Under the Hood series: Basic Recovery Cooling System Inspection (or How do I check my coolant?)

Most people know that the car has something in the radiator to keep it from overheating. In the summer it's usually called coolant, in the winter it's usually called antifreeze. The radiator and the coolant/antifreeze are part of the engine cooling system. As the coolant heats in the cooling system it expands and because the system has a pressure cap the system creates pressure. Each system has a recommended pressure. The examples I have here today are a '83 S10 truck, 01 Nissan Frontier and 06 Toyota Avalon. The S10 uses a 15 psi pressure cap, the Frontier a 13, the Avalon a 16. You can usually read the cap psi on the cap.

Make sure your cap matches the OEM specs for your car cooling system. 

As the coolant heats, expands and pressurizes it will sometimes reach more pressure than the system wants. The cap has a spring loaded seal that will open and allow some of the pressure to be released as overflow. Once the pressure is lowered, the spring will reseat the seal and stop the flow. This is how the pressure cap regulates the system pressure. There was a time when the overflow tube was connected to a hose that just directed the overflow coolant under the vehicle and onto the ground. Not only was it not evironmentally friendly but checking radiator coolant level and topping it off was something you couldn't neglect without causing overheating and possibly expensive complications. Also, "topping off" did not mean fill to the top. You had to allow room for the coolant to expand. A radiator has a core and two tanks. If the tanks were across the top and bottom, allow 2" of space for expansion. If the tanks were along each side, 4". 

Overflow systems no longer go directly to the ground. Newer systems direct the overflow to a coolant recovery tank. Overflow collects in the recovery reservoir as the cap releases pressure hot and as the system cools the coolant is drawn back into the radiator. The recovery tank on these systems is not under pressure and has either a screw-on type cap or just a snap-in-place type. It is simply a bottle to hold coolant for the radiator until needed. 

There are usually marks on the outside of the recovery reservoir that you can use to determine if there is a need to add coolant. There are two level marks, one for minimum and one for maximum. If yours says hot and cold instead of min and max, just think of it as the latter. As long as the coolant level is between the two marks you are fine. Don't obsess over keeping the level at one mark or the other. It varies.

Now just because the level is in range at the overflow reservoir doesn't mean your radiator coolant level is good. The recovery bottle reflects only what has gone through the overflow hose. It is possible to have a low radiator level and a full recovery bottle. If your cooling system has a leak it may not create the vacuum needed to draw coolant back from the reservoir as it cools. To check your radiator coolant level you'll need to remove the pressure cap. Do that only after the engine has cooled completely and has no pressure on the system. You can feel the top hose and give it a squeeze to determine if it has cooled and has no pressure. Once it is safe to open the cap you'll need to press down firmly on the cap to overcome the spring. Press down firmly and turn the cap counterclockwise to a full stop. Once the ears on the cap are aligned with the open spaces on the radiator you can pull the cap straight off. 

While you have the cap off is a good time to inspect the condition of the cap seals. If one or both is cracked, swollen, missing or damaged you should get a new cap. Look down inside the radiator for the coolant. Some designs are better for that than others for determining coolant level with a quick look. The S10 truck lets you see down into the radiator very well. The level is slightly lower than it should be but not terribly so. You can see the mineral deposits on the tubes but they are still open and no overheating. The system was topped off to bring the level more into the expansion range. 

This Grand Caravan has a design that offsets the neck and doesn't allow such a good view. In this case the coolant level could be fine but just out of sight. If your car is like that just add a slight amount of coolant to see if the level will come into view. 

Some manufacturers make it difficult to even find the radiator cap. 

What to add? As usually is said, check your owners manual. You may be more confused after though. When you check the owners manual it usually looks like the safe bet is go to the dealership and get your coolant. Technical information

Basically, if your radiator is old school and made of real metals you use the old standard green antifreeze/IAT. If your radiator is an aluminum core with plastic tanks you use one of the universal extended life antifreezes. 

The next thing to bear in mind is that your coolant is a blend of 50% water and 50% antifreeze. That mix is recommended for best protection with no problems. If your chosen antifreeze says it is a concentrate then you'll have to make the coolant mix by adding equal parts antifreeze and water, preferably distilled water. This is why you can also find pre-mixed coolant 50/50. It's ready to pour into the system as is. If your cooling system has always been properly maintained and you know the coolant in they system is a 50/50 mix then all you have to do when you see it needs a topoff is to add a mix you've made or a pre-mix. If you've no history available the car could possibly have coolant that is mostly water, or even mostly antifreeze. You can determine what sort of mix is in the car though. If you look at the chart on the back of most antifreeze bottles you can see that a 50/50 mix provides -34F freeze protection and 266F boilover protection. 

You can use one of the hand-held bulb type antifreeze testers to determine the mix. This particular tester shows that if you see 5 balls float in the sample then it is good to -34F. Since you need a 50/50 mix to get -34F that will that let us know if the mix is correct. 

Those testers work very well with the standard green IAT coolant and may work just fine with later coolants as well. I wasn't sure though so usually on later systems I use a refractometer for testing the mix. 

So we've covered some basic cooling system maintenance. How to check the coolant levels, what sort of coolant and what sort of mix. I've mentioned checking the radiator cap seals. It is also possible to pressure test the cap. A cap that doesn't hold enough pressure will release to much coolant to the overflow. 

When you are finished and ready to install the cap be careful that the cap is fully fastened. Some caps have arrows that will be aligned with the overflow tube when fully closed. 

I want to mention something before I wrap this up. The cooling systems we've been looking at are recovery type. The coolant that is released from the system goes to a coolant recovery bottle and is stored for recovery once the system cools. There is another type that may appear similar but is not the same system. The tank on this system is the actual cooling system reservoir and under system pressure. You would take the same precautions before opening this cap as you would a radiator cap. Let the engine cool completely before opening. The radiator on this system has no cap and isn't readily accessible. The coolant is added to the reservoir if needed and there is no overflow bottle. 

As always, thanks for reading and I hope this helps you in some way. 

Kenneth Hayes

G&G Auto Repair