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  #1  
Old 11-26-2007, 10:49 AM
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Engine problems update

1996 SL500

Anyway to make a short story long, here's what happened:

Car was running perfectly, but had a very very small tick occasionally, my mechanic mentioned it, but we never took it any further for a couple of years. I change the oil every 7500 miles with Mobil 1 Synthetic.

The other week the car lost a ton of power and eventually left me stranded with cylinder misfire codes. We thought it was the MAF or a timing chain jump at first, but it ended up being the fuel pressure regulator, fixed it and the problems was fixed, but keep in mind that the oil got flooded with gas.

So now the car is back together, but it has a HUGE klacking. My mechanic first thought was a rod knock, we take it to a couple of engine guys and they listen around and say they can't tell without cracking it open, pretty inconclusive. We did check compression and it's very strong in all cylinders, my first impression was piston slap, but there is no oil consumption and good compression.

My mechanic is a personal friend, so he gets down to getting his hands dirty as a favor. First he verifies there is low oil pressure. So he pulls the valve covers and sees the lifters are weak, but the springs are in good shape and a leakdown shows the intake/exhaust as well as the head gasket are looking good. My mechanic says the top end looks extremely clean and well maintained.

Next step, we lifted the engine, dropped the pan and my mechanic took a peek at the main bearings and rod bearings, he said they all looked very good with minimal wear. Cam and crank also looked good. Pan and screen were clean as I change the oil often.

So at this point the engine runs perfectly, except for the very loud clacking which we are pretty sure is the hydraulic lifters from low oil pressure. Our next and probably final step is to replace the oil pump itself, including the pressure relief spring, but my mechanic is not very optimistic about this. He feels that with the gas that flooded the oil some sludge might have been knocked free and is now blocking an oil passage, but admits this is a guess since he can't see inside the engine.

He thinks I have always had low oil pressure, maybe due to the oil passages, but the gas flooding made it worse. Keep in mind that I have had a faulty oil gauge for a couple of years, I just never got around to fixing it since this was kind of a beater.

Anyone care to input their tech? At this point it seems like the bottom end is strong, and the top end is in good shape as well other than the possible oil passages.
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  #2  
Old 11-29-2007, 08:24 PM
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Sounds like the classic "Cam Oil Line Fittings (Oil Guides)" issue. Look in the DIY section or do a search for a link. Good luck.
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  #3  
Old 12-04-2007, 01:50 AM
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* spinedoc, you said ". . my first impression was piston slap, BUT there is no oil consumption and good compression." Piston slap doesn't usually result in noticeable oil consumption or noticeable compression loss. That's one reason piston slap is so difficult to pinpoint! If the noise isn't that bothersome (i.e. you can hear the radio over the noise), piston slap can be driven a long time. Another is location. You can usually rule out the bottom-end as the noise source, but it's unclear between mid-engine and upper-end.
* The light tapping for 2 years, well before replacing the fuel pressure regulator, was also before so much fuel was injected that the engine wouldn't even run. Did the loud "klacking" come after the fuel dump that stopped the engine? Then again, how much was the engine cranked before the pressure regulator was diagnosed ( ". . gas that flooded the oil. .. )? If it was cranked quite a bit, there's your fuel wash.
* Fuel wash, from a defective pressure regulator or stuck injector and usually while the engine is being cranked (and not running), is probably the most common cause, on start-up, of piston and cylinder scoring (the excessive cylinder-to-piston skirt clearance then leads to the noise called piston slap). Find a bore scope and look for cylinder damage (through the spark plug holes, just moving each piston, sequentially, to BDC) before doing any more serious work.
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Old 12-04-2007, 05:52 AM
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Excellent info, thank you. I will run it by him. I thought with piston slap you would definitely see some low compression and oil consumption if it was bad to the point of making noise?

On a related note, he showed me the oil pan. It had metal sludge on the bottom, fine flakes of metal mixed with the oil that formed a mud like substance, not much, but it was there. Since we could not see 7 and 8 with the subframe blocking the way he wants to pull the engine up and measure those bearings just to make sure.

In relation to the fuel pressure regulator I did keep driving the car after it began to bog down as it was progressively getting worse. I drove it until it completely stalled out on me, so am not sure what damage I did myself by driving it. Basically it had a light occasional tapping, then this happened and it stalled out, and after the fuel pressure was fixed and the car started up it had the klacking. I'm not sure how often it was cranked by my indie though during diagnosis and repair.

Quote:
Originally Posted by Robert Squires View Post
* spinedoc, you said ". . my first impression was piston slap, BUT there is no oil consumption and good compression." Piston slap doesn't usually result in noticeable oil consumption or noticeable compression loss. That's one reason piston slap is so difficult to pinpoint! If the noise isn't that bothersome (i.e. you can hear the radio over the noise), piston slap can be driven a long time. Another is location. You can usually rule out the bottom-end as the noise source, but it's unclear between mid-engine and upper-end.
* The light tapping for 2 years, well before replacing the fuel pressure regulator, was also before so much fuel was injected that the engine wouldn't even run. Did the loud "klacking" come after the fuel dump that stopped the engine? Then again, how much was the engine cranked before the pressure regulator was diagnosed ( ". . gas that flooded the oil. .. )? If it was cranked quite a bit, there's your fuel wash.
* Fuel wash, from a defective pressure regulator or stuck injector and usually while the engine is being cranked (and not running), is probably the most common cause, on start-up, of piston and cylinder scoring (the excessive cylinder-to-piston skirt clearance then leads to the noise called piston slap). Find a bore scope and look for cylinder damage (through the spark plug holes, just moving each piston, sequentially, to BDC) before doing any more serious work.
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  #5  
Old 12-04-2007, 08:14 AM
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IMHO pulling bearing caps on the rear cyls is a waste of time. If you have low oil pressure it is a bad pump or too much clearance in the bearings causing leakage faster than the pump can supply oil.

I would replace the oil pump or rebuild itand see what happens, this I believe you can do without removing the engine. Some shavings is normal in oil sludge.

If it is too much clearance, the bearings will all be shot and it is time for a rebuild. No sense fooling around with two bearings, imho.

Also, I would not run it so long on my oil changes even with synthetic. I would also go one grade thicker on viscostiy or even two.

You probably should fire your friend and get a mechanic who has mercedes experience, too.

It may be a beater to you but these cars are expensive to repair, and most likely some type of neglect has put it in this shape.

With decent care, the bottom end on those v8s are about impossible to wear out. Cam chain guides are another matter. They require preventative replacement at (mileage varies on the recommendation) maybe 120 to 180K miles.

Tom W
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Old 12-04-2007, 08:23 AM
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I'm not sure what "decent care" is on this vehicle, but I changed the oil every 5000 miles with synthetic, and do all the other maintenance items. I drove the car like a grandmother, and my wife is even easier than I am on the car.

Even with this easy driving, we still replaced the trans at 80k, and now the engine stuff.

As for finding another mechanic, we have been to 3 different engine shops and they all concur that he is doing the right steps if we want to try and get lucky and save the engine on the cheap. Yes the car is a beater to me, but I would rather have it around than have to spend money on a new one that I could use for an investment.

I realize that it will need an engine, but my mechanic has no problem looking into it and knows that if we can't find the issue the next step is a rebuilt engine. If it wasn't for the rebuilt trans and immaculate shape of the rest of the car, I wouldn't have bothered to go this far.
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  #7  
Old 12-04-2007, 12:54 PM
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* spinedoc, did you buy this car (R129.067 w/ M119.972) before it had, say, 50K on the odometer? If you did, I don't understand the sludge with 5K synthetic oil changes. You know that despite the fact that grannys can drive very slowly and carefully, they routinely forget about maintenance (the real saving grace is the lower mileage, not the maintenance record).
* You absolutely need to find not only the noise-creating DAMAGE but also the CAUSE for that damage in the old engine before you start up a replacement engine. All you've found is the sign of the damage, the fine metal "slurry" or metal chips (which is it?) in the pan. Unless there's damage on rod bearings, cyls 7 and 8 (you've checked all the rest; how about a couple of main caps?), you don't have an oil-pressure related problem. Besides, I understood you to say there was oil pressure, possibly low-end of pressure range, but still acceptable. If the oil pump stops delivering oil even momentarily at road speed, there'll be bearing and pump damage, guaranteed, and a clear pressure problem hot. There are several soft bushings (timing chain idler) in that engine which could disintegrate and leave metal chips in the pan, not affect oil pressure, and cause some noise.
* If the damage turns out to be fuel-wash related scoring, make sure you cover the cause of that fuel delivery (electronic? or just mechanical pressure regulator). Don't carry the cause from the old engine to the replacement.
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Old 12-13-2007, 09:13 AM
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Thanks Robert. Currently the engine has been lifted, and we are looking inside. Here's what we have so far:

The oil pressure is VERY low, 5psi.
The main bearings measure ok
The journal measures ok
The rod bearings are thin, but the weird part is they look burnt, or like they got hot.

Right now we are assuming that the low oil pressure is due to the clearances and we are replacing the bearings while we have the engine up. I'll have them take a peek at the timing chain idler, etc.

Is it worth replacing the $450 oil pump? I had heard the oil pump does not provide pressure, only circulation.

This is almost definitely the last thing we will try before moving on.

If anyone is interested in a clean 96 SL500 with a rebuilt transmission drop me a PM.
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Old 12-19-2007, 04:16 PM
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* True, in the strictest sense an oil pump just moves the oil (like that Zen conundrum of the single clapping hand). It doesn't, by itself, create the pressure. The clearances along the oil pathways create the resistance-to-flow and pressure is a measure of that resistance. Increase the volume of oil delivered while keeping the oil clearances the same increases the pressure (e.g. increased rpms). Increase the clearances while keeping the oil delivery volume the same and the pressure decreases (e.g. worn bearing inserts).
* So, what it means in useful terms is that you need to determine whether the oil pump still has the capacity to deliver the oil. You do that by looking at the condition of the pump rotors and housing, and measure the rotor-to-housing/rotor-to-rotor clearances (clearances are by far the most important thing; a few scratches won't matter much).
* If you've also found your excess clearance problem (beyond the oil pump) along the oil pathway (like a scored bearing or journal), then you've got both delivery and resistance and your oil pressure should be back to normal.
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Old 12-20-2007, 06:27 PM
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* Spinedoc, how did this turn out? Did you find oil pump, oil-line fitting, or oil circuit damage? Or was it a bad sender, gauge, or somebodies imagination?
* And the "huge klacking" was from what, if not from oil pressure loss? Piston slap from cylinder/piston skirt scoring of a fuel-washed cylinder, disintegrating bushing?
* Please follow up with this and bring it to a conclusion. I and several others who contributed to your interesting questions would like to know the outcome. What I'm upset about is the situation that the issues were solved and those solutions are not being posted. No further posting presumably means that noone knows what the figg is going on and the car is sitting in the parking lot with most of the engine in the trunk! And even that situation ought to be posted as a conclusion.
* One of the weaknesses of this forum is that concluding or "fixed" posts are not required. The paid subscriber tech sites REQUIRE a concluding/fixed post to end a thread or the member is suspended!!
* I got that off my chest. Sorry for using your thread as an example.
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  #11  
Old 12-20-2007, 07:01 PM
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Quote:
Originally Posted by Robert Squires View Post
* No further posting presumably means that noone knows what the figg is going on and the car is sitting in the parking lot with most of the engine in the trunk! And even that situation ought to be posted as a conclusion.
Well you hit that one on the head. Everything else was checked and we came to the conclusion that it was the bearings and clearances that were causing the low oil pressure. At this time just the parts alone for that would run right under 1k, and the labor to get them in. While in there, there is so much that I could involve myself to have a truly fresh engine that it just wasn't worth it.

I found a nice warrantied engine with 27k that I am going to drop in. I have the old engine for sale here, it seems like something good for someone who didnt have to pay labor and did the rebuild themselves.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=007&sspagename=STRK%3AMESE%3AIT&viewitem=&item=170179863291&rd=1

And I completely agree and apologize for not posting my resolutions here, as I am still in the process. As I stated before the car is a beater for me, and an everyday driver for my wife so it's not high on my list of priorities. But for the price of the new engine, I could never find anything as nice even at an auction.

I'm not sure what happened to the techs on here, it's not like it was a couple of years ago. But I guess there is no money in posting on the forums.
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Old 12-20-2007, 07:24 PM
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Quote:
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I found a nice warrantied engine with 27k that I am going to drop in.
Can you tell us what you paid for the motor? Did you or your tech find it at a salvage yard?

What is your mechanic going to charge you to install it?
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Old 12-21-2007, 10:03 PM
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* Spinedoc, Many thanks for the reply and conclusion. Guess you're going to wash your hands completely of the old engine, and not really try to pinpoint the causes. Wish I was there. I've done several hundred engines in my time and find it interesting to establish the "forensic timeline" of an engine's demise.
* Be sure to check a few things on your replacement engine before you put it in the car. The most important item would be a cylinder leakage test. That can be easily accomplished (with a relatively inexpensive leak-down tester) with the engine on the floor. In fact, it can be checked before it's even off-loaded from the delivery truck. For my money, any value over 25% on any cylinder and the motor should be refused.
* If the cylinders seal well, check the crank seals. If the engine has been pressure washed, you won't have any evidence of prior leakage and should just go ahead and replace the 2 seals while the engine is still out. With the engine in the car, those seals are a lot more trouble. Of course plugs and valve cover gaskets are easier out of the car too. I know you said 27K miles. Be sure that the odometer wasn't broken for several years in that 27K car (common problem; good speedometer indication but no odometer function). Yes, it's all happened to me.
* Best of luck to you. Give the car some good work now and, if you're still interested in getting rid of it, you'll be able to take your time selling it for top dollar.
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Old 12-22-2007, 09:03 AM
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It sounds like the previous owner ran it low on oil, and probably never changed it at all for years.

Even if he or she had changed it even once in 10K miles this would not have been the result.

I am sorry if you think folks didn't respond to your posts adequately. I did when I saw it.

Tom W
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Old 12-22-2007, 10:20 AM
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That's not the case at all, but I do appreciate the input.

Quote:
Originally Posted by t walgamuth View Post
It sounds like the previous owner ran it low on oil, and probably never changed it at all for years.

Even if he or she had changed it even once in 10K miles this would not have been the result.

I am sorry if you think folks didn't respond to your posts adequately. I did when I saw it.

Tom W
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