Tell me what you think is wrong here with this D6T C9 engine

[Vetech63]

This is a D6T S# LAY00704
This machine has been sitting the last 3 weeks waiting for me, and I just got to it today.

Their mechanics story.......The machine is going through 6 gallons of coolant a day. When you run it hard, coolant will spit from the overflow tube. I have cleaned the radiator core, removed and cleaned the belly pans. I have not been able to find an external leak anywhere.

The owners story (He showed up right after their mechanic left). I repeated what the mechanic told me and got "Well, I don't think that's right." He says he was told that the coolant loss was about 2 gallons over several days and that coolant wasn't added until the machine started to run hotter. He isn't aware of any leaks that have been seen.

The operators story.......He seems to think there has been coolant leaking from around the radiator neck because its been wet there. He also says that when working a machine horizontally on a slope, the water loss seems to be worse when the left side of the machine is downhill.....versus the right side being downhill. I'm like at this point.

First thing I do is check the coolant level and its perfect, right in the middle of the site glass before cold start up. I then pull the engine oil dipstick......

Its good, no signs of water that I can see. I then remove the radiator cap and it is still under pressure from the last time the machine was ran 3 weeks earlier. At this point nothing is making sense.
I start the machine to let it warm up and during the warm up I notice a small amount of what I thought was smoke from under the radiator........its the end of the crankcase breather hose. I then remove the hose from the breather housing so I can watch what is happening......

Yeah, its steam but not a crazy amount. I cleaned the inside of the housing where the hose hooks up and continued to run it at idle. No doubt it is steam, little water droplets formed.

Here is my question for you Cat guys. Is there anywhere inside this engine that would create steam........with no pressure loss in the cooling system at operating temp @ idle? Loss of coolant possibly at high idle only through the radiator overflow line? (unproven as of yet)? ...........but the cooling system remains under pressure for 3 weeks? With no signs of coolant in the engine oil and no external leaks??

Someone help me out here because I'm missing something.

 

[Mobiltech]

If it’s losing 2 or more gallons and the oil is not milky I would doubt that it’s all leaking into the crankcase unless it’s running hot enough to steam it all out the breather . If that’s the case the breather should look creamy.

Did you check water pump weep hole for a stain or dirt collecting?

If not water pump I would next do a rad pressure test or overflow pipe in a bottle bubble test under full load.

 

[Truck Shop]

Should I or should I not.--I should.

Crack between valve seats-9 years ago C15 that pulled exact same stunt. Did a bottle test nothing was
confirmed. Rad test nothing was confirmed. Until engine was at full temp at top rpm. Never showed
white smoke at stack. No leaks externally. Water pump had been changed by Cat thinking that was problem
along with oil cooler, zero change. Crack had to expand just enough with higher egt. 2-cents.

 

[Nige]

Did you open the oil pan drain to check for any coolant accumulated in the pan.? I doubt it but worth checking just to tick the box.

Otherwise I’m with my learned friend Mr TS of a cracked head, or at least something cracked upstairs.

 

[Vetech63]

If it’s losing 2 or more gallons and the oil is not milky I would doubt that it’s all leaking into the crankcase unless it’s running hot enough to steam it all out the breather . If that’s the case the breather should look creamy.

Did you check water pump weep hole for a stain or dirt collecting?

If not water pump I would next do a rad pressure test or overflow pipe in a bottle bubble test under full load.

Water pump checked also…..no issue.

 

[Vetech63]

Should I or should I not.--I should.

Crack between valve seats-9 years ago C15 that pulled exact same stunt. Did a bottle test nothing was
confirmed. Rad test nothing was confirmed. Until engine was at full temp at top rpm. Never showed
white smoke at stack. No leaks externally. Water pump had been changed by Cat thinking that was problem
along with oil cooler, zero change. Crack had to expand just enough with higher egt. 2-cents.

This is making sense as the symptoms are identical.

 

[Vetech63]

Did you open the oil pan drain to check for any coolant accumulated in the pan.? I doubt it but worth checking just to tick the box.

Otherwise I’m with my learned friend Mr TS of a cracked head, or at least something cracked upstairs.

I did not check the drain plug. Since I didn’t see anything concerning on the dipstick as far as higher level or gravy I didn’t see the point. I’m just shocked that the system holds pressure and is not putting water out somewhere that I can positively identify.

 

[Nige]

Don't get too hung up on the fact it holds pressure when cold.
An example. A case of a 3516 that would hold pressure in the coolant system for ever and a day when it was cold.
Get it hot and it would leak, but into the crankcase unlike your C9.
Turned out to be a cracked liner.
These things happen and because yours is pumping out water vapour (assuming that there is coolant and not just water in the radiator. Does it smell of anti-freeze.?) from the fumes disposal tube suggests that the crack is higher up than the cylinder block area per my example above.

 

[Vetech63]

Don't get too hung up on the fact it holds pressure when cold.
An example. A case of a 3516 that would hold pressure in the coolant system for ever and a day when it was cold.
Get it hot and it would leak, but into the crankcase unlike your C9.
Turned out to be a cracked liner.
These things happen and because yours is pumping out water vapour (assuming that there is coolant and not just water in the radiator. Does it smell of anti-freeze.?) from the fumes disposal tube suggests that the crack is higher up than the cylinder block area per my example above.

Makes sense. It does smell of antifreeze. The customer is downsizing their fleet and is trying to decide if this machine should be part of that process. I told the owner today that I would be guessing at a solution to this at the moment.

 

[Nige]

Pull the valve cover off and run it.? That might give you a better idea of the soruce.

 

[Cmark]

An oil sample should be a high priority IMO.

 

[Junkyard]

I had a C15 do what Truck Shop said as well. No it was not the one Miller has now lol.

I’ve never used one but they make a kit to test for the presence of combustion gas. I wonder if that would help narrow it down?

I second the oil sample.

 

[JD955SC]

Does it have an EGR cooler?

 

[Nige]

Does it have an EGR cooler?

Not an LAY - too old. TIER 3 maximum, maybe even TIER 2.

 

[Mobiltech]

Cracks between the valves are very common on a c15. Cat told us the head could be reused if you see 2 or less.
We didn’t reuse them like that but apparently it’s a thing.

 

[John C.]

I would think that two or less would refer to you could only repair two or less and still be able to reuse the head. Is my interpretation right?

 

[Vetech63]

I got to play with the troubleshooting a bit more today. I believe now what I thought was steam.........still was but it may have been condensation, there was no steam today. Here is what happened today.

I started the machine this morning and let it idle at 800 rpm for the first hour. The radiator coolant level was right in the middle of the sight glass.
* Ran for one hour @ 800 rpm with no signs of leakage, over pressure, temp gauge running in the middle of the sweep.

** I bumped the engine speed to 1400 rpm and did a hydraulic stall off and on. Same results as above, everything normal.

*** Bumped the speed up to 1650 rpm.........same hydraulic off and on stall, normal as above.

****Bumped the speed to 1850 rpm.......after about 1-1.5 minutes, the overflow hose starts to spew out coolant. The temp gauge has never wavered.

I ran the machine through the same scenario again...same results. This time when the overflow hose started spewing, I backed the rpm down to 1400 and within 20 seconds the coolant loss stopped, and all was normal again. I performed this several times with the exact same result.

This engine isn't showing any of the traditional signs of overheating from a head gasket or crack. I can point to nothing. What IS making possible sense is a flow restriction of the internal radiator core that can't pass the volume of coolant at rpm's higher than 1800. Once the surge tank floods the water pump just can't force that flow of coolant through the radiator. It quickly overcomes the radiator cap pressure setting and spews out the excess pressure. I have found no hoses to be restricted and the water pump seems sound.

Does this seem like a reasonable conclusion? Is there any type of baffling, or anything besides the thermostat that can restrict the water flow in this type of system? The engine has not overheated during any of this and the temp gauge never wavered.

 

[Junkyard]

Could the cap be weak….? Wrong for application and too low of a pressure rating?

 

[Tyler d4c]

Perhaps you need to out a pressure gauge on the top and bottom of the radiator to rule out a clogged core or wrong pressure of a cap

 

[Nige]

Has anyone looked at the water temperature regulator.? I know it doesn't quite fit the symptoms but if it was not fully opening........??

Does this seem like a reasonable conclusion? Is there any type of baffling

The radiator on this tractor is AMOCS type. That means the inlet (left side) and outlet (right side) are both at the bottom. The illustration is from a D10 but the design is the same idea.
The bottom tank is divided by a transverse baffle. I'm not sure if that baffle is welded or has a silicone seal that is designed to prevent coolant returning direct to the cold side without having to flow up/down through the cores. It might be worth taking some inlet and outlet coolant temps.
I've even seen cases where the seals at the bottom end of the cores started to fall apart and the pieces lodged in the tubes in the inlet (front) side of the cores blocking partially the coolant flow.