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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #1
As the title suggests, I’ve got my M117.968 engine block exposed.

My intake manifold is soaking in a degreaser/water solution, my heads are at the machine shop getting hot-tanked and inspected, and I’m in my garage with a very nasty engine block and I want it clean.

I'm planning on pulling the water pump so as to be able to use my garden hose to pass a continuous stream of water and chemicals through the coolant passages, but that’s about the only bright idea I’ve had for cleaning out the coolant passages.

I’m particularly concerned about the coolant passages because they’re coated in the dreaded mayonnaise-like oil/water crap often read about on this forum.

My other concern is safely cleaning the cylinder head mating surface on the engine block, it’s got the normal stains and nastiness from having a head gasket pressed against it for 29 years.

Any of you who have successfully cleaned these surfaces in the past, please share your tips, particularly unsafe and potentially damaging practices to avoid! I’d really appreciate it.

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1988 560 sec
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689 Posts
Put some wd 40 soaked paper towels in the cylinder bores before you start it will catch a lot of the crap.

I use scotch brite pads to clean aluminum surfaces the abrasive is mild and wont remove any block material. If you need to scrape use a brass scraper and be cautious a slip and a ding of a cylinder bore is to be avoided. Red scotch brite is a bit more aggressive than the green and is a good place to start.

After cleaning check the block for flatness if you have an Accurate straight edge and a .001 inch feeler gauge.

Start with some brake cleaner to remove the gunk and get things loose.

Best of luck looks like you have a full plate , please post your progress.
 

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Moderator
1991 500SEC 50K mi. 1987 560SEC Now 153K mi. 2020
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4,412 Posts
In addition to the above assistance..

'Plastics my boy, Plastics' from The Graduate movie...

Old credit card, plastic tools from Harbor Freight.. there are some chemicals that will make the job easier...

My friend Mike, used an abrasive spinning pad.. I do not know which would be appropriate..

Saw this just now:

M.
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,184 Posts
Don't try flushing the cooling passages with the heads off!!!

Get a cheap 90 degree die grinder from Harbor freight and a 3M roloc disc pad and some green discs. It'll clean the block deck in seconds.
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #6
Don't try flushing the cooling passages with the heads off!!!
Are you cautioning against that method out of concern that cleaning solution would overflow into the oil passages and drain into the oil system?
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #7
Put some wd 40 soaked paper towels in the cylinder bores before you start it will catch a lot of the crap.

I use scotch brite pads to clean aluminum surfaces the abrasive is mild and wont remove any block material. If you need to scrape use a brass scraper and be cautious a slip and a ding of a cylinder bore is to be avoided. Red scotch brite is a bit more aggressive than the green and is a good place to start.

After cleaning check the block for flatness if you have an Accurate straight edge and a .001 inch feeler gauge.

Start with some brake cleaner to remove the gunk and get things loose.

Best of luck looks like you have a full plate , please post your progress.
Thank you! I've got plenty of pictures to post, I'll keep you all abreast of my progress.

Thanks everyone for your suggestions! It looks like I'll need Scotch Brite pads; I already have an assortment of scrapers at my disposal.
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #8
I only see oil residue on the top portion of the water pump interface in the timing cover.

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I’m trying to figure out where exactly the gasket failure took place here; it looks like the coolant leaving the block comes out through the top portion of the water pump, unless I’m mistaken. Does anyone know if this is a common mode of head gasket failure
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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Are you cautioning against that method out of concern that cleaning solution would overflow into the oil passages and drain into the oil system?
Yes, I don't see how you could avoid it. You've got all those cooling passages on the deck, along with the cavities for the timing chains, the pistons, etc...
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #10
Yes, I don't see how you could avoid it. You've got all those cooling passages on the deck, along with the cavities for the timing chains, the pistons, etc...
No you’re absolutely right. I just want to get this crap out of my cooling passages.

On that note, it might not be oil. This stuff is white and mayonnaise-like in some areas, but dryer and less slimy in other areas.

The biggest thing is that it doesn’t seem to respond to degreaser. This is a problem because most of the contaminated areas I can’t get a brush or a scraper into.

Add to that the fact that I don’t see a point of failure in my head gaskets, and I’m stumped as to how to proceed.

Who else has encountered this before? Could it be silica gel from the expansion tank? Mine is OE Mercedes, I replaced it about two years ago. Do those come with silica gel pouches in them? I’ve heard of those rupturing and wreaking havoc in Volkswagen products.

Here’s a close up of the block. It shows both manifestations of the contaminant. Slimy and wet, versus dry and grainy.
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Here are my head gaskets. They don’t have any points of failure that I can see. Perhaps somebody here can see a spot where oil and coolant mixed?
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1991 500SEC 50K mi. 1987 560SEC Now 153K mi. 2020
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4,412 Posts
I hear your pain.

My friend Mike, who owned & operated a Volvo Indepenet shop for decades, used dishwashing liquid to clear the oil in a cooling system. He recommended after introducing some 'Palmolive' dishwashing liquid or similar to the cooling system & driving...

Followed by several flushing road tests, it was oil-free

An idea.

M
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #12
I hear your pain.

My friend Mike, who owned & operated a Volvo Indepenet shop for decades, used dishwashing liquid to clear the oil in a cooling system. He recommended after introducing some 'Palmolive' dishwashing liquid or similar to the cooling system & driving...

Followed by several flushing road tests, it was oil-free

An idea.

M
That‘s not a bad idea, but I’m still not convinced it’s oil, given the stuff’s indifference to degreasing products.

Here’s a picture of the intake manifold coolant passage, still coated in the crap.
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I soaked the IM in a water/Simple Green solution overnight, yet this white sludge persists.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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OK, I think I just realized you pulled the heads because of the white stuff in the cooling system. Is that correct?

Try dripping some vinegar on the white stuff. If that softens it then you've got calcium deposits from the water. Put everything back together, flush the cooling system with a commercial flush that's safe for aluminum, and be happy.
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #14
OK, I think I just realized you pulled the heads because of the white stuff in the cooling system. Is that correct?

Try dripping some vinegar on the white stuff. If that softens it then you've got calcium deposits from the water. Put everything back together, flush the cooling system with a commercial flush that's safe for aluminum, and be happy.
Yes sir, that's why! Sorry if I didn't make that clear in the beginning 😅

I'll try vinegar as you suggest.

I do think the MB citric acid flush would've removed calcium deposits though. Over the three or so years I've owned this car, I've used the MB citric acid flush twice.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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I do think the MB citric acid flush would've removed calcium deposits though.
You would think so. Hope you are wrong. Either way, those deposits do not look like oil. 9 times out of 10 the coolant ends up in the oil, not vice-versa. To get oil in the coolant you need a pressurized oil passage to leak into the cooling system. In that case, the oil does not mix with the coolant; it forms a film on the top, just like when oil spills on water.

Yeah, from your original post I was thinking you were doing a valve job and discovered the deposits in the process.
 

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1991 R129 500SL
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1,805 Posts
...might you consider having your aluminum engine block and your intake manifold "hot tanked" also by the machine shop where your cylinder heads are being processed...IMHO, it would save you a lot of time but with better results.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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It's a long way from a short block installed in the engine compartment to a bare block in the hot tank (and back again). Might as well plan on a complete rebuild at that point.
 

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Premium Member
1991 560SEC
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221 Posts
Put some wd 40 soaked paper towels in the cylinder bores before you start it will catch a lot of the crap.
I think you are asking for trouble using paper towels. There is a good chance of that paper disintegrating. I just bought package of 30 microfiber towels, 16'X 20", from Walmart for $10.
 

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1991 560SEL (M117.968)
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109 Posts
Discussion Starter #20
What flush does everyone recommend for getting rid of oil residue? I know there's an MB alkaline flush, but the part number listed here and on other sites leads me to a leather cleaning agent.
 
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