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I'm in the middle of a long-planned intake + vacuum refresh on my '91 560 SEL. I knew there was a bit of coolant under the intake in the valley. After getting the intake out, there's a bit more than I thought. Or rather, it looks like a very small amount has been accumulating over a very long time. The car has 163K miles on it and generally has been well maintained over the years. What I'm most interested in: for any others that have seen this, what has the eventual culprit been? I had assumed it was failing intake gaskets, and indeed that could be it on mine. But, after looking closely, I'm not entirely sure. There could be some seeping out from the head gasket itself. There's no white smoke in the exhaust, nor signs of any oil in the coolant, nor signs of any coolant in the oil. Pics are below; you can see the coolant/sediment trail from the very edge of the driver's side intake down to the valley.

I'm also curious about what others have done "while in there." What I already am doing / have parts for is: new intake gaskets, all new vacuum lines and connections, new rubber boot + frame for the air guide, new rubber hoses (breather hoses, hoses that connect to the fuel injector air ports, and hoses that connect those things to the ICV), new rubber rings to seal intake upper / lower halves, new rubber throttle bushing, new expansion tank cap, fresh coolant. I'll also give everything a thorough cleaning. I did the fuel injectors and carriers themselves a while back, plus a rebuilt ICV.
 

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I can’t comment on if you have a leaky headgasket or not, but in my case I did. I would think about replacing the throttle position sensor while there . Its a bugger to get to after its all back together
 

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+1 on the TPS located in the throttle body assembly deep inside the intake assembly. Especially on Gen1 cars where a 3-in-1 air valve is used in place of electronic on Gen2. A must to replace while 'down there....'
 

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You're most welcome...another tip:

Not sure you know yet but.....any URO brand parts in that stash you're putting together, immediately exchange for another brand if not OEM.

Especially rubber parts...
 

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I'm in the middle of a long-planned intake + vacuum refresh on my '91 560 SEL. I knew there was a bit of coolant under the intake in the valley. After getting the intake out, there's a bit more than I thought. Or rather, it looks like a very small amount has been accumulating over a very long time. What I'm most interested in: for any others that have seen this, what has the eventual culprit been? I had assumed it was failing intake gaskets, and indeed that could be it on mine. But, after looking closely, I'm not entirely sure.
Hey Robert,

I feel your statement: "a very small amount, over time" is the most accurate here...

To me, the 'tracks' suggest the intake gasket, though maybe another source.

Were I you, I'd go with what you are doing & the course you've set, then wait & see/monitor. Its certainly has not been a catastrophic event you relate/show.

One can always go deeper later if needed.

Cheers man!

MBL


Oh gosh, In addition, I encourage what you've done already: Clean that shmutz offa there! :))
 

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I would not rule out the possibility that someone cleaned the engine with a degreaser and you are seeing remnants of that chemical. Mike
 

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Well I was going to keep quiet since its a huge job, but I would hedge my bets a little and check the compression rate on the cylinders. In my case there was a bad headgasket between cylinders 7&8. You could have the same thing and while it won’t positively rule out a leak from there it will give you more info. If the cylinders are low you have to go farther I am afraid.
 

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Robert, when hou get that TPS, read the thread on adjusting it. Its an on off switch really and not a potentiometer. Its adjustment does affect your idle if not correct.
 

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7/8 have been oil weepers over time, may have some coolant as well.
 

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Well I was going to keep quiet since its a huge job, but I would hedge my bets a little and check the compression rate on the cylinders. In my case there was a bad headgasket between cylinders 7&8. You could have the same thing and while it won’t positively rule out a leak from there it will give you more info. If the cylinders are low you have to go farther I am afraid.
Headgasket failure on cylinder #8 killed the original engine in my car.
 

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Thanks everyone for the replies - ALL helpful. I appreciate the support. A few replies of my own below - feedback welcome on any of it, especially if I'm off course. And a few recent pics to show progress... So satisfying cleaning / renewing beautiful pieces like the intake and the fuel distributor! Yay for new vacuum bits.

Does anyone have the proper torque spec for the intake bolts? I'm not seeing that in the service manual.

Robert, when hou get that TPS, read the thread on adjusting it. Its an on off switch really and not a potentiometer. Its adjustment does affect your idle if not correct.
Yes, indeed. I'll search later this morning when I have time, but if you recall the thread title by chance, please pass along. What I did last night after getting the TPS (locally) is follow the testing procedure in the service manual (07.3.0712-152/1). I think the design is this: The full throttle signal (0 ohms between pins 2 and 3) should happen RIGHT AT the physical full throttle stop, anything less than that physically should register infinite resistance. The idle signal (0 ohms between pins 2 and 1) should happen AT the physical idle stop AND continue for 0.2mm of movement - i.e. you should continue to get that idle signal with just a bit of movement past the physical idle stop. I played with the mounting of the TPS in the throttle body to get what I just described. Definitely want to get this right before getting it back in the car!

Headgasket failure on cylinder #8 killed the original engine in my car.
OK, got it - thanks for your experience. I can't quite tell at this point.

Well I was going to keep quiet since its a huge job, but I would hedge my bets a little and check the compression rate on the cylinders. In my case there was a bad headgasket between cylinders 7&8.
OK, got it - thanks here too. I looked more closely yesterday before cleaning it up and I think there's a good chance it is indeed coming from the intake, not the head. But, can't be sure. Having figured out now how to get the intake out, as laborious as it is, it's not that crazy hard. So I'm planning to button it up and see if the slow leak goes away. A compression test is a good cheap way to look further.

I would not rule out the possibility that someone cleaned the engine with a degreaser and you are seeing remnants of that chemical. Mike
Totally possible. That said, there was still some parts of the sludge that were wet, and I've owned the car for about a year now and driven it ~8K miles. So whatever it is, it's continued to seep as I've driven it.
 

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Just closing the loop on this thread... After a bunch of cleaning in the valley and where the intake mounts, I got the refreshed intake + air guide + fuel distributor back in the car. Vacuum lines + hardware all replaced too. The car is running well and the valley, for now, is dry. I've got a cheap USB endoscope that I can use to have a look down there and see if it stays dry over time. The more I looked at it, the more I wondered actually if the coolant fitting at the driver's side rear of the engine was the culprit. Part of the trail definitely came from there. Really hard to tell for sure. If I get a definitive answer eventually, I'll circle back. Thanks again for the help!
 
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