Water disappearing - need some help !

[TobyArnot]

WARNING - THIS IS KINDA' LONG, BUT I WANT TO BE THOROUGH.

O.K. - I need some help before I lose what's left of my mind. In the last few weeks, my 350/350 '70 C-10 Stepper has started "drinking" water. I say "drinking" because I am having to add 1/2 - 1 gallon of water to my radiator daily. I and several car-buds have looked all over and we can't find any obvious leak. Nothing dripping anywhere. New 16# cap holds pressure on 1-ton big radiator. No problem overheating (except in a slow drive-thru on a hot southern day w / A/C on. ) LOL!
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Now, I would think "blown head gasket". O.K. No water in the oil, no oil or exhaust in the water. No water in the tranny.

NO RUNS, NO DRIPS, NO ERRORS !

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I have put nearly 5000 miles on this truck with no significant problems. Still runs fine with no high speed miss. Buddy followed me for several miles & no sign of white smoke out exhaust.
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This is what I get for spending too much money on her.
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DETAILS:Basically stock 350/350 - PO likely 25-30K miles??
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Only other thought I've had is a hairline crack in a cylinder head between the water jacket and the exhaust port. "Sucking water out at speed???" I really don't want to tear into a good running engine, but this has got to stop.
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O.K. gang, Help me solve this puzzle. It's my Daily Driver.

[Vintage Windmills]

If you don't have an expansion tank, maybe coolant is expelled as it heats up and expands. Are you filling the radiator to the top when its cold?

[Lee H]

With no expansion tank, stock set up, water level should be about 3 inches below the top. Anything above goes out the overflow as your driving.
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[71swb4x4]

I agree with the others. Either add an expansion tank, or leave it 1/2 gallon low and keep checking it. If it still loses 1/2 gallon every time you have a problem. I suspect it's as the others above say, you are loosing it when it expands, and that probably always happens while you are driving so you don't notice any dripping.

[Stocker]

Have you tried pressure testing the system? Check for leaks with engine off & preferably cool, so small drips won't evaporate before you see them.

[TobyArnot]

Allright gang,.
I do have an expansion tank plumbed from radiator overflow to bottom of a JEG'S plastic bottle. Doesn't seem to ever have anything in it. (vented top-open).
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Sytem was pressure checked and held 16-13# for at least 5 minutes after shutdown during heat-rise period. No carbon mo. in water...New STANT cap 16# (too much?)
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Now, maybe you guys understand my frustration. I've been around SBC s all my life and can't remember this ever happening before.
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That being said, am I chasing a problem that doesn't exist. Is 3"-4" below the cap normal? I noticed that the highest point of the top hose is higher than the fill tube. Is that normal? I have tried filling it cold, filling it idling with the thermostat open, running with the cap loose, about every senario I can think of. Same result. Drive 25-30 mins. on freeway and - BINGO - water low. I'm going to resist the urge to check it for a day or two. Maybe that's "THE NEW NORM.".
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Anyway, thanks for all the expertise. I will keep you all updateD as it goes.

[cdowns]

expansion tank recovery system is dependant on having the proper type of radiator cap

i'd check real good the waterpump weephole

[71swb4x4]

I think 3" is normal.

[kieth]

I had a customer with a Freightliner Tractor, it was losing about the same amount of water everyday, we thought it was going to be overhaul time (7-$12,000.00 until he pulled up one day and we popped the hood open and saw a very fine mist coming from one of his heater hoses, it was just a mist and it evaporated instantly....mystery solved......just replaced the heater hose.......we had been trying to find it for a month. sometimes it is something simple. Kieth

[Vintage Windmills]

I'd let it idle with AC on while on some pavement and inspect for leaks while it warms up and gets hot.

[fatboys69]

Had kinda the same problem, was loosing water n could not figure out where it was going. changed everything, water pump , heads , gaskets , hoses , had radiator cleaned and check all to no avail. AFTER buying a rebuilt engine and pulling the old one out I found the problem, a leaking freeze plug BEHIND the motor mount. May wanna check them as well. JMO

[bmfm64]

Does it continue to get lower and lower or does it seek a level and land there?
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[TobyArnot]

Hey guys,
All good advice. I'm think I'm going to try the "idle 'til it leaks or blows" test.
At this point, I'll let here blow steam til the cause shows up !

[Stocker]

Originally Posted by TobyArnot

I do have an expansion tank plumbed from radiator overflow to bottom of a JEG'S plastic bottle. Doesn't seem to ever have anything in it. (vented top-open).

Start with a radiator full of coolant, and your expansion tank 1/3 full of coolant.

New STANT cap 16# (too much?)

Close enough -- 15# is OEM. With a sealed system (that is, with an expansion tank) you need a cap for a sealed system -- standard cap will not work.

[TobyArnot]

UPDATE:
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Filled the rad., ran @ idle for 20 min. w/AC on. Never got over 200*, nary a leak.
Shut off, let it cool down, stiill no drips. Open cap and -BINGO- down 3".
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Screw it, I'm gonna drive it and see what blows first!

New STANT cap 16# (too much?)
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Close enough -- 15# is OEM. With a sealed system (that is, with an expansion tank) you need a cap for a sealed system -- standard cap will not work.

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What is a "correct" part # for a cap. I have a new cap and it's supposed to be correct.
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STILL AT IT !

[treveiger]

Have you left it go an see if it gets lower then 3 inches
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[bmfm64]

My truck always runs a little low too, where is your overflow mounted? Is the lid higher than radiator cap?

[TobyArnot]

Originally Posted by bmfm64

My truck always runs a little low too, where is your overflow mounted? Is the lid higher than radiator cap?

I'm using a plastic catch can from JEG'S. see pic, mounted straight up, on right front inner fender, about level with the exhaust port. sorry no picture. It's late. Line runs from rad. overflow to bottom fitting. I pulled the top fitting and it's grommet out. Left about a 1/2" hole in top. This should work.
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I'll keep digging !

[bmfm64]

So once it goes down 3 inches does it stay there or does it continue to lose water?

[chopnchaneled]

Would your 350 happen to be a vortech? Had an issue with mine using coolant and it turned out to be the intake gasket was leaking into the cylinders while running.

[Shyguy]

Originally Posted by chopnchaneled

Would your 350 happen to be a vortech? Had an issue with mine using coolant and it turned out to be the intake gasket was leaking into the cylinders while running.

Yep, my brother had a '95 and '98 with the leak in the intake gasket. After he replaced the gaskets he had no further problem.

[TobyArnot]

Originally Posted by bmfm64

So once it goes down 3 inches does it stay there or does it continue to lose water?

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That would be the current test. Filled it last nite, drove about 20 mins. last night. Drove it 20 mi. to work this a.m. on freeway. I'm going to resist the urge to top it off. Gonna' drive some more later and see where we are.

Originally posted by chopnchaneled
Would your 350 happen to be a vortech? Had an issue with mine using coolant and it turned out to be the intake gasket was leaking into the cylinders while running.

Not a Vortec -strickly old-tec.

AGAIN ; Thanks to all of you for your thoughts and input

[Crabass]

I'm inclined to agree with Chopn and Shy, I think there's a good chance that coolant is being pulled into one or more cylinders. Had the same thing happen to a 4.3 with about 150K miles. It finally got bad enough so that I began to notice that when started cold the exhaust seemed to "steam" a little more than usual, or than other vehicles that were started at the same time (depending on ambient temp and humidity). Finally figured it out when I started it cold with the radiator cap off------blew coolant out of the open radiator a foot or so. Turned out that the steel shim factory head gaskets had deteriorated enough to let intake vacuum suck coolant into a couple of cylinders. Yes, even though I had always maintained clean and correct antifreeze/water mixture.
I agree also that intake gaskets are a very likely suspect. You might consider pulling the spark plugs to see if there is any unusual discoloration. I'd think if there was some, but evenly so on most or all plugs, that might be more likely intake gasket related; if just a couple or few are more heavily discolored, more likely head gasket or something cracked. And if I'm making no sense, just disregard me completely, I won't be offended.

[domeier]

Originally Posted by TobyArnot

Shut off, let it cool down, stiill no drips. Open cap and -BINGO- down 3".

That's about where mine runs. I don't have an expansion tank, so it just blows out the excess until it hits about 3" down, and stabilizes there. Is your expansion tank working? Does the level go up and down?

[domeier]

Hey, I just remembered something: When I bought my truck, I found that some friggin moron PO had sealed the bottom of the front right fender with silicon. That just happens to be where the coolant overflow tube dumps. There must have been a gallon of coolant drained out of there when I cut out the sealant. I guess that doesn't apply to your particular problem, but something for people to look out for anyway.