Engine Cooling 101


Start with the basics!

This is a basic primer on things to consider in order to get the most out of your cooling system. There are a bunch of facets to this issue so here goes. Keep in mind this is the Gospel According To Bob so after you read this research it yourself and make you own decisions. There is a lot of misleading info out there. I will try to clear up some of it. Keep in mind that every scenario is different and in my many years of building and working on cars it is readily apparent.

Back To The Basics

The reason here is this… many of the inquires I get is "I need to buy an electric fan for my (fill in the car of choice) because I am overheating. My buddy said that I need this electric fan.". Here are a couple of noteworthy issues that pop up immediately.

You need a fan shroud – If it had one put it back. If it doesn’t have one put one on. If the fan and shroud are intact make sure the fan is positioned inside the shroud lip and within 1 inch of it’s diameter. If you are outside the shroud, the shroud is broken, or you don’t have one, you are just beating the air! Most electric units have a built in shroud but it will only capture the footprint it has attached to it. You may have to direct the rest of the radiator face through that unit for maximum effect. Look at most late model automobiles. No Gaps!

Position is everything – The closer you can get to the radiator core the better. 1 to 1 1/2 inches is the best configuration.

Air Flow is Everything – The stock bladed and clutched fans move the best air at idle but take a bit more to run at speed. So if your concern is volume while cruising this is a no brainer. Stick with the stock units. Just make sure all the rest of the package is right. Most stock fans perform better than the aftermarket flex style units. The aftermarket Derale HD units seem to perform better than the same Imperial HD units, both usually better than stock. The Flex-a-Lite units are, for the most part, very poor performers.

Blocking off all the exit paths or directing air headed for the radiator is always a benefit. Make it go through the radiator not by it or around it! The crossmember blades ( little black plastic strips hanging down) that you see under the nose of a lot of new cars can actually account for a 15% airflow input.

Urban Legend #1An mechanical fan cost HP and an electric fan will recover that HP. Interesting but in my opinion not so. Cool, you have removed the fan, clutch and spacer from the water pump. You gained some HP from the rotating assembly. Now you have an electric fan. Note the key word here "electric". You just transferred the load from the water pump to the alternator. Keep in mind that some fans can use up to 80 amps to start and 30 amps to run. Some more some less. You may have to upgrade your wiring / alternator to make this happen. Cost involved could be major. HP benefit questionable. More electrical to go bad. Also at low speed it could be an advantage but at speed the fan unit which is not running actually can cause overheating because it is sitting right in the middle of the prime cooling area just hanging out blocking air! Take a look at most of the flat motor style aftermarket fans. Hold it up and look through it. That’s what the radiator sees! Usually about a 50% blockage.

Urban Legend #2Aluminum radiators are better – Aluminum units actually do not pass heat better than equivalent brass/copper types. Especially at idle or low speed. Basic Physics 101. But most aftermarket aluminum units are of the oversize variety so it does cool better overall. But we are in an apples and oranges comparison. The aluminum units cost lots more, have far more problems relating to repair and are very prone to long term vibration/stress cracking along with some corrosion issues if not maintained. Some weight savings but from a cost and durability standpoint really not a good “bang for the buck” deal.

Urban Legend #3High Volume / Aluminum Water Pumps are better – Don’t count on it! Most aluminum pumps are more for weight savings than performance. At idle HV pumps can actually not cool as well. It is because they move the coolant so fast through the radiator that it doesn’t have time to dump off all the heat it should. At speed it is almost a wash. Poor choice, again cost versus return, not good!. Same theory applies to running with the thermostat removed. The system actually needs some restriction to slow it through the radiator in order to let the radiator do its’ job.

Reference reading


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