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Hi, I'm new to this forum. I'm hoping that somebody can help me on this one.

Could a water pump make a knocking noise, but only for a minute during a cold start? I've got a 2007 Base Model PT with 2.4L NA engine with 88,000 miles.

The first time I start the car in the morning, I hear a very light knocking noise (my wife probably wouldn't even notice it). It only lasts for about a minute and then it's gone. It will do it again if I let the car sit for a while, maybe 5 hours or so. The weather around here is 20 - 40 degrees F.

I have changed the oil every 2-1/2 to 3 months (about 3,000 miles) using semi-synthetic 5W-30 oil. I've used Castrol GTX, Valvoline, Penzoil during this period. I only recall hearing this noise over this winter, about 2 - 3 months maybe.

I know the water pump, timing belt, etc. are due around 100,000 miles. I was hoping to get them done next year, since I'll be around 100,000 miles. I also need shocks, structs and possibly tires, but don't really have the money for all of it. Just did thermostat, thermostat housing, upper and lower motor mounts, both control arms, ball joints and sway bar bushings.
 

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It sounds more like a lifter making the noise. Does the frequency of the knock seem longer than a noisy lifter would be? My PT has made that noise since around 80,000 miles, especially when cold. Now at over 263,000 miles, it still makes that noise when cold, but still seems fine.
 

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Could be the tensioner for the power steering/ac belt. Mine made a similar noise to yours...until the bearing failed and the pulley came off.
 

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It doesn't sound like a water pump-type noise. If it is from this area, you may want to locate the noise source by safely supporting the right-front of the car and removing the splash shield. You can then listen and locate the noise better. Diagnose first.
 

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Discussion Starter #5
Doug in Florida said:
It sounds more like a lifter making the noise. Does the frequency of the knock seem longer than a noisy lifter would be? My PT has made that noise since around 80,000 miles, especially when cold. Now at over 263,000 miles, it still makes that noise when cold, but still seems fine.
Not sure how long a noisy lifter would be, but mine is definitely cold related. It was around 45 degrees this morning and it didn't make the noise. I've listened to the engine from above and didn't really hear the noise, so it seems like it's coming from middle to bottom. Wouldn't the lifter noise be from the top?

Cudapete said:
Could be the tensioner for the power steering/ac belt. Mine made a similar noise to yours...until the bearing failed and the pulley came off.
I assume you're talking about the main serpentine belt tensioner? Was your noise only during the 1st minute of a cold start or every start? And did it stop after a minute?

ImperialCrown said:
It doesn't sound like a water pump-type noise. If it is from this area, you may want to locate the noise source by safely supporting the right-front of the car and removing the splash shield. You can then listen and locate the noise better. Diagnose first.
I was thinking it's not, but wanted to check with others. I heard the sound once while I was adjusting the lower motor mount. I had the splash shield off and it sounded like it was more lower to middle end of the engine. I may get a stethoscope and try and determine to true location. But, wanted to rule out the water pump.
 

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IC has the right approach. Take the splash shield off and try to locate the noise. The lifter noise may be difficult to accurately locate the noise, since it may be deceiving. But, like others have suggested, it could be a tensioner, or even connecting rod noise, etc. sounds like it is external to the block, it could be the a tensioner (accessory belt or timing belt), a belt itself, etc. If it sounds internal to the engine, then I would go with a lifter first, then consider something like a connecting rod. At that point, your choice is to just watch it to see if it gets worse, especially in warmer weather, or try to fix it. I would tend to keep an eye on it, but there are others here with plenty of good experience and great experience that may feel otherwise.
 

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The evaporative vapor purge solenoid also pulses a duty-cycle and may be heard at some times and not others. You can feel the 'heartbeat' by placing your fingers on it while hearing the noise. This is often confused with a lifter noise. Locate it with your underhood vacuum map.
 

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Discussion Starter #8
ImperialCrown said:
The evaporative vapor purge solenoid also pulses a duty-cycle and may be heard at some times and not others. You can feel the 'heartbeat' by placing your fingers on it while hearing the noise. This is often confused with a lifter noise. Locate it with your underhood vacuum map.
I'll have to check this item out. Maybe that's all it is. It certainly is in the right location and some of the complaints I've read about them sound close to mine.
 

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a belt with a chunk missing can be mistaken as a knock also.

the evap purge solenoid could be the culprit also.
most dont cycle until engine is running in closed
loop mode (warm)

pulling serpentine belt and cold starting it will
help narrow it down.with belt off and engine off
spin all accessories by hand and listen for noise.
 
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