I am no OM603 expert but know enough to be dangerous. My experience are:

1) don't throw new parts at it unless you know the root cause. It may mask the symptoms.

2) make sure coolant is ok. No air in cooling system. Run car to temperature or whatever you feel comfortable with but making sure the system is pressurized. Then do a hose squeeze test next morning. The hose should be soft and NO pressure in system. Assuming the system is air tight. If it is still pressurized then the head likely is breached.

3) gas in coolant test: cold engine first. Fill radiator to the brim or close to it. Start engine and check coolant level. If level rises and overflow or bubbles coming out then head is likely breached.

Good luck.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Thanks for the input. I've got a leak down test kit coming today, which should give some intel.

I did the hose test last night/today and the top radiator hose did not feel pressurized. There was a brief air surge when I cracked the expansion tank cap however, so that might be gasses in the coolant.

Any other ways to identify air gaps in the coolant?

Leak down test is mainly for piston ring, health of cylinder. It is not going to tell a breached head. The head leak is too minute.

Do the fill up test. That is all I can offer.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Here's a video of it idling. Looks like the head may be leaking exhaust gasses...

https://youtube.com/shorts/kLKTljkOVRA?feature=share

Yup

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10

Would a cracked head lower compression? Cyl 2 and 3 only have 250psi, whereas the others have 350psi.

I'm now feeling torn between finding a whole new engine, vs swapping heads.

I would see what is out there in complete engine land. You do want to find another engine with a better head than the #14 though.

That engine has probably experienced a serious overheating before as well. Warpage of the head alone is not really repairable on these engines. I am thinking cheapest approach to a satisfactory conclusion.

I live in rust belt land. A body check is needed to establish the extent of the rust before more money is spent.

If nothing else I know what serious rusting versus relative minor rusting looks like. What you are seeing may be far less than what is present rust wise. Probing until you reach back to solid metal is the test.

I would probably save dollars by going the complete engine route myself. Finding a high number head already on a good engine. I prefer to find an engine still in a car with perhaps accident damage. I will not buy or pull an engine without establishing the condition of it first.

Of course there is no way to be positive. Yet the chances of that head just being scrap metal now is fairly high. In my estimation.

I suspected breech between the two cylinders head gasket perhaps from head warpage. As well as whatever the original issue was. Not cracked head for that issue.

X2

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10

Ok, so you'd think in this scenario, a new head gasket, or head rework, would restore compression in these two low cylinders?

Dissertation? Much ado about nothing.

Let me give you some honest advice from my experience. If the engine fires up in cold with 1 glow, 1 or 2 spin, then the compression is 'good' to run. 250psi is not bad for a cold engine. If 2 cylinders are breached then the engine might not run smoothly at idle or at speed. Or might smoke. Same psi may just be a coincidence.

I looked at the video and I think the head is done for. You have 3 ways to fix it, listed in the order of expenses.

1) use blue devil sealant. I have good result. Some purists here would frown on it but it is not their car. Follow the instructions to the letter and it will seal the head, hopefully for good. I got over 20k from it for little $.

2) change the head. #14 head is okay. I wouldn't spend the effort or money for a #17 or higher head unless it fell from back of a lorry.

3) new or used engine. It has to be a proven engine. Too much labor to put in a dud one.

Good luck, PM me if you want more info.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

That car is so rusty that I would think twice about putting too much effort into it, especially in Northern California where there are still good ones around. I live in the bay area and bought and resold multiple #17 and #22 heads from Pick n Pull in the last few years, so with some effort and luck you can get them for under $200 if you want to do that. They are a bit of work to pull, even after pulling 6 of them it's still a 4 hour job for me to get one off with hand tools.

I second the blue devil sealant on an engine thats teetering on becoming scrap.

Thanks for the advice everyone! Let's say I use Blue Devil, but it doesn't fix the problem. Could it cause any issues with the block, if I try to replace the head afterward?

Yes the pictured rust is quite ugly...but it seems to be localized to the areas shown. Everywhere else under the car is surprisingly clean. Hopefully getting the car running will be straight forward, and then I can start on rust cleanup! It seems like the best bet would be to chop up a junkyard w124 for replacement spots.

Almost no tolerance for surface metal removal if warpage exists. On those heads.

A little history perhaps. The early 603 3 liter engines had an excellent lower block. The problematic head caused the engine to be withdrawn from production for a few years. Then they over bored the block to 3.5 liter and put a very refined head on it to release that engine again. The heads where great but the 3.5 lower blocks had major issues.

So that engine was withdrawn as well. Yet a 3 liter block with the 3.5 head is an excellent almost bulletproof engine. My guess and it is only a guess is the better 3.5 liter heads may be easier to source now than they have been for some time. As I suspect demand is down.

To add to the general misery it is felt that the # 14 head does not like to be overheated much.