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98 E320
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Discussion Starter · #1 ·
Hi all,

I just found out that there is the oil leak from the star shaped bolt which is located under the alternator (I guess) on the driver side. I can see the oil seeping out of the bolt very slowly. Please see the attached picture.
The bolt is at the right size of the picture.

What's the bolt used for? Can I just buy the replacement bolt from the dealer and replace it? It seems that the bolt holds the alternator (is it?) in the place and I don't understand why the oil came out from it.

Need information from you guys and girls. Thanks for your help.

Steve
 

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1997 E320, 1997 S320
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2,946 Posts
i might be wrong from looking at the pic, but looks to me like your tranny cooling line is leaking fluid. if you wipe it with a white paper, is it red? if so buy new cooling lines and replace both even if only one is leaking, they are cheap.
 

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98 E320
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Discussion Starter · #3 ·
Hi,

It's the oil not the transmission fluid. The size of the bolt is E14. Should oil even come out from the bolt? Somebody told me it's the A/C compressor. Should oil even been in there at all? It seems that I can easily unscrew the bolt and if I do that, will all the oil been drained?

Thanks.

Steve
 

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1997 E320, 1997 S320
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I just found out that there is the oil leak from the star shaped bolt which is located under the alternator (I guess) on the driver side. I can see the oil seeping out of the bolt very slowly. Please see the attached picture.
The bolt is at the right size of the picture.
i don't think that is your alternator, but it is actually the ac compressor. i am attaching a picture of the compressor which looks exactly like the one you have in the picture. so the oil leaking must be compressor oil. i would just tighten the bolt a little more, than clean the area good with some brake cleaner and monitor to see if leak persists. also you might want to have an ac specialist make sure you don't need to add more compressor oil, not sure what consequences are if you ran compressor with very low oil but probably not good.
 

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'01-E320 & 02-ST2
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JFFR it's helpful when posting a pic to isolate part of it in some way so it's easir to figure out. Free software is available, like paint.net.

I've attached your pic with a large black circle around what you seem to be describing. If it's from that bolt, it's impossible. That simply screws into the block. Thus, if that bolt is the source, it's more likely that the leak is above it, and there is known leak area above it (the oil port behind the diamond shaped cover). Now if there is no oil above the compressor, there are other possibilities. But realize that the cooler line right there could be pumping fluid out the top, and degraded ATF is black/gray, looks and feels just like motor oil. That is also a known leak area.

More diagnosis is always a good thing. :thumbsup: But there is no oil supply behind the bolt I circled.

Good luck.



Edit: if it's the bolt holding the tranny cooler line, that is exactly where the leak is, not the bolt but that fitting. It's just pushing fluid up and you can't see that from the perspective.
 

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99 E430, 01 E430 Sport, 00 SL500
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According to gregs210, the oil can be leaking from above or it's shot up from the cooler line's fitting. I suggest
Clean the oil on the bolt, wrap the cooler line's fitting with some aluminum foil, drive the car.
If the bolt got oil after the drive, the leak is from above. If not, it's the fitting that leaked.
And what's on the belt?
 

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1997 E320, 1997 S320
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And what's on the belt?
ac compressor (see above post #5). it's either compressor oil leaking from compressor, tranny fluid leaking from cooling line, or both. op needs to clean the area good with some brake cleaner and monitor where leak is coming from, also tighten the bolt op mentions it's leaking.
 

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'04 G55 '80 280GE '99 S420 '98 E320 2011 E350 2016 GLA250
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Had the same exact scenario.. "Why would oil be dripping out of the fastening bolt of the A/C compressor?? Does the bolt somehow have a connection with the block??"

Come to find out, the engine oil was leaking from a timing case cover gasket Waaaaaaaaaaaaaaay in the heck away from this bolt you are looking at.

It's amazing how far oil can travel within an engine bay, then poke it's ugly head out in the oddest places.

So, what you need to do is spray the whole area with a cleaner of your choice (Simple Green, Marine Clean, Brake Cleaner, etc), and look with your eagle eye to see where it's originating....

Report back..

G
 

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98 E320
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Discussion Starter · #10 ·
Hi guys,

Mystery is solved. You guys are awesome. I did exactly what you told me. I sprayed the brake cleaner above the AC compressor so I will know if the oil comes down from the top. Then I removed the star shape bolts (size E14) that holds the compressor and not suprising, no oil came out. I started the engine and the oil started to leak but not from the inside of the bolt hole that was exposed. It was from the right side of the bolt. On the right side is the edge of the oil pan and the oil traveled from the bottom of the oil pan to the edge of the bolt and made it look like it was leaking from the bolt. Very interesting.
I double checked and there was no sign of leaking above the compressor. The brake cleaner did a wonderful job.

Next step, I'll need to re-seal the oil pan gasket, Hope it's not too bad.
This site is the best. I appreciate your helps.

Steve
 

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98 E320
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24 Posts
Discussion Starter · #11 ·
Sorry that I need to bring ths thread alive again. It's so difficult to diagnose the oil leak. After crawling under the E320 for a few days, I found that I was wrong and the leak was probably not coming from the oil pan.
I looked very carefully and coudn't see the oil coming from the seal of the oil pan. It's strange that it will always take around 10 seconds to see the oli leaking so the oil must travel from somewhere.

I checked the area around the A/C compressor and it's still clean. I cleaned all the area around the compressor using the brake cleaner before.

What area above the oil pan could be the source of the leaking?
Thanks for your help.

Steve
 

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1922 Ford T no OBD, no ECU, no SCN
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37,842 Posts
Don't we already have exact topic by a member who had PS pump leak couple years ago?
Tracking small leaks between engine attachments can be a nightmare, so here is what I do.
1 Wash whole, warm engine with water under good pressure. I spray whole diesels, but on gasoline engines cover spark plugs and coils
2. wipe off any gunk you see in the area you are testing (would not hurt to do it on whole engine anyway)
3. take the car for a drive around the block and check if you can pinpoint the leak. If no leak visible, take the car for longer drive.
In the case of very hard to pinpoint leaks -stuffing paper towels in the area is a good method.
Timing is crucial on the job. If you recheck the towels after 2000 miles it might be too late.
BTW I didn't mention about checking all fluids levels assuming I don't have to on this forum?
 

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99 E430, 01 E430 Sport, 00 SL500
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There's some fluorescent dye that you can add to oil then shine a UV light to track the leak. Don't get the dye that comes with sealant.
Clean the engine first with engine degreaser, spray below the spark plug wells only then rinse with water. Be careful not to get water in the spark plug well. Follow the direction on the can or bottle.
 

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2001 SLK 320(222K Miles), 2002 E320 Special Edition(186K Miles)
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3,472 Posts
Or sprinkle the whole area with baby talc. It's messy, but it tends to show clear flow lines of the oil.
 

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2003 Mercedes S430
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806 Posts
There is no need to put dye in engine oil. If you can't see the black oil, then the dye isn't going to help.
 

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98 E320
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24 Posts
Discussion Starter · #16 ·
You are right. Even I add the dye to the oil, it won't help me much. The problem is that I can't see what's behind the A/C compressor. I mean not directly above the compressor but 45 degree angle on the right side of the compressor. The compressor blocked the side view. I can see the oil dripping slowly from the bolt even the engine is just idling. I can see everything directly above the compressor and there was no leak at all directly above the compressor.

Is the oil pan still possible the source of the leak? I think in order to find out where the leak is from, I need to remove the compressor.

Thanks.

Steve
 

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2001 E320 - Brilliant Silver/Ash: 107,000+
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17,193 Posts
It's a lot of oil leak. May be 30 drops per minute. I can't drive the car at all. Thanks.
Ouch! I have one too but it is minor because I have driven at least 2000 miles since I had to add a quart. But I have been trusting the car's oil measurement sensor recently. I need to pull the dipstick and see what that indicates. I planned to do that today but it got dark before I could get around to it. I don't see any drops but I figure those must be caught by the under belly engine pan.
 
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