Esmagamus guide: living with you car's cooling circuit

This Esmagamus guide covers basic steps anyone can take to avoid any issues with one of you car's most important systems: the cooling circuit.

Includes:
-Brief introduction to the workings of a closed circuit cooling system;
-Maintenance;
-Troubleshooting;
-Explanation of galvanic corrosion processes and scaling;
-Appropriate coolants;
-Peculiarities;
-Emergency procedures.

Once read, you will have acquired the basic knowledge to keep your cooling circuit in good order. I am available to answer any questions.

Step 1 System components - what they do

The purpose of a cooling system is fairly obvious: the engine produces heat and a certain amount of it must be dissipated. Some cars, such as the VW Beetle and the older Porsches did away with the cooling circuit and used an air-cooling set-up. Most cars use a more convenient water cooling system, one of the reasons being that air-cooled engines work at much higher temperatures, causing an increase in nitrous oxides emissions.


The heat source: an engine has water passages going through the block. The coolant also has to cool the engine head(s) which is usually the hottest part of an engine.

The radiator: usually sits behind the bumper, a know exception being the old Mini that had it mounted to the left side, with a permanent belt driven fan sucking air from the wheel well. Some radiators have a built in expansion tank.

Expansion tank: as the coolant heats up, it expands. The expansion tank has a MAX marking on the side, above which is air. Overfilling of this tank causes excess pressure build-up. This tank usually has a pressure regulating cap. A crack on the cap can lead to loss of coolant or boil-overs. The pressure in the circuit keeps the coolant boiling point higher than 100ºc. This tank may or not be a header tank (the highest point on the circuit, more on that later).

Radiator fan: sucks additional air through the radiator. This may be driven from the engine or, as it shows on this diagram of the Alfa Romeo 164 3.0 V6 circuit, it is electrical and controlled by a thermal switch, the contacts closing as a rated temperature is reached.

Heater core: heats air going to the cabin. In an emergency (the coolant is boiling) it can and should be used as an emergency radiator by setting the cabin heater on max heat and airflow.

Engine thermostat: just like an engine can't run too hot, it also should never run too cold (reasons omitted, trust me). As the engine warms up, the thermostat keeps the coolant from flowing into the radiator. This speeds the warming up of the engine and of yourself in those winter mornings. Usual symptoms of a thermostat stuck open are very long warm-up times, ventilation system blowing cold air (though this can also mean a blocked heater core or one that is filled with air, see peculiarities section), a cold engine at highway speeds, etc. If stuck open, the coolant will simply boil. When replacing a thermostat, consult the technical data for your particular engine.

Sensors and switches: some cars only have a danger light wired to a thermal switch on the pump body. Most have both a thermal switch and a variable resistance temperature sender connected to an indicator. There's still another thermal switch for the fan. As some systems run on two fan speeds, this sender may have two sets of contacts, one activating a lower speed when the AC is on or the engine is getting too hot and a second set of contacts activating a faster "emergency" speed.

Other components:
-Some cars have oil to water heat exchangers. These transfer heat from oil to the coolant. Other designs do away with the heat exchanger and have instead a small oil radiator.
-Belt driven fans are usually mounted on clutches that lock as they heat up. Electric fans have associated  thermal switches, usually closing the power to the coil of a relay that then energizes the fan.
-Throttle bodies are sometimes also connected to the cooling circuit. This also has the function of regulating idle air through a bimetallic valve fitted next to the throttle plate or just prevent icing on the throttle plate; as petrol takes heat as it vaporizes, icing can become an issue on very cold days.
-Turbochargers are frequently water-cooled.

The more heat sources the system has, the more important it gets to keep it dissipating heat at its maximum capacity.

Comments

[Phoenix17]

This is otherwise very comprehensive and well written, but I have to request that you add something that could potentially be fatal to someone's car.

NEVER MIX DIFFERENT TYPES OF COOLANTS!

Different makes of cars take different coolant types! Mixing stock "old" coolant that's in your car with off the shelf coolant from the auto parts store can have disasterous consequences if they are not the same. This is particularly true for most German cars and some Japanese cars. For instance, mixing Prestone Green with pink G12 can cause it to gel and clog thermostats, sensors, water pumps and small lines while also causing heavy corrosion deterioration on aluminum parts.

I still prefer a complete drain to empty, water fill and flush (while bleeding as you say), drain, and then new coolant. However when you are replacing your coolant with the same kind, this method is alright because new and old of the same type mixing will only cause dillution, not coagulation. But if you are replacing one kind for another kind, be sure and get every last bit you can out of the system before replacing it with the correct mixture of new.

Case in point, my 1995 Audi 90 requires pink coolant. Can't get it in Advance Auto or AutoZone and the stuff they carry won't mix with it. Replacing my whole system for green would have been acceptable and it would have worked in my car only had I chosen to do so by eradicating all the pink first, but since pink is a "lifetime" fluid I chose to go with it again. I always assume lifetime to mean about 80-100K miles of average driving even though they'd have me leave it in there forever, but that is a different story.

Like I said above, this is otherwise very comprehensive and well written. It will be a big help for someone trying to do it themselves for the first time. Remember kiddies, always get the air out. If you're running the car and see the temp climbing but can't feel hot air from the heater (that should be turned on), you have a bubble in the line and often cracking open the bleeder will get it.


**
You might also add to run the heater fully "hot" and fan speed low when flushing the system to clean it out as well, otherwise it is bypassed in many cars. Also, there are chemical kits to buy that can help clean out some silicone deposits and acid treatments that can help for calcium and limestone buildups (if you or someone used tap water a lot).

[Phoenix17]

Also, if you do a complete drain like I do, you'l' have to take some extra time to get the air out before you even start your car. Wait for it to fill. The smaller the water column heights the slower it will spread water to the far side of the car, so you might want to pressurize it just a little. In my case I just use my mouth to put pressure on the tank, listen for the fluid shift, hold, and release. Usually bubbles will fly up into the tank and fluid will drain down a little each time.
Also, crack open the bleeder taps and pressurize it and listen for air escaping from them. When they stop you can close them again until you run the engine and do the main system bleed. Revving the engine about 1/3 total rpm can help speed up the water pump and give it a quick push that can help dislodge persistant bubbles. As can dropping it down off the ramps (if you've put it on ramps).
Check the level a few times each day (when the engine is cool) even after you think you're done, you might be suprised to see you need to top it off again.

Sorrry this is so long winded. But failure to do it right here can cause very expensive repair costs. Burned head gaskets, warped heads, etc. I don't want anyone to try this thinking it's always straight forward and end up in the shop out $2500.

[MacGyver1138]

This is good stuff. Basic vehicle maintenance is something too many people overlook.

I can say from experience that oil in the coolant or vice versa is bad news indeed. My wife's car had an issue with this two years in a row thanks to old deteriorated gaskets.

It is also worth noting for people with pets that antifreeze is VERY poisonous, yet it tastes and smells sweet to animals. If there are any puddles of it laying around, make sure to clean it very well, and keep animals out of the area until you can be certain you have the leaks fixed.

[Yerboogieman]

Ever since the late 90's, they've added a chemical that makes it taste bitter.

[caarntedd]

Nice work. Most of my thinking is done in the pub, not the cafe, hence no instructables.

[Esmagamus]

I suppose you can still have your pint with the right hand and type with the left at the same time. A "bloke's guide to drinking beer" sounds award winning.

[kelseymh]

Very nice overview, with a good level of detail! I wonder if you might want to add links to other sites with useful detail for readers (I don't claim that I know any, just asking).

[Esmagamus]

Thanks for the constructive criticism. I didn't want to go into too much detail. The purpose of this guide is to give a basic knowledge of how things work together. Further research is always encouraged but may be pointless for most purposes.

I may include some links to other sites, this guide is just something I knocked together from scratch in a café.