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Old 10-25-2019, 09:27 PM   #21
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Originally Posted by OlgaAK View Post
What if it is three minutes? It looks like I can get a kit to test for combustion gases in the radiator at the same kind of shop that will have a thermostat. But I am anxious now and will appreciate any info.
If itís 3 minutes coolant is not circulating. Itís sitting in the water jacket until it boils. Normally in that time the thermostat would open and the water pump would move coolant.

Why was your radiator replaced?
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Old 10-25-2019, 09:44 PM   #22
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If the bubbles start within seconds of starting, I think you have a combustion leak when cold. Go to the parts store and get a block testing kit. That will tell if you have a blown head gasket or not.
I misread your timeline. Even after several minutes it could still be a head gasket. The block test would tell. I have also seen water pumps with corroded or broken impellers create this. Do the block test
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Old 10-25-2019, 10:22 PM   #23
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If the bubbles are showing up and building high pressure before it even warms up then I suspect compression is getting into the cooling system from a head gasket or cracked head/block.
Yeah a bad head gasket can/will do that.

First things I'd check would be the cap, thermostat, and I'd make sure all the air was bled out of the system.
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Old 10-25-2019, 10:27 PM   #24
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What is a compression test? I will need to run it to get to the store and back. About 60 minutes total driving.
an hour with a cooling system failure and your engine could be nuked. It may not even live the whole hour. Its nothing to mess around with.
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Old 10-26-2019, 01:41 AM   #25
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Off hand, it looks to be compression/combustion gas leaking into the jacket (coolant) water, so I'd say a coolant test is where I'd start. When you're looking at it on idle it might seal up when the engines warms up, but under load it will blow.

This is my experience in the marine world: I ran some engines with some serious liner cracks for a few hours, but turn the engine off and the coolant disappears.
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Old 10-26-2019, 10:57 AM   #26
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To clarify, when I say that the expansion tank is boiling, I mean there are a lot of bubbles. The fluid is not actually very hot.

I am not in a place until later today to drain the radiator level to be able to directly test the gases in the radiator itself, but I used the block testing kit on the expansion tank and it is staying blue.

How much faith can be put in a test done using the expansion tank rather than the radiator itself?

I drove the bus 20 min this morning and it wasn't until I got to the shop that the engine temp dial finally hit 180. It stayed at 100 for the first half of the drive, despite that being somewhat mountainous roads.

I bought a new thermostat and some form-a-gasket, plus pfte tape to reseal the bolt on the bottom of the radiator. I'm also going to get some Blue Devil and read up on water pumps and maybe buy some parts for that before going to a place where I can really work on this.
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Old 10-26-2019, 11:00 AM   #27
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Why was your radiator replaced?
Because my (now-former) mechanic told me that the leak I was seeing was due to a faulty radiator. Since then it has become clear that the fluid is coming from the pinhole in the expansion tube. I think he just wanted to sell me an expensive repair and took advantage of my trust.
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Old 10-26-2019, 11:30 AM   #28
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that line marked in red

in your first post... think of it as a way for steam or air to get out of the cooling system... when that starts having bubbles or boiling go through the the smaller hose.. is the smaller hose hot to the touch? when the small hose is hot to the touch does the bigger, upper hose get hot also? If the smaller hose is like too hot to touch and the bigger hose is cool enough to hang onto or cold, that would indicate the thermostat is not opening very far or not opening at all. the cool water from the radiator is sucked up from the lower hose pump through the engine block, up through the cylinder head then out through the thermostat and upper radiator hose. when the thermostat is shut there is usually a small "bypass" hose to allow a minimal about of coolant to circulate, this also helps in the case of a stuck thermostat.


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Old 10-26-2019, 11:35 AM   #29
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do you have time to telephone?

discuss test strategy and trouble shooting.

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Old 10-26-2019, 01:21 PM   #30
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God bless the guy who was working at the auto parts store. He used to work for Cummins and spent over two hours in my bus pointing out all the most likely issues. He said that he didn't like my 9 pound radiator cap and sold me a 13 pound one. I got the bus up to about 200 degrees just now and peeked in the expansion tank and don't see any bubbles. Maybe this issue was just the radiator cap? I will keep looking in that tank and listening for sounds. On the other hand, there is something defective with the radiator fan and I will begin researching how to fix that. It's not related to the bubbling though and isn't an urgent issue. It just explains why the bus runs slightly hotter when I'm stuck in traffic than while on the highway.
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Old 10-26-2019, 07:31 PM   #31
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Wow that would be great if it’s just a radiator cap.
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Old 10-26-2019, 08:59 PM   #32
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I fail to see where a loose fitting or not enough pressure cap is going to cause aeration of the water. I doubt the cap is the fix, though I also recommend a high PSI cap.
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Old 10-27-2019, 03:11 AM   #33
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I fail to see where a loose fitting or not enough pressure cap is going to cause aeration of the water. I doubt the cap is the fix, though I also recommend a high PSI cap.
I have a theory based on some chemistry. When you increase pressure in a closed system like a cooling system, your boiling point will rise. IIRC, the boiling point of most coolants is not that much higher than regular water. In an engine that's running hot, it could be boiling the coolant out of the system. Apparently it's a significant issue in Ford versions of the 6.0l, and it seems most Fords in general as I'm always having to top them off.

Since OlgaAK mentioned that he thinks his fan is defective, thus lowering the cooling capacity at low speeds, it seems quite possible that could be why it was boiling coolant with a lower pressure cap but now is ok.
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Old 10-29-2019, 02:32 PM   #34
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The problem came back. I called a dozen mechanics, all insisting that it must be a head gasket despite no other signs of that, before someone finally asked if it had air brakes and told me to come in.

Half an hour later, the mechanic had drained the air tanks and done some tests with the air compressor. The pressure in the radiator continues to rise even when the bus is off, well past the limit for either radiator cap (he stopped testing as it approached 30 psi).

It seems like the air compressor is leaking pressure into the radiator and needs to be replaced. The new part arrives tomorrow, repair planned for Thursday. Fingers crossed that this will be the last $1500+ repair for a while...
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Old 10-29-2019, 02:52 PM   #35
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Ouch. Sorry to hear that!
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Old 10-29-2019, 02:54 PM   #36
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Sure beats a head gskt repair of worse a head.
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Old 10-29-2019, 05:32 PM   #37
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I have a theory based on some chemistry. When you increase pressure in a closed system like a cooling system, your boiling point will rise. IIRC, the boiling point of most coolants is not that much higher than regular water. In an engine that's running hot, it could be boiling the coolant out of the system. Apparently it's a significant issue in Ford versions of the 6.0l, and it seems most Fords in general as I'm always having to top them off.

Since OlgaAK mentioned that he thinks his fan is defective, thus lowering the cooling capacity at low speeds, it seems quite possible that could be why it was boiling coolant with a lower pressure cap but now is ok.
I read it more as aeration, than boiling. Water boiling point does go up under pressure by about 3* PSI. A 12lb radiator cap will raise the boiling point to around 242*. I've never seen a slow boil in an overheating radiator.
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Old 10-29-2019, 05:34 PM   #38
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Can someone explain to me the relationship of air in the radiator from a brake compressor? The systems are not connected in any way. Sounds like you're about to be taken for $1500.
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Old 10-29-2019, 06:29 PM   #39
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Can someone explain to me the relationship of air in the radiator from a brake compressor? The systems are not connected in any way. Sounds like you're about to be taken for $1500.
X2, Olga.
Don't know your bus engine wise but, hard to believe the compressor is cooled by the radiator or any other part of the engine coolant/system.
Try to get a 2nd opinion if not too late!
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Old 10-29-2019, 07:46 PM   #40
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X2, Olga.
Don't know your bus engine wise but, hard to believe the compressor is cooled by the radiator or any other part of the engine coolant/system.
Try to get a 2nd opinion if not too late!
Nothing but oil going through the compressor. Oil is cooled by the radiator, but not directly. The first thing that comes to mind when I see bubbles in the radiator, and think of a blown head gasket, I look for milky oil.
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