YM155D issues: maybe head gasket, maybe radiator, maybe?

[graysonh]

Foreword: Been getting some work done on the new 155D but it's got some heating/pressure issues. I started a new thread to make it more searchable for anyone else in the future whom it might help; hope that's not bad form here. Also, I'm sure this issue has been discussed likely many times but the vBulletin search feature is not being much help in finding old threads.

The problem: Started mowing on Saturday, thick knee high grass, more wet than ideal, some hills. After about half hour I had steam venting violently from the radiator so I shut down. The temp light did *not* come on, but I think my lights may have been reversed? (The manual says the left light it temp and the right is oil pressure. But then it says that the oil light comes on with the ignition, and on my tractor the left light comes on. So the right side light is likely temp and I don't know if it's connected.) After ten minutes or so went by I checked water temp and it was way down so I filled the radiator all the way and started, did not see any bubbles. I was very much expecting sign s of a blown head gasket but from what I can tell, the bubbles are there almost every time this is the problem. So I drove the tractor back and parked. After it cooled down again I blew out the radiator screen with an air compressor. It was extremely dirty/clogged. I blew for 20 minutes straight and finally got it mostly clear. I haven't put the tractor to hard work since then.

Head Gasket still seems possible but I've now checked three times for bubbles and found none, cold start twice and somewhat warm once. Maybe just the clogged screen? Radiator was flushed thoroughly last week but I never cleaned the screen until afterwards. Maybe radiator cap not keeping pressure? Seems like a no-brainer to buy a new one anyway. The steam was so violent that it must have already been well over boiling point, though. Another thing to note is that the hydro fluid is milky and nasty. Maybe the bad hydro is causing the engine to work too hard? Simply lifting the mower (Woods RM42, pretty typical small yanmar mower) puts a noticeable strain on the engine, though I'm not sure if this is normal.

Anyway, any help very much appreciated. Happy to get my answers from old threads to save typing time, just haven't found any that are totally relevant.

 

[winston1]

I think you are on the right track with the cooling issue. Just watch and see what happens.

You need to change hydraulic/transmission fluid and clean the suction screen.

The 155 should handle that mower fine.

 

[normde2001]

You made the most typical overheating repair. My first tool in my tool box was a whisk broom. Do you have a radiator screen?

 

[Gunny]

Cleaning the screen will help, but you may want to dig a little deeper.

I had one tractor that was running a bit warmer than I liked and I kept the screen cleaned, but with the fan shroud and close quarters between the engine and radiator, it was impossible to even shine a light properly in there to inspect the radiator.
I'd already done all the other checks for overheating and couldn't nail anything down that might be causing it and I was getting ready to suspect the water pump was weak.
We had a long wet week back then, so one day I drained the radiator and removed it completely from the tractor. As soon as I got it out into the daylight, it was easy to see that all four corners and a pretty wide band across the bottom of the radiator fins were well blocked by stuff that must have made it through the screen, or somehow pulled in from the sides, but in any case, a pretty good percentage of my cooling area was being blocked.
I blew all that out from the rear of the radiator, reinstalled everything and the tractor never had any overheating issues after that.

I did take a couple of hours to remove, clean and reinstall everything, but well worth it.

May not be your problem, but it may be worth checking before you start throwing dollars at your problem.

 

[graysonh]

Many thanks to all. I ordered a new cap ($5) from Hoye and also a temp gauge ($35 I think). Both worthwhile purchases I think regardless of what the problem is. So we'll take it from there.

Yes, there's a screen but it wasn't plant material in the fins -- more like straight up dirt! Still don't really understand. It it's a heck of a lot cleaner now.

Very First time I ever used a tractor, probably 12 years ago I was mowing tall dry grass for a family friend with his new kubota and had the classic chaff-in-radiator overheating. I had no idea and thought I had destroyed the machine! Went to him with my tail between legs, he came over, swept the screen and I was back on it right away.

 

[California]

I think my lights may have been reversed? (The manual says the left light it temp and the right is oil pressure. But then it says that the oil light comes on with the ignition, and on my tractor the left light comes on. So the right side light is likely temp and I don't know if it's connected.)

Is your indicator light panel like this?
(Photo from my initial setup/minor renovation of the YM240 in 2003. The lights on the right were dangling at my knee. )

Test the temp light bulb and its electrical circuit: Turn the ignition key to On. At the temp sender, slide the connector partly off the sender and slip a grounding wire in, to ground the wire that goes to the dashboard. The dash light should come on.

 

[graysonh]

Alright, good news, mowed for an hour and a half last night with no overheating issues or radiator venting! Looks like it just needed to be blown out real good. Still excited to receive the temp gauge, will help put my mind at ease and let me enjoy my seat time. Rad cap probably an unnecessary desperation purchase but it's only $5:thumbsup:

The fins were clogged with what must be straight up red dirt, like it came in as mud and then caked.

California, here's my light setup. Figure it's less important to fix if there's a temp gauge there instead.

 

[California]

Everybody buys an old Yanmar and immediately wants to hack a temperature gauge on.

On the other hand Yanmar's engineers designed to make it so it would never overheat if the cooling system is maintained. These things are designed to run much harder than our typical use - 24/7 powering a ditch pump for example or the marine engine version (same engine, different stuff bolted on) running for days.

I suggest get the warning light working properly, test it occasionally, trust Yanmar's designers, and just get on with using the tractor.

At most buy a new temperature sender if you don't trust the old one (test it on a stove in boiling special fluid). With the new radiator cap, you would sense overheating (heat, smell) long before you approach boilover temperature. The light will come on before boilover.

I started off with the same experience as you, a plugged radiator exterior causing heating. And like you, cleaning the fins solved the problem. I've never seen the temp light since (except when testing it) nor felt that the engine was running excessively hot, on three Yanmars I own/owned. The temp gauge I bought immediately in 2003 is still in its box.

Trust Yanmar's designers, they got it right. Spend the money on maintenance as Yanmar intended, instead of for additional sensors.

 

[graysonh]

Everybody buys an old Yanmar and immediately wants to hack a temperature gauge on.

On the other hand Yanmar's engineers designed to make it so it would never overheat if the cooling system is maintained. These things are designed to run much harder than our typical use - 24/7 powering a ditch pump for example or the marine engine version (same engine, different stuff bolted on) running for days.

I suggest get the warning light working properly, test it occasionally, trust Yanmar's designers, and just get on with using the tractor.

At most buy a new temperature sender if you don't trust the old one (test it on a stove in boiling special fluid). With the new radiator cap, you would sense overheating (heat, smell) long before you approach boilover temperature. The light will come on before boilover.

I started off with the same experience as you, a plugged radiator exterior causing heating. And like you, cleaning the fins solved the problem. I've never seen the temp light since (except when testing it) nor felt that the engine was running excessively hot, on three Yanmars I own/owned. The temp gauge I bought immediately in 2003 is still in its box.

Trust Yanmar's designers, they got it right. Spend the money on maintenance as Yanmar intended, instead of for additional sensors.

Great advice, California, thank you. More about an overall outlook and good for me to remember. Also, I need to just get over my fears of anything electrical! I always feel lost before I even start when it comes to wires. Goal for 2017!

 

[clemsonfor]

Milky hydro has nothing to do with over heating but do dump it and fill with new fluid!!! Your not doing anything but rusting the internals and getting bad performance of 3pt.

You still could have a bad head gasket but if that screen is clogged that's the problem I stop ever 30 mins to hour to tap it out depending on how thick the grad I am cutting is.

When you over heat pull that screen out and drop back to a high idle once filled with fluid, you don't want to cut one off hot it will just get hotter unless it's already in danger zone or too late.