B7100 HST thermosiphon radiator level, bubbles in radiator. head problems?

[Kenonf]

Hi,
I have a B7100 HST and it is a thermosiphon type, 5000+ hours, I lost the first hour meter....
I guess I blew the head gasket about 3 years ago, and figured it out about a year ago, because it kept dumping antifreeze out of the overflow hose.
I did a compression and test and one was low, So I replaced the head gasket. Machinist removed .001" of and inch to get back to flat, commented that it was in great shape. and I put it back together.
About a month ago I look and the radiator is low, hmmm. I add anti freeze and watch for bubbles while running, dam bubbles again. Worth mentioning my son did stall the tractor a couple of times while mowing.
So, I buy a new head gasket and o-ring and RnR the head gasket again. The cylinder closest to fan has a lot of carbon on cylinder, thought we had a cracked piston. Cleaned carbon off and every thing looks great.
I put it all back together and run, dam bubbles in radiator.
A week goes by, pull out compression tester and remove injectors, first cylinder closest to has a little carbon on injector, so either low pressure or bad injector... got that.
Cold engine, got down to about 38 degrees F here last night, poured a little 15w-40 into the cylinders and gave it a spin, after about 5 sec I get a little smoke from the injector holes. screw in the tester and about 500 in first cylinder, and about 475 in the other two. I let each of them sit at pressure (about 20 min) to see if there is any pressure loss, none.
Now what....?
I was going to bring it into town and get the fuel pump tested and fixed and a new set of injectors.
Why am i getting a few bubbles on the radiator...could it be I had trapped air in system after RnR and they were just working themselves out.
Do I need to put it back together and run till hot and check compression, or was cold and oil enough?
Just a novice diesel repair tech but wiling to try.
Thank you,
Ken

 

[Kenonf]

And can anyone with this type cooling system check their radiator fill level and if below the fill port measure down, and give me a number as to how far down from the top?
Thanks,
Ken

 

[Rob111]

Big bubbles or little bubbles? is it a constant, always the same bubble flow.
I would do a pressure test on the radiator. Water in oil?
AND if a machinist told you he removed .001", he is really good! It's not so easy to have only .001" removed.
Rob

 

[tjkubota93]

You can get a tester that you draw air/gasses from the radiator into while it's running. The fluid changes colors if combustion gases are present. That's how I have always checked a suspect one. Mine was off the Matco truck. this is just the first pic I found that the tool looked similar. Mine came in a cardboard box. You could get one just for the $ you have spent on gaskets so far.

And what he said up there. Radiator pressure test. A head gasket would leak radiator pressure if combustion leaks are making bubbles.

I had a truck with a bad head gasket come in. I pulled the radiator cap (cold engine) and started it up. It shot coolant 15ft in the air onto the shop ceiling. Turns out the head gasket was really bad!

 

[rScotty]

Well, Ken that's a tricky one. It does sound like you're on the right path. But something's sure not right.

OK...compression checks.....I think a cold compression check is fine for checking for gross leaks or broken parts, but if I understand rightly your tractor is running almost OK. That means you are looking for something subtle or caused by heat.
I think I'd check it again hot. Very nifty that your gauge can test for the ability to hold pressure in the cylinder for 20 minutes....or even one minute. I'm remembering the old cheaper gauges that just held the max in the gauge itself until you manually let it out.

Ever tried a bore viewer? I always wondered about those tools that let you look inside the cylinder and show it on a screen. Never had one though. Wonder if you could borrow one just for grins. Doubt it would tell you anything subtle, but fun to look.

Lets see. Carbon in number one plus some bubbles......but no obvious mechanical problems. Yep, that sure does sound like a leak where the water vapor is cooling off the combustion. If so, it wouldn't necessarily mean measureable water diluting the sump oil until some hours had passed. So that test - although absolutely diagnostic - might miss the first signs. I understand that you can get the same fuel-rich burn with a poor injector but that's not how they usually go bad. Don't blame you for wishing; at this point that is what I'd be hoping too.....although not really believing that was it.....just straw grasping. Hey, did you swap the injectors around to check? Would that work?

I agree that the machinist has to be good to take off only a thou over the length of the head...but then that's why he's a machinist and probably using a big ol' heavy grinder whereas I'm just a hacker doing engine work with a hobby mill. But even so, I could probably hold close to that number on somthing nearly that size if being very careful. A good head grinder can do tenths. But a leaky head usually requires more than a thou.

Musing now.....Compression leaking out of a cylinder, past the gasket, and into the water and then appearing as bubbles doesn't automatically mean that the reverse path exists. Although when it does, it can sometimes easy to see the stain on the head or block. What I'm saying is that I never assume that a compression-out leak also means water-in. One doesn't automatically mean the other.
And along that line, a connected stain form the cylinder to the water jacket on either block or head and from water or gases always means that a leak is there of course....but I've seen leaks in the gasket that didn't leave enough to see on the metal.
I think from what you are saying that you already know this stuff, but just making the point.

The changing water level in the radiator with modern machines having a trapped overflow has perplexed me too. In fact, I'm still wondering about it. Now I can't swear to it, but it seems to me that if I fill the radiator almost up to the filler neck that the level won't be happy until it drops down to a new level somewhere between what I filled it to and the top of the radiator tubes proper. There seems to have a level that it wants for a max and it and will put the water somewhere until it falls to that lower level. One would think the extra fluid would appear in the overflow reservoir, but I've looked and am not convinced it is completely accounted for there. That could have something to do with bubbles, too.
Just a historical note: Old cars didn't have those overflow reservoirs. Overflow from overheating simply soaked the radiator, the grill, and any bystanders as it was spat out onto the ground. It was called "piddling".
But on the positive side, engines that didn't overheat wouldn't lose a tenth of an inch of water from one year to the next.....not even over several years. And if they did, it was generally the radiator cap gasket at fault.

I've never been so deprived of amusement that I would deliberately open up the radiator cap to see if the coolant had bubbles in it. Maybe that's because of being afraid of what I'd see. So I have no idea if bubbles in the cooling fluid are normal or not. For all I know that could be the normal state. Especially with the cap off and the corresponding reduction in system pressure.
On a possibly related note, I do know that it's normal to see bubbles in high pressure pump lines due to the pressure changing so rapidly around the impeller. There's a whole field of study about that kind of thing. Google "turbulent flow" and be prepared to read for awhile.....
Those are high pressure bubbles and will definitely grow and burst when the pressure is let off. But is this the same? I don't know.

As for the stalling causing the problem....Hmm...is it that easy to stall your HST with mower? Mower too wide? Too low? Florida grass? BTW, 38 F is cold?? Naw, that's about the temp. where I start to argue with myself whether I need to turn on the block heater for an hour before starting....and then decide against it and go for a lengthy warm up instead. Back to the stalling. Yes, it probably means that your son was loading it too much and yes, diesels do tend to overheat rapidly right before stalling. But before the overheating gets to that point where damage happens what usually happens instead is the pressure release cap lets go with a shriek that everyone within half a mile can hear.

My suggestion: Swap those injectors around because it's easy, but might as well also get ready to pull the head again. Now aren't you glad you cleaned up all those engine bolts and pre-greased the threads? Especially the exhaust side and water jacket side.

And BTW, maybe you should try to break yourself of the habit of trying to read the future by looking at radiator bubbles;
you'll see nothing but problems in there.


good luck,
rScotty

 

[Kenonf]

Okay yes I screwed up, pressure gauge would show max psi until I released pressure in the system... Ugh.
So, I unhooked all injectors and swung one line out over the ground and gave the starter a whirl. No spray. The other two ip nipples were left open, and each shot out a little drop of diesel up about a foot. Swapped injectors and nothing, put the last one and nothing again. Moved tube to number two and viola spray of diesel, ok all three injectors work on the other two nipples so I know something is wrong.
Pulled pump and the injectors off and them off at the diesel shop and they check them out. Found delivery valves worn, , and injectors sticking open. Got them back this morning, and put it back together. Started it up and wow what a difference, took about one minute to quit smoking like the engine was laboring, and then a drive test. Ran the fence line and the first few minutes I saw dripping from whistle, after about twenty, no more drips. Get back to shed and let it cool off for a bit and open radiator, fluid level at about the bottom of the neck, it was still warm when I had to go home, so I will see tomorrow. The parts guy at Kubota laughed at me when I mentioned the gasket and his suggestion was to give it some heat and time, then worry.

Machinist may have said a few thousandths off the head... That was a year plus ago....I remember asking if I needed to get the head gasket spacer for it now and he said no.

I saw a post where the poster had installed a recovery bottle on his tractor, maybe I will hit the u-pull yards and see if I can find a small one.

I wonder how long that injector has been inoperable, I would also like to crack the injector lines while running and see if engine reacts the same each time.

I know it stalled the last time I would crack the third injector.

Thank for the comments, learning as I go.
Now I'll rebuild the HST on it....

Ken

 

[Kenonf]

Thinking back, the machinist pointed to where he thought the first leak was on the head by looking at the pattern from the old gasket.

The bubbles were small and about the size of a kernel of corm, rising up the radiator neck very 3-4 seconds. That was the first time. I probably pulled a "mister negative" as my wife would call it, and assumed the worst after replacing the head gasket a second time. I also ran the tractor up a dirt mound to allow any remaining air to rise to radiator today. I will pull radiator cap tomorrow and see how it looks.

The mower in question is a Rhino SE-4, a four foot wide bush hog, and the property is wooded with small trees and grapevine interspersed between trees, with old fire lanes thrown in to make it fun. So stopping the mower with one cylinder barley running at best was probably easy for the occasional stump or dirt mound. The mower has a 1/2" shear bolt that I will reduce to a 5/16" bolt inside a piece of plastic tubing to correct for the hole dia.

We have Pensacola bahia grass in a few areas where it will give a dull mid mount mower " Kubota RC-60-71B" a problem.
I will also mention that we have cogon grass on another property, that gives the b2920 a rough time with a 4' mower and the l4200 a rough time with the 5 foot bush hog. Used to put the b7100 in turtle and crawl while at 80% of full throttle to mow that grass.
Nasty stuff.

I like the exhaust gas detector, need to check that out.
Head gasket was $60 from Kubota and I am sure it was blown both times I replaced it.
Thanks again,
Ken

 

[Kenonf]

Hi again,
Two days of use and the dripping form the overflow whistle has stopped and radiator level has settled on about halfway down the neck. My negative outlook was proven wrong again.
Glad to have it back and the rebuilt pump is wonderful.
Ken

 

[Egon]

Good show!