How important is flushing the cooling system?

[knurlgnar]

I have heard repeatedly that ethylene glycol based coolants are supposed to be flushed once every couple of years to prevent corrosion. And I think I believe it to be true, but my experience shows otherwise. I currently drive a '91 Lesabre that I know hasn't had anything done to the cooling system for about 10 years. There is a good chance, in fact, that it is still running on the factory coolant. (!!!) It's an old car, but I think I might get it flushed anyway.

But here's the issue: There are two other cars in the family, (a '91 and an '82) that have simmilar stories to my LeSabre. The oil has been changed ritually and they have been treated well, but the cooling systems have been neglected. The '91 Ford Escort is still running on the same coolant as it was in '94, and the '82 Buick, well, that one broke a radiator hose back in the '80s but other than that it has had no service done to the cooling system since we got it back around '85. None of the cars have ever had any related trouble.

I don't get it. Why aren't they leaking?

 

[darryld13]

The short answer is that you should be as diligent about changing coolant as changing oil. Just like it may take years and thousands of miles before evidence of oil neglect throughout the engine shows itself in multiple repairs, years neglecting coolant will bite you big time by the time repair is forced upon you. It takes a long, long time for corrosion to eat from the inside out, so I am not surprised that you haven't had any leaks. However, I would be surprised if you were lucky enough to not have any damage from neglecting to change the coolant if you drive any meaningful distances. Remember, corrosion of the cooling system refers to the internal system (i.e. the water pump, heater core and engine galleys and path ways) as well as the radiator. Dull, brownish and sludgey coolant (rather than the bright green, red or orange) is evidence of corrosion - worse, the brown could be corrosion from the engine as well as the cooling system. The sludge eventually will clog up the galleys in the engine and radiator, causing hot spots and overheating. Making matters worse is that the water pump and heater core are at risk with weak antifreeze circulating.

I am surprised that you haven't at least had to replace or replenish at least some of the coolant in over 10 years - half of my flushes come as a result of changing my hoses, belts, water pumps and thermostat.

[ May 24, 2004, 01:11 AM: Message edited by: darryld13 ]

 

[rgl]

The color of the coolant I think also gives a false sense of security. I drained 3 year old (apparently factory) coolant last week, and the bucket looked bright green. However, when I put some in a shallow pan you could see that it was actually an ugly opaque olive color, not the clear sports-drink green. The anti wear and anti corrosion additives are sure to have taken a pounding just over that short period of years.

 

[Matt_S]

Sorry for the long reply, but I'm concerned that you don't understand the importance of this issue. Please continue reading.

Darryl definitely has it right. You don't mention whether or not you've actually looked at the coolant, though. If it's really the original, it will be a nasty, nasty brown from the engine block rusting, especially considering GM was using the standard green stuff back at that time. If it's still green, it can't be more than 3 or 4 years old. Even so, it needs to be flushed.

My recommendation would be to get a Prestone flush kit, if the car is not already so equipped, and a bottle of the strongest radiator cleaner on the market. If it's actually brown, get two or three bottles and do the cleaning more than once. My experience tells me that a neglected cooling system is very hard to recover from. The brown color tends to come back repeatedly until you've flushed it multiple times. This will bite you big time if you don't correct it. The coolant can turn acidic and eat head and intake manifold gaskets, as well as the water pump and everything else Darryl mentioned.

Finally, many people advocate a simple coolant drain and refill procedure, with no flush. This, however, assumes that the system has been maintained properly. On a neglected car, you need a good, thorough cleaning and flush. If you let this go, it can and will cause overheating, too. In the winter it can freeze, which will destroy the engine, so don't put it off. You might even want to consider paying for a power flush this time.

 

[knurlgnar]

In the '82 the coolant has lost nearly all hint of being green. There's no use putting money into that old thing, as it'll be junked when the insurance runs out anyway. I'm think I'm going to get my buick flushed (it has a little less than 150k miles on the odometer). As for overheating, it runs at around 160 degrees. Tried a few different thermostats including one from the dealership and they never helped. The temp does go up to 235 on a warm day (when the engine fan kicks in) if it sits there idling, but will drop down quickly once the car starts moving. It has always done that. I know other people with 3800 series I engines and theirs seem to hold a relatively constant temp. Has anyone else had this issue?