I have a pretty nasty coolant leak in my car. I have to fill my radiator about twice a day. Anyways— because of the frequency that I have to fill my radiator I keep a bottle of coolant in my car. Typically it sits on the floor of the passenger side. Is it safe to drive around for 3+ months with a bottle of coolant? Occasionally there is very small spillage in my car. I am primarily concerned about potential exposure to vapor / fumes.

Best, James

  • Welcome to Motor Vehicle Maintenance & Repair! Oct 14, 2022 at 9:30
  • What kind of coolant? Why don't you fix the leak? Nov 14, 2022 at 0:57

2 Answers 2


Non-toxic antifreeze

If you want an essentially non-toxic antifreeze, they make antifreeze based on propylene glycol. It's amazing, the difference 1 carbon atom can make to toxicity - methanol is poisonous but ethanol is fun! Propylene Glycol is a sweetener, look at the ingredient list on cakes at Walmart and you'll find it.

It is vital you do that if it is leaking where local pets can drink it up because it tastes sweet. Ethylene glycol will kill them dead, and then you will have their owners to deal with. Propylene glycol will not.

If no freeze concerns, use far less antifreeze.

First, you should be cutting antifreeze at least 50/50 with water, per the instructions. (unless you're buying it pre-diluted, which means you're paying a lot of money for water, stop doing that).

If freeze is less of a risk, you can dilute antifreeze a lot more.

If you don't have cold weather to deal with, you can use straight water. However you will need an anti-rust additive, which is "the other stuff" in antifreeze besides glycol.

The engine will perform better with antifreeze instead of water, even in warm climates - however since you're just blowing coolant through the car, I see no reason to bother with antifreeze until you fix the leak - unless you need it to avoid freezing.

Better to fix it, though

It's usually pretty cheap to fix - just a $20 hose + putting it in. You're spending much, much more than that on the endless merry-go-round of trying to keep it topped up. Some people need to spend a lot of money because they can't spend a little.

But ignoring it is a huge problem. You may be accustomed to oil, where you can let it run 20-40% low and it's not a huge problem. The car is not designed to run with ANY coolant missing. There is no acceptable level of low coolant.

How it really works

You see the "spare fluid" tank, but that's just a borrow tank. Once you start the engine, a check valve prevents new coolant from entering the pressurized system. You are losing coolant inside that pressurized system and it has little room to spare.

The farther you drive it, the more it loses. It could well uncover critical engine parts and do serious damage. This is NOT getting refilled from the "spare coolant" tank - that can't happen yet.

Only after the engine is stopped and starts to cool down, the check valve allows more coolant to be sucked in from the "spare fluid" tank. It can only suck in a limited amount - that may not be enough to replace what was lost! Nothing will tell you this except popping the radiator cap on the now-cold engine and looking.

That tank you're looking at Does Not reflect the level of coolant in the engine. Get it?

What could go wrong

So if you run it even a little with a known leak, you are already allowing the head to lose coolant, which means you are slowly cooking the head. The first thing to go will be the valve seals, which will result in dramatically increased oil burning, inability to pass smog, and eventual destruction of the catalytic converter from making it work so hard. Then you'll have problems with burning valves, and eventually blow the head gasket. All an expensive head repair.

But even worse, the coolant leak could become much worse at ANY moment and that will greatly accelerate the above problems. You will not get any advance notice of this, nor will you even know it is happening.

Once your car has blown up, that will end your exposure to antifreeze fumes. So your exposure to fumes is going to self-limit by way of the car engine blowing up. If you can't afford to fix a hose, that will be the end of the car for you and you're gonna be walking.

You might want to just start walking/carpooling/taking the bus now, save up the fuel and antifreeze money not spent for that hose repair or whatever it needs.


The primary ingredient in most coolant is Ethylene Glycol. It is fairly poisonous if ingested but also can cause some respiratory effects:

Respiratory Effects - Ethylene Glycol

To quote that section from the link:

Inhaled ethylene glycol can irritate the respiratory tract (Wills et al. 1974).

Throat and upper respiratory irritation were the most common complaints after prolonged experimental exposures in humans (4 weeks at concentrations of 1–25 parts per million [ppm]). Exposure to 60 ppm aerosolized ethylene glycol caused noticeable respiratory irritation. Exposure to 80 ppm aerosolized ethylene glycol was “intolerable” because respiratory discomfort developed rapidly. Pulmonary effects typically occur 12–72 hours after ethylene glycol ingestion. Pulmonary edema, adult respiratory distress syndrome (ARDS), and death have occurred in persons exposed to ethylene glycol (Gordon and Hunter 1982; Haupt et al. 1988; Piagnerelli et al. 1999).

The following respiratory effects often occur 12 hours or more after exposure in victims of severe ethylene glycol poisoning:

Tachypnea Hyperventilation Kussmaul respirations Such effects most often reflect physiological compensation for severe metabolic acidosis rather than primary lung disease (Friedman et al. 1962; Godolphin et al. 1980; Parry and Wallach 1974). Autopsies [(Vale 1979) of ethylene glycol victims revealed the following:

Pulmonary edema with diffuse hemorrhagic exudates Bronchopneumonia (probably caused by aspiration) Deposits of calcium oxalate crystals in lung parenchyma

Casual exposure is very unlikely to cause any problems unless you are sensitive or allergic. But long-term exposure can be problematic.

Keep the bottle sealed, try to avoid spillage inside the car, and ventilate well if you do spill some.

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