Engine coolant freezing temp.

Factual Questions
1

I drive a 2002 Honda CRV. The Owner’s Manual says that the engine coolant should be replaced after 10 years or 120,000 miles. I am nowhere close to either of these limits. Because of this, I figured that I could just leave the coolant alone.

My mother recently asked if I had checked the antifreeze level in the radiator. I had no idea what she was talking about. She said that there is some little gizmo I could by that would tell me the aproximate freezing temperature of the engine coolant. I’m assuming this is based on the density of the coolant which will change depending on the amount of ethylene glycol or whatever they use these days.

Here’s my question. Do people still do this? Is there a need to worry? I looked up some old threads. The last post in this this one says there is no need to bother. My manual says nothing about this. My coolant is still at the “max” line in the radiator resevoir.

2

While Honda may think that the coolant is good for 10 years, I doubt they consider that the coolant usualy gets diluted over time for a variety of reasons. If you have a small leak and need about a pint of fluid, you are just as likely to add 1 pint of water as 1 pint of water/coolant mix. So, yes, you can check the density of the coolant mixture and determine what the freezing point is. Do you need to? Probably only if you’ve ever added more water or coolant to the system.

I also doubt that the radiator hoses are good for 10 years or 120,000 miles. I get a bit nervous with any hose (or belt) much older than 4 years. And if you replace a hose before 120,000 miles, you’ll put in new coolant too.

3

Anti-freeze mixtures generally do not freeze but turn into a mush which will not circulate and cool the engine properly.

The anti-freeze doesn’t wear out but the rust and oxidation inhibitors do, The radiator and cooling system needs a periodic flushing and the mix and level needs to be chacked regularly.

4

Engine coolant = the liquid in the cooling system. For most climates, it should be a 50/50 mix of water and antifreeze, which has a freezing point of -34 degrees Fahrenheit (-37 C).

The coolant level is the amount/volume of coolant. The level in the overflow jar* is not a reliable indicator. If you want to be sure it’s full in the engine and radiator, you need to remove the radiator cap (cold engine only!) and check it there. It should be up to the bottom of the radiator cap hole.

The antifreeze protection is the freezing point of the coolant. This is what Mom was talking about. It can be checked with a hydrometer made for that purpose, the gizmo she referred to.

I wouldn’t say the coolant “usually” get diluted. It certainly can get diluted, but only and specifically if water is added to it. If the water/antifreeze proportion is not thus altered, the antifreeze protection will not change, regardless of time or mileage.

As spingears mentioned, corrosion inhibitors in the antifreeze get used up doing their job. When the coolant reaches a certain acidity level (~pH8.5), it’s time to flush out the system and replace the coolant, with a fresh water/antifreeze mixture. “Conventional” antifreeze is typically good for about 2-3 years or 30,000 miles. Long-life antifreeze is designed to last longer, and if your car’s first recommended coolant flush/replacement is 10 yrs./120,000 miles, the factory antifreeze must be a long-life type.

It’s not a bad idea to check the coolant level, to be sure none has been lost by the type of leak that doesn’t lower the level in the overflow jar. It’s also not a bad ideal to check the antifreeze protection, as it’s always possible that it has been altered, without your realizing, during some previous service. And it can’t hurt to have the acidity of the coolant checked. But barring any specific problems along those lines, you figured right – you can leave it alone.

*An overflow jar is a reservoir outside of the pressurized cooling system – it just has a simple plastic dust cap. A surge tank is a reservoir that is part of the pressurized system, with the “radiator cap” on it rather than on the radiator itself. Most auto parts and service people don’t make the verbal distinction, calling both types a “reservoir” or “overflow jar.”

5

With a surge tank, coolant level is checked in the tank. There should be a line/mark on the side of the tank showing the correct level. It will not be up to the bottom of the cap hole, rather usually several inches below that.

6

The gizmo of which she speaks can be purchased at any auto parts store, but I don’t think you would need one. It is basiically a tube with lead in the bottom and allows you to check the specific gravity of your coolant. You can then reference this with a chart (or some are labeled on the tube), and find your approximate freeze temperature, mainly based on the alcohol content in your coolant.

Most antifreeze jugs I see have the various ratios’ freezing temps on the jug. So if you use a 50/50 mix, you can determine the freeezing temp from there.

I would spend your money (maybe $5 or $10) flushing the radiator and filling it back up with a 50/50 mix, so you know what your coolant is. The only danger of freezing is when people refill a leaky coolant system with water, which would dilute the mixture allowing it to freeze easier.

If I were you, just check the coolant level when you car is cold (don’t do it when it is hot - you could get a face full of boiling coolant), and if it needs adding, just make a 50/50 mix or buy a jug of premixed antifreeze. With a car as new as yours, I would guess your coolant level is just fine.

7

All modern US autos use a 50/50 mix of etheylene glycol and water as a year around coolant. Operating level in the expansion tank must be maintained. The simple hygrometer is cheap insurance against watering down of the coolant by service personnel. A radiator flush at least every 3 or 4 years assures against a stopped up radiator or loss of rust and oxidation protection.

8

I use a this thing that looks like a miniature meat baster with little balls in it that, when filled with coolent, will tell you the freezing point of the coolent depending on which balls are floating.

9

This is not exactly true. Etheylene glycol, yes, but the additive packages may not be compatable between different types of antifreeze.

10

Well this has certainly proved more complicated than I thought it would be. Thanks everyone for your answers. I’m getting the oil changed and the tires rotated next week, so I’ll have someone check the fluid too.