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Old 07-15-2013, 01:41 PM
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Originally Posted by eric32 View Post
Hello guys I have an issue here with overheating at idle and only at idle on both of my chevy s10's one is a 86 other is a 96. This is mostly info about my 96 but both trucks are pretty much the same outside of engine combo's and power. I can drive at 25 mph or up and have no problems with truck running hot what so ever even in 90 degree weather and high humidity.

Truck runs about 180 to 190 until I get stuck in traffic and have to sit for several minutes. So yesterday I wanted to see just how much of a problem I have so it was running a steady 190 then I sat outside my house and sat there watching it idle and the temp gauge and within about 5 minutes it got up to 210 then after a few more minutes it got up to 220. Temp gauge shows 210 then a mark then 250.

I purchased a laser thermometer gun and it did register almost the same as what the gauge did on the thermostat housing and read over 215 on the radiator and over 200 plus on the corner of the aluminum head.

Everything on cooling system is fairly new and very clean as I don't drive that much and all new 50/50 mix antifreeze. I am running a regular 160 thermostat with two holes drilled for bypass and I have also ran a 180 stat and there is no difference in how the temperatures go. I have tired the high flow thermostat before but they make the engine run too cold down the highway and during winter months its horrible so can't use them. I am currently using a high flow water pump oem style and I also tried using a stock oem water pump and neither one makes a difference in temperature for idle.

I have more then enough radiator as I am running an aftermarket all aluminum 29/17 two core radiator and each row is one inch each so that is not the problem there. Running a flex fan that pulls very good as feel anyways as you sit at idle if you put your hand toward the radiator you can feel it pull air so I am thinking its a shroud type issue as you can see in my pictures its a home made deal and nothing fancy. Does anyone have any suggestions as to what I should or can do.

I don't think a clutch fan will make any difference but I don't know as I have never used one just read some people don't like them and some are ok with them. From what I read flex fans work better for low speed air flow. I honestly want to keep my flex fan as I like it running all the time and not have to depend on a clutch style to engage as I like the peace of mind its running. I will do what I have to do to get this fixed.
The motor runs normal temps on the highway. That tells me that you have enough radiator and that the air has a way in and a way out. The problem is with the amount of air that the fan is pulling through the radiator and that ain't much. Air, water and electricity will always take the route of least resistance. The route of least resistance in your case is the fan pulling air from everywhere except through the radiator. It's obvious from your photos. It's pulling air from underneath, from the top and from the sides behind the radiator, but not THROUGH the radiator.

Either buy a commercially-available shroud or construct one yourself, closing the fan off so that it cannot see anything but the radiator. Keep the flex fan if you want to and see how it operates with a shroud. I don't like flex fans because they generally don't have enough pitch to move enough air. If you lay the fan blade down on the work bench and measure from the edge of one of the vanes to the work bench surface, you will find the pitch. I normally like about 2" to 2 1/2" of pitch on a steel OEM-type fan blade.

You might think you are doing yourself a service with a flex fan, but think about it. It takes fan speed to lay the blades back and that speed comes from the motor turning the fan. Now, if it takes hp to lay the blades back, how in the name of all that is holy are you saving any power?

Also, I think you are misunderstanding how a fan clutch works. It's like a small torque converter. There is no on or off, just a certain amount of slip based on resistance of the fan blades to the air, so that it drives the fan blade at full speed at idle and gradually begins to slip as the rpm's increase because you don't need any fan at all at highway speeds over about 35.

Another misconception you and others have is about operating temps. An internal combustion motor needs to run at 195 degrees or more to burn off acids and other non-combustibles.

So, there you have it.
1. Shroud with fan blades halfway in and halfway out or 2/3 in and 1/3 out, you get the idea I'm sure. Leave 1" of clearance all the way around between the tips of the blades and the inside of the shroud. The motor is on flexible mounts and torques over under power.
2. A real fan blade assembly with 2" - 2 1/2" pitch. 7-blade, 18" OEM steel is best. If you really want to move some air, use a fan blade assembly from an 80's Olds diesel. I think the pitch is right at 3". Be careful and don't choose a fan assembly from a serpentine arrangement. The blades are oriented differently. Stand in front of the radiator and look down at the top of the closest blade. If the orientation is Northwest to Southeast, it's a conventional fan blade. If the orientation is Northeast to Southwest, it's a serpentine fan blade assembly.
3. 195 or higher high-flow thermostat
4. Fan clutch

Last edited by techinspector1; 07-15-2013 at 01:52 PM.
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