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Tapping noise at idle


taxman

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My neighbor has a 1995 SLS w/ 66K miles. He's the original owner and has done all the dealer recommended services for the last ten years (no, the car is not for sale and if it ever is I'll have a check ready...sorry guys). The car has a slight tapping/rapping noise at idle, hot or cold with the noise being slightly more audible during a cold start up. I've driven it and done several WOTs, today being the most recent so I don't think there is cabon build up. I crawled under the car and the tap seems to be more audible from up top. There are no codes. It sounds similar to a valve tap on an old Chevy pushrod V-8. It's no the A/C compressor or an exhaust leak. Any ideas? The stealership wanted a $400 deposit just to do a diagnosis.

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As a long time GM man I cannot resist the comment "typical GM lifter/and/or valve noise."

The thing that jumps to mind is the fact that it's a 10 year old car with 66k on the clock. That's 6.6k a year. Did he change the oil @ 3k, or every 90 days? If he changed @ 3k, the car has not been maintained properly. The oil's additives break down or become contaminated, especailly the detergents in the oil.

Something tells me that a person who only puts 6.6k a year on a car doesn't change the oil @ 1.6k, so I'd be willing to say that the lifters are the least, full of varnish/and/or crud, or at the most completly destroyed.

I have 67k on mine, I run the dog crap out of it, change oil religioulsy @ less than 3k, and it's more quiet now than it was when it was new.

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I have a 95 SLS with less miles then that one at 60,000. Only had 10,000 on it 3 years ago when I paid $7800.00 for it. Yes a cream puff, no ticking. The only problems the car has had happened in the last month they were shift solenoids, fuel pressure regulator, and ISC actuator motor, about $150.00 in parts.

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While I am not a big supporter of oil additives, I can and do recommend Marvel Mystery Oil for the symptoms that you describe.

It is primarily a highly refined mineral oil that can get past some varnish buildup and free sticky lifters, if that is the problem.

It may be helpful to curing the condition, it certainly will not hurt anything if sticky lifters is not the problem.

Change the oil and filter, substituting one quart of Marvel Mystery Oil, for one quart of your regular oil. You will often notice the change within minutes, but depending on your conditions it may take a day or so of normal driving.

You normally do not need to add Marvel routinely to your oil. I will do so on a yearly basis, as a personal choice, to help keep any varnish from building in all of my vehicles..

Below is a link to one of our Caddyinfo discussions on this product. My reply is number 10 or 11 in the list, and an additional reply next to the bottom.

Marvel Mystery Oil

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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I wonder if MMO can be used in a transmission. I've never tried the stuff, but after reading some of the posts about it, I think I'll give it a try - in the engine oil, of course.

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I wonder if MMO can be used in a transmission. I've never tried the stuff, but after reading some of the posts about it, I think I'll give it a try - in the engine oil, of course.

I would NOT recommend it in the transmission. The automatic transmission needs fluid with very specific co-efficiency of friction specifications, to function correctly.

The wrong amount of friction can easily damage your automatic transmission.

Very abbreviated reasons.

To slippery will cause soft shifts and the clutches will not lock up properly; causing high heat, burnt clutches and overheated fluid.

Not slippery enough will cause hard shifts, and damage to driveline from the constant hard shocks. At crawl speed in traffic, the clutches will try to stay engaged to much and overheat, again burning the clutches out early.

It is best to use only the fluid recommended by the manufacturer, to avoid damage by using fluid with the wrong co-efficiency of friction.

There are a few additives that may help as sealers, but I would not add MMO to the automatic transmission.

-George

Drive'em like you own 'em. - ....................04 DTS............................

DTS_Signature.jpg

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