All Forums  CMC - GARAGE/SHOP TALK  Share your Tips  Got a cooling problem at highway speeds?

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Screensize: 640 x 480 800 x 600 1024 x 768 1280 x 1024 UserName: Password: Format Mode: Basic  Help  Prompt  Format: Font Andale Mono Arial Arial Black Book Antiqua Century Gothic Comic Sans MS Courier New Georgia Impact Lucida Console Script MT Bold Stencil Tahoma Times New Roman Trebuchet MS Verdana   Size 1 2 3 4 5 6   Color Black Red Yellow Pink Green Orange Purple Blue Beige Brown Teal Navy Maroon LimeGreen Message: * HTML is OFF * Forum Code is ON [quote][i]Originally posted by blownEFI[/i] [br]If your engine temps are ok at slow speed, idle, and driving around town but then the temp slowly creeps up while driving at highway speeds, then this tip might just help you out. I had this problem on my Challenger and so did a friend of mine on his '64 Sport Fury. In this tip I'll explain what the problem was and how we fixed it on our cars. The problem was we were not getting enough air flow through our radiators at highway speed. Now you're probably thinking to yourself "but wait a minute, the air [i]has[/i] to go through the radiator doesn't it? It has no other choice right"? Wrong! As you're going to see, how and where the air flows has everything to do with [i]pressure differentials[/i]. Air is a gas and therefore it is also a fluid. Gaseous and liquid fluids are all subject to the same physical laws of fluid dynamics. Differences in pressure cause fluids to flow, therefore a difference in pressure will cause air to flow. The direction in which air flows is determined by the relative locations of high and low pressure areas. Air will flow away from the high pressure area and towards the low pressure area. The magnitude of the pressure differential will determine the volume of air that flows. The greater the pressure differential the more air will flow. When you get your car up to highway speeds it begins stacking the air up in front of it creating a high pressure area directly in front of your radiator core. Normally the area behind the radiator core is at a lower pressure than the area in front of the radiator. It is that pressure differential that causes the air to flow through the core, from the front side to the back. Remember, air flows [i]from[/i] the high pressure area (front of radiator) [i]to[/i] the low pressure area (behind the radiator). The bigger the difference in pressure between the front side of the radiator and the back side of the radiator the more air will flow through the core. Anything that [i]increases[/i] the pressure differential is good, and anything that [i]reduces[/i] the pressure differential is bad. On some cars (like a lot of our older Mopars) the design of the front end allows a huge column of air to blow up [i]underneath[/i] the front of the car. The area from the bottom of the bumper down to the ground is where this big column of air blows by at highway speeds. So what? Well, that column of air then blasts up past the K-member into the enclosed engine compartment thus raising the relative air pressure in the enclosed area under the hood. This increased air pressure in the engine compartment [i]reduces the pressure differential[/i] between the front of the radiator and the back of the radiator. The reduced pressure differential causes less air to flow through the radiator core. Instead the air tries to spill out all around the outer edges of the radiator to the sides, above, and below where the pressure is lower. What you have to do is figure out a way to increase the pressure differential between the front of the radiator and the back of the radiator. You can achieve this in one of two ways. 1) Lower the air pressure in the engine compartment behind the radiator, or 2) Raise the air pressure at the front of the radiator. Either way you will be increasing the pressure differential and causing more air to flow through the radiator core. How do we do that? Well, one way you could solve it would be to install an electric puller fan on the back side of your radiator and run it all the time, even on the highway. The fan will generate a low pressure area at the back face of the radiator and cause air to flow through the core from the front side. This is exactly what is going on when you are sitting still idling at a stoplight or driving slow around town. You don't have enough speed to stack up enough air in front of the radiator to create a big enough pressure differential to cause enough air to flow through the core to keep the engine cool, so you're artificially increasing the pressure differential by running a fan. Ok, but what if you have a viscous fan or a flex fan that doesn't work at highway speed and you don't want to (or can't) install an electric puller fan? Or, what if you just don't like the idea of running the fan [i]all[/i] the time, even on the highway? Here's a better solution: Install a small air dam (somtimes calles a spoiler) under the chin of your car. This does two things simultaneously. It reduces the area through which the big column of air can blast underneath the car and therefore will lower the air pressure in the engine compartment behind the radiator. The air that the dam blocks will stack up in front of the car... joining the air that is already stacked up in front of the car thus increasing the air pressure in front of the radiator. Higher pressure in front of the radiator and lower pressure behind the radiator causes more air to flow straight through the radiator core. I installed an air dam on my Challenger and it lowered my highway running temps 25 degrees with no other changes. After seeing this my friend (who was having the same problem) installed one on his '64 Sport Fury and it lowered his highway running temps the same amount! [img]http://users.anet.com/~sdurr/images/finished/new5.JPG[/img] Stephen Durr stephendurr@boiseoffice.com 70 Challenger R/T 500 ci, fuel-injected, supercharged [/quote]   Check here to include your profile signature.