[reinventthewheel]

I just got a 79 300td that needs a lot of help. I've fallen in love and we're stuck together so it has become quite a project.

It sat in the rain for a long time neglected, and then someone did an inadequate conversion to SVO. Just a primer pump, coolant heated filter & extra-hot glow plugs, no other heaters (although it was in really warm weath in central Cali for most of that) and ran it like that for a couple years without doing all the work a long-neglected diesel needs.

I'm gutting out the interior and doing lots of rust removal, and starting with a lot of fluid changes. It's been about 1500 miles and I just did the second oil change, did a Moly Diesel Purge, about to do the atf & power steering fluid/filter changes.
The valves were adjusted shortly before I got it and supposedly the compression was good but don't know the numbers. Going to do a compression test soon.

Anyways, it has a lot of blow-by. Steamy air that will rattle the valve cap.
I was going to drive another few hundred miles and let the new oil flow through before worrying about it, but I just found out that SVO can cause piston rings to stick, which can then cause blow-by.

So, I'm wanting to move forward with something that will help unstick the piston rings. Maybe Moly Motor Clean? Or another additive?
Any other suggestions?

 

[Stretch]

Do a leak down test / apply low pressure air (say 5 PSI - you need low pressure high volume!) via the glow plug holes to determine where most of the air is escaping. You should get a much better idea of engine health this way - don't forget to rotate the engine by hand so that the valves are closed on each cylinder before you check for leaks.

When rotating these engines you need a 27mm socket for the crank shaft pulley. Do not turn these engines over on the cam shaft pulley - do not turn them in an anti-clockwise direction (taken as you stand in front of the engine {in the car} looking at it) as the timing chain can snag if spun the wrong way.

Let's hope it is just valve stem seals.

EDIT:- you are better off removing all the glow plugs before doing this type of check (compression test included) instead of tackling the job via the injectors as once removed the little heat shields that sit under the injectors should be replaced.

 

[300Dman]

Don't mix it with your Crankcase Oil and run it like that (leave that for the Gasoline Engines) but Marvel Mystrey Oil dumped into the Cylinder is safe to use (slow, need to let it soak a week or so).
In can go in through the Glow Plug Holes or after removing the Injectors.
Before runing the Engine crank the Engine with the Glow PLugs or Injectors removed to blow out any Liquid Oil that might be present (preventing a Hydraulic Lock).
After that change your Oil.

http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1495985-piston-rings-gummed-up.html

Compression Test...how low is low..... - PeachParts Mercedes ShopForum

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DIY Links by Parts Category - PeachParts Mercedes ShopForum

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[reinventthewheel]

apply low pressure air (say 5 PSI - you need low pressure high volume!)

How can I apply that kind of pressure/volume? Do I need to seal it off?
Was planning on taking out the injectors anyway to add some injector line heaters (eventually want to start running on svo again) and do a compression test.
I'll get new heat shields. Do they have to be replaced every time? I plan on getting new injector nozzles in a month or two when I have enough cash, will I have to replace the heat shields again?


300dman:

(slow, need to let it soak a week or so)

Letting it soak for a week isn't an option. It's my only vehicle. I can maybe to 48 hours, is that gonna do it?
Also, how much oil should I put in?

Before runing the Engine crank the Engine with the Glow PLugs or Injectors removed to blow out any Liquid Oil that might be present (preventing a Hydraulic Lock).

Crank it with the starter? Or slowly by hand?
And blow out the oil from the injector holes? Sounds messy.
Also, is that really going to get enough of the oil out? I'm worried this could be an easy way to destroy my engine if not done exactly right ...

 

[MB1316]

How can I apply that kind of pressure/volume? Do I need to seal it off?


Was planning on taking out the injectors anyway to add some injector line heaters (eventually want to start running on svo again) and do a compression test.

I'll get new heat shields. Do they have to be replaced every time? I plan on getting new injector nozzles in a month or two when I have enough cash, will I have to replace the heat shields again?


300dman:



Letting it soak for a week isn't an option. It's my only vehicle. I can maybe to 48 hours, is that gonna do it?
Also, how much oil should I put in?



Crank it with the starter? Or slowly by hand?
And blow out the oil from the injector holes? Sounds messy.
Also, is that really going to get enough of the oil out? I'm worried this could be an easy way to destroy my engine if not done exactly right ...

Crank it with the starter and excess oil should blow out quickly with a few 15 sec. cranks. Any small amounts left will just get burned up when you run the engine. My guess on the amount of oil put in would be 3-4 tablespoons or 2-3oz. each. I'm sorry I don't know enough yet about the other questions yet. Any advice on these?

 

[300Dman]

How can I apply that kind of pressure/volume? Do I need to seal it off?
Was planning on taking out the injectors anyway to add some injector line heaters (eventually want to start running on svo again) and do a compression test.
I'll get new heat shields. Do they have to be replaced every time? I plan on getting new injector nozzles in a month or two when I have enough cash, will I have to replace the heat shields again?


300dman:



Letting it soak for a week isn't an option. It's my only vehicle. I can maybe to 48 hours, is that gonna do it?
Also, how much oil should I put in?



Crank it with the starter? Or slowly by hand?
And blow out the oil from the injector holes? Sounds messy.
Also, is that really going to get enough of the oil out? I'm worried this could be an easy way to destroy my engine if not done exactly right ...

My personal though is it is a bad idea to depend on an Old Mercedes as your only transportation. I know mine has spent weeks in the Driveway waiting for me to get parts, tools or find the knowledge I need to fix it.

Some have said that if you replace the Crankcase Oil with Synthetic Oil and drive for about 2-300 miles it will free up sticking Piston Rings.
Synthetic Oil also makes Winter starting easier.


Some have used that Engine Overhaul Additive to their Oil (I do not remember which one was used; it is somewhere in the DIY Repair Section) and claimed it un-stuck their Piston Rings.

The Injector Heat Shields are supposed to be a one time use item. Best to buy them cheaper from an online seller a long with some Oil or Transmission Filters so that you can make the amount to get the Free Shipping.

I think I saw some one recommend a Leak Back Test. The problem is that while Harbor Freight sells a Cheap Leak Back Tester it is set up for Gasoline Engines.
You would need to fabricate or buy their Diesel Compression Tester (not the expensive one that is over $100) so you can use one of the Compression Tester Adapters.

When you blow out the Oil you are going to use the Starter Motor to Crank the Engine and either the Glow Plugs or the Injectors have to be out of the Engine.

When I did mine I used 1/4 cup of Marvel Mystery Oil. However, if you do not have the time to let it soak I would not bother.

 

[reinventthewheel]

You would need to fabricate or buy their Diesel Compression Tester (not the expensive one that is over $100) so you can use one of the Compression Tester Adapters.

Was planning on buying their $25 compression tester kit anyway. Does it have an adapter to fit to a standard schrader valve? Then I could just use any air compressor, or I suppose even a bike pump, which is more accessible.

When I did mine I used 1/4 cup of Marvel Mystery Oil. However, if you do not have the time to let it soak I would not bother.

Is that 1/4 cup total or per cylinder? I'm going to try to let it soak for 4-5 days and make this work.

 

[reinventthewheel]

Oh, I see now what you were saying:

Harbor Freight sells a Cheap Leak Back Tester

You mean get this and then use fittings that come with the diesel compression tester?

Also, if I'm pulling the injectors out for 4 days, is there something I can soak the nozzles in that will clean them out?

 

[300Dman]

The Compression Tester Adapter ends where the Air Compressor fittings are supposed to go have I believe Pipe type threads.

If you have the Stock Injector Nozzles Carbon can Plug up the holes in the tip #12 in the Diagram.
The holes/passages #14 and #15 are not likely go be cleaned by simply soaking them in something.
On my Own Mercedes and most of the Injectors I pulled off of Junk Yard Cars the Passages were completely Plugged with Carbon.

If periodical Diesel Purges were done that might have kept the passages clean. But, once they are solidly plugged I am not sure if any chemical will clean out the Carbon.

 

[reinventthewheel]

Ok, I only managed to do the MMO soak for three days. (ended up using the glow plug holes instead) I changed the oil with a synthetic and drove about 100 miles.
The blow-by isn't any better but there's definitely less smoke at idle/when cold.

I'm headed up to Portland and have a garage up there I can use and a friend with more experience who can help with the leak-back test and a compression test.
Hopefully working the synthetic oil through for another 700 miles will help and she does ok on the drive.

 

[Mercedes mechanic]

and she does ok on the drive.

If I could recommend something?


Redue the ring soak, but drain the oil out first. Then leave the plug out of the pan. Since your friend has a car and you have time. Pour gasolene, in the same amount into the cylinders, rotate 240* every few hours, making sure the cylinders are full enough.


Once you have gone thru a gallon of gas, the crud on the rings should be loose/melted, on the way to the drain hole.


Doing a compression test or leakdown test will not show you anything about the condition oil the oil rings. Which are not really rings, but wipers.

 

[reinventthewheel]

So you're saying do the soak with MMO again? And then this other soak with gasoline?

After putting $40 worth of oil into the engine I'm not real motivated to drain it out again right away, but maybe after a couple thousand miles more I could do this.

I think the leakback test was suggested to find out if there is a leak in some other part of the engine. I'm not 100% sure that it is the piston rings causing the blow-by.

 

[Mercedes mechanic]

So you're saying do the soak with MMO again? And then this other soak with gasoline?

After putting $40 worth of oil into the engine I'm not real motivated to drain it out again right away, but maybe after a couple thousand miles more I could do this.

I think the leakback test was suggested to find out if there is a leak in some other part of the engine. I'm not 100% sure that it is the piston rings causing the blow-by.

It was a suggestion. When you have the time.

No MMO, only gas. #1 and #2 Rings have nothing to do with oil blow by. Just the oil rings. They all gather crud between them until they spread apart (marked by red dots and arrows). When they spread apart they no longer wipe the piston bore clean or provide enough seal for the downstroke. Rings make compression only on the upstroke, with the oil also in the bore, it gets burned along with the diesel, causing alot of smoke.

I wonder how many diesel Mercedes there are in L.A?

 

[reinventthewheel]

Might be trying the gasoline next week

rotate 240* every few hours

I'm guessing you mean degrees? Like turn the power steering belt or crankshaft nut 3/4 of the way around?

making sure the cylinders are full enough

how full is full enough?

 

[Mercedes mechanic]

Might be trying the gasoline next week



I'm guessing you mean degrees? Like turn the power steering belt or crankshaft nut 3/4 of the way around?



how full is full enough?

Yes in degrees. Well full enough so that it does not get messy.

you can put the old oil back in and run it until its warm, then change the oil.

Note that before you even attempt to start the engine, make sure all of the combustion chambers are empty and that all of the gas is out of them.

 

[JHZR2]

After putting $40 worth of oil into the engine I'm not real motivated to drain it out again right away, but maybe after a couple thousand miles more I could do this.

Kreen (from Kano labs, makers of Kroil) is a good product that many have been having really good experiences with. Id dose some in the fuel, and apply properly into the oil. Drive, then at the last 50 or so miles, add a more vigorous dose and drive very lightly and carefully.

After the oil change, give her an IT.

 

[reinventthewheel]

Thanks for all the info, this is really helpful

you can put the old oil back in and run it until its warm, then change the oil.

What is the advantage to doing that instead of just putting new oil in?


and, re: jhzr2:
I think I might try this Kreen stuff out, I was considering an engine flush type additive of some kind anyway as an additional cleaner before doing the gasoline and a valve adjustment.

After the oil change, give her an IT.

What's an IT?

apply properly into the oil.

Are the "proper" directions on the bottle?

 

[JHZR2]

and, re: jhzr2:
I think I might try this Kreen stuff out, I was considering an engine flush type additive of some kind anyway as an additional cleaner before doing the gasoline and a valve adjustment.


What's an IT?


Are the "proper" directions on the bottle?

IT=Italian Tuneup

Here we have an ongoing thread about Kreen:

Kreen Update - Bob Is The Oil Guy

 

[Mercedes mechanic]

Thanks for all the info, this is really helpful



What is the advantage to doing that instead of just putting new oil in?

To flush all the crap out, without mixing it with the new oil.

 

[MB300Dave]

Don't mix it with your Crankcase Oil and run it like that (leave that for the Gasoline Engines) but Marvel Mystrey Oil dumped into the Cylinder is safe to use (slow, need to let it soak a week or so).
In can go in through the Glow Plug Holes or after removing the Injectors.
Before runing the Engine crank the Engine with the Glow PLugs or Injectors removed to blow out any Liquid Oil that might be present (preventing a Hydraulic Lock).
After that change your Oil.

http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1495985-piston-rings-gummed-up.html

Compression Test...how low is low..... - PeachParts Mercedes ShopForum

You can find more info below.
DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

Snowtire just did his with this method & had excellent results using the Marvel Mystery oil method.