Thursday, November 23, 2017 Detailed Auto Topics
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Late model General Motors vehicles have had more than their share of problems with intake manifold gasket failure

Many times these vehicles come to us, leaking again after having had the intake gaskets replaced elsewhere. Any number of things have been blamed, from Dexcool coolant to defective gaskets. I feel neither of these adequately explains the large number of repeat failures suffered by these engines.

In many cases the previous shop has elected to replace the original Dexcool with standard type coolant in a hope to prevent problems. The repeat failure of the gasket without Dexcool seems to indicate it is not the cause. I have also seen many brands of gaskets used, again with equal instances of repeat failure. It is unlikely multiple producers of intake gaskets would all have the same problem.

GM lower intake gasket coolant leakage, left side

GM lower intake gasket coolant leakage, right side

Stopping the repeated failures involves understanding how the system operates. These engines have cast iron cylinder blocks. The intake may be either aluminum or plastic and cylinder head may be aluminum or cast iron. These dissimilar materials all expand at different rates when normal heating and cooling occurs. Because of this difference in expansion rates there is movement between the components.

Typical GM intake gasket and cylinder head

When the intake gaskets were designed this was allowed for. A flexible O-ring type seal is placed around each opening, held in place by the plastic gasket-backing. As the components move, the O-ring "rolls" back and forth on the intake and cylinder head surfaces. The smoother these surfaces the longer the O-rings will last. When machine work is rough the O-rings wear and are pulled away from their backing. Very rough machine work, even on new replacement components, is a leading cause of failure in my experience. 

Very rough GM engine block and cylinder head surfaces

Cylinder head and block seal surface, in area of coolant leakage

GM cylinder head machine work at sealing area of intake port 

Once the seal is damaged, pressurized coolant can run pass. If the coolant is dirty, it brings debris with it, vastly increasing the problem. The debris is abrasive and wears the surfaces even more.  When coolant leaks, air enters the system to fill the void. The presence of oxygen provides a catalyst which tremendously accelerates corrosion. Corrosion makes the surface far worse.

Mechanical distortion on intake gaskets from rough surfaces

The first symptom noticed is usually a low coolant level. While the level needs to be filled, many people simply add water. This aggravates the situation by diluting the corrosion protection of the coolant. Left unattended, the vehicle will quickly deteriorate to a not economically feasible to repair (NEFR) state. That is, the cost of proper repair can quickly exceed the value of the vehicle. A proper repair can involve replacement or repair of the intake manifold and/or cylinder heads. Replacing the intake gaskets alone, when the engine is in this state, is an expensive exercise in futilely.

Selecting a shop that will perform a root-cause diagnosis is imperative

Making a proper repair in a timely manner, can provide many miles of trouble free use. Treating the symptom [leaking gasket] alone will become very expensive and frustrating.

  • Keep corrosion protection adequate by properly replacing the coolant when needed.  Time is more critical than milage, specific gravity and pH are even better indicators.


  • Never add plain water to the system, this will dilute the corrosion protection.  Coolant being low indicates a problem. Dexcool and distilled water should be pre-mixed before adding.


  • Act quickly, diagnose and repair the problem as soon as it begins.  Time is critical to preventing further damage.


  • Choose the proper shop, someone who will solve the problem, not just treat the symptom.




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