B7100HST dies when hot

[hardway7885]

Hey all, new to the forum and having problems with a tractor. I've got a B7100HST tractor with 842 hours, 16 hp D750 motor, i'm working on for a friend and it is dying once it gets warmed up. The tractor was supposedly overheated to the point where the antifreeze was evaporated out of it and shortly after is when this problem developed. It will start very easily and run for approximately 10 min. great and very strong with no smoke. After that the rpms start to gradually drop and fluctuate up and down,accompanied with blue/black smoke, until the motor eventually dies which takes probably another 3-4 min, it also loses major power once the rpms start to drop. It will restart easily and then soon die again. It sounded to me like it was gradually starving itself of fuel, so I cleaned the fuel filter and make sure the lift pump was pumping sufficient fuel. Both checked out, so I pulled the injector lines off to find that the injector pump was pumping plenty of fuel out the top with decent pressure, shoots fuel about 6 inches out of the top of the pump. So, I figured that the block or head had cracked when it was overheated and the crack was sealing when cold and opening back up when hot causing a compression drop. I checked the compression cold and it had 450 PSI on all three cylinders after about 18 compression cycles, after letting it run until it died I again checked the compression and it was exactly the same, 450 PSI after about 18 compression cycles. This leads me to believe there isn't a crack or lack of compression causing the problems. What does this sound like to you guys?

Any help is appreciated.
Thanks in advance.

 

[85Hokie]

could this be a vapor lock ? take your fuel cap off and run it again - any change?

The antifreeze boiling out is a bad sign......but truly the water alone in this situation is the best coolant possible. The radiator is full when cold and then when you can check again after cooling the same?

There is no water pump on this model - all about hot water rising and cooling and failing back down to the lower radiator.

If you run the engine with the radiator cap off - under a pumped system you would see water flowing once the thermostat is opened.....here the water should sit still for a while until it gets hot and then it will probably come over the top, HOWEVER if there are bubbles........bad news, head gasket or worse......

report back to us

 

[hardway7885]

The coolant seems to remain constant. It was just a little low when I first began looking at it and after two heatup/cool down cycles it appears to be the same. I don't think it is anything to do with the fuel cap as it has plenty of fuel coming out of the lift pump and injector pump even after it dies. I pulled the fuel line and injector lines right after it died and fuel is getting there.

 

[North Idaho Wolfman]

Fuel shortage would be my # 1 choice, while it's running and getting hot crack an injector line at the injector and look for fuel and RPM drop.
You might also want to pull the injectors and have them tested as they might be floating open when they heat up, pull the return line off and look for excessive flow on the return, that would definitely point to an injector that is floating or not spraying right.

 

[hardway7885]

I've cracked all three injector lines one at a time after it got hot and started to run poorly. All three have fuel coming out around the line and the rpms drop significantly. I don't know about the injectors failing when hot, but i'm going to hook up another gravity fed fuel tank i've got on a stand today to rule out fuel starvation before the injector pump.

 

[Daren Todd]

I think your on the right track with rigging it up and trying it with some known good fuel. It kinda sounds like you may have some gas mixed with your fuel. It can make it do some pretty strange things sometimes.

 

[hardway7885]

Okay, it seems that we have found a solution. It was in fact bad fuel causing the problem. I took good fuel and another tank on a stand to bypass the fuel system up to the injector pump. I let the tractor run until it died and then hooked up my tank and tried to start it. After sputtering a little it smoothed out and ran great. To rule out a blockage I dumped the good fuel out of the tank and put some of the fuel in the tractor in my tank and the tractor was again running poorly. Dumped out that fuel and put good fuel in it again and it was running great.

I smelled the fuel in the tank and it smelled like gasoline or kerosene or something like that, so it has been contaminated with something and isn't pure diesel fuel.

Thanks everybody for all of your help, it is greatly appreciated.

Sent from my XT1031 using Tapatalk

 

[Tooljunkie]

Awesome that you figured it out.
Now others will see that assuming fuel is good isnt always The case.

 

[hardway7885]

I was able to confirm that it was in fact gasoline that was accidentally added to the tank. After draining the fuel and filter and filling it back up the tractor now runs beautifully. Thanks for everybody's help.

Here are links to a couple of videos of it acting up for anybody having this a similar problem in the future. The first is of it running and starting to drop rpms and die, the video was started after the rpms started to drop and the fuel lever was never moved from full fuel the whole way through the video. The second is of trying to start it after it died.

https://www.youtube.com/watch?v=f_mM-eqlVUI

https://www.youtube.com/watch?v=0rwzS0zaMoc

 

[North Idaho Wolfman]

You need to change your settings for the videos.

 

[hardway7885]

Okay, settings set to public, videos should be good to go. Thanks.

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