Clunking/Knocking during startup

I tried searching a bit but couldn't find what I was looking for. I have been googling the hell out of this issue and not coming up with any solid answers so figured I would ask you guys finally.

I have an 05 GT pushing 160k miles. It has basic bolt ins, cams, and intercooled Paxton 1200. The problems started after doing an oil change and putting in the first full synthetic oil the car has ever seen. I used 15000 mile 5w-30 Mobil 1 with a Mobil 1 oil filter. I drove the car around that night with no issue and drove it to work the next morning. I started it up to leave for lunch and noticed a pretty loud knocking/clunking noise under the car and I could feel it near my feet as well. It hasn't stopped since. It seems to go away after the car warms up, but it's tough to tell with the cams and the car being so loud.

I thought I might have put the intercooler piping back on too close to something it was knocking into, but there's enough clearance around everything. I read up some issues with oil filters so I swapped that with an OEM one with the same results.

Basically I'm hoping the full synthetic didn't mess anything up. Not quite sure where the knocking is coming from exactly but when I lifted the car and started it up, it's definitely sounds like it's on the bottom end of things.

Did I put the wrong weight in? Should I do another oil change with a different oil? Any input or similar experiences would be greatly appreciated. If the motor is about to go, I don't mind hearing that either

Thanks in advance

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Without hearing it my guess would be Cam Phasers. Sounds like a rod when they go. Mine went shortly after a cam swap when I had my 2005. Replacement resolved the problem. In my case the engine would run fine at startup and then sound like a rod was thrown after a quick rap of the throttle. The clatter sound began as engine speed dropped and would stay there until the car was shut off and restarted. Cam Phasers was the problem. You could try returning to 5W20 as thicker oils have caused issues with the VCT system since it uses oil pressure to vary the cam phase position while the car is running. Cheaper than replacing phasers on a hunch in the event that is your problem considering the mileage on the car.

redfirepearlgt said:

Without hearing it my guess would be Cam Phasers. Sounds like a rod when they go. Mine went shortly after a cam swap when I had my 2005. Replacement resolved the problem. In my case the engine would run fine at startup and then sound like a rod was thrown after a quick rap of the throttle. The clatter sound began as engine speed dropped and would stay there until the car was shut off and restarted. Cam Phasers was the problem. You could try returning to 5W20 as thicker oils have caused issues with the VCT system since it uses oil pressure to vary the cam phase position while the car is running. Cheaper than replacing phasers on a hunch in the event that is your problem considering the mileage on the car.

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I read a little bit about the cam phasers. I just thought it was so weird that it happened after an oil change with no issues up to that point. I wasn't sure how much different the 5w30 would be as a full synthetic vs a conventional in terms of viscosity.

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2NY said:

I read a little bit about the cam phasers. I just thought it was so weird that it happened after an oil change with no issues up to that point. I wasn't sure how much different the 5w30 would be as a full synthetic vs a conventional in terms of viscosity.

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Which is why I mentioned the oil change as a POSSIBLITY, not a Probability. Chances are its the Phasers or the passages and journals feeding them that may have gotten clogged with debris loosened up in the engine this late in its life by the introduction of a different oil with different additives in it. Not a wise move IMHO.

So to review my laymen analysis:

1.) and very remotely its a viscosity related issue...and I only say this with regard to the age of the engine. Most findings I came across where oil caused this issue (years ago) was when idiots would put 20W50 in the 3V thinking they were doing something to improve performance with less than 1/3 the miles you have on yours currently.

2.) More likely changing to a different oil with different additives may have loosened up debris that has now made its way into the passages and journals ofthe VCT system and is causing the problem.

3.) Most likely its the Cam Phasers failing either from age or contamination created by the introduction of the new oil type.

Oh and 4.) I could be completely off target in my hunch of your problem since I am going by a description of the problem and not standing in front of the car when it makes this noise you describe, though it sounds very similar to what I experienced when mine went out at about 36K.

Good luck.

redfirepearlgt said:

Which is why I mentioned the oil change as a POSSIBLITY, not a Probability. Chances are its the Phasers or the passages and journals feeding them that may have gotten clogged with debris loosened up in the engine this late in its life by the introduction of a different oil with different additives in it. Not a wise move IMHO.

So to review my laymen analysis:

1.) and very remotely its a viscosity related issue...and I only say this with regard to the age of the engine. Most findings I came across where oil caused this issue (years ago) was when idiots would put 20W50 in the 3V thinking they were doing something to improve performance with less than 1/3 the miles you have on yours currently.

2.) More likely changing to a different oil with different additives may have loosened up debris that has now made its way into the passages and journals ofthe VCT system and is causing the problem.

3.) Most likely its the Cam Phasers failing either from age or contamination created by the introduction of the new oil type.

Oh and 4.) I could be completely off target in my hunch of your problem since I am going by a description of the problem and not standing in front of the car when it makes this noise you describe, though it sounds very similar to what I experienced when mine went out at about 36K.

Good luck.

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I appreciate your honesty. TBH on my side, I beat the crap out of the car when I drove it I drive it hard and love every bit of it. So I figured it was getting close before I had to start replacing some major things. If it is the phasers, I would be surprised that they last thing long after the cam swap. Although, sometimes I wish I could give this damn thing up lol

Thanks again for your help! Appreciate your insight

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2NY said:

I appreciate your honesty. TBH on my side, I beat the crap out of the car when I drove it I drive it hard and love every bit of it. So I figured it was getting close before I had to start replacing some major things. If it is the phasers, I would be surprised that they last thing long after the cam swap. Although, sometimes I wish I could give this damn thing up lol

Thanks again for your help! Appreciate your insight

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no prob. I buy mine to drive them and enjoy them as well. Only pheasant should be kept under glass if you get the meaning. Nice looking car BTW.

redfirepearlgt said:

no prob. I buy mine to drive them and enjoy them as well. Only pheasant should be kept under glass if you get the meaning. Nice looking car BTW.

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Thanks man. It needs a little TLC lately

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