The strange case of the hot 755 compact tractor

[DrBill]

Hi everyone, first post. I have a 755 deere/yanmar.. The series who's downfall it seems was overheating.. Mine started doing this and I decided my tractor was not going to do this.

I bought it from a friend who is the nicest guy in the world, but not a techie guy, so he had the dealer do everything, including a rebuild approx 100 hours before I bought it. Soon after running out the tractor I knew I had some oil leaks,, and smoke coming out the vent pipe,, I was worrying some,, then the temp light starting coming on. I then started looking close at this rebuilt engine and saw JB-Weld on the oil pan seam, and knew right then,,, what a mess,,, I'm going to build this engine,,, correctly.

I took it down,, a disaster,,, wrong bolts everywhere,, some so long they had cracked internal bosses off the aluminum covers...please fill in the blanks from here,, it would take 5 pages to explain... Everything was wrong.

I rebuilt the radiator, water pump , engine (to exact spec, including head). After assembly I started a great running tractor, but after 20 minutes run time, overheated again !

Assuming I missed a crack, I ran and chemically checked for pressure and exhaust in radiator during 5 or 6 run hours,, none,,,,, but it still would get hot under load in 10 minutes.

I would let it cool,,, add more water,, try again..

10 running hours ago, I loosened the radiator cap to first position when overheated. It puffed enough steam to heat a skyscraper with a lot of pressure behind it.. After it cooled, I removed cap, refilled with what to seem more water than ever before to fill it up.

Since that moment, it has never ran hot again,,, July heat, full load with 60 inch belly deck, overgrown grass, and the deck has the peerless 1 to 2 turn overdrive gear box. The clear radiator vent hose doesn't even get steam vapor in it... It's happy..

My question is,,, surely someone has seen this before on these tractors,,, what did I do ? Did I release an air lock,,, blow loose a blockage ? Remember, I had run the engine a lot with the radiator cap off when checking for gasses. I figured that would release air lock issues,, maybe not....

In the past 10 hours running under these loads, it has lost no coolant level either....

I wish I knew more about this, as I would like to swap over to my regular coolant instead of water. Right now, I'm not afraid to run the tractor,, but I'm afraid to touch the coolant !!

Thanks

 

[tman1020]

I'm thinking u did not get the block full at first fill. Possibility blockage at thermostat.

 

[DrBill]

I agree, the point being, how do I avoid this in the future ? I don't know of a refill process I haven't already done at the beginning.. No bleed screw on top of thermostat housing? I'm beginning to think what I've ran into might be an issue with prior posters of overheating 55 series tractors, in spite of their bad radiator placement design.

Whatever this tractor was mad about in its cooling system,, it did not give up the answer easy.. Today, I can't make it overheat... I can't explain how it went from impossible hot, to not...

 

[Bladehauler]

is there a small air bleed hole or valve in the thermostat ? if not i would pull the thermostat out , fill with coolant to that point , reinstall the t stat and finish filling .

 

[boggen]

for me, after a flushing of the coolant system and its time for a refill with proper water/anti freeze mix...

i do initial fill with engine off,
then keep the cap off, turn tractor on, and wait for thermostate to open up. 5 to 15 minutes (it depends)
and then finish filling / topping off
put cap back on,
after some time running machine and it has had time to cool down to open the cap back up, i may add just a little bit more.

==============
were you on nice perfect level ground when filling it backup?
was tractor jacked up for some reason?
did you have the wrong water/anti freeze mix ratio in it?
did you ever check thermostat to see if it was working correctly? taking it out and boiling it
is there a third party engine block heater on the tractor?
does the tractor have a heater? and after initial fill, never turned tractor on and turned heat high as possible / full blast, to work out any air in the heat element inside cab?
did ya run houses UP then back down. forming a upside down U shape in idea were air could gotten trapped?
is water pump electrical, and perhaps bad connection some place? or is water pump ran directly off driveshaft or like on engine?
does tractor have "winter fins" in front of radiator, so you can close them in winter to get a warmer engine and keep coolant from freezing solid, did you have them closed by chance?

and 100 buck question is.... are you sure temp gauge not broken? or cruded up with something?

 

[DrBill]

I knew this post might be unanswerable, but typed it as an interesting story if no one had dealt with it.

It's beyond the basics.. I tried to not make the first post too long,, but to explain more let me add some more info.

During the hard time while I was trying to check exhaust gases in radiator,,, I knew I had an air lock or pocket somewhere.. The water pump was pumping water well,, the radiator was full,,, but I could hear popping sounds and sizzling noises coming from inside the block in a small area. (a Hot pocket) ,,,,,

I could not move the hot spot or make it flush away. I had started to believe I had a crack in that area causing a pressure bloom.. As we know now,,, not the case.. But at that time, I could not define why I had this..

Only when I let it overheat good, then loosen the radiator cap (a dangerous maneuver ) did I cause enough pressure drop to break loose this trouble spot.

After I saw that I had accidently fixed this thing, I recalled years ago reading an article dealing with a yanmar,, the water pump design, and a blockage that could occur, and what to do and not do.. (Of course I didn't need the info back then)

I'm going to change the coolant and get the right stuff in it. If I cause the same problem again, I'll report it.
Thanks

 

[RandyT]

Sounds like an air lock situation with the cooling system when drained and refilled. the old Gator 6x4 with the 20hp kaw will air lock the cooling system if totally drained and refilled, like in an engine disassembly and reassembly and refill.

 

[bohaslup123]

got a 755 and when refilling the radiator I allow the motor to run with the cap off for approximately 10 minute allowing the air pockets to escape. you may have to do this a couple time but the air will eventually be removed-good luck

 

[aginn]

My old fiat allis had a bad radiator hose that separated inside and acted as a flapper valve to block coolant flow. It acted a bit like what you are explaining. It was maddening to find but simple to repair once I knew what the problem was. What got me was that it didn't get hot every time. It only happened about once every 5 or six uses. Which was 5 or 6 times too many.

 

[DrBill]

Thanks everyone for your replies. I did change coolant yesterday and got something besides hard water in it.. I flushed everything out on a large concrete slab so I could inspect the water and any objects or debris that might have been inside the cooling system.. It was all clean.. (I would have paid 100 dollars for a dead rat or something to explain my prior problems)

I did leave the top hose off the top of the radiator at refill just to see it fill as I finished filling.. The capacity for this tractor is one gallon and that's what I got in it.. Ran it a few minutes with cap off.. Of course the tractor is fine, no more overheating..

I'm sorry for this boring thread, most of my writings are usually more fun, but this situation will always be a mystery to me. The overheating was why I remanufactured the engine in the first place, and I had tried all the normal things long before I decided to take it down..

While building the engine, I knew something was strange because I couldn't find a root cause as I wanted and expected.. The engine for sure had a sloppy dealership build, a lot of head wear overlooked, etc. but nothing blown or broken that would say here's the problem..

Then after assembly, the engine was overheating exactly the same times and ways as before the build. I knew I had an air lock or something as mentioned in my two posts above, because I could hear the water boiling in the cylinder furtherest from the radiator, but I could not make it move or clear until I released the radiator cap under a super hot condition. You will never hear me recommend that to anyone !

Over the past few years while working with this tractor, I read dozens of posts all over the net about 755 overheating problems.. Most posts would die out without a final answer or conclusion other than it had to be a crack somewhere.

I can't help but wonder if some of those other tractors might have been doing something like mine did..