Engine knock on startup

2010 FORD CROWN VICTORIA
111,744 MILES • 4.6L • V8 • 2WD • AUTOMATIC
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HEYMAN764
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Hello, I have the car listed above it is a police interceptor that runs very well, smooth as silk. For some reason every time I start up that car after letting it completely cool down (on a cold start) I hear some kind of knocking sound momentarily for one to two seconds then goes away. I am not sure what could be the cause although I know these engines can be picky about their oil filters. Is there anything that can cause a knocking sound on start up? It currently has a prime guard oil filter. Could the anti drain back valve not be doing its job? The engine runs very well and is very quiet with lots of power and does not make the sound when I start it up once it is warm, only does it when the engine is cold.
Thanks
May 7, 2018 at 1:40 PM
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STEVE W.
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I suspect you are correct in that the drain back valve is not doing its job and it is starting up dry. I try to only run OEM filters on vehicles that have a history of being "problem children" like the CV. You could connect up a mechanical oil pressure gauge to confirm it or swap the filter for a Motorcraft unit and see if it goes away.

One option that is not a difficult add on would be an oil accumulator. It collects pressurized oil and releases it back into the system if there is any cavitation or pressure loss in the oil system. I have put a few on ex-police vehicles that became fire service cars. You use a solenoid valve to connect them. In use you start the engine up, push the prime button and let it charge the accumulator. Release the button, now check your oil level and top it back up. From then on when you do a cold start you push the button and hit the key, the accumulator will dump the oil into the engine to pre-lube it, then as soon as the engine is running okay you push the button again and step on the throttle a bit to recharge the unit. I added them because the cars could easily set a week or two and it did not seem to matter which filter was on it, they would rattle on start up. They did not with the accumulators but you had to remember to push the button both times, the second time is more important as you have extra oil in the system and it could cause an issue if it gets splashed around by the crankshaft.
May 8, 2018 at 2:26 PM
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HEYMAN764
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I went ahead and did a oil change with Motorcraft synthetic blend 5-20 and a Motorcraft filter. After starting it and letting it sit for awhile, fired it back up and did not hear the sound at all. So hopefully this took care of the issue. Also, I know that most wear and tear occurs on start up, but can hearing this sound be actually causing damage or more wear to the engine?
Thanks.
May 8, 2018 at 3:45 PM
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STEVE W.
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Yes, knocking means metal on metal contact. Even a few seconds at 600 rpm is bad. It can easily lead to a spun bearing if the bearing metal galls on the crankshaft.
Good to hear the filter did the trick.
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May 8, 2018 at 4:51 PM