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How to Diagnose a Bad Water Pump

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  1. step : Checking for Coolant Leaks (0:15)
    • Check the engine temperature gauge to see if the engine is running hot
    • Check for a sweet smell, similar to maple syrup
    • Look under the vehicle for fluid the color of your coolant
    • Soak up leaks with a paper towel to check the color
  2. step : Diagnosing a Coolant Leak (1:27)
    • After the car has run, listen to hear if the cooling fans are running
    • If the fan is not running, that may be the cause of the overheating condition
    • Allow the engine to cool down
    • Check the coolant reservoir level
    • Twist off the radiator cap
    • Check the radiator coolant level
    • Low coolant indicates a leak
    • Visually inspect the upper radiator hose for leaks
    • Check where the upper radiator hose connects to the engine
    • Visually inspect the lower radiator hose for leaks
    • Check where the lower radiator hose connects to the engine
    • Visually inspect the heater core hoses by the firewall for leaks
    • Check where the heater core hoses connect to the engine for leaks
    • Look into the engine compartment from underneath for leaks
    • Trace any leaks back to their source
  3. step : Checking the Water Pump (7:40)
    • Locate the water pump
    • Look for the weep hole behind the pulley
    • Check the weep hole for leaks
    • A leaking weep hole indicates damaged seals inside the water pump
    • Look for sticky dried coolant around the water pump pulley

Hi. I'm Mike from 1AAuto. We've been selling auto parts for over 30 years!

In this video, we'll show you how to diagnose a failing water pump. These tips should cover most vehicles. This vehicle here has a complaint from the owner of overheating or running hot. The gauge was between normal operating temperature, about half way, and to hot. It never actually overheated, but they also complained of a coolant smell, which is like a sweet smell. A lot of people describe it as like a maple syrup smell, not as tasty smelling, but very sweet and sugary.

To start looking for leaks, we're going to start by looking under the vehicle. Is there anything leaking on the ground? Coolant can be green, orange, pink, blue, sometimes it's yellowy universal color, of course, this would be straight water, if you're running straight water in a climate where you could run water. It will probably be hard to tell what color these are if they've leaked on the ground. You'll have to take a paper towel and soak it up from the ground, and then you'll be able to tell what color it is.

The overheating condition tells me there's something wrong in the cooling system. How do I know that it needs a water pump? We have to start at the basics first. If the temperature seems stable before I shut the vehicle off, and it's warm, I want to listen and see if the electric fans that pull air across the radiator are working because that will cause, if they are not working, the car may overheat while it's sitting in traffic and idling because you have no air flow over the radiator.

This is exactly what would be behind the radiator in this vehicle. Most cars have a similar setup. They have two cooling fans. One would be a main cooling fan, the other one will come on when you turn your air conditioning on for additional cooling. It's typical that if you just have your car idling without the air conditioning on that only one fan will be running, and then when you turn the air conditioning on, the other fan should come on as well because your air conditioning puts an extra load on the engine and it needs more cooling.

Even though this coolant reservoir is full, that doesn't tell the full story because the owner did tell me that he topped off the coolant reservoir. The coolant could still be low in the radiator. Now, in this particular vehicle, it has a cover. I had to remove all the plastic clips to pull this off to get to the radiator cap. With this out of the way, just to show what's going on, before you open the radiator cap, you need to let the vehicle cool down. Wait however long this take because you need to open the cooling system, which when hot is under pressure. Opening a hot radiator cap will cause a bunch of steam and boiling coolant to come out. Treat it with the same caution as a boiling pot of water on the stove. It's just as dangerous. Even if it's just warm to the touch, there still might be pressure. Wait until it feels like ambient temperature before opening the radiator cap.

This one feels nice and cool, so I'm going to open it up. I'm going to look inside and check the level. When you look down in here, you might be able to see part of the aluminum radiator core, but coolant should basically be at the top of this filler neck. It should be really full of coolant. This one is not. It's low. I can actually see the aluminum radiator part of it. It's maybe, like, an eighth of the way low, so I shouldn't be able to see any of that radiator. I want the coolant all the way up to the top. That still tells me that because this is low, there is a leak somewhere in the system.

I'm going to start with the obvious. I'm going to look, I can see the top radiator hose right here by the filler neck. It looks nice and dry. This dirt, this stuff, that's from driving down the road. The clamp looks good. I don't see any signs of dried coolant, or even leaking coolant. Follow the hose. It goes into the engine compartment, connect to the engine up here. Again, that looks nice and dry. I don't see any signs of leaking or dried coolant.

I'm going to go find the lower radiator hose. It's on the opposite side of the radiator on this engine. You can kind of see it. That's where it goes into the engine, so I'm going to backtrack and follow it down. I can just see where it's going into the radiator. That looks nice and dry. I don't see any signs of leaking coolant. Radiator hose looks in good shape. Follow it back up, see where it connects to the engine. It also looks to be in good shape. No leaks there.

I'm going to look up here towards the firewall. There should be a couple of rubber hoses going into the firewall. Those are heater core hoses. This vehicle has a couple of other hoses for rear heating, but just looking at all those junctions in there, I don't see any leaking coolant or any signs of leaking coolant. Follow those hoses back to where they connect to the engine. It's difficult to see, but they do connect. The heater hoses are here and I can see them. They go down and they connect into the engine. They are nice and dry and I don't see any coolant leaking. I don't see any signs of coolant. You might see coolant puddling on top of the engine here in the opening, or signs of dried coolant. I don't see any. I'm going to move on.

We've got our vehicle lifted into the air, but you can do this by simply looking underneath. On the ground there, I can see there's some coolant that dripped out from somewhere, so now I want to find where that came from. Of course, if you're on pavement and you can't tell what color that fluid, and you're trying to figure out if it's coolant or not, you could use a paper towel. That's orange. That's coolant from my vehicle here. I want to find out where it's coming from. I'm just going to put this down here.

Here's a clue. This is some coolant that dripped down and dried. It's sort of dried, but you can see it's real sticky and slippery, almost like a soap and it has the color of coolant, kind of orangey. It we follow it up, it's pointing up somewhere towards the engine. There's a rubber cover here. Your vehicle may have a plastic shield here protecting the engine. Go ahead and pop out clips or bolts, whatever is holding it in. This way, I can flop it up out of the way and I can see on the engine if anything is leaking.

You may need to look for signs of coolant leaking or dripping down the engine. On our vehicle here, the engine is made out of aluminum and there's some light, white, sort of, drips, but they are dried and they coincide from this area here, which is the water pump on our vehicle, and dripping down.

Many water pumps have weep holes in the bottom of them, which is behind the pulley. When the pump seals are damaged, coolant will weep out of the hole. It starts out as a drip and eventually as it gets worse, it will leak like a firehose.

This is another example of water pump failure. You can see the dried coolant. It's been leaking down the engine for a long time. All this grime is stuck to the engine. The water pumps, in both of these examples, will need to be replaced before they fail completely.

This is our old water pump from our vehicle. You can see there is the weep hole there. It's actually dry. What that does is this part of the water pump is sealed against the engine, so there's coolant up against here. The shaft that drives the impeller here to pump your water goes all the way through and it's turned by the drive belt on this pulley. There are seals inside on that shaft and if they fail, they will leak out here at the weep hole. On this one, it appears that the seals had gone bad and it was leaking out of this little pressed in fitting here. You can see it's corroded and it's wet with coolant, and that's where our coolant leak was coming from. Typically, if the water pump is failing internally, you'll have coolant come out of that weep hole.

Water pumps aren't a normal wear item, but if you have a vehicle with a water pump driven by the timing belt, it can be hard to replace when it fails. A common practice is to replace it during regular timing belt maintenance. The next time you need a water pump, visit 1AAuto.com and for water pump installation videos, visit our YouTube page

Thanks for watching. Visit us at 1AAuto.com for quality auto parts, fast and free shipping, and the best customer service in the industry.

Tools needed for replacement:

    General Tools

  • Flashlight

  • Materials, Fluids, and Supplies

  • Paper Towels


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