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Diesel runs great for 1/2 hour then very low power.

Discussion in 'Yanmar' started by Cal, May 3, 2010.

  1. Cal

    Cal New Member

    May 3, 2010
    This has me baffled. I started my YM240 (24 hp diesel) this spring and it runs absolutely fine for about 1/2 hour - plenty of power under load, no smoke, no blowby, everything seems normal. Then, after about 1/2 hour it starts losing power and in a period of about 3-4 minutes it loses so much power that it can't climb a small grade unless I drop it into 1st gear. Yet, once on the level it will return to the original RPM. (Maybe it will eventually not regain the RPM but I haven't waited that long yet before putting it away.)

    I've done this at least 5 times now. I've even roto-tilled a 50x50 garden completing 2 full passes on the whole thing before it started losing power. In other words, I wasn't running under a light load for that initial 1/2 hour - at least not in my garden due to all the clay.

    Once it cools down, it runs fine again - for about 1/2 hour.

    I've replaced the fuel filter and loosened the fuel tank cap to make sure it wasn't pulling a vacuum. I also removed and checked the fuel return lines to make sure they weren't restricted. Nothing made any difference.

    When it starts losing power there seems to be light white smoke - I had to get the exhaust between me and a dark wall to see it.

    If it was broken rings, sticking/cracked valves, etc. then I would expect it to have a problem as soon as it started. That's why I've been focusing on the fuel system.

    Tonight I tried to pull the injectors but I found out that's going to require a special puller and probably lots of penetrating oil considering the age of this thing. I think it's about 30-35 years old with about 1800 hours and never rebuilt. It's one of the older green ones. The serial number is 1000104 in case that means anything to anyone.

    Any thoughts?

    OK. I'll admit one more thing but I'm not sure it's the cause unless maybe it has gummed up something. But why would it only cause problems after 1/2 hour? When I went to fill the tank I added maybe 1/2 gallon of gasoline (probably more like 1/4 gallon) then filled the tank the rest of the way with fuel oil. I figured a 1/16 mixture (approx) wouldn't be a serious problem. The first time I had the power loss I took it back to the barn, siphoned off all the contaminated fuel, and refilled it with fuel oil.
  2. Live Oak

    Live Oak New Member

    Dec 21, 2003
    Welcome to Tractor Forum Cal! Have you check the engine coolant and oil. The symptoms you bring up give me some suspicions of a head gasket problem or a possible warped/cracked cylinder head.

    If you find oil or combustion contaminants in the engine coolant or coolant in the engine oil, this is a dead give away that your have cylinder head/gasket problems.

    The next time the engine acts up, if it is possible to safely remove the radiator cap, do so and watch the coolant for continuous bubbles circulating.

    Has the tractor ever overheated in the past?


    SHARTEL New Member

    Feb 11, 2009
    Welcome to TRACTORFORUM Cal!

    TF Admin's diagnoses is near exact of my own suspicions:

    1)- The fine, white exhaust is typically, coolant diluted with fuel in the YM240's combustion chamber.

    2)- The duration of time for the symptoms to occur indicate the engine coming up to temperature (1/2 hour), which, again, indicate a blown head-gasket and warped head. Both probably at this juncture.

    3)- As TF Admin stated, there is a strong possibility that cold starting and examining the radiator coolant may show nothing until the engine comes up to temperature. Then, exhaust bubbles will most likely be present when this happens. If your model has an overflow bottle (some don't), you may see boiling and exhaust bubbles in the container.

    Fortunately, you have a very strong, reliable and well supported model. Even though it's a domestic Yanmar, made for import to the U.S., it shares nearly everything identical to the Grey Market tractor, YM2000D. Both models share the exact same 2TR20 (A) engines. These engines are very simple and easy to work on. Even if you have little mechanical aptitude there's nothing too complicated about the removal, inspection and re-installation.

    Should you need suggestions for parts support, let us know your general location (city-state) and I can provide you with the nearest (and honest dealer) who knows their product and technical advice.

    And btw...all the YM240 tractors were green :).

  4. Cal

    Cal New Member

    May 3, 2010
    Well, I'm even more confused now.

    What you said made sense - in fact I felt a little stupid for not checking the radiator coolant myself. (I hate to admit it but I have a mechanical engineering degree and also had my master auto mechanic certification for many years although I only did side jobs in my garage. I haven't done any mechanical work though since I moved out here 25 years ago other than maintaining my own cars so I've forgotten a lot.) Anyway, I loosened the radiator cap so it wouldn't hold a lot of pressure then ran it again until the first sign of it starting to lose power then took off the radiator cap and the water almost "foamed out". It looked almost aerated - the dark green coolant looked light green - so I figured you were right.

    I finally got the head off tonight. (It wasn't hard. My time has been limited because I've been busy with customers plus I had to go out and replace some broken tools and get a deep socket to remove the one head nut.) Unfortunately, I see no sign of any problems with the head, gasket, or sleeves. I expected to see some sign of where it had been leaking.

    Any other thoughts? Is it normal not to be able to see where the leak was?

    Shartel, I'm just north of Ann Arbor, Michigan. A nearby dealer would be nice but mail order works, too. (Although mail order probably means hiring the neighbor kid to mow the lawn again.)

    Also, what do you think - is it worth the $50 or so for a shop manual or can someone give me the torque specs and valve clearances? I'm thinking:
    (a) that I had a manual but I can't find it now so maybe not. (I've had the tractor for 25 years. Who knows what might have happened to the manual.)
    (b) I might try to fix the diff lock after the last mowing and rototilling this fall. I have no idea what that will involve so a manual might be helpful.
  5. Live Oak

    Live Oak New Member

    Dec 21, 2003
    Have you set the cylinder head on a workbench and put a machinist ruler up to it and check under the ruler edge with a set of feeler gauges? Typically, anymore than a .002 gape between the rule edge and the gasket surface of the cylinder head indicates a warped head. Check the block deck in a similar fashion. Warpage can be severely aggravated when full operating temp or a heavy load on the engine is encounter do to increased heat and a leak could be wide spread or localized.

    You should also check for cracks that may be very subtle but open up when hot. A local engine machine shop can magna flux the head for cracks for you as well as hot tank it.
  6. Cal

    Cal New Member

    May 3, 2010
    Any reason to suspect that a little gasoline in the fuel (as mentioned in my original post) would cause this? From what I've found on-line it doesn't seem like it should but I'm not sure.

    I pretty sure a diesel won't run very well if at all on pure gasoline because it won't ignite under pressure (well, not under typical diesel pressure anyway) but I'm not sure if it would cause a more powerful explosion if there was enough diesel fuel to ignite the mix in the first place.

    It just seems odd that this seemed to happen about the same time as my little mixing error.

    BTW, TF Admin - your avatar is great. John Wayne is one of my favorite actors and that was a truly classic scene. It was from The Cowboys if I recall correctly - the one with the young boys on the cattle drive? Ned Pepper comes to mind but I may be mixing movies now instead of fuels.
  7. winston

    winston Member

    Aug 19, 2008
    valve setting .006". head torque 127-133 ft. lbs. Get there in about 3 stages working from middle, back and forth toward ends. You mention not being able to see where your gasket was leaking. Recently, mine started putting bubbles into my overflow bottle, not real bad. I changed head gasket, could not see where it was leaking. After installation of new one the bubbles were gone. Can't always see where it's leaking.

    SHARTEL New Member

    Feb 11, 2009

    Yeah...it's typical to not actually see the cracks until you use Zy-glow or magna fluxing. As was mentioned earlier, a machinist straight edge and feeler gauges will show the uneven or warped areas...and it doesn't take much to bypass coolant through the head gasket. Pulling the valves and checking the seats may also prove to be 'crack' revealing. Cracks between valve seats and into the head happens quite often.


    A manual may seem like an expensive and poor investment until you need it :)

    SHARTEL New Member

    Feb 11, 2009
    Welcome Winston!

    Nice to see another Yanmar 'nut' and owner here :D

  10. Cal

    Cal New Member

    May 3, 2010
    Looks like the head is warped. There's about a .003 gap.

    Thanks for the help everyone - I'll let you know how it ends up.
  11. Cal

    Cal New Member

    May 3, 2010
    Well, that wasn't it. I took the head in to a pro to have it checked out and it wasn't warped or cracked.

    So, after replaced everything, it started up fine and ran for about 1/2 hour before it started losing power again. This time there was more smoke - not constant but more - and it definitely looked and smelled of oil. (Since the smoke was very light before, it was very hard to tell if it was oil or water.)

    I also noticed something else - it was there before but I didn't think much about it at the time because it's barely noticeable. There's a sort of erratic "popping/poofing" sound when it starts losing power. It sounds to me almost like a cylinder isn't firing and you're just hearing the unburned exhaust coming out.

    I'm beginning to wonder if the smoke is somehow related to incomplete combustion during one cycle that results in too much fuel the next cycle and this is causing the smoke? But I don't know if unburned fuel oil would do that or not.

    Injectors? When initially trying to start it up after rebuilding it, there didn't seem to be much force behind the injectors but I'm not sure how much to expect. For the initial start after rebuilding it, I cracked the nut at the injector to see when the fuel was reaching that point and it finally started dripping out but not shooting out with any force.

    On the other hand, I don't see why an injector pressure issue would have anything to do with temperature.

    Valves sticking? But why would valves start sticking only after running for 1/2 hour?

    A cracked valve? But they checked the head for cracks and didn't see anything - including on the valves.

    If it means anything to anyone, when it loses power it:
    (A) just loses power; not RPM (at least, not initially) - on the straight and level it will still return to the original RPM once any excess load is removed.
    (B) starts to deteriorate rather quickly considering the fact that it takes 1/2 hour before it even begins to lose power. If I think I notice it on one loop around the house, it will be definitely noticeable on the second loop and on the third or fourth loops feels like it may not even make it back to the barn on the straight and level.

    I remain completely baffled. Any other ideas or tests anyone can think of?

    Edit: Shartel, you said, "Cracks between valve seats and into the head happens quite often." Assuming you literally mean "between the two valve seats", that was checked by the machine shop. The guy I took it too only rebuilds engines. However, we did not remove the valves to check the actual seats.
    Last edited: May 23, 2010
  12. winston

    winston Member

    Aug 19, 2008

    The amount of force at your injector line would depend on how loose the fitting is. You have a small volume but a high pressure. Just a thought. How about taking your exhaust manifold off and running it for the 30 minutes and see which cylinder is causing the problem? Also check your muffler and make sure it's not stopped up. Thanks for the welcome Shartel.:tractorsm
  13. TractorTech

    TractorTech New Member

    May 2, 2010
    Back to your original post, I would have checked the bottom of the fuel tank for foreign material. If the fuel valve/outlet has a strainer, it might be clogged. If it doesn't, the outlet opening might be clogged. In either case, the engine gets enough fuel to run for awhile, then is starved for fuel. Stop the tractor for 15-30 minutes, it starts and runs fine until it is starved again.
  14. Cal

    Cal New Member

    May 3, 2010
    BTDT. There's nothing in the tank. It looks very clean. Also, removing the cap to release any potential vacuum in the tank doesn't help. Besides, it takes about 30 minutes before it even starts to lose power then it goes from full power to almost none in probably less than 5 minutes - after 3-4 loops around the house from the time it starts it seems like it might not even make it to the barn. Also, it doesn't come back after 15 minutes. (I haven't tried 30 but I'm not sure that's necessary considering that it takes 30 minutes to start noticing the problem.) It seems to need to cool down first.

    However, this has been mentioned before so maybe I'll just go out and make absolutely, positively certain that nothing is blocking the fuel.

    This thing is driving me nuts. Is there any chance that a hot injector could do something like this? Or a hot injector pump? (Doesn't seem likely to me but???) There was a slight difference in the patterns on the pistons when I took the head off but it was only slight and didn't strike me as anything worth worrying about. (But then I'm not a diesel expert by any means.)

    A friend and I were brainstorming on this today and we considered the possibility that the water isn't circulating as well as it should thus causing overheating. However, it never gets hot enough to even force any anti-freeze into the overflow tank. (I only filled the radiator to about 1/2 inch below the filler neck.) When I tried to remove the radiator cap as it was losing power a lot of water started to come out but it wasn't steaming and I was able to tighten the cap again with my bare hands. This overflow of antifreeze when removing the cap was what made me think the idea of a blown gasket might be correct. Unfortunately, I don't recall trying this when it was working correctly so I don't have anything to compare it to.

    The overtemp light has always come on long before it overheated. In this case, I'm relating "overheated" to what I've seen in a car - steam coming out of the radiator because the cap pressure has been exceeded or, if not that, then taking the cap off results in massive amounts of potentially dangerous steam. I think I've been able to remove the cap with bare hands and no real danger in the past even after the light came on but I can't be sure - it's not something I normally "test". I do know that I've never seen it overheat enough to cause any amount of steam. I was certainly able to loosen it and retighten it today with no real danger other than some hot water coming out. Having said that, I noticed the last couple times I used it last fall that the temperature light seemed to be coming on even earlier - after about 2 hours of regular mowing of the lawn. There were no other symptoms and I assumed it was simply that the sensor was getting even worse. I'd forgotten all about that until brainstorming with my friend today.

    Sorry this is getting so long but I keep hoping that I'll either figure it out myself as I think about it while writing things down or someone out there will have an "ah-ha" moment based on more details. As it is, I'm not sure I'd even trust taking it to the local John Deere dealer - I'd like a diagnosis rather than a "let's just tear it all down and rebuild everything" solution that would probably cost more than the tractor is worth. I'm sure it will be relatively simple once it's diagnosed.
  15. Cal

    Cal New Member

    May 3, 2010
    This is getting ridiculous. I took all the fuel lines off to check and, as I expected, everything was very clean. Unfortunately I managed to break one of the bleed screws in the process so I had to order a new one - $1.25 plus $6.00 shipping and more delays. I finally got it back together and it's doing the same thing.

    However, I may have finally found something. This time I loosened the lines to the injectors, something I should have done a long time ago, and discovered that just barely cracking the front one (maybe 1/16 turn) caused the engine to die if I didn't re-tighten it very quickly. Cracking the rear line about 3/4 turn made no difference but a significant amount of fuel came out - i.e., the rear injector pump seems to be working fine but not the injector.

    So, I guess now I'm going to pull the rear injector and have it checked. (Which, of course, means purchasing a removal tool and another shipping charge, more delays, more $$ to the neighbor kid for mowing the lawn, finding and paying someone to check the injector, and probably ordering a new injector with yet another shipping charge. I'm just hoping it doesn't end up being one of the lower injector components which will mean pulling the head again! Man, I'm really looking forward to this.)

    So at this point I'm curious about a few things:
    1. Does anyone has any idea what a typical injector life is for this tractor? Mine has about 2400 hours on it.
    2. What are the odds that it would be one of the lower injector components? In other words, should I just go ahead and order a new injector ($100) along with the removal tool?
    3. Is there a reasonable alternative to purchasing a $60 removal tool?

    I'm also a bit curious why it only happens after coming up to temp.
  16. winston

    winston Member

    Aug 19, 2008
    If you go to tractorbynet and type in "injector removal tool" under search the first post has detail on removal. After reading it you may decide to spring for the store bought version. Sounds to me like you are headed in the right direction with your problem solving. Good luck.
  17. wjjones

    wjjones Moderator Staff Member

    May 27, 2010
    Seems like i have heard of this before it ended up being a clogged exhaust system, muffler restricted,etc.
  18. Cal

    Cal New Member

    May 3, 2010
    FINALLY FIXED! And, surprise, surprise, it turned out to be something really simple. So, I'll bare my ignorance in hopes of helping someone else. (It turns out that TractorTech was very close.)

    First, I got disgusted with not being able to find the problem and just paid the neighbor to mow my lawn all summer. (I have to admit, it was nice not having to do it myself and the price was right since it was a friendly neighbor.)

    Then I finally decided to look at it again a week or so ago but the tractor wouldn't start. I found out the o-ring on the fuel filter had started leaking and all the fuel had leaked out of the tank. Luckily there had only been a gallon or so in it. It turns out that the leak was a good thing because I was preparing to tear down the whole engine this time. When I removed the filter I noticed that the filter bowl was necked down in the middle - this was the first clue to the cause of the problem.

    It turns out that when I changed the fuel filter the steel 'disk' on the bottom of the filter was stuck inside the bowl but there was nothing on it to indicate that the paper filter had ever been attached and it was stuck so firmly (wouldn't move at all) and so square that I thought it was supposed to be there and just installed the new filter. Apparently that pushed the new filter up too far and sorta, barely, kinda restricted the fuel flow - just enough that it would run for almost 1/2 hour before it quit. I suspect that there was also a temperature factor in there that caused just enough expansion of something to finally cut off the fuel. Apparently when fuel flow gets that low it affects the injector pump for the rear cylinder first.

    I think the old filter bowl with its 45 degree o-ring seat fooled me into thinking the slight extra force to seat the o-ring was from that odd seat rather than the force on the filter itself. (I had to play with it quite a bit to get it to seat correctly.) It seems that there was enough force on the filter that the filter bowl was stretching when it got hot and that's what made it neck down in the center - and eventually caused the o-ring to come part way out. At the end, there was no way to get either of the metal disks from the old filters out of the filter bowl because the center of the bowl was now too narrow for them to fit through. After receiving the new filters and filter bowl, I finally forced one of the metal disks out of the old one just to see what would happen and the plastic cracked.

    So my tractor is now back in action and I just spent over an hour mowing part of the field behind me with no problem. Maybe next year I'll get ambitious and try to fix the diff lock.
    Last edited: Oct 23, 2010
  19. winston

    winston Member

    Aug 19, 2008
  20. GVTT55

    GVTT55 New Member

    Sep 14, 2011
    I need some help. I have a similar problem like Cal's.
    I have a TT55 that was purchased in 2003. My tractor starts up and runs full power for about 20min then slowly dies. I have done the following:
    1. drained full tank, replaced with new fuel
    2. blown out full line from pump line to tank to make sure filter in needle valve is clean.
    3. replaced full filter.
    4. cleaned air filter and removed it during the 20 min to see if it was the problem.
    5. cleaned drop filter in pump primer
    6. have not cleaned injectors or replaced fuel pump.

    What am I missing? only 670 miles on tractor. Please help

    I am going to check and see if their could be any lines that are constricting the fuel flow to the injection pump.
    Any suggestions please help!