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Discussion Starter #1
Have a 2000 Cadillac DTS and it has developed a noise under the hood. One day I started the car and a strange noise sounded when I started the car so I immediatedly shut the car off. My neighbor said do you have any oil in it??? I had to let the car sit and check the oil stick later to see how the oil was in it. I only had to add a little bit of oil to have the dip stick where it should be. I have always had to keep an eye on the oil stick because the car always needed oil added to it before the oil life ended.. Where it goes I do not know.

Know I hear a noise that I hate to say sounds a bit like a rod knock. I do hope this won't be a major engine problem. Any advise or suggestions you can give me would be greatly appreciated. I am unemployed at this time and cannot afford a major overhaul.:mad:

Thanks,
Bev
 

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White Diamond '03 DHS (with DTS floor shift)
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Bev,
The lower end is pretty strong. We have rarely if ever heard of a rod knock. Is this noise continuous or does it go away after 30 - 60 seconds or so?
 

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95 Fleetwood Brougham / 01 DTS / 11 CTS Lux / 11 DTS Platinum
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Bev, just for the record even those of us who are employed can't afford an overhaul on a N* not to mention they don't get overhauled, they get replaced.

Now to better answer your question I think Ranger is leading into the fact that it sounds like a phenomenon known as Cold Carbon Rap. Do a search, there's plenty to read about it. He's also correct in saying that the lower end of the N* is built to last. They're a very strong engine and built to run, which is where this cold carbon rap comes in.

The N* is a high performance engine and needs to be run, hard on occasion. This is NOT a grocery getter car and that's probably the worst way to treat a N* car. The saying here is "Drive it like you stole it"

If the noise goes away after 30 seconds or so after start-up then that's most likely the problem. Take it out and run it through the paces giving it some hard redline shifts. Burn the carbon out and see if the noise comes back.

If the noise doesn't go away 30 seconds or so after start-up the DON'T DO THIS. It may be something more serious.

BTW the N* is also designed to protect us from ourselves. The engine holds approx 9.5 quarts of oil. During a change with a filter you add 7.5 quarts of oil. It's my understanding that there's an oil manifold which retains about 2 quarts at all times. When the CHECK OIL LEVEL message comes on you're 2 quarts low leaving you 7.5 quarts of oil. Don't worry you're still very safe at that point.
 

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A little more description of the "noise" would be helpful. I can tell you it doesnt like a lack of lubrication right off the bat. I agree you need to let it run for a bit to see whether its consistent or goes away.
 

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Bev, just for the record even those of us who are employed can't afford an overhaul on a N* not to mention they don't get overhauled, they get replaced.

Now to better answer your question I think Ranger is leading into the fact that it sounds like a phenomenon known as Cold Carbon Rap. Do a search, there's plenty to read about it. He's also correct in saying that the lower end of the N* is built to last. They're a very strong engine and built to run, which is where this cold carbon rap comes in.

The N* is a high performance engine and needs to be run, hard on occasion. This is NOT a grocery getter car and that's probably the worst way to treat a N* car. The saying here is "Drive it like you stole it"

If the noise goes away after 30 seconds or so after start-up then that's most likely the problem. Take it out and run it through the paces giving it some hard redline shifts. Burn the carbon out and see if the noise comes back.

If the noise doesn't go away 30 seconds or so after start-up the DON'T DO THIS. It may be something more serious.

BTW the N* is also designed to protect us from ourselves. The engine holds approx 9.5 quarts of oil. During a change with a filter you add 7.5 quarts of oil. It's my understanding that there's an oil manifold which retains about 2 quarts at all times. When the CHECK OIL LEVEL message comes on you're 2 quarts low leaving you 7.5 quarts of oil. Don't worry you're still very safe at that point.
I have NEVER heard that before. To the best of my understanding it only holds 7.5 qts.
 

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Discussion Starter #7
I appreciate all the advice. I have to admit I do baby the car and perhaps I should take the car out and Wot as you say to get the carbon out. I am only afraid I could do damage to the engine if it is something else. What do you advise??

My husband was thinking of taking the serpentine belt off and if the noise went away he figures it is some other problem and not the engine.

Should we do the serpentine belt first or just take the car out and wot to get rid of carbon build up??

Bev
 

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95 Fleetwood Brougham / 01 DTS / 11 CTS Lux / 11 DTS Platinum
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Hmm I could swear that in one of the oil threads around here someone mentioning that there was an oil manifold above the pan that retained approx 2 quarts. We had a small discussion about it and that was it. I was amazed back then and asked some questions.

Maybe they were wrong. How can we find out?


EDIT: OK there is definitely an oil manifold in the N* the question now is how much oil does it retain.
 

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Bev, if the noise doesn't go away after 30 seconds or so after start-up then it's probably not a carbon problem.

If you suspect one of the accessories to be the noise then remove the belt and spin each pulley by hand. The problematic pulley will have drag on it or spin roughly.

And yes a better description of the noise would help.


I appreciate all the advice. I have to admit I do baby the car and perhaps I should take the car out and Wot as you say to get the carbon out. I am only afraid I could do damage to the engine if it is something else. What do you advise??

My husband was thinking of taking the serpentine belt off and if the noise went away he figures it is some other problem and not the engine.

Should we do the serpentine belt first or just take the car out and wot to get rid of carbon build up??

Bev
 

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Discussion Starter #10
My husband said the only way he can explain the noise is that it sounds like a rod knock.

Bev
 

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If it sounds like a rod knock and does not go away after a minute I would not give it any WOT treatments.

No need to "remove" the serpentine belt. Just put the drive lug from a 1/2" drive breaker bar in the square hole on the belt tensioner. Use the bar as a lever and release the tension just enough to allow the belt to slip. That will stop all the pulleys and accessories. If the noise continues, you can rule out anything driven by that belt.

Codewise, yes there is an oil manifold (not exactly sure what it's purpose is), but I don't think it retains any oil. I just cannot imagine them designing an engine that retains 2 qts of dirty oil.
 
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Have a 2000 Cadillac DTS and it has developed a noise under the hood. One day I started the car and a strange noise sounded when I started the car so I immediatedly shut the car off. My neighbor said do you have any oil in it??? I had to let the car sit and check the oil stick later to see how the oil was in it. I only had to add a little bit of oil to have the dip stick where it should be. I have always had to keep an eye on the oil stick because the car always needed oil added to it before the oil life ended.. Where it goes I do not know.

Know I hear a noise that I hate to say sounds a bit like a rod knock. I do hope this won't be a major engine problem. Any advise or suggestions you can give me would be greatly appreciated. I am unemployed at this time and cannot afford a major overhaul.:mad:

Thanks,
Bev
Could be piston slap like the LS GM motors get. Just off the top of my head and I didn't read the other posts to see if anyone else mentioned it. If that is what it is, its just a yucky noise that goes away shortly after startup and doesn't do much if any damage. Good luck.
 

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I don't think the Northstar's have piston slap...just the 3.1, 3.4, 6.0 and maybe the 8.1s. But I haven't heard many of the LS1s. Could it be the lifter's making noise before the oil gets into them? Or do DOHC motors not have lifters? I can't remember, it's been a while since my auto shop class. I know with my 4.9, when the motor's been sitting a while, I'll go to start it up and I'll hear a clicking sound for about 30-45 seconds until the oil gets to the top of the engine then it's smooth. IIRC, my dad's 3.1 Lumina does the same.
 

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Right. The oil manifold I think is there to maintain oil pressure. In other words it keeps the pump primed so there is no dry start-up. I think it also is responsible for distributing oil into different circuits throughout the bottom end. As far as oil retention, I don't really know but that's what I read.

Cold carbon rap is essentially piston slap.
 

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I just spoke to a GM tech friend of mine. He said while it is uncommon in the N* your noise is likely a cold start knock, esp. if it goes away in less than 30 seconds. It is much more common in the 350s. My Suburban has had a cold start knock for years. It sounds like a rod know for about the first 15 seconds after being started. He heard it and said to leave it alone.
 

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Discussion Starter #17
I should state that my car sat for awhile because my father recently passed away and we were using my husbands car and then I used my dads car since I brought it to my house to sell for my mom. Then when I started it ,it made a noise that I shut the engine off almost immediately. I cannot explain the noise. My husband then checked the car later and just saw it needed just a little oil added to it and now it makes a noise like a rod knock. The noise I first heard was different then the rod knock.

I recently purchased the 3 factory service mauals on my car. This is one thing it tells us to do. After a major engine repair or long periods of non-use, Lifter Clatter at initial start up is normal. This should go away after 10-15 minutes of operating the engine at 1500RPM. Operating the engine in this manner will purge all air out of the lifters. They tell you to do this while sitting in the car with the hood closed.

We are still going to release belt tension on the serpentine belt but do you advise the above tech info. I was waiting to do anything on the car until I had a set of books on the car.

Bev
 

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There are no lifters in a 2000 + Northstar so this isn't the problem.

Even in a pushrod engine WITH lifters 10 - 15 minutes is way to long. Lifter tap should go away within 30 seconds of startup unless there's an oil delivery problem. If the engine has been overhauled the lifters should have been primed on the bench before assembly.

I would promptly return the manuals that you've purchased because they're junk.

I recently purchased the 3 factory service mauals on my car. This is one thing it tells us to do. After a major engine repair or long periods of non-use, Lifter Clatter at initial start up is normal. This should go away after 10-15 minutes of operating the engine at 1500RPM. Operating the engine in this manner will purge all air out of the lifters. They tell you to do this while sitting in the car with the hood closed.

We are still going to release belt tension on the serpentine belt but do you advise the above tech info. I was waiting to do anything on the car until I had a set of books on the car.

Bev
 

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I have something very similar with my 99 deville, when I start in the morning as I did just today, I get the very same rod knockish sound. I start the car go back in the house push my coffee press down, pour it into a cup and by the time I get in the car to drive away its gone. But that sound give me chills everytime I hear it. What cvan be done about this cold carbon build up other then putting my foot into it?
 

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You can take it to the dealer and have an upper engine decarbonization treatment done, but it is a lot more expensive and less fun and next time the carbon builds up, you'll be back again. Just take it out and "drive it like you stole it".
 
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