Coolant too full

I am writing on behalf of a friend who has recieved a Chevy Monte Carlo '95 from her fiance’s parents. The car was purchased in 1997 and has over 150,000 miles. My friends fiance put antifreeze in the vehicle when they first got it this past winter. The antifreeze was put in without the car running, which I do not know if that matters.

The low antifreeze, now coolant light was on today so my friend checked under the hood and liquid is way over the full line.

I know this is limited information so I am just using this as a starting point, because it is their only vehicle and the two questions I would like to know are

1- What damage/wear and tear will occur if the car is driven with the coolant being overfilled and

2- How can they drain the fluid to get it to acceptable levels?

I will provide any other information- if they know- that u guys need but am just starting with this for now. Thanx.

Just bumping this up

I assume you’re talking about the fill line in the coolant resevoir. When the car cools off, that coolant will be sucked back into the radiator providing there are no leaks in the small transfer hose between the radiator and resevoir. I never heard of any damage being done if the resevoir is too full.

I assume that you are looking at the reservoir bottle. You should also check the radiator because that could be low. If you do find that the radiator tank is low, fill the radiator up with 50/50 mix and use a turkey baster to bring the reservoir to a level between low and high. Monitor the reservoir level over the next week. If the reservoir fills up again, recheck the radiator. If the radiator level low, you may have a cooling system leak that is allowing air to be drawn in when the engine cools down instead of drawing coolant back from the reservoir bottle. Have a mechanic look at it.

Why was the antifreeze added originally?

When the car is completely cool pull off the radiator cap and look into the radiator the check the level there.

If this is one of those systems that has only one cap (the plastic reservoir) and it is indeed showing full but the indicator light/s is/are on then it may be that the sensor for the coolant level is bad.

Perhaps it should just go to a shop for an evaluation of the cooling system. A cooling system problem can turn out to be a fast way to kill an engine.

Thanx guys- just called her and her fiance answered and basically re-affirmed what you guys are saying, think he called CarX. Anyways, I guess now the issue is no longer an issue. Thanks again guys!

now coolant light was on today so my friend checked under the hood and
liquid is way over the full line.

Hmm. I suspect something else is going on here. This could be a symptom of something like a bad head gasket causing the coolant to get “pushed out” of the system and into the overflow tank.

I had a similar situation with a 1993 Oldsmobile 88. My wife was driving home and the low coolant light came on. When I checked the situation, the coolant was low in the radiator, but was almost overflowing in the overflow reservoir. The rubber hose leading from the radiator to the overflow reservoir had deteriorated and would collapse as the vacuum in the radiator tried to suck the fluid back in. In other words, this rubber hose acted as a check valve. A dollar’s worth of new hose and a couple of new clamps and 10 minutes of time solved the problem.

Everything said here so far is spot on, to use a britishism. I would add that a bad radiator cap could also be a cause of these symptoms. So when you check the overflow hose and tank, and when it is cool, you check the radiator, you can also replace the cap, and it can be tested, but the time and trouble is hardly worth it. But what you can do for a quick test is to warm up the engine till fluid is going into the overflow tank, shut it off, and monitor the returne of fluid to the radiator, with careful observation you might be able to tell just where the problem (blockage) to the return flow is origniating.

That’s interesting, JoeMario. What route would the coolant take to the overflow tank via a bad head gasket? Doesn’t coolant go to the overflow tank when the head gasket is working properly?

The OP said they last filled the coolant this past winter, so I assume the car was running fine for a while. Then the coolant light comes on (indicating overheating) and the overflow tank is quote: “way over the full line”.

An overheating engine will cause the overflow tank level to rise above normal, but none of us can see how far “way over the full line” is in the OP’s tank. The level is apparently way beyond the normal rise/fall levels of the tank.

Something is causing it to overheat. One possibility is a leaky head gasket is pushing combustion gasses into the cooling system, which forces the coolant into the overflow tank to rise way beyond normal.

I agree with some of the other replies on things to look for as to what’s causing the overheating. The OP seems concerned with his fluid being “overfilled”, but rather he/she should be concerned with what’s causing the overheating (coolant light on).