I recently purchased a used OM603 head via ebay (with the help of gsxr). It was advertised as "excellent working condition." The casting number had been ground off (strangely enough), but the oil and coolant passages suggest it is a #22 head. I received the head yesterday and plan to take it to a shop to have it inspected for cracks and have its flatness measured. I will share those results as they come available. But upon arrival, there is a significant other concern which has come up.

The head has major erosion at locations where it meets coolant passages in the block. Some of the erosion is deep, but narrow. I measured one to be 0.12" deep (1/8"). Some of the erosion is wide, but shallow. Some are stained green, so I suspect this is due to use of green coolant by the prior owner. It appears to have occurred in places where a coolant passage in the block meets the head, but does not continue into the head. I have no idea why they are designed this way. In looking at pictures of the head gaskets, it appears that they have holes at these locations, but for reasons which don't seem clear since the coolant has no where to go (but erode the aluminum near the hole).

I have attached some pictures of the problem areas. The first photo shows the general head condition. The problem areas are the oblong larger discolored areas which are vaguely triangular. The second photo zooms in on the deep, narrow damage. It is hard to tell it is even there until you see it in person. The third photo shows the widest erosion area. I think the coolant got behind the head gasket at this location, since the damage is wider here than the head gasket hole. The 4th photo shows where the erosion is closest to the cylinder. It is hard to see, but the erosion is within 0.03" of where the metal band of the head gasket used to sit.

Most of these are too deep to machine off. You can only remove 0.02" from a 603 head, so eliminating a 0.12" deep eroded spot isn't possible. What do you all think? Should I send it back (seller has a 30 day warranty, but I have to pay shipping)? Would you use this head on your car? Is there an easy fix like high temp RTV to keep any future coolant (zerex g-05 of course) from getting to these spots. If it requires welding, I am not going to bother (or risk damage to the rest of the head). Maybe with proper coolant, no more damage would occur, but who knows.

My #14 head is not showing signs of cracks, but you never know what tomorrow holds. I bought this used head to be a permanent solution. But with these erosion problems, I am not sure I will have any confidence in it. Any suggestions on how to proceed? This was a big purchase for me, so I am a little disappointed in finding this significant damage.

Attached Thumbnails

       

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

this is when you deal with paypal/ebay and the seller.

+1. You can't use a head that has erosion like that. I would also suggest there is no permanent solution, but to avoid overheating no matter which head you are running.

Good luck.

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Chief

1991 350SD

Some questions. Was the head billed as "the good number" head or generic? Are you into the head for low money? You might not need to pay return shipping, talk to the seller first. ( don't send neg feedback / start a claim until they reply.)

If you are into the head right, it is usable and would seal as is but at the limit I'd use.

To make a better fix, sand blast / glass bead the affected areas. Be sure to plug all the holes in the deck , tape off the valve cover side to keep grit out. Clean all the grit out of the eroded areas, use metal filed epoxy ( JB weld type ) to build the areas up. Lightly sand the epoxy to make it level. This does work if erosion does not extend into the fire ring ( the steel band around the head gasket. ) Some of the epoxy is trapped between the head and gasket so it can't escape, any exposed epoxy is just there for the ride.

The best fix is to weld up the areas. This isn't as big of a deal as it seems for a high end automotive machine shop.

Can select thickness head gaskets be purchased for this engine? If so the 0.002" max can be pushed farther. If not, sinking the valves / increasing the combustion chamber in the head can be a creative way to make it work.

thicker head gasket is available.

Thanks for your thoughts and suggestions. I was hoping for some sort of consensus from the forum, but so far that hasn't occurred. Additional input is appreciated.

I spent $750 on the head (included old-style straight prechambers, valves, cam holders/bearings, hydraulic lifters, and he unexpectedly threw in the valve cover). It did not come with the cam or injectors. So in one sense that is a reasonable price, but at the same time, I bought the whole car 6 months ago in quite decent condition for $2500.

I sent several emails (prior to the purchase) to the seller prior to the purchase where we discussed flatness requirements for an MB head as well as cracks. I never explicitly asked about erosion of the head surface, and he never explicitly claimed it didn't have any erosion. He said it was not warped and had no cracks. Prior to the purchase, I said as long as it can be machined less than 0.5 mm (the max) and meet MB flatness specs, I am good. But clearly it cannot meet MB flatness specs with small erosion holes.

The seller has perfect ratings on ebay and I still assume he didn't mislead me intentionally. He may have simply not noticed the damage or perhaps subconsciously chose to not see them. He never cleaned the head, so maybe he never really inspected it much. He did NOT make any claims about the casting number. He openly admitted that he had no way to know which casting it is.

According to the FSM, you can remove at most 0.5 mm from this head (0.02"). I will have to look into whether that is already accounting for thicker head gaskets. Thanks for that suggestion.

I suspect something like JB weld to fill the holes would end up being okay, but doing such an expensive repair and having to rely on JB weld is a bit disappointing.

Thanks again for the suggestions. I really want this to work out.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Based on the original photos, it's definitely a #22 head, no question on that.

The erosion is a little worrisome, however I'm not entirely clear on where the erosion is in relation to the cylinders. The fourth photo shows a section fairly close, but if that area isn't deep, it may not be an issue. If the immediate area around most of the cylinders is good, it should seal combustion pressure properly, which is the main concern.

Worst case, if you did have leakage near the erosion points, where would the coolant go? Probably outside the block (for most of them), right? There are only a couple points on the head gasket where oil passes through so that is not likely to be an issue, unless there is erosion near the front pressurized oil passages, which would definitely cause more concern.

I think the options are:

1) Send it back
2) Use it as-is
3) Ask the machine shop if they can weld material at the erosion areas, and mill it flat
4) Check into sealants in small amounts at the suspect areas (Right Stuff, or Hylomar?)

I'd probably start by taking it to a competent (!) machine shop for a professional opinion. And to verify it's flat within spec. If it's not flat, then you have an easy decision - send it back.

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I know folks will get all warm and queasy at the thought, but corrosion pits are routinely filled with JB Weld over in the VW community on their Vanagon WBX heads. I'm talking about pits around the entire perimeter of the sealing surface. I found a few similar corrosion pits on the first #14 head I pulled, and had I not of replaced it with a new #22, it would've gotten the JB Weld treatment. On this one, I'd either pay to have the pits TIG'd or JB Weld and coat the gasket with Hylomar

My concern is what caused that corrosion. It could be yucky coolant, it could be overheating, it was probably both. Have you checked that the head is flat within spec? Is there corrosion in the coolant passages inside the head?

Sixto
87 300D

Thanks everyone for the additional input. I am waiting on getting a puller to remove the prechambers, and then I plan to take it to a local shop to have its flatness checked. I will post again about that.

I looked into the epoxy idea a lot yesterday. JB Weld is steel filled, so its coefficient of thermal expansion will not be similar to the aluminum head. There are aluminum filled epoxies out there, but most of those are not intended for exposure to water. If you buy epoxy intended to water exposure, it is not designed for high enough temps. I found a lot of folks online using epoxies for head repair, but not many people using epoxies where they are exposed to water/coolant. So complicates things slightly.

Welding is interesting because it is either 1) the absolute correct answer or 2) the worst solution because you will warp the head. I have welded a steel bike frame together and lots of fun blowing holes through the thin tubes and then having to fill them up again. Compared to thin bike tubing, welding on a massive aluminum head doesn't seem too bad. But I am not ready to tackle this myself and wouldn't really trust anyone locally to do this. If the head truly requires welding, I will send it back.

Sixto- there is not any noticeable erosion in the coolant passages. It is odd to me that the problem occurred only where the coolant hit these dead-end passages. Maybe someone did a citric acid flush and didn't rinse it out well. If the citric acid got between the head gasket and head, it could have been munching away there for ages, long after the rest of the car was getting normal coolant. If my new head gasket didn't have a hole at this location, I think my problem would be solved. But the gaskets all appear to have holes, even though the coolant has no-where to go.

Auspumpen-Could you clarify regarding the hylomar? Did you mean this hylomar spray?
HYLOMAR Polyurethane Sealant, Aerosol, 20 ml, Blue - Sealants - 13P428|HUBRA01 - Grainger Industrial Supply
I have not used any of they hylomar products, so when someone says hylomar, I don't exactly know which product they mean.

Thanks again everyone. It will probably take a week, but I will post again with the flatness measurements.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

I can't wait a week for this story to unfold! Use any old straight edge to measure the head with the valves and prechambers installed since you're looking for severe warpage.

Sixto
87 300D

Check straightedge trueness by placing two together and look for lack of light (hint go to home depot and pick out a good aluminum yardstick). Use feeler gauges between straightedge and head to measure warpage.

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BTW, I like the possibility that the PO poured Simple Green full strength into the cooling system to clean out stubborn oil from the head gasket failure that led to replacing the head.

A Rube Goldberg way around the corrosion spots is to etch a channel around the corroded sites and embed a copper filament. The filament will press into the head gasket to ensure a seal around the corrosion site without need for treating the head directly.

The question I have about however you deal with the corrosion is whether the corrosion is neutralized as things are. If not, will welding or sealing neutralize or at least isolate the corrosion?

Sixto
87 300D

My guess those triangular dead headed coolant passages are there for some thermal design reasons. Those erosion areas are not in any critical part of the head (i.e sealing against coolant or oil or combustion) and should not be a concern IMO except for pic 4 where it is close the cylinder. I would let the machine shop check it out and make sure they do a pressure test.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Check it against the head gasket, are the HG openings the same size as teh corrosion spots?

Assuming a known good #22 can go for what, $1,500?
I would:
Sand the corroded spots
-(quickly and carefully) clean/ strip them with diluted lye
-Rinse with distilled water
-Braze them to build up material(immediately after stripping with lye)

Then let the machine shop skim the head flat. The brazing can be done with a MAPP gas torch and some "white metal rod" from your local welding house. be sure to practice on some scrap aluminum, it's a little tricky at first.

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