oil in coolant - PeachParts Mercedes-Benz Forum

benz350sdl · #1 12-08-2003, 12:42 AM

i recently overheated my 350sdl, and my 1st thought was a thermostat. when i opened the hood i noticed jelled oil oozed out of the top of the radiator seam. i looked in the coolant resevoir and there was jelled oil in there. But the oil looks fine, no coolant mixed in the oil or oilpan. So now i'm thinking headgasket. My freind pulled the head off and the head gasket looks fine. i sent the head out to be checked for warping or cracking. so far its not warped so bad, only 4-5 thousanths (not enough for a head gasket. they are checking for cracks in head tomorrow. pistons all come to top , flush. and cyl.'s are not out of round.

Has anyone else ran into this where oil is in the coolant system BUT NO coolant in the oil system?

BoostnBenz · #2 12-08-2003, 12:50 AM

The original aluminum heads on diesels were known to crack if overheated. One symptom was that overnight you could take the overflow cap off and it'd still have pressure. I would think that the oil is in the coolant, but no coolant in the oil because oil is under much higher pressure. You'll soon know the answer, good luck. There is a better design head out there which isn't supposed to crack like that. It probably was your thermostat that started it then, but this is a byproduct of what happened.

sixto · #3 12-08-2003, 01:49 AM

AFAIK, the 603.970 (350 SD/L) head is the later/latest design which is much less susceptible to cracks. Steve B. recently described in the tech forum (and someone posted the link in the Diesel forum) some inherent flaws with 60x heads that causes oil to leak into the #1 cylinder. Later head designs addressed this flaw as shown in Dave M's photos in the same thread.

Oil in the coolant is probably not cracks in the head since the cracks occur in the combustion chamber where there are no pressurized oil passages, only coolant passages. I don't fuly subscribe to the thought that overheating causes the cracks since the cracks cause overheating by putting too much pressure in the cooling system. It's still a chicken or the egg thing to me.

If you have a chance, share with us the part number of the head. I believe the 350s came with the -17- head and the latest design is the -22- head.

Sixto
95 S420
87 300SDL
83 300SD ... $950, see cars forum

gsxr · #4 12-08-2003, 04:09 PM

Sixto is correctamundo. And yes it is common for the OM603 head and/or gasket to fail with oil in coolant, but NO coolant in the oil. I'm not surprised to hear that at all. The head may be OK, if so you are quite lucky - a used head is ~$1000 if you can find one, new is $1600-$2000 depending on the source.

Note: If the head is "decked" to level it, you MUST measure the protrusion of the prechambers!! There is a very, very tight spec for that. If you shave the head they may protrude too far. MB sells precision shims in various thicknesses to "pull" the prechambers up into spec. The procedure is in the factory service manual.

HTH,

toknow · #5 12-08-2003, 06:33 PM

Quote:

Originally posted by BoostnBenz
The original aluminum heads on diesels were known to crack if overheated. One symptom was that overnight you could take the overflow cap off and it'd still have pressure.

I just want to understand this better, do you mean that if you leave the car without overflow tank cap during night, and later in the morning you will not be able to squeese the upper radiator hose because of pressure??? I thought that you will not have pressure since the cap off!! so, in my car (OM603), the coolant tank is not tight enough (the cap base), and there is no visible pressure in hoses, does this mean that there is still a possiblity for a crack in the head, there is no other symptoms. Can somebody explain this more?

gsxr · #6 12-08-2003, 06:45 PM

The Unabridged Unofficial OM603 Crack Test (UUOCT) goes as follows:

1- When cold, release any pressure by removing the cap & re-installing it.
2- Drive the car hard for a day or two, do some full throttle runs to the redline.
3- Let the car sit overnight (8-10 hours minimum)
4- In the morning, with the car stone cold, squeeze the upper radiator hose
5- If the hose is soft & squishy, or under vacuum, the head is *probably* fine
6- If the hose is so tight (under high pressure) you can possibly pinch it together with your fingers (like you can with the cap OFF), it's highly likely the head has a crack - even if there is no oil in coolant or vice-versa.

NOTE: This assumes a good cooling system with no leaks, no coolant loss, and a properly functioning radiator cap. This only applies to the OM60x engines with aluminum head, particularly the OM603 six-cylinder, which had weak heads in 1986/87.

If the car has the high pressure syndrome, eventually it will blow out the water pump seals, even if there are still no other symptoms. Trust me - BT, DT on two different engines. If left long enough (or you just keep fixing water pumps), eventually the crack will get worse and you'll get a worse symptom - oil & coolant mixing, rapidly fluctuating high operating temps, internal coolant loss, and eventually hydrolocking.

Does that help?

psfred · #7 12-08-2003, 06:47 PM

If you overheated it, expect at least a head gasket, possibly a cracked head as well. Even the new design is prone to cracking when overheated. Warps, too.

Peter

toknow · #8 12-08-2003, 07:01 PM

Thanks for the valuable information!!
Another theory, if the car has high miles (i.e. >150k), does this makes the engine easier on the head? I heard about original engines (OM603) with more than 400k!! On other words, when engine gets old and compression is less, and expansion factors between alum & iron settled, does this make it safe for the head to continue without cracking (No overheating)?
thanks,

gsxr · #9 12-08-2003, 07:12 PM

I don't think so. The older it gets, with more miles, the more likely the cooling system has corrosion and therefore more likely to overheat, IMO. It is imperative that the cooling systems be flushed totally every 2-3 years, filled only with MB anti-freeze (or G-05), and get the citric acid flush if required. Watch the temp gauge like a hawk, it should be 85-95C almost all the time except when climbing a hill or idling for a long time in summer heat, and then it still should never get over 100-105C. If it does, it's cooling system repair time!

MB acknowledged the corrosion problem and requires replacement of the plastic expansion tank to a new version with a silica gel pack installed. Engines from 1993 (?) and up have this already, but older engines need it. Besides, if your plastic tank is 10 years old, it needs replacing anyway - both of my cars had hidden cracks that I didn't see until I removed it. Details & part numbers are on the last page of this PDF file:

http://www.meimann.com/docs/mercedes/Citric_acid_flush.pdf

HTH,

benz350sdl · #10 12-08-2003, 11:26 PM

Well ,I found out today the head has no cracks in it and is not warped. I don't know if this is a good thing or a bad thing. I'm still not sure how the oil got into the coolant, beacause the headgasket looked good . Now i'm worried the block could be cracked

.if i knew that the block isn't cracked now would be a great time to replace timing chain, rebuild vac pump and have a valve job done. But why should i do all of that if the block is cracked.

BoostnBenz · #11 12-08-2003, 11:30 PM

How far overheated did it get? I would imagine it'd take a LOT of heat to do that to the block.

benz350sdl · #12 12-08-2003, 11:37 PM

guage went into the the red. there was jelled oil in the rad. the resevoir all the cooling system. the oil was jelly like, not milky. And NO coolant in the oil

#13 12-09-2003, 12:10 AM

The head gasket does not have to have a visual flaw to be bad. As you have oil mixed with the coolant, it's a gurantee that the gasket failed if the head checked out fine.