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1991 Chevy S10 Blazer 4dr 4.3l TBI “5LM60”
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Discussion Starter · #1 ·
I replaced my water pump due to a bad bearing and followed all specifications according to the haynes manual. Every once in a while there is a strange whining/grinding noise almost like a blender. My coolant is at the correct level in the radiator, but it almost sounds like an air bubble is trapped and keeps getting circulated through the system. I had this issue ever since replacing it, as well as first startup.
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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What brand of water pump did you install? Are you positive that the noise is coming from the water pump, and how did you check that? An air bubble moving through a cooling system would generally make more of a gurgling type noise, rather than a 'whining/ grinding' noise. Is the noise constant, or does it vary (pitch &/or frequency) with engine RPMs?
 

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1991 Chevy S10 Blazer 4dr 4.3l TBI “5LM60”
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56 Posts
Discussion Starter · #3 ·
What brand of water pump did you install? Are you positive that the noise is coming from the water pump, and how did you check that? An air bubble moving through a cooling system would generally make more of a gurgling type noise, rather than a 'whining/ grinding' noise. Is the noise constant, or does it vary (pitch &/or frequency) with engine RPMs?
The noise varies with engine rpm, but goes away, and the noise only started after I replaced it. It is an Orielly’s brand.
The sound almost matches a power steering pump noise, but I never messed with that and it isn’t low on fluid, and that would be a massive coincidence that the power steering makes this noise only after replacing the water pump.
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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The noise varies with engine rpm, but goes away, and the noise only started after I replaced it. It is an Orielly’s brand.
The sound almost matches a power steering pump noise, but I never messed with that and it isn’t low on fluid, and that would be a massive coincidence that the power steering makes this noise only after replacing the water pump.
Are you certain that it's the correct pump? The O'Reilly's (MasterPro?) part may not be a fully identical pump to the OEM Delco specs. I am partial to using OEM parts whenever possible to minimize the chance of lesser quality clones (but definitely not a guarantee anymore). And, even new parts can be defective. If you are positive that it isn't coming from the water pump, it could be the PS pump, or maybe the bearing of the alternator or idler pulley on its way out. It isn't totally out of the question that it could be a coincidence that another part is the culprit.
For reference, here's a link for a GM water pump & its specs, for comparison against the pump from O'Reilley's.
 

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1991 Chevy S10 Blazer 4dr 4.3l TBI “5LM60”
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56 Posts
Discussion Starter · #7 ·
Are you certain that it's the correct pump? The O'Reilly's (MasterPro?) part may not be a fully identical pump to the OEM Delco specs. I am partial to using OEM parts whenever possible to minimize the chance of lesser quality clones (but definitely not a guarantee anymore). And, even new parts can be defective. If you are positive that it isn't coming from the water pump, it could be the PS pump, or maybe the bearing of the alternator or idler pulley on its way out. It isn't totally out of the question that it could be a coincidence that another part is the culprit.
For reference, here's a link for a GM water pump & its specs, for comparison against the pump from O'Reilley's.
The other thing on that, the pump is correct and matched the water pump that was on there. It is the masterpro and I have not had any issues with that brand for anything.
 

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The other thing on that, the pump is correct and matched the water pump that was on there. It is the masterpro and I have not had any issues with that brand for anything.
Sounds like the impeller is making contact with the back cover.
 

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I replaced my water pump due to a bad bearing and followed all specifications according to the haynes manual. Every once in a while there is a strange whining/grinding noise almost like a blender. My coolant is at the correct level in the radiator, but it almost sounds like an air bubble is trapped and keeps getting circulated through the system. I had this issue ever since replacing it, as well as first startup.
A little time spent with one end of 3-4 ft piece of heater hose @ your ear can oft help pin point more precise source of annoyance.
 

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I replaced my water pump due to a bad bearing and followed all specifications according to the haynes manual. Every once in a while there is a strange whining/grinding noise almost like a blender. My coolant is at the correct level in the radiator, but it almost sounds like an air bubble is trapped and keeps getting circulated through the system. I had this issue ever since replacing it, as well as first startup.
Check your alternator belt and make sure it's tight. Put a long screw driver to the alternator and the other end to your ear when you hear the noise. Sometimes they make that sound.
 

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1991 Chevy S10 Blazer 4dr 4.3l TBI “5LM60”
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Discussion Starter · #15 ·
Are there any other 'details' missing that might help folks with suggestions for fixing the issue?
Alternator bearing IS going out and makes a faint grinding noise, because its a dry bearing, (i am planning on replacing it), my power steering pump works like a charm and has the correct level of fluid.

When I heard the noise again it was coming from the water pump. I have replaced the belt, tensioner, and idler because they had horrible bearings. The sound happens after it is warmed up and I start the engine after it sits for about 10 minutes.

On the water pump, there is a threaded plug on the top. Was I supposed to run the engine with that open for a few seconds when I installed the pump?
 

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You shouldn't have to remove any plugs...just run the engine for a few minutes with the cap off to help burp the cooling system. Place radiator cap back on and make sure your overflow is at the correct level too. After a few warm up/cool down cycles, you should not have much air in the system.

You could take the belt off and spin the pump/fan manually while moving the shaft in and out. You may be able to hear or feel something if the impeller is hitting the pump. Of course that would only be the case if there was a serious defect in the pump.
 

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Check your alternator belt and make sure it's tight. Put a long screw driver to the alternator and the other end to your ear when you hear the noise. Sometimes they make that sound.
Caution when using stiff object as listening device. If it contacts a moving item while searching, a painful blow to your head is possible.
 

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1991 Chevy S10 Blazer 4dr 4.3l TBI “5LM60”
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Discussion Starter · #19 ·
You shouldn't have to remove any plugs...just run the engine for a few minutes with the cap off to help burp the cooling system. Place radiator cap back on and make sure your overflow is at the correct level too. After a few warm up/cool down cycles, you should not have much air in the system.

You could take the belt off and spin the pump/fan manually while moving the shaft in and out. You may be able to hear or feel something if the impeller is hitting the pump. Of course that would only be the case if there was a serious defect in the pump.
I will try that later today
 

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1991 Chevy S10 Blazer 4dr 4.3l TBI “5LM60”
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Discussion Starter · #20 ·
Check your alternator belt and make sure it's tight. Put a long screw driver to the alternator and the other end to your ear when you hear the noise. Sometimes they make that sound.
I finally caught the noise when it was loud enough today. Alternator bearing. I knew it was going out but I have put it off. I did replace the tensioner a few months ago, so I think that is what is causing the noise to be intermittent. I think when I replaced the tensioner, it put more pressure on that bearing causing it to get louder, and it finally made noise after I replaced the water pump.

I have also confirmed it is my alternator with the screwdriver trick. It is ordered in through oriellys and will be here in the morning.
 
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