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Old 08-12-2010, 10:41 PM   #1
PushnFords
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Water Pump Impellers & Overheating

My towing and hauling truck is a '93 Silverado 4x4 with a 350 and auto trans. I've been having cooling system problems:

Started out with the gauge not working = replaced sending unit and wire pigtail
Gauge read really low all the time = replaced instrument cluster.
Gauge took forever to warm up = replaced thermostat that was stuck open.

Now if I drive down the highway it'll run 210-215 empty or 220-225 pulling a vehicle (on a 100 degree day). If I let it sit and idle it'll overheat pretty quick. I checked the radiator and it had a lot of gunk in it so I replaced it with a newer one off of my parts truck which was nice and clean inside but no change. A guy at work told me he'd seen some with the water pump impeller on backwards (pump from a V belt application) so I pulled the pump tonight. But...I don't know if the impeller is on backwards or not...never really paid much attention to one before. Is this right?



Any other ideas? I'll probably do a test for combustion gas in the coolant when I put it back together. But I'd think a head or gasket problem would make it overheat more on the road at speed than it does?

Derek
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Old 08-12-2010, 11:25 PM   #2
Boog
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Re: Water Pump Impellers & Overheating

The impellar looks correct in that pump to me.
So you've replaced the radiator, thermostat. What about the fan clutch and shroud? What about the state of tune of the engine itself? How does it run? Slow ignition timing causes one to run hotter than it should. A weak engine tends to run hotter. One other thought is the wrong water pump can cause one to overheat. You mentioned it. Earlier pumps turn opposite direction to later pumps. Are you using the instrument panel temp gauge only to determine how hot it is running? Possibility the temp sender unit in the head has been changed and it's the wrong one? It has to match the gauge in calibration. Maybe some of this helps.
Also a change from the 5 blade fan you have to a 7 blade can help.
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Last edited by Boog; 08-12-2010 at 11:28 PM.
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Old 08-12-2010, 11:50 PM   #3
PushnFords
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Re: Water Pump Impellers & Overheating

Quote:
Originally Posted by Boog View Post
The impellar looks correct in that pump to me.
So you've replaced the radiator, thermostat. What about the fan clutch and shroud? What about the state of tune of the engine itself? How does it run? Slow ignition timing causes one to run hotter than it should. A weak engine tends to run hotter.
The fan clutch seems to be in good shape. It free wheels when cold and has quite a bit of resistance when hot...no play in the bearings either. The factory shroud is intact and in place. I just did a tune up on the engine so it has new plugs, good wires, new cap/rotor, fuel filter, PCV valve, etc. I checked the timing last night. With the connector on the firewall unplugged I showed 0 degrees on the balancer which is what the emission sticker states. I also bumped the engine over to find TDC on #1 and confirmed that the balancer mark is in the correct location. I've never had a 350 before but it seems to run and drive good. It does have 208K on it but the previous owner put a set of reman heads on it not long ago. I haven't noticed it burning any oil and it runs smooth.

Quote:
Originally Posted by Boog View Post
One other thought is the wrong water pump can cause one to overheat. You mentioned it. Earlier pumps turn opposite direction to later pumps. Are you using the instrument panel temp gauge only to determine how hot it is running? Possibility the temp sender unit in the head has been changed and it's the wrong one? It has to match the gauge in calibration. Maybe some of this helps.
The pump and fan in the picture is what I removed from the truck tonight so if the impeller is correct the pump should be fine. I've been double checking the instrument gauge with a infrared temp gun and I've been taking readings directly off the gauge sensor. The dash gauge isn't the most accurate at lower temps but when it is over 200 degrees it has been spot on.


Quote:
Originally Posted by Boog View Post
Also a change from the 5 blade fan you have to a 7 blade can help.
I'll keep that in mind although I'm a pretty firm believer that the factory designed the truck to run ok and stay cool in the factory arrangement so if I can't get it to do the same I have a problem that needs fixed. After I fix the problems then I start looking into improvements.
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Old 08-18-2010, 12:38 AM   #4
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Re: Water Pump Impellers & Overheating

I replaced the pump and the hottest it has gotten since is 205. I couldn't get gaskets locally to compare the pump off my truck with the pump off my parts truck so I just swapped them. I'm assuming the impeller was backwards though.
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Old 08-18-2010, 08:08 AM   #5
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Re: Water Pump Impellers & Overheating

Well you've made some headway with it. By the way what temp stat did you put in? I'll tell you different brand stats do not perform the same as you might expect. Have you gotten the cooling system checked for combustion yet?
There could still be a blockage somewhere. Does it have good circulation through the heater core?
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Old 08-18-2010, 05:14 PM   #6
PushnFords
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Re: Water Pump Impellers & Overheating

Quote:
Originally Posted by Boog View Post
Well you've made some headway with it. By the way what temp stat did you put in? I'll tell you different brand stats do not perform the same as you might expect. Have you gotten the cooling system checked for combustion yet?
There could still be a blockage somewhere. Does it have good circulation through the heater core?
I put in a 195 degree thermostat. It was reading 205 after a 70-80 mile drive and then idling for a few minutes. I never did check the cooling system for combustion. I was planning on it before I completely refilled the antifreeze but ran out of time. Then since everything was working ok I never went back and did it. The heater seems to be working fine although the heater hasn't gotten much use lately!
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