What I found is there are 3 types of clutch fans. (1) Standard (2) HD (3) Server Duty (mostly for trucks). What is the difference between a standard duty and heavy duty fan clutch? One of the primary differences between a Standard Duty, Heavy Duty, and Severe Duty fan clutch is the driven fan speed when engaged. A Standard Duty fan clutch will lock up 60 to 70 percent when engaged. A Heavy Duty fan clutch will lock up 70 to 80 percent when engaged. A Severe Duty fan clutch will lock up 80 to 90 percent when engaged. Why does my cooling fan make a roaring noise? When the clutch shoe inside the part gets stuck, it fails to disengage. This causes the fan to lock up on the input shaft. When the fan is locked up, the cooling fan is permanently engaged. This causes the roaring noise. You can ask the customer a few follow up questions to determine whether the fan clutch is the culprit behind the roaring noise. Is a HD clutch fan better than a Standard Radiator? Standard and HD units are, though. BTW- a better radiator will make a MUCH bigger difference in temps than a switch to a HD clutch fan ever will. And once you're over about 30-40 MPH the fan isn't doing squat anyway. The forward motion of the car moves more air through the rad than any fan ever could. Hope this info helps the V8Buick Community. VET (Navy)
Hi Vet, thanks for the information on the fan clutches. I put a HD AC Delco one on my Suburban (8.1L) and it makes that roaring noise some times. I thought it was normal...
Don't think it's normal. Ever since I had this roaring sound, I spent a lot of time investigating why. I've had a few performance cars and the most noise comes from from the exhaust system. My Buick had some serious dedonation issues. The engine mechanic has done everything to keep the engine temperature as low as possible. He started with removing the clutch fan that came with the Buick and installed a HD model clutch fan.
I'd start doing business with an expert like TA or Todd at Stage Won.. they would have your answers and most likely the correct parts.
You are dead-on. Todd and have become friends. I have purchased several engine parts from TA, first class parts. Love these two companies. Todd have been especially helpful and has gone out of his way to help me. VET
The noise is because the clutch is locked or close to it. Which fan do you have? Aftermarket fans generally have equally spaced blades, OE are not equally spaced to help reduce noise when locked. I can’t exactly recall but I believe the difference are, standard clutch has a bimetallic spring on the front that locks at a temperature. The others just rely in the internal fluid to engage the clutch. The fluid heats and moves internally to engage the fan. I used to test these in a wind tunnel. I’d you cruise them at too high of speed you will back the fluid. They generally are filled through a small hole then plugged with a metal ball. When the fluid gets too hot, you’ll see the metal around the metal ball turn blue. The maximum speed is dictated by your pulley (crank/water Pump) ratio. As far as detonation is concerned, what is your total timing? There is an advance bushing that can fall out. Most people set initial and if the bushing is missing, it will cause the timing to over advance. It’s worth a look.
Rob, my Buick was built when I bought it. The fan blade is a 7 blade. I believe that was standard for the 70 455. The original clutch fan is what Buick used, should be a GM Delco. The shop changed it to a Delco HD thermostatic spring type fan clutch. This is the fan clutch that is making the roaring sound. Could be defective. I contacted Todd Miller and bought one of his thermostatic spring fan clutch and it's also a HD model. We addressed the dedonation issue by installing a MSD ignition system and also a new adjustable carburator dashpot. Total timing is set at 32 degrees. The previous owner had all kinds of heating problems. When I purchased the car, I found a ton of repair receipts and mechanic notes. Mechanical note: Distributor needs rebuilding. I rebuilt distributor, it's total advance was set at 42 degrees, reset it back to 35 degrees. This distributor is original to the car. When my mechanic went over the distributor, he found the springs were to light. That when we decided to go the MSD route. This Buick has been butchered by the previous owner. Right now, it's running great with no heat problems. Once the new fan clutch is installed, i'am confident the roaring will cease to be a problem. I put my car into the shop to have a lot of upgrades done, it's been 19 months now. In two weeks, I should be on the road. I purchased this car in July of 2021 and had to wait in line until November of 2021 to get my car into the shop. I have only been able to drive it for 160 miles to date. I'am sure you might wonder if I'm frustrated, the answer is YES.... I was lied too about how this car was in contours condition. The body, frame, transmission and differential are super good. The engine had someone inside it that surly didn't know what they were doing. It was a mess, but it's in prime condition now. Thank you for your help, concern and advise. I'am sure i'am on top of this Buick now. It's been a long road and not much fun either. VET
Rob, for your reading, all you wanted to know about Clutch Fans. How Clutch Fans Work Both thermal and nonthermal clutches are filled with silicone-based oil. The low viscosity oil channels energy to the fan by transferring centrifugal hydraulic pressure from the clutch housing cavity to fluid coupling teeth and the clutch plate. This causes the fan to speed up or slow-down in conjunction with the engine’s temperature as hydraulic pressure increases or decreases. Thermal Fan Clutch Thermal clutches are equipped with a thermostatic valve that allows hydraulic fluid to bypass the clutch plate when necessary. As engine temperature varies, a temperature-sensitive bimetal coil spring expands or contracts, opening or closing non-return inlet and outlet ports between the hydraulic reservoir and the clutch cavity. When the engine is cold, the non-return drain valve opens, and draws oil back into the reservoir. This reduces hydraulic pressure on the fluid coupling and increases slippage, slowing the fan down or stopping it altogether. As the engine heats up, the drain valve closes and the inlet valve opens gradually. Once the engine reaches normal operating temperature, the cavity drains slightly, reducing fan speed. When the engine heats up beyond a certain point, the cavity fills up completely, increasing the fluid coupling’s efficiency and speeding up the fan to maximum rpm. Nonthermal Fan Clutch The nonthermal or “torque limiting” fan clutch is not equipped with a thermostatic valve. This type of clutch operates by centrifugal pressure generated between the housing and the clutch hydraulic coupling. In addition, the reservoir valves are pressure sensitive and less efficient. However, the built-it torque limiting function decreases maximum fan speed to between 1200 and 2200 rpm, depending on the application, when the engine reaches cruising temperature. Note: nonthermal clutches last longer than thermal clutches and are cheaper to replace. Power Loss and Fuel Consumption The 1970 Pontiac engineering brochure put it all in a nutshell with the following statement: “Fans. They cool. They also eat up horsepower. Conventional fans slurp up 20-24 horses at 6000 fan rpm. Flex fans, about 5 or 6. And clutch fans, about 4 or 5 horses. Take your choice. Why the difference? The flex fan blades flatten out at high rpm. Less resistance. Less drain. The clutch fan is thermostatically controlled. Cold, it runs no faster than 1000 rpm. Hot, it engages and picks up to 1800 rpm. All because of a little clutch.” As an added point, nonthermal fans are less efficient than thermal fans. This results in greater power loss and slightly higher fuel consumption. Please note: Flex fans have since been recalled because the blade roots are subjected to fatigue after extended use, causing blades to shatter at high speed. Replacement Since fan clutches lose efficiency after extensive motoring and tend to slip and cause overheating, consider installing a new unit when you repair or replace your water pump. Although you’re able to improve efficiency and lower fuel consumption by upgrading from a nonthermal fan to a thermal fan, the reverse is not true; never replace a thermal fan with its nonthermal counterpart. VET (Navy)
Mark, I have a 750 Holley with mechanical secondaries. The Holley works great, no bog no hesitation. From idle I go WOT, it cranks up the speed. I have to admit, I didn't realize the Buick like BIG carbs. So, sometime in the future I will switch to an 800 or 850 cfm. I'm still in the learning curve on these BBB cars. VET
