Here is what I've done so far: 1. Change radiator cap. 2. change thermostat. 3. Compression test.
My son talked it over with some diesel mechanics he knows at work in Colorado. They also think that since the fluids aren't cross contaminated either way the coolant problem is not related to the low cylinder test. That leaves 3 suggestions to follow up on.
First is the stuck check ball in the manifold which has me puzzled. I understand the test is to squeeze the upper radiator hose and listen to the sound. I tried that with the motor cold and didn't hear anything however with my hearing I probably need a stethescope so I'll get one tomorrow but exactly where should I listen for the sound? Also should the thermostat be in the open position for this test?
Second is the test for exhaust gas in the coolant. I haven't found this stuff locally but Northern Tools sells a kit which includes the chemical. I'll have to order this and wait a few days. I found the chemical at about $7.50 a gallon but the description sounds like you need the kit plus either a hose from the engine vacumn or a hand vacumn pump to make it work.
Third: Pull the heads and get them crack checked. I Talked to the master mechanic for our equipment division today. He had 18 years with Cat before coming to us but admitted to knowing little about the 7.3's. He said he had seen a couple cat engines with similar symptoms and they ended up testing positive for head cracks. Do any of the crack sealant chemical additives really do the job on a diesel with it's high compression and would it be worth trying heating the engine up, adding the chemical letting it mix and circulate with the coolant and then shut the engine off, keeping the system pressurized as it cools down hoping any crack opening up as the head cools would be sealed? Actually that was a 4th suggestion from an employee with a 6.9 at work but I'm wondering if anyone has experience with this type of fix.

 

Sorry to be tardy with reply..............

You state you changed the Tstat, not sure if you posted this before, did you use a Ford or IH tstat only........installed correctly.

The check ball is in the face of the upper manifold where it connects to the block. Listen at the manifold pipe, not the hose...........for the tinkle.

I would not as yet go any farther into it than a cooling system problem.

 

Thanks again!

The picture of the check ball made sense out of it all, including how the thermostat works without a bypass. The thermostat was the first thing I tried but I didn't know about the check ball and I don't remember seeing it visible like the picture shows but I also can't remember if I cleaned that gasket surface or if my son did. If it was free would it have fallen away from the surface when we turned the part over? I couldn't hear any sound when I did the radiator hose squeeze test so I put a plank with a pillow for my wife to lay on across the fenders, got the step ladder so she could get up there, and had her listen. She said she could hear a dull clink sound about a half second after I released the hose. Does that sound right or should I consider removing the manifold and doing a manual check?

The first morning the problem appeared I bought a discount parts house brand X thermostat but when we got the truck apart and saw how different it looked from the original I changed my mind about putting it in and went to the local Ford parts dept. That's also where I drew the first blank stare when I described the problem to a Ford truck mechanic. The Ford part replacement was installed exactly like the old one came out. Looked exactly like the old one did too.

Also my compressor chuck wouldn't fit on the compression test GP adaptor that I borrowed last weekend so I haven't done the pressurized cylinder test. I think my compressor will turn up to 150 psi so I'll look for parts to hook it up and complete that test too. Is there an easy way to tell when the valves are closed on #5 and #8 without pulling the valve cover or do I just keep turning the engine trial and error by hand untill pressure builds in the test cylinder?

 

When you installed the tstat did you put the copper pellet base in the block hole with the top hat toward the manifold. The dull clink could be the ball falling back yes.........the one in the pic is held in with a plastic retainer, some guys have mentioned they had a cork retainer?? if you clean the ball area do not take the ball out, just pick around it if able.

Your wife must love you mine will do something like that too, but only for supper out..

The only way I know exactly where the true #1 tdc is by removing the small cover on the front of the timing cover and seeing where the dowel pin is located on the gear. Then you can by hand turn the crank to the right compression tdc for a specific piston. Or you can do the finger on the GP hole and wait for compression.

Here is some info........

The timing mark is found on a little plate that is on the front of the engine on the passenger side. The plate is mounted so it is very close to the main pulley on the lower front of the engine which is mounted on the vibration damper. On the side of the vibration damper, is a line, which when lined up with the line marked (0) on the plate, tells you that the #1 piston is at TDC(top dead center) You can see the line on the damper, and it points to the line on the plate with the (barely visible) 0 mark on it.You'll have to find a way to turn your engine over by hand. Make sure you remove the power wire to the injection pump(so the engine won't start)and then rotater the engine till you can line up the marks.
The engine rotates in a clockwise direction as seen from the front of the truck, and for every 1/4 turn of the engine(crank) each next piston will arrive at TDC. So, When the line on the vibration damper is at the 2 oclock position, cylinders 2 and 5 will be at tdc. When the mark is at the 5 oclock position, cylinders 7 and 6 will be at TDC, 8oclock has cylinders 3,8 at TDC, and back to 11oclock, 1 and 4 will be at TDC.
Cylinder numbers are assigned 1,3,5,7 on the left(passenger) bank from front of truck to back, and 2,4,6,8 on the driver's side, front to back. Firing order is 1,2,7,3,4,5,6,8.

Ziggster

 

The logic you presented on the theory of a stuck check ball was so convincing that I removed the Tstat housing this evening. The ball was stuck in the up (in) position, which appears would block the exit hole. I pried it loose with a pick, hit it with a burst of air and it stuck right back up in. if I tapp the housing on a block of wood I can get the ball to fall back down. The ball in this housing appears to held in with a soft gasket type material. I'm assuming the ball should move freely behind the grommet and that gravity alone should make it fall. I'll see if I can pick around behind the ball with a fine wire or needle. I checked the exit hole with an inspection mirror. Tough to see well but it appeared to be round all the way into the ball chamber, however, the ball itself does not appear to be round. Is there only one exit hole from the ball chamber? and do you know if a person can buy the ball and grommet separate from the manifold? I really wanted to pull the grommet out and remove the ball to make sure I had the chamber clean and verify if the ball is still round but the grommet will be destroyed if I do.

Thanks for all the other information!

 

I have not seen the soft gasket, so best to call IH or Ford as to if there is a replacement ball and gasket, as yet I have not heard of one. With the ball not round as you say then sticking closed would stop air bleeding out. There should be only one sealing point/exit to the manifold from the ball hole however I have not ventured in to see. The way the ball works is it allows air out but holds back coolant until the tstat opens. While the tstat is closed the coolant circulates within the block bypass area and heater core, pushed by the waterpump. When the tstat opens it blocks the bypass and sends coolant to the rad for cooling.

Since you have the tstat out do the test...............

CAUTION:
The specified/required thermostat does not contain an internal bypass, since the bypass is located in the cylinder block. Whenever the thermostat is replaced, it is mandatory that only Motorcraft E5TZ-8575-C or Navistar 1807974C94 thermostat be installed.
CAUTION:
Do not attempt to repair any thermostat. It should be replaced if it is not operating properly.
Check the any new thermostat before installing it for correct opening temperature. Before suspending in boiling water, with a flashlight check where the rubber and the flat metal flange meet for bad seal. Tstat should start to opening barely at 180-192f, fully open 200-212f, allow to cool and check for rubber seal again.
Removal: Disconnect batteries, drain 4+ gals A/F, remove: as required, fan belt, alternator set aside, alt bracket, remove filter support from fuel filter then e/block. Disconnect upper rad hose at rad, remove tstat bolts and housing. Clean both faces, depression and holes in block, ensure check ball in goosekneck is clean, free and rattles "do not remove".
Installation is reverse proceedure, I do not use sealant on gaskets and faces. REMEMBER the tstat pellet(copper end) goes into the block. I do use a "very small amount" of sealant on the edge of the tstat face when installing into the recess, now go for coffee, allow sealant to setup, this has saved me from tstat slippage when the gasket and goosekneck are installed.
Manifold bolt torque......... 20ftlbs

 

Since you have the tstat out do the test...............

Thanks for the tips, the knowledgable advice and the instruction on how to proceed. I apologize for being such a novice but want to thank you for your persistence in helping trouble shoot and get my truck running. The furnace is down tonight and I've got parts strewn all over the floor since I got home from work. The truck will have to wait.

"If it weren't for bad luck I'd be having none at all !"

Don