* a buildup
of corrosion, gums, oils, goo'*, sediment, or any blockages.

But how are you to know this?? Well without chemical analysis, you won't.
Therefore follow the individual coolant manufacturers recommendations.

I like to think that a dollar spent in preventative maintenance,
is worth $100, in repairs... Which would you, rather spend?

Would 24k miles or 24 months be a good rule of thumb? I believe the user manual says you never need to flush the cooling system, although I may be remembering it wrong.

Sure! That'* as good a number as any.....
Whatever you decide, will be better than nothing at all.
And you know best what you can afford.

Just remember if you have an aluminum engine, you'll need a "non silicate" coolant.
Check your owners manual...to be certain.


More Coolant info:
http://www.texaco.com/texaco/prodsvc...d_coolants.htm

Material Safety Data Sheet:
http://www.setonresourcecenter.com/m...0/wcd030db.htm

Some Warnings about non silicate use:

To prevent “silicate dropout”, PPT/MONITOR recommends the use of any antifreeze that meets the General Motor’* Extended Life Coolant Specification (DEX-COOL®). These antifreezes are readily available at diesel engine supply stores.

When silicates present in antifreeze drop out, they build up and form a gel. This is called silicate dropout. A number of things can start this process: high silicate levels from incorrect antifreeze concentrations or improper use of coolant additives, impurities in very hard water, and severe engine temperature swings. “Boiler-scale” (calcium salts), especially present in used engines, present the largest threat of silicate dropout. It is therefore extremely important that used engines are thoroughly flushed. It is best to run the engine using only clean distilled water until much of the calcium salts have dissolved.

The main effects of the formation of this silicate gel are clogging of the heat exchanger, and engine overheating. Silicate gel buildup greatly reduces heat transfer to the coolant. When the gel coats the temperature sender, engine overheating can take place without notice. Silicate gel also carries abrasive particles to the water pump, where it wears away pump seals causing leakage and failure.

There are few effective methods for cleaning the gel from an already-clogged system. The heat exchanger must be removed and sent out for a thorough cleaning. The engine must be flushed with a caustic solution. The gel is not water soluble, so flushing with water alone will not work.

When using “Extended Life”, or “Low/non Silicate” anti-freezes, be careful NOT to mix with higher silicate antifreezes or hard water.

Use of too strong of an antifreeze solution can hinder heat transfer from the engine, and promote silicate dropout. Pure water conducts heat better than antifreeze and corrosion inhibitor; therefore, the addition of antifreeze or other chemicals reduces the water’* capacity to draw heat off the engine. A 1/3 solution is recommended so that no additional corrosion inhibitors need to be added.

The above an excerpt from:
http://www.perfprotech.com/home/fres...ing-basics.htm
( a boating engine performance company, but still good info)

Hint....
Use distilled water with any type of coolant.... there'* no mineral content in it.
That means no sediment from H_2O, and a longer life,
for the coolant additives...and inhibitors.