If you are reading this, chances are you are either having a problem with your cooling system, or would like to make it more efficient. Below is a list, both 1G and 2G specific, that can help when making your decision and troubleshooting a failed cooling system. This FAQ focuses on stock-style cooling systems.

Your cooling system consists of 5 major components. They are your Radiator, Thermostat, Radiator Cap, Water Pump and Cooling Fans. We will discuss these in detail throughout this FAQ.

To sum it up, there are only 3 reasons why your cooling system will fail.

1: Lack of flow
Typically this is caused by a failed water pump, a stuck thermostat, a blocked or clogged radiator. A failed water pump will have the tell tale sign of coolant seeping out of the weep hole. You will typically notice a large pool of coolant below your timing belt cover area. Barring any broken hoses from your Oil Cooler, this is usually a sign of a failed water pump.
A stuck thermostat will reveal itself when your car is at operating temperature, your coolant is full, however your upper radiator hose is cold. Eventually the pressure inside the system will exceed the radiator caps spring and you will start pushing coolant into your overflow. Change your thermostat.
A clogged radiator will reveal itself when all others fail. Usually, you can visually see debris in between the fins of your radiator. If there is enough of it, it will impede airflow past your radiator, and the efficiency of your radiator will not be sufficient enough to cool your engine. Flushing your radiator is as simple as removing it, pressure washing or hitting it with compressed air to blow the fins clean, then flushing the internals with water. Introducing aftermarket equipment in front of the radiator such as an FMIC or oil cooler without proper ducting will also impede airflow.

2: Lack of Coolant/Incorrect mixture
Typically this is due to a leak of some form. Find it and repair it. Your cooling system travels through a number of areas including your water pipe, turbo (if applicable), Oil cooler, water pump, throttle body, heater core and overflow container.
The ideal mixture is 50/50. That’s 50% Coolant (Ethyl Glycol) and 50% distilled water. This mixture works for most driving habits under most conditions, however, most of us do not fall under this “Average” driving habit, and increase of water into your cooling system will allow it to perform better. Water does a fantastic job of removing heat, so the more of it you have, the better. Do not run straight water, your cooling system requires coolant to lubricate and increase the boil temperature of water. A great additive for your cooling system is a product called “Water Wetter”, and is found at your local Advance Auto, Autozone, Carquest, Napa, etc.

3: Pressure.
As your cooling system heats up, the water in your system expands and your radiator cap keeps this expansion pressure in your system, raising the boil point of the water. As you drive your car, coolant will be pushed out into your overflow as the system creates pressure. Albeit a small amount, this amount returns to your cooling system once the car shuts off. As the engine cools, it creates a vacuum and barring all the funky Fluid and Thermo Dynamics, replenishes the cooling system by sucking it in back through the overflow via syphon.

There are mainly 2 reason why your coolant will not be sucked back into the system:
1. Radiator Cap: A poorly functioning radiator cap will allow for too much coolant to be pushed out and/or not enough seal to allow for the siphoning of coolant back into the system.
2. Overflow bottle/hoses: The overflow bottle should be below or at level with your theromostat housing, and a line inside the overflow bottle that goes down past the normal cold level for your coolant. Cracks or tears in the hose between the overflow bottle and thermostat housing will also impede a suction of coolant, and will pull in air.

Pressure can also come from the combustion chamber. A failed headgasket will either allow for coolant to enter the combustion chamber and be burned, or push air into the cooling system. Typically, the signs of a failed headgasket would be one or more of the following:
1. Foaming of coolant
2. Burning of coolant (White smoke)
3. Oil in Coolant/Coolant in Oil
4. Overheating condition within 10 or so minutes of driving
5. Overflow bottle filling up/overflowing at operating temperature
6. Coolant being pushed out of the rad cap under boost
7. Lack of return from overflow bottle to cooling system
8. Increase of pressure in cooling system/pushing coolant to overflow. (This can also be attributed to a failed radiator cap)

Lets discuss the 5 components, what they do, how they do it and how to maintain/increase their efficiency.

Radiator
Arguably the most important part of the system, the radiator is a heat transfer device and allows for flowing air through the fins to transfer heat from the engine to the air and dissipate. There are three things you need to remember about your radiator.
1. Airflow
2. Coolant flow
3. Airflow

In order for coolant to pass through your radiator, it must not be clogged. Ensuring your radiator is free from contaminants will ultimately keep it working as efficiently as possible. Your radiator hoses are also a must-maintain part of this important system. Cracked, worn, or soft radiator hoses are just a few heat cycles away from failing. I have personally seen a car cooling after a run down the track and the upper rad hose splitting open before my eyes!

Airflow is also THE key to a properly working radiator. We add FMIC’s, Oil Coolers, Transmission Coolers, Power Steering coolers all in front of the engine cooler and then wonder why our coolant temperatures start to skyrocket. If you look at a stock DSM, you’ll notice there are many plastic shrouds all around the radiator. These are there to direct air directly to the radiator, and not let it bleed off from around the car. When adding upgraded components to your car, it is crucial that you imitate these factory shrouds by building your own ductwork to direct air to the radiator. Without airflow, the radiator cannot do its job. A great test for this is to turn on your fans with the hood closed and see if it will suck a piece of paper to your FMIC. If it can, chances are your airflow is pretty good.

Thermostat and Radiator Cap
These two critical parts of the cooling system can be the difference between overheating and overcooling. The thermostat keeps the pressure in the system, upping the boil point and keeping all that nice expensive coolant in the car.

There are three seals in the rad cap. One on the outside that seals the water neck housing. Second seal is on the inside that is spring loaded and seals inside the water neck housing. This one maintains the pressure in the cooling system. Once pressure builds past 11 lbs with a stock rad cap from the coolant heating and expanding, its pushes past this seal into the over flow until pressure falls back below the rad cap specs.

How does it come back in when it cools ? There is a third seal or valve which works in the opposite direction. Its the round metal thing in the middle of the second seal. When coolant contracts, this valve opens and allows coolant from the overflow to flow back into the coolant system. Under pressure and expansion, this metal valve is sealed shut against the second seal. The cooling system constantly goes through this cycle of expansion and contraction which your driving, the rad cap needs to be functioning properly on order for it to do so.

A 16lb rad cap will cause all your lines to be a little more pressurized than a stock rad cap, but will increase boiling point. You’ll notice your overflow coolant level fluctuate more with a 11 lb rad cap than a 16 lb rad cap. I like to keep my cooling system a little more “loose” with the stock rad cap.

The thermostat is what regulates your temperature, and oddly enough, the pressure in the system as well. Pressure is defined as a resistance to flow, and the thermostat creates just that. Without a thermostat, you will eventually overheat due to lack of pressure, so keep it in there. Your thermostat can fail both open and closed, and it’s pretty easy to figure out what will happen in either circumstance. Installing too low of a temperature thermostat will cause an overcooling condition, which can be just as harmful as overheating. Your ECU depends on the engine getting to a certain temperature for normal operation, and if the car does not get to that temperature, the ECU will always think it’s simply still warming up, keeping it in openloop mode. In openloop, the ECU depends on its internal tables to tell how much fuel to introduce, and typically, this is a rich mixture. Also, the ECU depends on the coolant temperature to begin learning fuel trims. This temperature is around 180 degrees for a 2G, and 190 for a 1G. Also, using a colder “racing” thermostat to try and combat an overheating problem is rarely the solution. A car that overheats will overheat no matter at what temperature the thermostat opens, it will just take longer for it to happen.

Water Pump
A variable displacement pump, the water pumps job is simple; Keep the coolant moving through the system. The water pump rides on a sealed bearing and is spun by the crankshaft via the alternator/water pump belt. The “weep hole” is a small hole at the top of the water pump and in a failed bearing/pump circumstance, coolant will drip out of this hole. Typically it is best to replace the water pump every time you do a timing belt job, as you need to remove the timing belt in order to do it. Ensuring a good seal between the pump and block as well as between the water pipe and pump will prevent you from having to do the job more than once. Take your time!!

Cooling Fans
Properly installed, shrouded and working cooling fans are critical to not overheating in stop and go traffic. A 1G has a thermoswitch at the bottom passenger side of the radiator that controls the fans on/off, whereas the 2G has an ECU controlled setup. Different combinations of setups can both do the job equally (2 pullers, 2 pushers or one of each). The OEM fans work great, and if you can keep them, do so, however most of our upgrades prohibit such an idea, so they came out with slim fans. In this scenario, bigger IS better. If you can cram a 14″ slim fan in there, do it. The more airflow you can provide to your radiator, the better.

Hoses
Last but not least are all the coolant lines and hoses. As your car ages, so do the parts, and with the expansion/contraction of your coolant lines, the eventually will begin to deteriorate. Check your lines every so often to ensure there are no soft spots, cracks or tears as these are signs of impending failure. The smallest soft spot will eventually lead to a leak or split in the line.

Coolant Mixture
Lets take a look at the coolant mixture. What is the best mixture? Some will say 80/20 water/coolant, some say 70/30, some will say 50/50, but it’s all in what works for you and your area/driving style. If you live in a hot area, a 75/25 mix might work, but colder areas require more coolant than water, so a 50/50 is best. Ensuring your coolant mixture is correct, and that the system is full at all times will ensure your car cools itself properly. Air is the enemy to your cooling system, and it ALWAYS comes from somewhere. Be it a cracked line, a failed rad cap, or improperly burped system, air will cause all sorts of heating/cooling conundrums that can drive a person mad. If everything above is in good working order, you will never get air in the system, period.

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