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I have a 04 GTO LS1 engine and it's only seen 55K miles. Just today I finished a 30 mile drive and upon turning my engine off in the driveway, I heard a "thump thump" sound just as the engine finished its last turn. I was alarmed so I turned it on and shut it off again. The same "thump thump" sound came from the engine as it shut down. I tried it again, and I only heard one "thump". Again, and only heard it once.

On a normal basis this engine runs beautifully, and still has great gas mileage despite my occasional lead-foot joyriding. With oil changes, I always give it valvoline full synthetic 5w-30 oil with a half can of sea foam and a full bottle of Lucasoil synthetic oil additive in the oil pan. The problem can't be because of poor upkeep...

My dad's saying it's a timing problem, and eventually that my engine will do something called 'dieseling' where it'll start turning in reverse when I shut the engine down. Is this true?
Moreso, what in tarnation would I do to fix it?

Thanks ya'll.
 

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is a scrub
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You're not saying you run seafoam in the thing full time, are you?
 

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Dieseling wont happen with a modern fuel injected car. When you shut the ignition off the injectors shut off. Also it wouldn't run backwards as fuel comes from the intake side of the engine. Your problem could be the valves not seating fully and your getting a little blow back. If you have the means do a leak down test.
 

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Maybe check to see if you have bad motor mounts or something like that. Perhaps a bad motor mount situation is allowing the motor to rock as it dies... ?
 

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1 LITER DUC EATER
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why are you running seafoam??!! its supposed to be used as a cleaning agent, not an oil additive at every oil change. if i recall the manufacturer recommends not driving over 200 miles after putting seafoam in your crank case. that shit makes your oil thin as water.
 

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Australian Body American V8
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FPFQ, these motors aren't rocket science brah, Gas Tires Oil! 93 octane, z rated, Mobil 1...start there and if you continue to have problems seek an lsx mechanic
 

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~СЛАВА Г&#1045
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GM clearly recommends against using any additives at all.

Edit: Please take your care to a good mechanic you trust and have it checked. Without clear signs and visual inspection, we're all just taking guesses here!
 

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is a scrub
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Please tell me you're not running seafoam in it full time.
 

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Bangin Gears
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I've heard putting in a 1/2 can of seafoam in 50miles before you change your oil, but never running it all the time.
 

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Well hopefully you havent been running seafoam in it full time or else you might just be SOL. I really hope you had enough sense not to do that. I wouldnt use any oil additives either. Pretty sure there is nothing lucas oil additive can add that a quality synthetic motor oil already has in it.
 

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Just call me "nubs"
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This is miserable. Running a half can of seafoam with an oil change.

The guy who ran water through his cobra engine to clean out the oil comes to mind.
 

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additives are all a joke, sea foam special this synthetic additive that blah blah......all junk......run good oil and thats it......ive never used any additives just a good synthetic after break in, my motors are clean as new and run awesome and make good power and after well over 15 builds ranging from stock to near 1000hp ive yet to have a failure (knock on wood) lol
 

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Jesus Smurfing Christ. Where to start?
Tell dad to leave his 1970's advice back in the 70's, as someone has already explained.
Seafoam, all the time? NO its a solvent, not a lubricant.
When engines make BAD noises, dont keep starting and stopping it. You may make it worse. CHECK IT OUT.
FPFQ indeed.
 

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Oh it's Friday night
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If nothing else, change you oil and filter before you drive it again and stop trying to overthink engine maintenance. If you can not explain to yourself why you are adding something to your engine oil, or to your gas for that matter, do not add it.
 

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is a scrub
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I still want to hear, "Yes, I run Seafoam in it full time."
 

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1LE
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From Seafoam website:
Seafoamsnakeoilsalesdepartment said:
The most frequently asked question about using Sea Foam is as follows: “After using Sea Foam in my oil, fuel, or through the vacuum line (to clean deposits from the combustion chamber) do I need to change my oil?” The short answer is: No you don’t have to change your oil after using Sea Foam in any application.See more information about using Sea Foam in oil in the How To Use section of our web site

When using Sea Foam in your fuel or through the vacuum line for carbon cleaning your oil does not need to be changed. Using Sea Foam in your oil, at 1 ½ ounces per quart, is a safe way to clean a crankcase, quiet noisy lifters as you drive. Sea Foam is not a chemical engine flush and therefore, it will not damage internal engine components or plug the oil pick up screen. Sea Foam is a petroleum blend with no chemical additives and is safe for long term cleaning or short term pre-service cleaning.

Sea Foam is a blend of highly refined additive oils and is compatible with all motor oils including synthetics. It is safe for all internal engine components and will not affect any seals, gaskets or o-rings. Sea Foam cleans oil deposits and varnish in your crankcase by safely/slowly re liquefying the old oil residue so contaminants may flow and be filtered. The longer Sea Foam is in your oil the cleaner your crankcase will become. When adding Sea Foam to clean oil, for long term maintenance cleaning, you must check your oil periodically for color and clarity, when your oil looks dirty change it. Because you added cleaning oil (Sea Foam) to your oil you may have to change oil before the expected service interval.

When adding Sea Foam to dirty oil before an oil change, for best results use 1 ½ ounces per quart of oil at least 100 miles before oil is changed.
http://www.seafoamsales.com/motor-treatment.html
 

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Running seafoam full time sounds iffy, but everyone else here is saying no additives. Disagree to a certain extent. Synthetic engine oil is chemically modified petroleum... with additives. Group III oils start from crude oil base stocks, Group IV are fully synthesized. All have Corrosion inhibiters, anti foaming agents ect (additives). Some oils have detergents. When you put an additive in, you are increasing the amount of additive in the oil, not introducing it. Additives are still there. I run 2 cans of BG MOA in mine every oil change. Been doing it since I've owned the car... so since 45k. Zero problems at 98k now and the inside looks like a 20k engine. 190 psi compression accross the board. Just got dynoed last month, still runs strong knock on wood. With that said, you can't go wrong running Mobil 1 straight up like GM recommends, but there are plenty of better options out there. Seafoam prob not one of them.
 
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