Possible/Probably Head Problems - PeachParts Mercedes-Benz Forum

thebenstenator · #1 09-21-2011, 04:01 PM

So, I have a 1992 300D. Here's a bit of the story. A little over two years ago I started having overheating issues with my car. It was getting way too hot and going through a lot of coolant. After many trial and error tests one day I went out to it and it was water-locked. Which means, head/head gasket issues, right? Yeah, and thus started the long process of taking off the head and replacing everything. We took the head in to a machine shop who planed, cleaned and inspected it, got it to good-as-new condition.
At this same time I was preparing to leave the country for two years and would leave the car with my dad to take care of and drive every now and then. So we were putting the head back on, following very closely every detailed instruction that we had (we had some sort of step by step print off thing, maybe I still do). We got it back on smoothely and everything and then came the time for me to leave, and I left, leaving my almost-ready-to-run car with my dad. He soon got it running and started driving it about once per week, just to keep it nice enough for me to come back to.

This worked for about 8-10 months, then. . . he went out one day to find that it had no electrical power to anything. The next months included many tests and failures to find the problem. After many months of the car sitting he was able to tow it to a mechanic who found out that the positive cable had been grounded and this was the cause of the electrical issue. They also did a pressure test on the coolant system and found no problem, BUT, they think that the head is cracked or the head gasket is blown (bran new) because it's still losing coolant.
So I've a few questions. Would a car still pass a pressure test if the head was cracked or the head gasket was blown?
What can I do, without taking the head off, to know for sure if it's cracked/gasket blown?
Could the head have been cracked the first time I took it off and the machine shop just did not detect it?
Is there anything that we could've done wrong in the re-application of the head gasket or head that would've simply misplaced the gasket or worse, cracked the head?

Any help would be great. Right now I'm re-looking at the option of re-tearing apart my car, or if worse comes to worse groancoughsellingitforpartscoughgroan, or something to that effect. I just want to be sure before I make a decision.

Thanks

piccolovic · #2 09-21-2011, 04:58 PM

Time to check the freeze plugs, which usually on the manifold side of the head. You may have to remove the manifold and visually inspect them. It should be easy to see if there's a problem. If such is the case (usually a couple of pin-hole rust areas), replace all of them at the same time . . . and CHECK TO MAKE SURE YOU HAVE A GOOD GROUNDING STRAP!!!! Usually a faulty/no ground strap is the reason for freeze plugs to rust through.

dieseldiehard · #3 09-21-2011, 05:07 PM

Sorry to hear your work didn't last.
Early OM603 engines with the infamous #14 series heads were prone to cracking and several iterations were done until MB got a reliable fix.
OM602 heads included things learned from the 86-87 engines and they are not known to have a latent weakness like the 603. Its possible a crack may form in any aluminum head if it is overheated. Another problem is warping, if really warped its suggested the head be replaced, as planing the head will fix it for a while but there are cases of the metal warping again and aluminum alloy gets annealed after having been overheated and that lowers its reliability.
You may just need a new headgasket but the only way to find out is to remove the head and inspect, and have it pressure checked and dimensionally checked.
DDH
PS did the previous work include a welded repair of a crack? if so that's your problem

dieseldiehard · #4 09-21-2011, 05:25 PM

Quote:

Originally Posted by thebenstenator

So I've a few questions. Would a car still pass a pressure test if the head was cracked or the head gasket was blown?
Thanks

If you mean a radiator static pressure check on the engine in the car the answer would be - yes it most likely would pass that test with a cracked head but it would probably fail if the gasket is leaking.
The only good test for a head crack on aluminum heads is using a special fixture clamped against the head to simulate pressures the head is subject to during combustion. Iron heads can be checked using a manaflux test. After cleaning them, aluminum heads will usually show a crack especially if it has started to travel it will be clearly visible, especially if located between valves.