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Hal, Chevy Master Tech
Category: Chevy
Satisfied Customers: 1031
Experience:  ASE and Chevy Master , 31yr Dealership exp,
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what are the symptoms of an intake manifold that is leaking

Customer Question

what are the symptoms of an intake manifold that is leaking water
Submitted: 6 years ago.
Category: Chevy
Expert:  Hal replied 6 years ago.

Hi my name is Hal, welcome. Your complete satisfaction is my goal. Please provide as much information about your concern as you can.


There will be no symptoms. You will have coolant leaking from the front or rear corners. Look for a corrosion, coolant trail, or coolant pooling up near the corners of the intake.


If it is leaking internally, you may notice the oil cap getting a milky appearance.

Customer: replied 6 years ago.
I ran a compression test on the engine, all cylinders have approximately 150 psi of compression, I have water coming from the front left side of the engine.. the engine makes no power past 2000 rpm (like it's running out of fuel), I have water coming from the left tail pipe, there are headers on the truck, so the left exaust is the left side of the engine.. the left exaust seems cold to the touch at the tail pipe, but the headers are hot.. the left header makes a hissing sound instead of an exaust noise, I have changed the fuel filter, fuel pump, O2 sensor, dist cap and rotor, I just took off the intake today, and it just lifted off with no exertion or prying on my part, just like it was loose.. what do you think my problem may be??
Expert:  Hal replied 6 years ago.

Well it sounds like you have a few different concerns here.


Coolant leak.

The left front is the most common area for the intake to leak. It will cause an external leak, running down the left front. ( did you see signs of this???)

It is possible if the intake was loose for the coolant to get into #1 cylinder intake port.


To verify that coolant is not getting into the combustion chamber through a head gasket or crack in the block or cylinder head. you can use a chemical tester called BLOCK CHECK. It is a blue fluid that changes to yellow in the presence of combustion gas.

You put some in a tester and it is inserted in the radiator opening. Then you let the engine idle. If the fluid changes from blue to yellow, you have a combustion leak.


The second way to check this is to remove all the rocker arms, so the valves will stay closed. Remove all the spark plugs and use a hose with a fitting that will screw into the spark plug hole. Use air up the cylinder and then look for bubbles coming out the radiator. Putting a tight fitting funnel in the radiator opening and fill it with coolant will allow you to see the bubbles easier.


This should not cause the engine to loose power around 2000 rpm though.


1st , What is the timing set at, and how did you set it?


2cd when this lack of power occurs, is it like running out of fuel, or does the engine start to miss/jerk feeling?

Customer: replied 6 years ago.

When the truck looses power It feels like it's running out of gas, it starts missing and making something like a valve knock noise.. That was the same way my mustang reacted to a lean condition caused by a fuel pump which wasn't putting out enough pressure.. So I just went ahead and replaced the fuel pump and fuel filter.. One thing that this motor does is really questionable is when I rev it to about 4000 RPM in park, it sounds like the valves are coming apart, then when I suddenly let off of the gas pedal, the engine dies, the exhaust smells really rich when it does this and I have to crank the starter for about 15 or 20 seconds before it'll start.. Also it will NOT hold a steady RPM in park above about 2000 RPM, it will start to miss and the RPM will deviate a few hundred higher then a few hundred lower.. It will Idle all day and not miss a lick.. I took off the spark plug wires one at a time while the engine was running and could tell the engine Idle went down and could feel a miss, so the cylinder was firing, all 8 cylinders were tested and are firing at an Idle, I don't think the timing chain is bad because of the high compression in each cylinder, I used a screw driver in the end of the spark plug wire and got a good inch of spark to jump to the spark plug.. I don't know how much coolant has gone through the exhaust.. Now correct me if I'm wrong, but if the intake is leaking coolant into the intake valve on one or more cylinders, wouldn't that go through the combustion chamber and change the test fluid from blue to yellow as well?


I have a spark plug that I welded an air fill valve on a few years ago so I could change the valve seals on my corvette, I can use that to fill the cylinders up with air, and since the intake is off anyway, could I not bring each cylinder to a spot where both valves are closed, fill that cylinder with air and see if air bubbled come up through the head water passages / jackets? This way I can remove the possibility of a cracked or leaking intake that may send the compressed air from the cylinder being tested to the atmosphere.. wouldn't this just test the block and the heads only... one more thing, I have owned this truck since it was new and it has never overheated...


There is no catalitic converter or EGR valve on this vehicle either.. and all exhaust runs through 3 inch pipe into a home made 5" Supertrap baffle off of a Harley Davidson about 4 inches past the rear bumper.. There are no mufflers on this vehicle

Expert:  Hal replied 6 years ago.
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Customer: replied 6 years ago.

this engine ran perfect for the life of the engine.. I removed the cat converter some 5 years ago and this engine has been perfect.. just all of the sudden while pulling my boat to the gulf of mexico ( which is 3 miles from my house) it started this stuff.. I lost no performance over time.. this happened all of the sudden..


the egr valve was eliminated when the edlebrock intake was installed back in 1996

Expert:  Hal replied 6 years ago.

Any kind of knock/noise will effect the knock sensor an retard timing. Since you have a detonation sound, View the timing with an ajustible timing light, to see if the timing is retarding. I know you have this apart, so checking this will take some time . Verify the cylinders are in good shape and not leaking into the cooling system.


What else has been modified on this engine?? I can't see what your dealing with, so I have to believe it is stock unless you inform me otherwise.


This is now turning into a drivability issue instead of a coolant leak issue. So I will need to know everything that has been done to this vehicle, and how it is set up.


I am only trying to give you suggestions as to what I have seen with throttle body engines over the past 25 years.