What causes a freeze plug to pop out?

Answer 1

Answer

The Short Answer is in your question: the coolant has frozen and expanded and pushed the frost plugs out in order to hopefully prevent potetnially very serious and expensive damage to your engine and cooling system.

The freeze plug fills a hole in the engine block's coolant jacket. Coolant mixtures in automobiles are usually a 50/50 mix of Ethylene Glycol, (antifreeze), and water. In extreme cold temperatures, the water expands in this mixture and the freeze plug, being the intentionally engineered weak point so as to prevent the engine block from being cracked or damaged, is pushed out of the block. Of course if you have no 'AntiFreeze' in your coolant. . . . . Even if it freezes up and doesn't crack anything nor push frost plugs out, ironically it will overheat and quite possibly seriously damage the engine &/or the cooling system including your cooling radiator and perhaps the heat exchanger for the passenger compartment which is also just a small radiator will also freeze up, expand and be destroyed as well. If it is anything more than just starting to set up and get a little bit slushy, it will NOT thaw your engine and cooling system out properly and can seriously damage these. The only answer is to get it into a heated building to thaw out for probably at least a day: depending on the temperature; and get the proper AntiFreeze/water mixture into it.

Various items added by DougRH:

This is one of those questions that basically contains the answer in the question. As the previous response correctly points out it is to relieve the incredible pressure caused when the water/coolant mixture (you DO have a Water & AnitFreeze/Coolant mixture in your car don't you?!) expands and has a lighter density and actually expands as it freezes than when it is in the liquid phase and (hopefully) prevents the very expensive damage of a cracked cylinder block &/or head(s). There are usually several such 'frost plugs' in an engine block with the number of them varying with the number of cylinders and the configuration of the block. Generally speaking there is one frost plug for every two cylinders. FYI: Life on our planet would not exist at all or as we know it if not for this very unique 'quirk' of nature!

This maybe splitting hairs, but this transpires when the coolant actually starts to crystallize and freeze at + 4 Celsius. It will not push the frost plug out until it starts to convert from a liquid to the solid form or is completely frozen.

Ethylene Glycol, and it's newer more eco friendly and less toxic version: Propylene Glycol (PLEASE use this one!) have the lowest freezing point with a mixture of 2/3 coolant to 1/3 water. It actually has a lower freezing point when mixed with water than it does when undiluted. If you have it available, using distilled water is preferable. Any mixture with a higher ratio of coolant to water than 2/3 will actually have a higher freezing point and will be a less effective coolant as its viscosity will be higher than the system is designed for and will not be able to transfer heat to and from the coolant fast enough to work properly to cool and protect your engine. Note that in modern day vehicles that the term 'coolant' IS more applicable than 'AntiFreeze' as it also raises the boiling point of the coolant to allow the engine to operate at a higher and more efficient temperature than the boiling point of water where they are currently designed to operate at. This boiling point is further raised by the cooling system being pressurized. This is why removing the radiator cap of a (suspected) overheated engine to check the coolant level in these conditions is so dangerous: Once the pressure is relieved, the boiling point drops significantly and all of the coolant can instantaneously turn into a vapor and thus occupy a volume ~ 1000 times more than when it is in liquid phase and thus it violently erupts in a very powerful geyser of VERY hot and dangerous scalding substance! You can not possibly move fast enough to prevent being (very badly) scalded and burned if this happens!

There are additives in coolants that do things such as inhibit rusting and a lubricant for the coolant pump etc as well. These are generally depleted after 2 years at the most. It is an erroneous notion that your coolant mixture never 'wears out' and needs to be replaced. Eventually it will start to lose its temperature modification qualities as well. Modern coolants do last longer but you should add a 'coolant system recharger' solution that replenishes these additives before the start of the second winter that it has been in your vehicle. Before the start of the forth winter at the very most you should get your cooling system cleaned and descaled, power flushed, pressure tested and repaired and a new high quality coolant/water mixture installed as necessary. In older systems it is a fairly standard practice to use a radiator cap with a lower pressure point because of the weakened sealing points in the system. This makes having the proper mixture with its higher boiling point even more critical.

Note that there are 'longer lasting' coolants on the market now that last up to five years and more and more new cars are coming equipped with this as manufactures are competing for are business are trying to supply vehicles that won't need a tuneup or major maintenance for 100,000 kilometers. Such coolants are usually a different color.

Also note that with a variety of different coolants now being available on the market if you are checking the coolants freezing and boiling points you need to use the specific tester for the type of coolant that you are using. Obviously you also need to check it under the specified conditions: coolant temperature, taping the tester lightly to jar any air bubbles attached to the floats etc that will give erroneous readings.

A winter tip: If you have an Air Conditioner (AC) on your vehicle it is actually a 'heat pump' This means that it can and will 'pump heat' both ways! While newer vehicles are getting better at warming up quickly and properly in cold conditions. Some still take quite some time before you can get any heat transferred to the passenger compartment from the coolant as it is not yet warm enough to do so.

Being a heat pump, your AC system can and will start pumping heat into the passenger compartment in ½ ~ 1 minute! You just need to set it to AC mode, turn the temperature up and turn the AC fan on. Being an air conditioner it recirculates the normally cool air inside the vehicle. However in cold weather, the condensation from the moisture in our breaths condenses and fogs up the windows and can even freeze on them. So in spite of the cold outdoor temperatures, in heating mode the system brings in dryer cold outside air and forces the moisture laden air out of the interior to prevent this. However you can use this method until the engine and coolant get warmed up and then switch it over to normal heating mode.

Regardless AC systems should be operated at least once a month in winter to drive off any condensation that can and does build in the refrigerant in cold weather that will cause corrosion and damage to the AC system over the winter if it is not used.

Vehicles that are always used for very short runs that do not get up to normal operating temperature in short runs in the winter get water condensing into the oil and it turns it from a very effective lubricant into a acidic and more caustic mixture that actually erodes the surfaces that it is supposed to be lubricating! Getting the engine well warmed up evaporates and drives this water out of the crankcase and away from the oil and lubricated parts. If your vehicle is like this then it is likely being worn out at a rate up to 10 times faster than normal. If you see a thick light creamy/white colored and textured mixture on the oil filler cap and/or the dip stick when you are checking the oil level (you DO check it regularly right? Without the (proper) oil (level), your engine will last about as long as you will without blood! The presence of this is a symptom of water in your oil and your engine is now being damaged and destroyed at a VERY fast rate! If this is the case get it repaired ASAP. Often the problem is very minor: a low cost plugged

EGR (Exhaust Gas Recirculation) valve or the clean air inlet part of this same pollution subsystem that often has a small air cleaner of it's own to avoid particulate and contaminating materials getting into the crank case that will damage your engine. Both of these are very low cost items and should be changed as part of a regular tuneup and maintenance schedule, especially in older vehicles that are burning oil.

(Diagnostics: If you exhaust gas is very thick, smoky and oily under heavy load such as climbing a hill or under heavy acceleration, your piston rings and likely the pistons themselves as well as perhaps the cylinder bores are worn out. If the exhaust gets smoky when you first start the car up, your valve guides and perhaps the valves themselves are worn out.)

If you do not see any signs of water in your engine oil, but you are turning the vehicle off after running it but rarely getting it warmed up to proper operating temperatures do two things: Make sure it gets well warmed up fairly regularly and follow the oil change time intervals even if you have not traveled the allowed distance between oil changes.

I use a synthetic 5W-50 oil (Canadian Tire) that has a VERY wide temperature range and is more stable over much broader temperature ranges and is suitable for all weather conditions and protects your engine better.

When your oil is changed, the new filter should be filled up several times with new clean oil until it will not absorb any more oil before putting it onto the vehicle. A vehicles engine wears more in the first 15 ~ 30 seconds every time it is started because of the lack of lubricant than it does in 8 hours of driving! This lag is considerably longer when doing an oil change as the oil pump and filter are dry and unsaturated. Especially under these latter conditions, you can quite clearly hear the engine quieten down as the oil starts to reach the surfaces requiring lubrication. Having the new oil warm when putting it into the engine also helps as it has not thickened up from the cold weather that retards its flow.

FYI: If the rubber seal in the radiator cap is all bloated, warped and wavy, you likely have hot (exhaust) gases leaking into your coolant system from the cylinders and have either a leaking head gasket &/or a cracked head or cylinder block.

Proper coolant & heating/cooling systems maintenance is VERY cheap compared to the damage that it can cost if your coolant is not in proper operating condition!

NB:Many people that are not mechanically inclined tend to 'tune out' noises that their vehicles make because they do not understand them and are intimidated by them. Do NOT do this! Your 'Spidey sense' / gut feelings and intuitions will be right more times than not. If you hear something new and different, especially if it 'sounds bad' do not drive it any more than absolutely necessary until you get it checked out. In my many years of repairing and maintaining vehicles I reinforced this with all of my clients very strongly. At times it would be nothing significant and was either quickly and easily fixed or was nothing to worry about at all, or perhaps something that I could and would attend to the next time they brought it to me for other required work. There were just as many times that it needed to be attended to and repaired immediately or it would cost them $4,000 ~ $1,000 of dollars versus perhaps $400 ~ $100 if done immediately.

Again, I want to reiterate that more often than not, your instincts about the seriousness of the problem will be right more often than wrong even if you don't know anything more about a vehicle other than driving it and putting fuel into it.

One common example of this is when your brake linings are worn out and you start to get a very rude and terrible grinding sounds during breaking perhaps accompanied by erratic jerking braking. If you continue to drive it under these conditions it will cost you ~ 10 TIMES MORE to get the brakes repaired!

NEVER have worn out brakes on just one wheel replaced. Brakes jobs should ALWAYS be done in pairs: front &/or back. Some newer vehicles require that all 4 wheels have their brake linings replaced when any of them are worn out, but this is currently quite rare.

If you can't whoa, then don't Go !!!

Don't drive your vehicle in an aggressive, reckless manner that usually just uses up considerably more fuel, wears your vehicle out quicker, cost s you more in repairs and depreciation and is considerably more dangerous AND stressful to everyone including you and your occupants and in urban settings does not usually get you anywhere quicker: Easy does it and slow and steady are very good advice for vehicles and people.

Take care of your vehicle and it will last a long time, cost you less to operate, be more reliable and take care of you.

(8 >) Happy and Safe Motoring (< 8)