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Smoking mystery marvel

1229 Views 13 Replies 8 Participants Last post by  knottyrope
Good morning everyone!

I have a 1998 John Deere 425 w/AWS.

I have noticed a persistent (hydraulic?) yellowish leak coming from the rear of the tractor, almost directly between the rear wheels on the right side...when looking at the rear of the tractor.

I have tried to pinpoint the leak, but its pretty difficult to do so.

Any others have this problem and/or any ideas where it is likely coming from?

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I would clean the area surrounding the leak, using a chemical that cuts grease & oil. I've had success with Brake Cleaner, use it when the metal is cold for safety. If possible raise the vehicle for access, run it and look for a fresh leak. I use my "mechanic's mirror" and an LED light to help.

Somebody else may come with some known likely places to look, mine had a fill tube seal leak when I bought it, easy fix, drain it below the tube (it should already be below the tube), remove the tube and replace the o-ring seal, Deere calls it a "packing".
Sounds good...thank-you, Fred!

Prior to me owning the tractor, it was owned by a corporate farm, who while they maintained the tractor mechanically; cosmetically it is a bit rough.

I already replaced the dipstick tube, but this appears fresh, clear yellowish in color, which may indicate it's clean fluid at least.


Brian, Check your swash plate O rings. Most of the time these O rings crack and start leaking. It is very hard to tell where its coming from even if you wash the trans down. I replaced my O rings and had no leak for about a month. Then developed another leak. Turns out my dipstick tube was loose and leaking out past O ring. Replaced and haven't had a leak in 6 months.
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Hi Kevin,


What/where is/are the swash plate?

Again, the fluid is a clear, yellowish fluid...hydralic fluid?

You are right in that it is hard to locate the leak as I cleaned the tractor up and still could not discern where the leak was coming from.

Is the swash plate "O" ring a bigger job?

Coincidently, I replaced my dipstick tube last fall.

Thank-you again.
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The John Deere Low Vis Hygard trans fluid is a golden or yellow color, so this is what you are seeing. The swash plate O rings are located at the end of your speed control shaft, well on the shaft that connects to the speed control. Just follow your foot pedal that makes the tractor go forward and reverse back to where it connects to the shaft coming out of the trans. and under the bolt and washer are 2 O rings. You will need a small pick to get the O rings out. Also will need snap ring pliers. I have a set with right angle jaws which makes it much easier to get the snap ring out. Some people have done the work with the trans in place. There is a hole in the side of the frame to fish a socket and extention thru to take the bolt out. I partially took out the trans from the frame. I unbolted everything that connect to the frame or was in the road, but left the drive shaft connected. I then jacked the frame up so the trans would fall down to access it better. After that it was a lot easier to replace the O rings. When you get the O rings out and put the new ones in, make sure you use plenty of vaseoline on the O rings before installing. OH and one last thing you have to drain the hydro fluid before you start. It took me about 2 hours when I did it only because I never did it before. I think a could do it in an hour now. Having a tech manual doesn't hurt either, especially if you get stuck. Good luck.
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I have a k301 that runs great but smokes like crazy. I was planning to drain the oil, replace it with marvel mystery oil, pour some down the spark plug hole, and then run it like that for a while for pushing snow. I'm hoping a ring is stuck and it will pop loose and fix my problem, or valves would heal themselves. Does this sound like an ok thing to do?
Mark add Marvel Mystery Oil but don't use it without the normal oil inside the engine. Don't add more than the amount they tell you on the label. MMO is something I have used for years and is good stuff but is not a lubricant like normal oil is. It is an additive only. MMO may clear up your problem but I would be looking at the breather system also. Roger
So how does the head gasket affect oil burning? the head gasket had obviously leaked oil when I got it, I took off head and then torqued it back on using same gasket. also, if I pour some marvel mystery oil down spark plug hole, how much should I pour in there?
Mix MMO in the gas and the oil. It tells you on the bottle how to do it and how much. Pouring it in the carburetor will just make lots of smoke and kill the engine. The fact you had a bad head gasket would make the combustion poor and not burn all of the fuel in the engine. This would wash down the cylinder walls which could dilute the oil, lower the compression, cause oil burning and engine damage. See if the oil smells like gasoline and you will know for sure. The gasket was probably not leaking oil but partially burned fuel because of low compression which looks similar. Put a new gasket in the engine, tighten the bolts correctly, the MMO where it belongs and run it a few hours to see what happens. I personally don't use MMO in the oil except in old engines. I only use MMO in the fuel at a rate of about 1 ounce to 4 gallons of gasoline. Roger
I would pull the head and put MMO on the rings from the top side. Let sit overnight and then blow excess off with compressed air. Reassemble and it should be as good as it can get.
I have used Marvel as a combustion chamber soak before. I just roll the engine close to TDC, pour in enough to cover the piston, and roll over by hand a couple times to coat the cylinder and valves. Roll back to TDC and cover the piston back over with MMO. I let it soak a few days, MMO is not a fast working solvent.
I once did a little experiment, I had a Kohler K301 I was freshening up a head gasket on. I took the head off, and since I didn't need the tractor anytime soon, I covered the piston and valves with MMO, and let it soak about a week. All the hard carbon deposits could be easily wiped off with your finger. Top of the pistons and valves were as clean as new.
If you are doing it with the head on, go ahead and let it soak as I described, but take the spark plug out and, with some rags over the plug hole, crank the engine over a few times to blow all the remaining MMO out. If you leave the oil in the cylinder, you will hydro lock the engine and not be able to crank it over.
Also change the oil, as whatever seeps by the rings will get in the oil.
If you are to use it in the oil, don't go over the recommended amount. I think its 20% MMO 80% oil. The MMO is pretty thin, and would not properly lubricate an engine at running temps.
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Thanks for all the great information. I will order a head gasket and try the MMO treatment.
I had a stuck ring in my truck years ago

run it until engine is hot, pull plug and spray in wd40, PB blaster and let it cool off, crank it over a few time with plug out to purge oil and repeat again a few times

after 5 times I had compression again for a while
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