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Basic Cooling System Advice - Updated


Rick Norwood
07-19-2007, 01:57 PM
General - Today’s radiators are thinner than older model radiators, and are made from aluminum and plastic, requiring good regular routine maintenance to avoid problems. Each of us has to decide how to maintain our vehicles, and what we can afford to do. This Post is collection of information that has been gathered from this Forum from many different contributors to answer some very common cooling system questions, provide information, and offer a little advice, all in one location. You may not totally agree with everything you read here, but at the end of the day, I hope some will benefit by it. Thanks to all that have contributed.

Troubleshooting – If you are experiencing problems with your cooling system, like overheating, a Good place to start is a thorough flush along with new Antifreeze, a new Thermostat and new Radiator Cap. This will take care of a lot of problems. It is well worth the time and expense to replace all three items at the same time. A new Thermostat, Radiator Cap, a bottle of Flush, and 2 gallons of Antifreeze should run less than $40 USD and is very good routine maintenance. It is also a good idea to fill your system with straight water and bring your engine up to operating temperature to test everything out as a last step, prior to adding new Antifreeze. Once you are satisfied that there are no leaks and all is well with your system, then drain the water out and then add the new Antifreeze.

Antifreeze - If you remove your Radiator Cap and check your antifreeze level in your Radiator first thing in the morning before starting, while the truck is SHUT OFF AND STONE COLD, you should have antifreeze right up to the top of the filler neck of the Radiator. It is also recommended that the coolant level in the Overflow tank is kept to the “Hot” mark even when cold, add as required to keep both of these levels as stated. The Antifreeze should be a clean, bright Orange (or Green) in color and should not be brown, or muddy in appearance. NEVER mix the two colors! If it is other than a bright color, immediate and proper maintenance is required to avoid future costly problems besides overheating. Keeping these coolant levels to their proper marks and air out of your system is absolutely essential. Check both levels weekly. After ANY cooling system maintenance, regardless if you did the work yourself or had the work performed at a Garage, your system will usually burp air out through the overflow tank for a few days. 1 to 4 quarts/liters is not uncommon. Check these levels daily for at least a week after any work is done. Do not take it for granted that the Garage completely filled your radiator or got all of the Air out! Air in a cooling system that is filled with Dex-Cool® is probably the largest single most contributing factor to cooling system failure. See this thread: http://www.automotiveforums.com/vbul...d.php?t=469926 Even though it is NOT recommended, there are websites on the internet that claim you can mix the two colors, however there are also websites that claim catastrophic results if you do. Play it safe, NEVER, NEVER, NEVER mix the two colors together. If you want to change from one color to the other, completely and thoroughly flush the system first! Most Antifreeze is concentrated, and is mixed 50-50 with water by the consumer. I recommend using DISTILLED WATER that you can buy at the grocery store for about 25-50 cents a gallon. NEVER try to run straight antifreeze, 60-40 is the strongest mixture you’ll probably ever need. Stronger mixtures will cause you to overheat. Small inexpensive testers are available at your local parts store that will tell you what your actual mixture is. Pre-mixed Antifreeze is also available in both colors. Ask your local parts store for the capacity of your system to determine how much antifreeze to buy, and add the proper amount of antifreeze to the radiator first (two gallons in most cases), and then top off with distilled water.

Over Heating, Dash Gage goes over 210° F - The most common reasons why an engine over heats are stuck thermostats, plugged radiators and neglected cooling systems. Here is a tip that may help you to determine whether your radiator is plugged. Start the engine and bring to operating temperature and shut off the engine. With the engine SHUT OFF, reach inside of the fan shroud and feel the temperature of the radiator cooling fins (not the side tanks) at the top and then at the bottom of the radiator. If the bottom of the radiator is cold or cooler than the top, the radiator is probably plugged and is not giving you the cooling capacity that you need. The bottom of the Radiator usually plugs up first and in all likelihood an extensive flush or possibly a Rod-Out is necessary. A Rod-Out is performed by a Radiator Shop, where the radiator is disassembled and a Rod is forced through the cooling tubes of the radiator to open the clogged tubes. Do not be fooled by the age of the Radiator. I have seen brand new Radiators plug up and cause over heating in as few as 15 months.

Dash Gage does not reach normal operating temperature – This is usually a stuck open thermostat, but can be a faulty temperature sending unit or a malfunctioning Dash gage. If your thermostat is stuck open, you will probably not get much hot air from your heater vents, and you may notice sluggish performance from your vehicle. Most Blazers, Jimmy’s and Sonoma’s normally run about one to two clicks to the left of the center mark (Center mark is 210° F) on the dash temperature gage.


No Heat or Very Little Heat from the Heater - Usually means that your heater core is plugged up; a stuck open thermostat will also cause this problem. You can try various flushing methods and products to open up a plugged core, but as a last resort, you may have to replace the core. One method is to remove both heater hoses at the firewall, attach a garden hose to the heater hose fitting, and flush as much of the scale out as possible. An old garden hose with the male end cut off and a hose clamp will usually fit over the smaller hose fitting. If your dash gage doesn't reach normal temperature, and your heater is blowing cold air after flushing, it might be time for a new T-stat.


Thermostats - Blazers, Jimmy’s and Sonoma’s usually run best with 190° - 195° F thermostats in them. In warmer climates, 180° F thermostats can be used. A word of caution here. Our engines depend on a minimum operating temperature above 175° - 180° F to operate the fuel/emission control systems efficiently. This temperature directly affects the on-board computer system. NEVER install a T-stat colder than 180° F. If your thermostat sticks open, your temperature gage will not reach proper operating temperature causing the engine to run too cold, waste gas, and give you lousy performance. If it sticks closed, you’ll overheat. There is no fix for a stuck thermostat (open or closed) other than to remove and replace them.

Radiator Cap - The original AC Delco caps are bad. If you still have the Radiator cap from the factory, replace it with a Stant cap or something other than the AC Delco brand even if you are not having any trouble at the moment. Defective radiator caps, regardless of the brand name, will cause air in the system and problems.


Gurgling or Slushing sound - This is air in the system usually caused by a defective Radiator cap or allowing your overflow tank to run dry. Flush the system and replace the cap with something other than the AC Delco cap and keep an eye on the coolant levels for the next few days after replacing the cap and add as required.

Leaks in General - Go to AutoZone or your local auto parts store and rent/borrow the Radiator Pressure Tester. It is basically a small hand held tire pump with a radiator cap and a Pressure Gage on it. With your engine turned OFF and COOL, attach the pressure tester to the radiator and pump it up until you reach the pressure rating of the Radiator cap. Then have a flash light handy to start looking for leaks around the engine.

Leaks or Antifreeze smell inside the cab - You will probably notice a sickening sweet smell and possibly a fogged up windshield on the inside of the cab, and possibly wet carpet on the floorboard. This is usually caused by a leaking Heater Core and normally requires the core to be removed and replaced. This is not a job for an inexperienced mechanic. You can buy a small plastic fitting at your local parts store that will allow you to remove the two heater hoses at the fire wall and jumper the hoses together until repairs can be made to the heater core. The small plastic fitting accommodates the two different sizes of Heater Hose found on most GM vehicles. Of course, you will not have any heat as long as the hoses are jumpered together.

Hoses - Hoses should not show any signs of bulging, swelling, cracking, splits or leaks. If they do, replace them.

Water Pumps - Most have a small Weeper hole in the bottom of the water pump casting, and sometimes may be difficult to see due to the water pump pulley. This little hole is normally on the dry side of the main seal where the water pump bearing is. If you notice antifreeze leaking out of the weeper hole, or running out of the front of the pump or pulley, it means that antifreeze is leaking past the Seal and into the bearing. It also means that your water pump is about to go. Replace it immediately.


Flushing -You should flush and refill your system a minimum of every two years, regardless of the type of antifreeze you use. Do not try to judge the condition of the antifreeze in the radiator by looking at the coolant in the overflow tank. This can give you a false reading, as overflow tanks can become contaminated and stained. Look into, or sample the coolant in the radiator. If you are over heating or notice that the coolant in your radiator is contaminated, or is muddy or brown in appearance, a thorough flush is in order. The best recommended method is the Reverse Power Flush. It is called Reverse Power Flush because the High pressure pump is attached to your system and forces the solvent to flow in the opposite direction than the antifreeze normally flows. This process should be repeated numerous times for best results, and be sure to remind them to do the heater core! If you cannot afford approx. $50-$75 USD for a Reverse Power Flush, there are a multitude of products and methods to flush your system with using a garden hose and system cleaners. One of the most Popular is the Prestone Flush and Fill kit, which attaches to your heater hose. Do a search on this forum.

Intake Manifold Gaskets - Blazers, Jimmy’s and Sonoma’s as well as most GM vehicles are notorious for having bad Intake manifold gaskets. If you have “Disappearing Antifreeze” meaning that your overflow jug is empty when you check it, and you have to constantly add antifreeze to it, and you cannot find any external leaks, this is probably your culprit. Usually a simple pressure test will verify this. Another symptom is coolant in the oil or on the oil dipstick. Coolant or water in the Oil will usually look like chocolate milk on the dipstick.

Head Gaskets - If you find your vehicle leaving a cloud of steam from the exhaust pipe, or your mechanic tells you there is exhaust gases in your coolant, you probably have a blown head gasket.

Stop Leak etc. - These Products comes in various forms and brand names. Use only in an emergency.

Fans and Fan Shrouds - Fans are either metal or plastic and should not be cracked, broken, have missing blades, or missing pieces of blades. Fans are balanced and will cause problems if cracked, broken or have pieces missing that throw them out of balance. An unbalanced Fan can cause Water Pump Bearings and/or Seals to fail. The Fan Shroud is the plastic housing attached to the radiator that funnels back and partially covers the fan. The Fan Shroud should first of all be there (not removed) and should not be damaged. I have seen engines with broken motor mounts lift off of their mounting pads and chew up fan shrouds with the fan blades, leaving big holes and gouges in the shroud and in some cases damaging the fan blades. In rare occasions, broken pieces of fan blades have been known to pierce the radiator (I know. Mine did). Replace the broken motor mount first, or you will continue to damage your fan or other components.

A Fan Clutch is the link between the fan and the water pump that allows the fan to operate at a reduced rate when the temperature is cold, while providing adequate cooling when the temperature is warm. A bad Fan Clutch can cause water pumps to fail as well as overheating. You should be able to hear your Fan during operation, especially upon acceleration. If you can’t hear your Fan working, or find that you are replacing water pumps too often or you are overheating at idle, but cooling off when moving, check your Fan Clutch. When your engine is SHUT OFF, your fan should rotate by hand, but it should not free wheel. NEVER TRY TO GRAB, TOUCH OR STOP A MOVING FAN. When you try to spin the fan blades, the fan should have drag and should not spin more than a revolution or so. When your engine is SHUT OFF, Grab the fan blades and see if you can wiggle the fan up and down or side to side, also inspect your fan clutch, you should not see evidence of oil streaking out of it. If you can’t spin the fan by hand, if it free wheels, or you can move the fan shaft, or see oil streaks, you may need a new clutch. NEVER TRY TO GRAB, TOUCH OR STOP A MOVING FAN. If you are lucky enough to keep your fingers, you could damage the fan. A Fan Clutch can sometimes be eliminated with a device called an Eliminator (go figure). This is really nothing more than a solid metal piece with holes drilled in it (to attach the Fan) that puts your fan into constant direct drive. The only real problem with these things is the noise. Typically they will make the fan HOWL VERY LOUD. If you can stand the noise, they work great. If your system is in good working order, you won’t need one. Some parts stores offer them as a replacement option to a new (expensive) Fan Clutch. Buyer Beware! Most people can’t stand the noise and have to remove them and end up buying the Fan Clutch, taking a loss on the cost of the Eliminator.

Dex-Cool® Antifreeze. - There are volumes of information on the Internet regarding Dex-Cool® Antifreeze which I will not re-hash here. The advertised claim that it will last 5 years or 150,000 miles is historically the exception rather than the rule in most vehicles. Air in the system and/or poor maintenance will cause the Dex-Cool® to turn highly acidic and start eating away at the engine and/or cooling system components, resulting in inevitable failure. There are test strips available on the Internet to check the Acidity level in your system. Keeping your system clean and topped off is an absolute must with Dex-Cool®. If you do not flush this stuff out and replace it every year or two max, you will in all likelihood run into very expensive repairs including replacement of the Intake Manifold gaskets, Head gaskets, Radiators, and/or Water Pumps etc. General Motors still recommends that vehicles that came with Dex-Cool® originally should continue to use Dex-Cool® as replacement or for topping off. GM continues to stand behind Dex-Cool®, claiming neglect and contamination is the real culprit. Prestone makes antifreeze that is yellow in color that is reported to safely replace Dex-Cool®.

Do yourself a favor; don’t wait for the advertised life (5 years or 150,000 miles) to expire before you maintain your cooling system. You’ll probably never make it.:2cents:

I personally will never use Dex-Cool® again. I have had too many problems, too many breakdowns, and spent too much money repairing my vehicles due to Dex-Cool®.

Good Luck!

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