Kubota B7100 Overhauled now will not run

[Sanddog]

With no water pump or thermostat you should be able to flush water both ways thru the engine and radiator.
Hopefully a Flush either way may indicate a problem area. Just curious, have any frost plugs been changed?

I believe the machine shop did put in some new freeze plugs in the block after the bored and vatted it.

The head came new from KumarBros and already had freeze plugs installed. Obviously, there was an overheating problem before I bought the tractor, thus the new head I mention. I ran a lot of water through the radiator and did not seem to be any restrictions, at least not that I could tell. I washed the radiator fins alot with water and do not now recall that it was terribly choked up with trash. I will blow the fins out this weekend with an air compressor just to make sure there are no issues there, but the radiator is not hot anyway, just at the top. I was wondering if the tractor should have a fan shroud? There is not one on there now and I have not noticed any attachment points.

 

[Egon]

The should would help but leave that till the coolant flow is solved. If no flow thru the complete engine it will be pull head again time and determine if it is the head or block.

The previous owner may have had a freeze plug fail and overheated the motor?

Please note I am not a mechanic and making some assumptions.

Keep the Faith and with peresverance you will prevail!

 

[deanocraft]

Are you saying the radiator does not get hot? I assume the engine has a thermostat like a gas engine... Could that be a problem?

 

[Sanddog]

Are you saying the radiator does not get hot? I assume the engine has a thermostat like a gas engine... Could that be a problem?

The radiator gets very hot but just at the top, does not seem to spread across the entire radiator after a short run but still hot at the top.

Actually, this little tractor does not have a thermostat, nor a water pump. It also does not have a fan shroud, but it should. After looking at pictures of other 7100s online, it looks like someone removed the fan shroud at some point. I ordered a new one, as I think that may have at least something to do with the heating problem.

I pulled the radiator back off and ran water through the block/head both ways and there is not an indication of any blockage. I also ran water through the radiator and it flows freely. I did observe that the oil cooler is in pretty bad shape and is unlikely to allow much air flow through it. I think that combined with the missing fan shroud are a definite problem.

I next checked the injection timing and found that is was five degrees off. Best I could tell by carefully watching for any indication of fuel moving at the pump, it was starting to inject at 20 degrees BTDC instead of 25 BTDC as indicated in my repair manual. I reduced the shim pack just slightly and got it pretty much right on at 25 degrees BTDC. Possibly this also could be contributing to the overheating??

After the new fan shroud arrives, I will anxiously put the radiator back on and see what happens this time.

Anyone know where to get a good aftermarket replacement for the oil cooler? A new Kubota oil cooler is over $400. It is pretty small cooler and I can see no reason it should cost anywhere near what they want for a new "factory" cooler.

 

[Leejohn]

I'm going to throw this at you. It seems like to me the way the cooling works and if there is any back pressure the water flow would stop. I would check and make sure some one didn't put the wrong radiator cap on it. You might try it with cap loose or without one.

 

[Egon]

Boys oh boys, what a conundrum. At this point alli can do is offer encouragement.

Probably the only factor on the oil cooler would be pressure rating. With size there should be room to attach some where in front of the rad.

 

[deanocraft]

No water pump? I'm at a loss... Sorry to sound confused, but I can't figure out how the coolant will circulate without a pump. To me, the description you gave sounds like the hot water is not circulating. It is only staying in the top of the engine and the top of the radiator, with the cool stuff at the bottom... Wouldn't that make for a hot head?

 

[aczlan]

No water pump? I'm at a loss... Sorry to sound confused, but I can't figure out how the coolant will circulate without a pump. To me, the description you gave sounds like the hot water is not circulating. It is only staying in the top of the engine and the top of the radiator, with the cool stuff at the bottom... Wouldn't that make for a hot head?

They were designed to be a Thermosiphon system and so the heat from the engine causes the coolant to circulate.

Aaron Z

 

[bigdeano]

The radiator could well be operating normally. My Isuzu diesel generator radiator will run at 170 deg at top of radiator and bottom tank will be room temperature. That's what they're supposed to do, cool the water. Does the cylinder head get too hot? Couldn't find it in your posts.

 

[KYErik]

If the coolant is not boiling/making a rumbling sound when it finally dies, I don't see why it would be seizing up because it is too hot. There is a lot of friction as new piston rings first wear against a freshly honed cylinder- and yes things will get tighter as the engine warms up.

Does this injection pump have a governor that functions at idle? I know diesel injection pump governors work well at maintaining engine speeds regardless of load, but I am not knowledgeable enough to know how effective they are at idle. I believe that maybe the engine is just being bogged down by all the friction (and slightly rising temps/increased friction) and the current amount of fuel injected to keep the engine at a slow idle isn't enough to keep it running. If it was mine, I would run the engine at 25% throttle the next time I started it and see exactly what happens when it dies (does it bog down slowly or quickly die just as you pulled the engine kill knob).

Leave the rad cap off and kill it at the first sign of steam if you are afraid to get it hot (the pressure behind the cap raises the boiling point).

Maybe even crack an injector line and make sure it is still leaking as the engine dies (to make sure the injection pump isn't losing prime or malfunctioning).