Antifreeze Low And Blows Out Reservoir Tank

Question:
I've notice over the course of the last week or so, I have checked in the radiator to make sure there is antifreeze. Even when I take the cap off when the car has been sitting for a long time to when the engine is cold, antifreeze will spew out, but there would be coolant left. Today I took off the cap and I did not see any coolant, so I added more. However, the reservoir tank was full (overfull, actually). I haven't noticed coolant in my engine and I don't see oil mixed in with the coolant.

Answer:
We really need to know the make and model and year vehicle you are talking about. Certain years of engines have certain things that cause the problem you're talking about. But in general I can give you these ideas...

Pressure in the cooling system even when it's cold is never a good thing. You have an internal engine problem. Most likely a blown head gasket. Now, I know you say you don't see any coolant and oil mixing. But that is not always the case with a blown head gasket. Most people think that's the only way to tell a blown head gasket is oil in the coolant or vice versa. But that is not the case.

Again, depending on the engine, a head gasket can be blown in such a way that the compression from the cylinder pumps pressure into the cooling system. Internal cylinder pressures run hundreds of PSI, the cooling system and radiator only run at 16 PSI. Therefore compression gas from the cylinder is getting into the coolant, antifreeze would not go the other direction into the oil.

A crack in a cylinder head will do the same thing. This can cause the engine to burn coolant, not contaminate the oil, cause excessive pressure in the cooling system and fill the overflow jug too high. The first thing I would do is remove all the spark plugs and look for signs of burning antifreeze. If it is the newer coolant you would see orange or yellow deposits. If it is an older car with the green coolant then you would see green deposits on the spark plugs. You may even find a spark plug electrode that is completely burned off.

Next you would need to do a cooling system pressure test. This will show any external leaks and if a blown head gasket or cracks of a cylinder head is the problem it may fill up that cylinder with coolant because the engine is not running and the pressure will push coolant into the cylinder. If this is allowed to continue, major engine damage will occur.

A cooling system pressure test will not really show an internal problem like this. You would need to look at other thing. Check the spark plugs for signs of burning coolant. Check the oil and oil filler cap for signs of contamination- a milky looking sludge.

Question:
While my wife was driving, she heard a loud bang under the hood then water through the top of the hood. I looked at it hours later. The overflow reservoir was completely full. I checked all the hoses and couldn't find where the water was coming from.

I started the car and no leaks. It didn't seem like the coolant was flowing but the car wasn't getting too hot after about 10 minutes. One fan came on. I touched the radiator cap and it was still very cool.

I turned off the car and took the radiator cap off. No pressure. I added coolant then started to see steam coming up. I poured more coolant and it just flowed out of the radiator as fast as I can pour it. The next day without starting the car, poured coolant in and the same results. I noticed that the side of the radiator was extremely wet. It looks like the water is leaking from the top of the radiator. Does this mean I have a bad radiator needs replacing or fixing. Or is it something else? Thank you.

Answer:
It sounds like the noise she heard was actually the radiator splitting or cracking. This can be cause by the engine overheating and building too much pressure. That will cause a radiator to split. Overheating and having too much pressure can be caused by something as minor as a bad thermostat or as major as a blown headgakset. When they fail, combustion from the engine is pumped into the cooling system which causes a lot pressure. It also will make the engine overheat. But it could also just be that the radiator failed.

Either way, it will need to be replaced first before looking at anything else. After that, it will need to be determined if something caused it to break, or it just broke. The fact that the cap or top does not get hot is just because the coolant level is too low to be at the top and is not circulating.