I’ve been battling this issue for over a year, it has been overheating since I purchased my mini excavator. I replaced the head gasket initially with no change. Then took the whole engine to the machine shop, put all new cylinder liners in, pressured checked the head, decked the engine and head. Replaced valves, water pump, thermostat and radiator. It still overheats and had blow by. So I replaced the head the a brand new one, no change. Just replaced the injectors with no change. It has an electronic lift pump, so I ordered a new mechanical one and will install that tomorrow. It heats to 230F in about 5 minutes of digging work, installed a mechanical temp gauge and checked it with a temp gun, and still has blow by. I’m at a loss idk what else it could be. I have over 3k invested in the motor and it still isn’t operational. Any suggestions?
Maybe it needs a bigger radiator. How well is the engine ventilated?
You would have been better to spend the money on a professional radiator and cooler cleaning instead. What happens if you don’t do any digging and just run the machine at 3/4 throttle? Try and find what’s making it overheat. What happens if you just track around? Should be able to narrow it down to engines or hydraulics. Does this machine have a separate oil cooler or is it built in? What is the ambient temperature when you are working it? Does it heat up as fast if it is cold out?
What mini excavator is it? If it's a cheaper off brand may not have been designed for optimal cooling.
It’s a gray market Hitachi ex 35-2 about a 2003 model. I retorqued the head and adjusted valves per my mechanic today, thinking the new head gasket might not have sealed. No change, overheats and has blow by. I noticed lower rad hose is 30 degrees or more hotter then the upper. It’s about 65 degrees here, it’s gets up to temp quickly whether cold or hot outside. It overheats under load with hydraulic use. Last week I added an electric fan on the hydraulic cooler which is next to the rad. At full throttle just sitting there it runs about 190F, cools down under idle. I saw they make 2 different direction water pumps but I did pull the upper rad hose last week and it was pumping out.
I wonder if it needs a specific thermostat or the thermostat is faulty. 190 isn't bad if it doesn't go higher.
New or old, did you test the thermostat? I'd be borrowing or renting or some how getting a good thermo camera and check the radiator, and every thing else. If this is a used machine/ engine, then maybe it has done this day one, could be something blocked internal or someone left a rag in there. I'd be checking flow through everything.
I once worked on a water pump that was used for fighting fire, it was a two-stroke powered unit . It only produced 175PSI instead of the 270PSI of the second same unit . After changing out the pump we found out the recoil had been wound backwards and the pump was starting backwards. It was a Wajax unit. If your water pump could turn backwards it would still cool, just not enough. Just a thought. Simon C
I put a new thermostat in it, checked it prior and it was working. Tonight I removed it, then flushed the block and radiator with a garden hose. It flew really nice both directions in both block and rad. Resembled but still overheated to above 200 after a few minutes when tracking back and forth. I pulled the cap and noticed the coolant wasn’t flowing as quickly as I would imagine for no thermostat. The water pump is new when I rebuilt the motor but I can pull it tomorrow and check if it’s slipping on a shaft. I used a regular temp gun to check the temps, I don’t have a thermal camera. I installed a new rad last week and there was no change, but reinstalled the old one because the fan shroud wouldn’t fit the new one
Interesting you mentioned the reverse direction. A few weeks ago I thought of this. Looked up the water pump for the v1505 and it appeared to have pumps that spun in different directions but had the same part number.
Impeller spinning backwards would make a huge difference.
On most engines (not sure about this particular one) coolant won't flow correctly if the thermostat is not installed.
Better make sure your impeller is not turning backwards or that is your problem from way back. Detroit Diesel made water pumps that could turn 2 ways for 2 different engines. Simon C
I’ll check it out tomorrow and make sure it’s spinning the right way and not spinning free of the shaft at high RPM. I just saw it has a 60 or 70mm impeller for the same motor. I installed the 70 last time
Rad cap could be suspect too. What coolant are you using?
Its not only the size of impeller, it is the direction of the flutes. Water pumps are non-positive displacement. If lower rad hose is 30 degrees hotter than the upper, something is wrong. Simon C
I replaced the rad cap this weekend suspecting that, no change. I just read online to check proper impeller direction. Just noted that there’s 2 different size impellers and directions. I’m assuming go with the biggest size? Making sure it spins the right way of course
Is the rad. cap the correct PSI rating?
The gauge is reading correct temp? The airfilter clean? Not over fueling? Does it act like a lot of load on it? Is it a turbo engine? Timing is all good? What is radiator inlet and outlet temps with the hand held ir? You never said what the temps checked at. Is there a bypass for quick warm up some place? Maybe too much by pass. All we can do is guess miles away.
You mentioned changing the radiator and that the shroud wouldn’t fit the new one. One thing I have found with the Kubota engines, is that the cooling system is designed for optimum air flow. If you are losing any air flow around the radiator at all, this will affect the temperature. Make sure all the shroud and insulation, including the foam is in place. Might be on the right track with the water pump also check to make sure fan is in correct rotation for a push or pull type fan. Most Kubota are either push or pull and they sell fans for either direction for most motors they sell. When I replaced the fan on my V2203 they had fans either way but most were pull type and I needed a push style.
On some equipment the rad shrouds and air flow is very important. On Lincoln welders the the cooling system is designed to work the best with the side doors closed.
Update. Yesterday I had a feeling the head gasket wasn’t sealing correctly due to the blow by and overheating. So I pulled the head, it all looked good, slight scoring on the cylinder liners but nothing I could feel which I figure is the blow by. Not sure how that happened with new piston, rings and liners. The head gasket looked great. I used a different one and put 5 coats of copper coat on both sides per one of the mechanics in the area. No change when back together but made me feel better. Today I pulled the water pump. It was the correct impeller size and correct direction according to the push not scoop orientation I read. Put it back together and no change. I ordered a coolant pressure gun that uses a garden hose and compressed air to clean the coolant system. Maybe the guy before me dumped a few bottles of head gasket fix and it’s just full of sludge that the garden hose can’t flush out by itself. But I’m pulling at straws. I had a few tractors that I overhauled where the block was half full of sludge and overheated.
I'm lost you had it all apart at a shop? And it wasn't cleaned out?
I believe he had the block in the hot tank after putting new sleeves and decking the block. Idk what else to do.
And the radiator input and output temperatures are what?
I just put my temp gun close to the upper and lower rad housing. Its 200F on top and bottom.
No coolant circulation.? Should be close to 20 Deg difference between upper and lower hoses.
I can see the coolant flow with the cap off
That’s not what the temperatures are saying.
And aim at all the areas of the radiator core. Is there a pump by pass? Thermostat out, top hose disconnected, start it does it pump? Cooling fan for radiator? Too small of radiator or plugged?
And what was the out come?
The top and bottom were 200F, randoms spots on the rad tubes were either 100 or 140. This is with the original rad and fan. Thermostat out and coolant flowing. There’s a small hose that comes off the water pump and connects to the thermostat house, no other by pass. I picked up an electric rad fan and was going to install that and the new rad tonight when the kids go to bed and re test. I did a chemical flush a few days ago and everything came out clean before, during and after.
Stupid question but have you verified the fan is installed the correct way? If it's on backwards they tend to not move air through the rad very well.
Yup fan was on the right way, one of the first things I checked. Put the new radiator and electric fan on. It heated to about 200 in less then ten minutes. I checked the temp at the thermostat housing with the temp gun and it read 210, 200 top of rad, 160 bottom of rad and 210 at inlet of the water pump coming from the lower radiator hose. I spent a while with the temp gun and the temp of the rad slowly rose to about 200 throughout the whole thing. I was thinking maybe the water was flowing to fast so I’m going to grab another thermostat tomorrow, as the other one I gutted as part of the diagnoses earlier.
The blow by is still concerning to me from the fresh rebuild. I’m not sure if the extreme amount will cause the overheating. It has decent pressure, smoke and drips oil out of the valve cover breather-after it warms up.
All the shrouds are in place, all the foam sealing strips between the coolers and around the sides are in place? The larger Hitachi excavators were known to overheat if the shrouds, guards and the gaps between the coolers were not all sealed up properly.
It appears like it’s all there and intact
Is this electric fan on there factory or was it a modification done to the machine? I can't say I've ever seen a mini ex with electric cooling fans before. Engine driven fans tend to move a lot more air than an automotive style electric fan.
Okay so you have blow by. How was this rebuilt engine broken in and what oil did you use and what was the condition of the head? Did you use plastic or metal? What was there when it was tore down, plastic or metal?
The engine was broke in with 15-40 oil and let at a high idle for 45 minutes. The head was pressure tested and valve guides replaced at the machine shop. I ended up buying a replacement head because it was still overheating and still have the same issues. What are you asking was plastic or metal? The head gasket was the 2 piece metal
It came with a mechanical fan. I put the electric fan on the new radiator because the shroud wouldn’t fit the new radiator
I think u just answered your own question. No shroud.
If after the airflow through the radiator is fixed. And it still over heats take that bypass hose off and block the ports.
Never put an engine to high idle and leave it there unless heavily loaded. Better to use light load and slowly increase load while varying the engine speed. Up and down on RPM is better and tends to prevent cylinder glazing and subsequent blow-bye. Sometimes it will clear with load afterwards. Just what I have done too many times to count. Simon C
What are your thoughts on break in oil? One I get the overheating fixed I plan on replacing the rings and honing the cylinders then do a proper break in
I still like to use a straight 30w oil for diesels for break in. I try and use a non-detergent oil, if available. I have used a 10/30 or 10/40 but notice more oil pressure loss after break in using those oils. Think that’s a personal opinion but I do watch that oil pressure closely.
Did you verify that the new head gasket matched all of the passages in the block and the head ? Especially the size of the coolant passages. Fuel injection timing set correctly ? The blow-by is a cause for concern. Has the head been manga-fluxed for leaks ? Is there any solder bloom on the radiator tubes ?
New head gasket was perfect match. The old head was pressure tested and passed. I got a new head anyhow after I still had problems. Tonight, new rad and thermostat installed. I confirmed the rad is cooling. Thermostat housing 210+, top rad 200, bottom rad 170-175, the same hose going into the water pump is 195 an inch before the thermostat. Had the temp gauge about red lined when tracking 50 feet back and forth a few times after I let it warm up.
The timing on this Kubota uses shims under the pump, when I put the pump back in I used the same shims it had previously. I’m not sure how to check timing on these engines
When temping near each injector when it’s running, one cylinder is 20-30F hotter then the others. It has new injectors
And what is the temp for the thermostat? 180? And what about the by pass hose? Turn that off for this test. By pass does just that by passes the themostat/ radiator for warm up. So try a 160 thermostat, if the radiator is working then? I say there is just too much bypass volume happening. Timing what fuel pump? I thought all the fuel timing, not over fueling etc was all sorted?
Thermostat rating is 180. Timing the injection pump I meant. I’ll pinch off the bypass tomorrow and give it a try
Drill down on the reason there are multiple water pumps available from which to choose. I see that your 4 cylinder kubota uses the same water pump as a 3 cylinder motor d905. 1000cc motor vs 1500cc Quite possible you have the wrong pump or pulley diameter so try a different combination. You can't assume the bigger 70mm impeller pump is better in all cases. maybe the pumps are different heights or displacements. maybe your pulley is turning your big impeller too fast or slow for the design of the housing etc etc. Try oem parts, assuming you are using aftermarket. Timing pump is matter of turning the engine over by hand to different marks on the flywheel and watch for fuel welling up into the pump outlets. find a manual online or utube etc
I’ll do some research tonight on the water pumps. The pulley is OEM. I’ll watch a video on the pump timing as well
It’s a v1505ka if that narrows it down with your information
Here are the details of your water pump. It doesn't appear that the impeller could be pressed on backwards or could it ??? When you checked the impeller how tight is it on the shaft ? Could it be slipping at engine operating temperature? Fan belts can develop a glaze on them and slip. I have seen it happen and they didn't even smoke or stink. Have you tested the thermostat in hot water to see what temperature it is opening-if it is opening at all. The fuel injection pump timing isn't set with shims that I can see. Or were you referring to the mechanical lift pump ? Strangely the camshaft for the fuel injection pump is mounted in the engine block.
So its just an old mechanical style multiple jerk pump? If so its a drip timing deal. Will the machine move okay with very little engine speed and low throttle position? Seems to heat more and faster with machine movement, are the brakes applied, even if it says they are not? Does if feel like the machine puts undue load on the engine?
The impeller appeared to be in the push not scoop orientation and was tight on the shaft. The belt is new and pretty tight, I didn’t notice any slipping. I was referring to the fuel injection pump timing for adjusting with shims. This engine doesn’t have the cam for a mechanical lift pump, so it has an electric lift pump. The machine has good power at all throttle levels. It has a light color smog when full throttle digging but not heavy. It heats up faster when machine moving, there’s no brakes on the machine. Then the muffler is off it seems like it uses a ton of energy to move the machine but put the exhaust back on and it seems to operate normally besides the overheating and blow by
Would a 60mm impeller vs a 70mm cause the coolant to back flow or not flow properly? When I had it apart I believe the casting was 80 or so mm and the impeller machined area was about 70, the extra 10 was for water flow by the shape of the casting
The motor was bastardized before me, so any part may not be original or was tampered with. It had all this issues prior to any machine shop work
Have seen some crazy hard to figure out problems in the past. Some would never have been figured out without some previous experience. Seen an engine block with 2 coolant holes for water to go from block to head that were 1/4 inch from drilled completely through. Had been overheating and destroying cylinders, never had another overheat problem. Had to look close with head off to see, not saying it is your problem, hope you find it. Simon C
I think I solved my excavator overheating. I only adjusted the “hp smoke screw” last year thinking that was the only adjustment besides high and low idle speed but apparently the “idle limit spring” which is a screw controls max fuel input for the IP. It’s under a tamper proof cap, same as the smoke screw. Both were marred up but when I read about it over summer I figured it idled fine so it doesn’t need adjustment, so I’ll just turn down the smoke screw. So yesterday I turned the idle limit spring screw in about 4 turns, a little at a time. I tracked around for an hour and used all the functions. Got it to 180 degrees and just under 200 after the hour of tracking back and forth non stop, take a 2 minute break and it cools to 180. Factory temp gauge is in the middle, a little higher when it was at 200 but not at the red. Given it’s 15 degrees outside but tracking back and forth for an hour she was as hot as I think it’ll get. No more haze under load, no power loss either. The screw must have been screwed way out for extra power, apparently that’s a hot rod thing to do besides the smoke screw. Kubota doesn’t give factory limits for the adjustments so it’s a trial and error. Last week when I drove it into the shop I let it warm up for 10 minutes and tracked to the shop and it got to 230 in the 2 minute drive. Everything in the entire system was rebuilt or replaced. Except for the Injection pump which will be here in a few days. I tried this last minute before install the IP.
Now you know why the last guy sold it.
If you ever get time to snap a picture of the back end of pump and post it I am sure many would like to see. Simon C