Disappearing coolant

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codfish

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So since I’ve owned this rig I’ve had a slow coolant disappearing act going on. ZERO water in the oil. No visible external leaks. No smell of coolant in the exhaust whatsoever.

Used the ole girl harder this weekend than usual, moving from one cabin to another. “Used” about 3/4 of a gallon of coolant during the 250-300 kilometres in all.

Now I can smell the coolant in the exhaust, and it is clearly on the drivers side. And once the engine is up to temps you can see the extra exhaust from the drivers side.

Intake gasket changed last year for rear oil leak.

Did a compression test today. Here are the results, and a pic of the plugs.

Any suggestions as to where to start? Won’t be right away as I’m off to work in a couple of days for 2 weeks, but might have time tomorrow to check any simple things.

Thanks
Codfish
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nvrenuf

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Seems like there's a chemical you can add to the coolant that will show if combustion gases are present (under black light maybe?).
 

codfish

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Head gasket or cracked head.
That was my guess too.

Would’ve liked to see a compression test with a cylinder way lower than the rest to indicate that.

And I forgot to mention that the cooling system will hold pressure for a week or more, without being driven or even started.
 

Old Guy Bill

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Was the engine hot when the compression test was done?
I would also suspect head gasket or crack.
 

fast 99

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May not show on compression. Another way using a pressure tester, pump it up to max [whatever the cap is rated at]. Let it sit for a few hours or overnight. Then either by hand or starter crank it over with plugs out. Look for coolant.

Spark plug on offending cylinder would normally be clean or cleaner than the rest if burning a lot of coolant. Didn't see that in posted pictures. It may end up being one of those best guess diagnosis. You know where the water isn't leaking, what's left?

My own SB would use a little coolant and run rough for the first 30 seconds after sitting overnight but otherwise ran fine. Was surprised when I finally looked into it. Both heads were busted, 1 head gasket was bad.
 

75gmck25

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Also check the bolts for the intake manifold . I used the bolts from my iron intake on a new aluminum intake, and never noticed that at least one bolt bottomed in out in the hole before the intake was tight.

It was leaking slightly in the back passenger side corner between the intake and the head, but slowly running down onto the exhaust manifold and evaporating. I could not figure out where the coolant was going, but I definitely had to top up every week or so. Finally one day it broke loose with a stream and started running out onto the ground.

Found new bolts that were 1/4” shorter and reinstalled the intake. No problems since then.
 

Matt69olds

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You might try retorquing the head bolts, remove the ones that go into the coolant and apply thread sealer.

You would think if the engine was burning coolant you would see a “steam cleaned” spark plug, your look pretty good.

It’s probably time for a leakdown test. Top off the radiator first, you know you found the problem cylinder when coolant starts to bubble in the radiator. Ideally, you would want to do the tests with the engine hot. You may have a tiny crack in a head or block that only leaks hot.

This might be a good candidate for the cooling system seal tabs. Those were SOP during cooling system service on the early 4100 Cadillac engines. They do work well for sealing minor flaws.
 

rich weyand

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Also could be a warped head, not just a cracked head or bad gasket.

On a 195 straight six, I put the head gasket on with #2 Permatex on both sides and torqued it down. What?! you say. Yes, but I got another 150K miles out of it, and it had 100K miles on it when I rebuilt it.

A warped head could be the result if the engine has been overheated in the past. It may not leak until it's warm.
 

Craig Nedrow

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No 2 and #4 look washed clean, which would be a head gasket.
 

codfish

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Leak down test done.

#7 the gauge went right to high (bad) then slowly went to low (good).

No bubbles in the rad at first, but once the gauge went to the low zone, the whole column of coolant in the rad started to rise to the point of spilling out.

Stopped the test at that point. Obviously communication between the cylinder and the cooling system.

Hopefully just a gasket:shrug:

Codfish
 

codfish

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We’ll finally pulled drivers side head. Thinking it got hot at some point before I got it. Had fun prying the head off. Gasket separated into 3 layers.

LOTS of fun cleaning the surfaces….

Back together now and running good. Lifters quieter now. Bonus. Once I get it back on the road I’ll see if the coolant levels stay put.
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codfish

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Inner layer of the old head gasket.
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