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  #1  
Old 04-01-2005, 03:24 PM
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help with mechanic-speak

So I took my car in to the mechanic to replace the motor mounds. It's a '91 350SD, runs great, but has a substantial oil leak (a quart every several hundred miles). He looked at it, and this is what he wrote down on the receipt:

"MAJOR OIL LEAK AT AREA OF THE TURBO CHARGE/AIR INTAKE CRANKCASE BLOW-BY AND TURBO CHARGER SEALS APPEAR TO BE THE CAUSE"

He said that it's probably not worth fixing because the turbo charger will run me around $1800 by itself, and then he said something about the blow-by (which I have no idea what that is) and that it'll take major engine rework to fix the leak, and that the more I drive it on the interstate, the worse the engine will get. He says it'll fail eventually, but couldn't say when.

Can someone give me some pointers on what he's talking about, especially about this blow-by?

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  #2  
Old 04-01-2005, 03:29 PM
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Blow By

The crankcase, that which contains the crankshaft and connecting rods, is the bottom side of the engine - you can see the bottom of the pistons from under there. Compressed fuel and air mixture burns in the cylinder on the top of the pistons. When the rings become tired and worn they allow some of this compressed and burning mixture to leak past and escape into the crankcase. That is called "blow by".
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  #3  
Old 04-01-2005, 03:35 PM
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when you remove the oil filler cap when it is idling, how much gases come out of the opening? raise idle by moving throttle linkage by hand - does it increase much? Will it cause the oil cap to blow off if you put it on loose?
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Old 04-01-2005, 04:44 PM
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If he says the turbo needs to be replaced look into having it rebuilt. I had mine done at www.forcedperformance.net

it'll be A LOT cheaper than $1800
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  #5  
Old 04-01-2005, 06:11 PM
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Quote:
He says it'll fail eventually, but couldn't say when.
It will fail when you can't keep oil in it which should be awhile longer. It is a costly job if you have to pay someone to do it but you have to ask yourself is it worth it. How long have you known your mechanic? You may want to get a second opinion on it. You can rebuild these engines and have blow by the minute you start it up. This trait is inherent in diesel engines.

Want to sell it with it's known problem?
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Old 04-01-2005, 06:14 PM
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I have heard so much blowby fear from folks then watched their cars run for years with no problems....
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  #7  
Old 04-01-2005, 06:31 PM
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Not to be the bearer of bad news but unfortunately the increased blowby is likely a product of a slightly bent connecting rod in cylinder #1. The connecting rod that attaches the piston to the crankshaft can get very slightly bent and wear the cylinder bore a bit oblong thus allowing a steadily increasing amount of oil to get past the piston rings. For some reason, and there are lots of theories but no real certainty why, this is a common problem for your model engine and there isn't a cheap fix. Engatwork is right that the solution may be to drive it until you can't keep oil in it. Try not to rev it any more than you need to and I think your mechanic is right that extended drives will make it wear out faster. You can probably figure that you have a certain number of limited hours left on that engine. Use them wisely.
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  #8  
Old 04-01-2005, 07:46 PM
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Question Leak or what

In the original post it was described as a "leak". Is it truly a leak, or is the engine consuming oil. Does it pee and mark it's spot with oil, or is it billowing from the tail pipe? If the turbo seals are leaking, a rebuild would be in order. I am with engatwork, get a second opinion. If blow by is substantial, would it not create a "runaway" situation and just destroy itself? Keep us posted, a leak is a pita, but fixable. A total engine rebuild is costly even if you do it yourself.
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  #9  
Old 04-01-2005, 08:23 PM
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About $10k+/-. Sounds like a rod bender going south.

I would replace the turbo, you should be able to get one for about $1,200 less then he quoted. I am pretty sure I have seen rebuilds in the $600 range.
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  #10  
Old 04-01-2005, 09:06 PM
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Quote:
Originally Posted by jivadent

"MAJOR OIL LEAK AT AREA OF THE TURBO CHARGE/AIR INTAKE CRANKCASE BLOW-BY AND TURBO CHARGER SEALS APPEAR TO BE THE CAUSE"
This mechanic has identified two separate issues.

One is blowby. The compression in the engine is bypassing the rings and pressurizing the crankcase. This causes excess oil to be pushed into the breather hose and then burnt by the engine.

The second is turbocharger seals. The oil leaks from the turbo and it enters the engine and is burned there. Or it leaks into the exhaust and smoke off.

It's not so simple to distinguish between these two cases so he just calls out both of them. It is probably not both of them, but is likely to be one of them.

With the history of the 3.5 L engine, most of us would believe that the problem is caused by a bent connecting rod which ovalizes the cylinder and causes massive oil consumption.

If the oil consumption increases to 1 quart every 250 miles or less, then you can be fairly well convinced that this is the issue. A turbocharger is unlikely to leak this amount of oil.

It's a very expensive proposition to repair this problem as it requires a complete rebuild of the engine.

Sorry for the bad news.
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  #11  
Old 04-01-2005, 09:48 PM
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On the blow by issue, did he give you an actual reading ? The amount of crankcase pressure will give you an idea of how long you have left. If you only have 2" - 3" of blow by, it can make a decent mess, but will not be substantial power loss or signify near death of the engine. On the other hand if it is too much higher.....

I'd be more concerned about the turbo. Long idle time will kill your turbo quicker then higher engine speeds. The center shaft of the turbo floats on oil pressure. The lower the oil pressure the higher the risk of leakage and turbo failure from shaft wobble.
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  #12  
Old 04-01-2005, 10:34 PM
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First, I want to thank you all for the substantial number of responses, all of which are helpful too.

Second, the rod-bending problem. I bought the car in August of '04, and I found out about the rod-bending then, while I was researching it. However, I came to the conclusion that the percentage of cars that have this problem is highly exaggerated. For one thing, there were only a handful of documented cases on the net, which, if it were such a big problem (I heard people saying it was like 50% of them develop it), there would be a lot more cases. For another, I asked my mechanic about it, who had heard of the problem, but had never encountered it, and he's dealt with around 50 350s. He also laughed when I told him about the 50% failure rate, and said MB would've done a recall ages ago if that was the case. So, I bought it knowing that there's a slight possibility of rod-bending. I got a good price on it, and the car is in almost mint condition, and as much a pleasure to drive as any car I've been in.

The mechanic I mentioned in the previous paragraph was my mechanic in Gainesville. When I moved here, I had to find a new one, and this guy, whose mechanic-speak I asked you guys to translate, is my new one (Sarasota mechanic). The Gainesville mechanic was hands-down the best one I've ever come across. Professional, knowledgeable, and only deals with MBs. Sarasota mechanic deals with German cars, and after this first, and probably last, dealing with him, he doesn't rank too high on my list. However, he did seem like he was knowledgeable. We talked about the rod-bending issue, and he told me he's only seen it once, and get this, it was in an '87 300SD! Not a 350. And it happened twice, because the guy got it repaired and it happened again. When he was checking for the oil leak, he checked the rods out, and he said he's fairly sure they're not bent, and that my oil leak doesn't have anything to do with that issue.

Now, about the $1800 turbo. One of the reasons I didn't care for the Sarasota mechanic is because he seemed to charge more than he should (i.e., $80 for a basic oil change). The Gainesville mechanic noticed the leak when I took the car in for its initial inspection, and he said something about the turbo seals, but he had only looked at it superficially. He said he'd have to look at it further, but he gave me a ballpark figure of $600, which is what a couple of you guys have been saying. So based on that, I think I'm just gonna drive up there in the near future for a day and have him check the car out and tell me his diagnosis.

In response to individual posts,

Quote:
Originally Posted by Pete Burton
when you remove the oil filler cap when it is idling, how much gases come out of the opening? raise idle by moving throttle linkage by hand - does it increase much? Will it cause the oil cap to blow off if you put it on loose?
Some gas comes out, but it's only slightly noticeable by touch. I tried looking around for a throttle linkage (I've seen it on a couple of gas cars, but never on diesels), but I couldn't find it.

Quote:
Originally Posted by engatwork
Want to sell it with it's known problem?
This is the by far the best of the 3 MB Diesels I've had, and I think the only way I would sell it is if it was on its last breath, or if I got a ridiculously good offer.

Quote:
Originally Posted by tomm9298
In the original post it was described as a "leak". Is it truly a leak, or is the engine consuming oil. Does it pee and mark it's spot with oil, or is it billowing from the tail pipe?
The latter, but only when I floor it. Every once in a while you can definitely smell the burning oil in the cabin.

Quote:
Originally Posted by D240
On the blow by issue, did he give you an actual reading ?
No, he just said there was a good deal of it.



Thanks again for all your posts.
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  #13  
Old 04-01-2005, 10:38 PM
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Quote:
Originally Posted by Hatterasguy
About $10k+/-. Sounds like a rod bender going south.

I would replace the turbo, you should be able to get one for about $1,200 less then he quoted. I am pretty sure I have seen rebuilds in the $600 range.
$375 + shipping at Forced Performance. Check out the website they are a good bunch of folks. Since I live in the area I was able to see their shop and they have a good setup.

Does it leak a lot of oil onto the ground? Or does it just kinda drip and consume all that oil internally? Also how's the exhaust look? What color and how opaque is it? (as in does it bellow, or a light puff every once and a while)

Just because a lot of 3.5l 60x engines had bent rods doesn't mean they all have bent rods. Need to look at all the symptoms first.

-Alan
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  #14  
Old 04-03-2005, 07:56 PM
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Ok, so here's another nail in the coffin for the Sarasota mechanic. Today I'm driving, and I notice this rattling after a while. I pulled over and looked underneath the car, and there's this pan just dragging along the road on one side. I'm not sure what it is, but it's pretty big. I looked underneath the car, and apparently they forgot the put one bolt in, and so after two days of driving, the pan tore in half, and the half that wasn't bolted in is now dragging along the ground! What a great job this guy did.
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  #15  
Old 04-03-2005, 09:16 PM
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Gabriel - while you are in Gainesville take it by Continental Imports and get them to look over it. Steve Brotherton (one of the owners) is one of the members of this site and will keep you on the right track with what may be necessary.

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