om617 952 idle wobble, compression test results, oil in coolant - PeachParts Mercedes-Benz Forum

83swagwagon · #1 09-25-2017, 02:13 AM

While trying to get to the bottom of the wobbly idle issue with my 1983 300TD wagon, a seasoned mechanic told me that the wobble was likely a worn spring inside the injection pump and that it was nothing to worry about. However I was noticing harder and smokier cold and hot starts, and it seemed to make a slapping/nailing sound in sync with the wobble. I figured a diesel purge wouldn't hurt-- and sure enough it seemed to cure the hot start issues I was having as well as gain some smoothness at idle and power in general. At least temporarily. The starting began getting worse again a couple days later when we took the wagon on a 240mi road trip from LA to Sequoia/Kings Canyon NP, so I began considering springing for some Monark nozzles and a pop tester.

But first thing first, I decided to pony up for a diesel engine compression tester to assess the health of my 252,000 mi om617.

What I found was the following:

#1: 320psi
#2: 285-290psi (2 tries)

#3: 355psi

#4: 310psi
#5: 190-180psi (2 tries)

I also noticed that the injectors from cylinders 2 & 5 showed some interesting symptoms:

#2: what looked like a burn or rust mark on business-end of injector
#5: quite oily/wet, small bubbles

Finally, I decided to pop the cap off my coolant reservoir to check the level because my heater seemed to kick in and out intermittently during the trip. That's when I saw the dreaded black sludge (new!). I stuck a paper towel down for a sample and probed it with my finger (latex gloves on), and it seemed to me that it was indeed oil.

My guess is that I probably blew the head gasket going up and down the grapevine, then up and down the mountain roads in the NP. I had previously replaced the radiator about 2k miles ago and replaced some leaky coolant hoses right before the trip with no sign of oil at those times.

Given the likely $2k + bill to replace a head gasket and the uncertainty of whether the oil is coming from the head or past worn rings, I've been considering springing for a nice used 952 motor-- but am wary of committing to that without compression numbers or service history for fear of ending up with a similar result after 10k miles (or who knows how many). No motor I have seen on the market has compression numbers listed, so I would like to know if there are some reputable used engine resellers in the greater Los Angeles area that could gain me some peace of mind.

Either that or I go with a Metric Motors long block... but... $$$$

Tempted though...

I just acquired the wagon 11 months ago and have been putting a lot of work into it. Sadly this is a new issue after 4k miles of ownership and I am facing some pretty tremendous sunk cost if I cut bait, so that option is pretty much out. Plus I love owning this wagon and have wanted one since I first drove one almost 18 years ago

What would y'all do in this kind of situation?

Maxbumpo · #2 09-25-2017, 07:58 AM

Price out a decent used engine for a wagon (wagon heads are different - they integrate the hydraulic pump for the SLS) and the cost of the swap, and then compare that to the cost of the head gasket work.

Did you adjust the valves on a stone-cold engine IMMEDIATELY prior to checking the compression? If you did not do that, the compression numbers mean NOTHING.

You could perform a leak-down test to see if the low compression in #5 is escaping past the valves (which adjusting would probably fix) or the rings (which may simply be full of carbon and not sealing well because of perhaps the mis-adjusted valves which compromised the compression to the point that fuel was not fully burned).

The only things know for sure is that you need a new headgasket or have a cracked head.

In your shoes, I'd focus on the compression a bit to see if bad rings can be eliminated. I'd adjust the valves and re-check compression, perform the leak-down test, and last resort pull the head to see if the cylinder walls are scored up by broken rings.

Maxbumpo · #3 09-25-2017, 08:00 AM

Beautiful car by the way, I used to have an '85 euro wagon in that color. The car is a keeper, heads and gaskets and engines can be fixed, but that body is becoming more and more rare and will only go up in value.

Diseasel300 · #4 09-25-2017, 10:09 AM

As said above, the head gasket does need changing. Oil in coolant (or vice versa) is not a good thing. You'll need to do a thorough flush of the cooling system to get rid of the oil contamination as well (don't skip this!).

Compression testing on the OM617 is iffy if you haven't done the valve adjustment first. The valve seats and faces tend to wear and then the valves get tight against the cam causing compression leaks. If you have a blown head gasket, the compression will often be low due to compression leakage through the head gasket breach.

If I were in your shoes, I'd do exactly what I did with my OM603's head. Take it to a machine shop, have it inspected for cracks, warpage, etc and have them machine the valves and replace valve guides. When you get it back, it'll be like a new head.

The bottom end of these engines tends to be very strong, most of their issues happen in the heads and are relatively easily solved. Unless you were blowing big smoke, having great difficulty starting, or have large amounts of blowby gasses coming out the valve cover, I wouldn't worry too much about the bottom end.

Diseasel300 · #5 09-25-2017, 10:12 AM

Another thing worth doing while you have the head off, is get your injectors rebuilt. Forum member Greazzer has a spotless reputation around here for doing a 1st class job rebuilding and pop-testing injectors for these cars. See his website here: https://www.dieselfuelinjector.guru

83swagwagon · #6 09-25-2017, 05:07 PM

Thanks guys! Appreciate the kind words and vote of confidence in the investment. I really do love these wagons-- and my girlfriend does too. Fortunately

Given that I performed the valve check/adjustment compression test on the cold engine with these results, it is on to the leak down test.

I actually tried this myself right after the valve adjust and comp test last week, but wasn't getting any pressure loss at TDC. I made sure the cam lobes were facing outward (valves closed) and was unable to register any leakage at 100psi. Stone cold engine-- or at least as cold as can be after 1 day in ambient SoCal temps.

It isn't clear if my leak down tester is garbage (I paid $50 or $60 bucks I think), or if I was setting up the test incorrectly. In any case I'm going to swing by my mechanic's shop down the street tomorrow and let him give it a go.

Honestly I've come to terms with having to remove the head for machining and gasket replacement. I'm even to terms with having to replace the head if it is cracked. $1200 for a wagon head from Metric in the valley. However I will certainly give the nice-used-motor route a shot. I'll put some feelers out there and keep an eye on the classifieds to see what comes up.

Diseasel300: Thank you for the rec on the injectors. I definitely prefer to avoid pop testing in my small, hot, un-ventilated garage.

Question: Is there a way to test rings with the head off, or is a visual inspection more than adequate? I was thinking it would be a good idea to test the rings before and after a good Kroil soak...

Diseasel300 · #7 09-25-2017, 07:08 PM

When you get the head off take a look at the walls of the cylinders. If you can still see crosshatching the bottom end is probably still fine.

83swagwagon · #8 10-03-2017, 08:01 PM

Update on the troubleshooting:

I took the wagon down the street to my mechanic to see what he could find via compression and leak-down test. Same results as above.

He confirmed that the #5 cylinder (closest to firewall) is the one correlated to the rough idle. He cracked the injector line and the nailing sound went away.

He also flushed the cooling system and noticed that the coolant seemed to be free of oil coming out. The reservoir was nasty, however. So he cleaned it out and ran it a few times to see if any oil showed up. Nothing so far.

I doubt the issue fixed itself, however we did recently reconnect the heater core to get the heater working again. The core was bypassed because the input and return lines were leaking (which we replaced)-- the core itself was fine.

I'm curious if it is possible that the core could have had old gunky coolant residue flushed out into the reservoir, which subsequently coated the inside when coolant retreated back into the system. It is a far fetched theory I thought of, and I don't really believe it myself, but I'm wondering if it is possible. Not getting my hopes up here.

Aside from that, we are going to remove the injectors and prechambers to borescope the cylinders. This way I can get an idea of what I'm in for on the bottom end.

If the cylinders look healthy, we will conduct another leak down (this time visually verifying exact TDC), visually inspect the valves from the inside with the borescope, then proceed to a good Kroil soak and see what that does to compression.

If we're looking good at that point, I am going to check out the injector service Greazzer offers.

Worst case: need to find a good used motor, or all-in on a Metric.
Likely case: head gasket and head machining, rebuilt injectors- or good used motor.
Best case: the oil I noticed was really just nasty old coolant residue trapped in a part of the system that hadn't seen use in MANY years, rings just need a good soak and rebuilt injectors to top things off

Pic of nasty coolant attached (prior to flushing).

SonnyMorrow · #9 10-04-2017, 12:53 AM

Yeah looks like you might be in for a used engine. But, with these robust om617's you can really get away with running them on low compression for quite a while. If however the head gasket is blown, that may explain your loss of compression. And if that is the case, you would obviously be better off replacing the gasket than installing a used engine. Your mechanic can check for a head gasket leak and you can go from there, I'm actually surprised he hasn't suggested that yet.

renaissanceman · #10 10-04-2017, 03:05 AM

Kings Canyon/Sequoia National park! Right in my back yard.

GregMN · #11 10-04-2017, 10:02 AM

Compression test "dry". If any low cylinders, like you have, then redo compression test "wet". If the numbers improve in the wet test, then it is the rings that are leaking.

jake12tech · #12 10-04-2017, 05:02 PM

A leakfown test will tell you exactly where the leak is coming from. Listen and it reveals. If it is just a head gasket, I don't personally think it would be wise or financially wise to put another motor in. It's a very easy job for the head gasket. If your engine never got hot it's likely the head isn't cracked or warped. At that point a head gasket and valve job will restore the compression. The bottom end is VERY strong on this car. The OM617 is the cream of the crop and then is the OM606 engines. Theres no reason why the bottom end won't exceed 400k miles.

83swagwagon · #13 02-10-2018, 02:49 AM

It's been a while, but here's the latest:

-Decided to go ahead and pull the head after I failed to remove the prechambers (they were stuck like crazy)
-Found evidence of coolant in #5 cylinder
-Head was pitted above every cylinder except #4, which was suspiciously clean
-Took head to machine shop: valve seats were pitted badly, 8 cracks were identified (appeared to be badly overheated at some point)
-Everything makes sense now (low power, smoke, rough idle, freaky compression readings).

Lesson learned for anyone looking for a reasonably priced wagon...

So I've been on the hunt for a new head. That has been interesting. Wagon heads are hard to come by, and my head is no good for a core. Metric motors is $2490 without a good core, but I know I'm getting the best product out there, and from a local business to boot. I also found a head out of state for $1600, reached out via email to make sure the ad was correct, which they confirmed, twice, only to find out several weeks later when they followed up with me out of the blue that the head they were advertising was for a sedan, even though the photos clearly showed a gear for the SLS pump drive. The price they quoted over email went up to $2400 when they realized the mistake, and they wouldn't honor the price. Can't blame them, but they didn't own it and that got under my skin. Their website has since been kind of updated, but the new photos still show a wagon head and part number, but now with a slightly lower price of $1500, and a disclaimer that the photos are stock and not representative of the actual product. Very confusing, but whatever

I found a head overseas for about $450, but international transactions wig me out a bit, especially when it is an unfamiliar marketplace (ie: NOT eBay). My guess is shipping will run another $250 at least. I may investigate anyways.

Alternately, I am considering flame spray welding or some other method of repairing my current head.

Any ideas would be greatly appreciated. It's a bummer of a situation, but here I am. I just want to hit the road again soon.

Junkman · #14 02-10-2018, 10:04 AM

Stop and be sure that fixing the current problems will get you where you want. Suspension, trans, climate control, misc little stuff. Now realize that what you have in current condition isn't worth much in dollars. Would you spend $2400 to have this car in its condition after head install? If so, buy the head and put it on.

Fix any external oil leaks, replace hoses and anything else that is easier with parts removed.

dieselbenz1 · #15 02-10-2018, 10:38 AM

Not sure if will fit with ease but have you considered a standard head but change the PS pump to the dual SLS pump.