Look at the blade angle on your fan. It's supposed to PULL air through the radiator as it turns, not push it. A reverse rotation water pump will try to flow coolant the wrong direction if the serpentine belt is mis-routed, also, even if the fan blades happen to be angled correctly. I have an idea the direction of rotation of your fan and/or water pump is the problem. Jerry
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“4 1/2” from the radiator “ is not good for optimal cooling. You also may have a air bubble in the system. Coolant should be only about 1/2 inch above the fins in the radiator. As HRL said, find out if your water pump is rotating the right way. Fill the system properly and add a properly spaced fan shroud. Start the engine and hold a piece of tissue paper to the front of the radiator. If it sucks tight to the radiator when the engine is reved up the fan (not necessarily the water pump) is rotating correctly. Good luck.
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Howdy Rowdy, The fan is pulling air through the core and back towards the firewall. I'll have to do some homework to find out what's going on with the water pump. I appreciate all the help, and will let you know what happens. Tramp
Your comment about the serpentine belt system gives me pause.
V-belt drives have the crank and water pump (all of the pulleys, actually) turning the same direction. As a general rule, serpentine belt systems will have the crank and water pump turn opposite directions to get more wrap on the crank due to the added force on the belt.
If you didn't change the water pump for the serpentine drive, that could be your problem right there.
Tramp, that symptom of repeated spiking temperature then dropping seems exactly like mine before I added the external bypass to the water pump. The stat opens then allows a batch of cold water to enter the motor then it closes and repeats. When it closes without the bypass, hot spots develop before the stat opens again causing the temp gage to show the spike of temperature. You have to have an external bypass if the passenger side cylinder head does not have it built in. If your water pump was rotating the wrong direction I don't think the temperature would drop back to 180 when it over heats.
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A water pump rotating backwards will severely restrict circulation, but won't make it flow backwards. A centrifugal pump like water pumps will still pump in the right direction, but flowrate will be WAY reduced. And if the vanes are straight and radial to the shaft, they can run either direction and won't restrict the flow as much as angled vanes.
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Tramp Seems like with that much space ahead of your fan that the aluminum radiator people could produce a core thick enough to solve your problem. Once on a 421 Pontiac we just barely caught the fact that mice had put a nest in the block water jacket mostly over a weekend !! Any chance that could be your trouble ??
I've done some homework, and found that the water pump is turning in the right direction. If I were to have a new radiator built, there is definitely enough room to make it plenty thicker, thereby increasing the coolant capacity. 59 talks about adding an external bypass to the water pump, and I'll have to do some more homework to better understand that possibility. What he said is how it's acting. Also, all of the sites that talk about coolant capacity say the 350 needs 17 quarts, which would include the block and heater core to fill. The 348 and 409 call for 23 quarts. I'm thinking of draining the coolant that is in the truck now and measuring to make sure just how much coolant it does have. I know when I flushed and refilled it this last time, it took one gallon of antifreeze and just over another gallon of distilled water to bring it up about an inch above the core. I also installed a new pressure cap 13#. Having a new radiator built can be done here locally, but it would cost me $800 or more. Again, I appreciate all the help. You can be certain I'll be doing the happy dance in my skivvies in front of the post office, and take an hour to draw a crowd when this gets straightened out.
If you think that bypass might be the problem, try driving with the heater on max heat. You don't need the fan on, just coolant flowing through the heater. The heater circuit will act as a bypass and if your temp is more stable, then you have found the problem.
