John Deere 950 Yanmar 3T90J Oil in Radiator

[TimberHole]

I just acquired a John Deere 950 from a friend. The tractor is in excellent shape and only has about 1,000 hours. The tractor is getting oil in the radiator but does not have water in the oil. Starts and runs perfect but I'm told it is overheating and will blow the cap off the reservoir. The previous owner replaced the head gasket but did not have the head magnafluxed or die penetrant tested. I'm fairly handy around a gas engine but completely new to diesels. I was talking to the folks at Hoye Tractor today and they suggested also posting on this site. Nice folks by the way.

I'm hoping this is a head or gasket issue but think it could also be a cracked block.

Here is my plan (mostly of my own creation):

1) Compression test
2) Pressure test each cylinder. Piston at the bottom, valves closed and 125 psi from the compressor in the injector port. Hoping this isolates the cylinder.
3) Pull head and have it evaluated by a competent machine shop. Check deck for flatness and head for cracks.
4) If none of this yields fruit, pull the pan, inspect for cracks and start the head scratching.

Am I overlooking anything obvious? It is my understanding that this engine does not have any type of oil cooler. Is there any other probable location where oil could enter the water jacket?

If anyone has had a similar issue or has any wisdom to offer I would sure appreciate hearing from you. This is a really nice little tractor and I'm committed to resolving this.

Thanks in advance.

 

[Spanner]

You're on the right track.
#2 is what we call a "Leak-Down" test I think. It pays to lock the crankshaft to prevent uncontrolled engine rotation just-in-case.

I seem to recall there is a small O-ring in the cylinder-head gasket which can be overlooked upon assembly and that might lead to oil/water mix. A distant memory. Don't quote me... But look for one in your new gasket kit.

The Gasket Kit is very Serial Number specific.

Also there was a change from 8 to 10 studs. I think the 10-stud gasket fits the 8-stud head. Ask dealer to check the DTAC solution for this.

Good Luck!
:wrench:

 

[TimberHole]

Thanks for the info and tips Spanner. I am going to do what I'll call a modified leak down test. The leak down tests are usually done at top dead center. I'm going to try it with the piston at the bottom of the stroke. I'll loosen the rockers to close the valves. My goal is to pressure test the entire bore with the head on to check for any pinholes or similar in the sleeve or leaks at the head. Not entirely sure it will work as I'll probably use a max of 125 psi as opposed to the 400 psi during compression. I figured it wouldn't hurt anything to try it before I pull the head. I'm hoping to avoid pulling the head and then finding nothing wrong.

 

[Spanner]

Kinda how I thought you were going to proceed.
You will be looking for bubbles in the radiator so fill it right up.
Also listen closely at the oil filler hole. You will have to refit the rocker cover but it's a useful diagnostic.
Am interested in your results. These were well-made engines.
Regards,
:wrench:

 

[TimberHole]

Thanks Spanner. I'll update this thread over the next few days. I think I'll get my compression tester tomorrow and I'm anxious to get started. Searching the web I find a lot of info on water in the oil but not so much on oil in the water.....at least on the little Yanmar diesels. Even if the block is cracked I intend to pull the engine and fix it. I do know the blocks are getting hard to come by. I would probably first pursue a professional repair on the block but hopefully that isn't my problem.

 

[Spanner]

Be aware your Compression Tester for Petrol engines will not handle the job on the Diesel engine.
:wrench:

 

[TimberHole]

Be aware your Compression Tester for Petrol engines will not handle the job on the Diesel engine.
:wrench:

Since I'm new to diesels I didn't have the correct tester. I ordered one from Hoye with the correct adapter for the little Yanmar. I also ordered their tool for pulling the injectors. Tools don't count in the total cost of repair :wink: I may have to modify it to run the pressure test but won't know for certain until it arrives. Maybe the air line will connect directly to the adapter that goes in the injector hole. Not sure.

 

[chriswheeler]

There is another place it could possibly leak, the liner seals. I replaced the liners in my 950 when I rebuilt it several years ago. Seams to me there were 2 seals per liner. The water jacket is between the upper and lower seals. The high pressure is on the piston side, and some fuel could be blown into the water jacket if the upper liner seal was leaking. Your compression test should pick this up as a cyl with the lowest pressure. One thing to look for first is to take a small coolant sample from the top of the radiator and see if it's oil or diesel ?? That might be a big clue.
Chris

 

[TimberHole]

Chris...thanks for the reply! Just yesterday it occurred to me that I might be seeing fuel in the radiator but couldn't figure out how that could occur. It will be interesting to find out for certain but I think there is a 90% chance you just nailed it. I thought about adding some fuel, engine oil and hydraulic oil to antifreeze in 3 seperate containers and stirring with drill motor to see which most closely resembled the radiator. Is there a way to definitively identify the oil in the radiator as diesel? It is the milky brown color of a milk shake. I'm thinking that is from combustion and that you are exactly right!

 

[chriswheeler]

We saw leaking liners in several large high hour stationary diesels I got to work on before retiring, and after your description of the problem, this seamed most likely. What usually brought this on is something failed in the cooling system and caused a unusually high operating temp, and wasn't caught in time to prevent the damage. ( use a quart jar like a old mayo jar, and take a full jar sample ) When you take the sample from the radiator, let the milky color settle out for a few hours, the oil will rise to the top of the sample, just smell it, if it's diesel, you will know right away. Also the oil in the sample will have a lite color, not a dark engine oil color. You could still have a cracked head, but it's less likely than a liner seal. This would also explain the high pressure in your cooling system. Now here is the bad news. To fix this you will need to find what cyl it is first. Then pull the head and the oil pan to remove that piston. Make a puller to remove the liner ( that part is simple ) remove the liner and install new O rings on the liner, re-assemble. If I had to go that far, I'd change every seal on all 3 liners so you don't have to do it twice. Just a suggestion
Chris