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Intake vs Head gasket question. #5288505 12/08/19 12:40 PM
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007 Offline OP
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After a lot of going back and forth with my carb which dumps fuel and my tranny with a stuck modulator I have come to the conclusion that I may be leaking coolant internally as my radiator level has dropped, still have white smoke and water droplets from the tailpipe. Plugs still look fine and I still have no water in the oil or oil in my water/coolant. Is there an easy way of telling which gasket(s) I may have blown? The motor, a 1970 396 was rebuilt not long ago and everything looks normal. I was going to drop in some of those AC/Delco coolant tabs as recommended by someone in my car club but I am not looking to band aid a serious problem even though I am not looking at the cost of having to possible do the head gasket(s). Smoke is the same out of both exhaust tips! Thanks in advance for opinions and/or ideas.

Re: Intake vs Head gasket question. [Re: 007] #5288510 12/08/19 12:52 PM
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Have you tried a cooling system pressure tester yet? Might be able to see where it is going, the fact both tailpipes looks the same isn't helping-either one smell like antifreeze when it's running?


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Re: Intake vs Head gasket question. [Re: 007] #5288518 12/08/19 01:02 PM
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If you fill the radiator all the way up when it's cold the coolant will expand and push some coolant out of the overflow. If you look on the side of the radiator there is a stamping on the tank that says "full cold".

Could this be what's happening? Also get a pressure tester and pump the cooling system up when it's cold and look for a leak.

The BB Chevy is a tough engine. While a blown head gasket or cracked head is a possibility it's veryvery rare.

The vacuum modulator is a 3 minute repair. If it's bad it will be a big vacuum leak and that could make the carb dump fuel.

Last edited by Chris142; 12/08/19 01:05 PM.

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Re: Intake vs Head gasket question. [Re: 007] #5288554 12/08/19 01:33 PM
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Before delving too far, i'd get a uoa after say 2000 miles on the oil. If you see potassium in the uoa then worry.


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Re: Intake vs Head gasket question. [Re: 007] #5288618 12/08/19 02:28 PM
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Do a cylinder compression or leak down test. Compare the #'s, and look for bubbling in your radiator.

If any of that looks off, you need to pull the heads. If not, get the manifold gasket, take it apart that far and look for signs of leakage. If nothing is found, do the head gasket too.

You wrote that the plugs look fine, but does the residue on all of them look the same which is more likely intake issue or one (or more) look different like a head gasket?

Last edited by Dave9; 12/08/19 02:31 PM.
Re: Intake vs Head gasket question. [Re: 007] #5288743 12/08/19 04:52 PM
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andyd Offline
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Check tranny fluid too . If the cooling loop in the radiator is split coolant may be getting into ATF


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Re: Intake vs Head gasket question. [Re: 007] #5288758 12/08/19 05:21 PM
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The great think with old engines is that you can do a lot of old diagnostics to narrow down things. These have been mentioned, but just to summarize:

1. Do a compression test and look for less than 10% variation between cylinders. If you have a low cylinder, you have a leak somewhere

2. A leak-down test, either on only the low cylinder or on all of them, can help you pinpoint the leak. As said, bubbling through the cooling system during a leakdown is somewhat definitive for a breached head gasket

3. Look for signs of oil and coolant mixing, including greenish or milky foam on the rockers. You can also check the cooling system for exhaust gases.

4. A cooling system pressure test can be a bit redundant with the above, but can give you additional information

5. One of my favorites-use a boroscope to look in each cylinder. Whether the engine has 10 miles or 100,000 miles on it, you should see some soot and other residue/evidence of it having been run. If one cylinder looks sparkling clean, you probably have a head gasket leaking coolant into the cylinder. Essentially what's happening in this case is that coolant dripping into the cylinder flashes to steam and more or less "steam cleans" the cylinder.


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Re: Intake vs Head gasket question. [Re: bunnspecial] #5288786 12/08/19 06:07 PM
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You should see coolant in the oil with an intake gasket failure. It would be much more likely for a head gasket to cause white smoke/coolant loss than an intake gasket. It would have to have failed on both the coolant port and intake port right next to each other for it to suck coolant through intake gasket, which would be near impossible. You’d certainly have coolant in the oil, too, with that type of failure.


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Re: Intake vs Head gasket question. [Re: 007] #5288795 12/08/19 06:22 PM
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Re: Intake vs Head gasket question. [Re: 007] #5288796 12/08/19 06:24 PM
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Originally Posted by mattd
You should see coolant in the oil with an intake gasket failure. It would be much more likely for a head gasket to cause white smoke/coolant loss than an intake gasket. It would have to have failed on both the coolant port and intake port right next to each other for it to suck coolant through intake gasket, which would be near impossible. You’d certainly have coolant in the oil, too, with that type of failure.


?? My last intake gasket failure, I had no coolant in the oil but did have white smoke and coolant loss (and hydrolock).

It was not necessary to have it fail on ports right next to each other, coolant can leak into the valley under the manifold and get sucked into any nearby or all cylinders as each opens and sucks more air in. However in my case, it was a coolant passage going up through the throttle body, so there's that, it didn't have a carb.

Last edited by Dave9; 12/08/19 06:26 PM.
Re: Intake vs Head gasket question. [Re: 007] #5288816 12/08/19 06:52 PM
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The spark plugs will tell you which cylinder is "burning water" (making steam)

My "guess" is intake gasket.


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Re: Intake vs Head gasket question. [Re: Dave9] #5288879 12/08/19 08:02 PM
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Originally Posted by Dave9
Originally Posted by mattd
You should see coolant in the oil with an intake gasket failure. It would be much more likely for a head gasket to cause white smoke/coolant loss than an intake gasket. It would have to have failed on both the coolant port and intake port right next to each other for it to suck coolant through intake gasket, which would be near impossible. You’d certainly have coolant in the oil, too, with that type of failure.


?? My last intake gasket failure, I had no coolant in the oil but did have white smoke and coolant loss (and hydrolock).

It was not necessary to have it fail on ports right next to each other, coolant can leak into the valley under the manifold and get sucked into any nearby or all cylinders as each opens and sucks more air in. However in my case, it was a coolant passage going up through the throttle body, so there's that, it didn't have a carb.


In your case, sure, if you had coolant dumping down the throttle bore then you can hydro lock the engine. However if antifreeze is leaking into the valley of a traditional “V” engine, it’s leaking onto the lifter valley. So yes, you would have coolant in the oil. I can’t make any sense of the second section of your post regarding the intake gasket leak, sorry.

Last edited by mattd; 12/08/19 08:03 PM.

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