Chevrolet V8 Intake Manifold

Bad Chevy Intake Manifold GasketsBad Chevy Intake Manifold Gaskets

You must remove a Chevrolet V8 intake manifold to repair two common problems. This includes the slow and mysterious disappearance of engine coolant and a check engine light that leads to a knock sensor problem. You'll find these issues on generation two and generation three Chevrolet V8 engines from the mid-1990s through the 2007 model year.

Although these are the two most common reasons to remove the upper plenum and lower portions of the intake manifold, these are not the only ones. In fact, anytime you remove a cylinder head or perform any kind of major engine work you'll need to remove the intake manifold.

What you see when you first take off the part might surprise you. From the factory Chevrolet used a composite intake manifold gasket made of plastic and silicone. Since the gasket is delicate and could crack from over tightening, General Motors uses a very light torque spec measured in inch pounds. Therefore, they installed thread locking compound on the manifold bolts to stop them from backing out.

This becomes an important point to make as we move our way down to the repair section below. What I want people to understand from this article is that improved gaskets are now available. And unless you have a bench grinder with a wire wheel, you might consider getting new bolts.

You can get rid of the plastic and silicone gaskets and go with a steel and rubber assembly from Fel-Pro and other suppliers. It's not often that I recommend an aftermarket parts solution. I'm a strong believer in AC Delco and General Motors replacement parts.

With that said, whenever I have a chance to replace something plastic with parts made out of metal, I go for it. The other important point to make is the replacement of the knock sensors and wiring harnesses while you have the intake manifold removed. This poor design eventually fails as the plastic connectors disintegrate from heat and age.

In addition, water gets down around the knock sensors and causes corrosion issues. The part of this that amazes me is the amount of vehicles that have experienced this problem or will in the future. This leads me into the next section where we'll talk about the symptoms associated with these common problems and the engines most affected.

Symptoms of an Intake Manifold Problem

Before we talk about the symptoms of the Chevrolet V8 Intake Manifold problem let's talk about the massive amount of vehicles affected by this issue. The plastic and silicone gaskets installed from the factory found their way into generation two and generation three V-8 engines.

This includes the popular 5.7 L Vortec V8 and the series of V-8 engines that replaced the legendary small block Chevy. The generation three engines included the displacement variety of 4.8 L, 5.3 L, 6.0 L and even the mighty 8.1 L V-8 truck engine. Note: I put the Vortec V6 problem on a separate page.

The symptoms of this intake manifold problem usually begin with a low coolant light. In the beginning a simple topping off of the coolant reservoir takes care of the issue for weeks or even months. However, as the leak picks up speed drivers realize they have a problem that needs resolving.

Unfortunately, when they go to search down the engine coolant leak, they usually find no signs of such a leak. This is because the intake manifold gasket is allowing coolant to slip past and down into the crankcase.

These small droplets will not harm the engine at first. In fact, sometimes the leak is so slow, the water boils off, leaving no signs of a problem. If drivers ignore the low coolant level they'll often hear gurgling in the heater system.

This becomes a sign of air pockets in the system. My mom's Chevrolet Cruze developed a coolant leak from the thermostat housing, but she didn't tell me until she had no heat. A special note about cracked Chevrolet V8 intake manifolds. In most cases we find gasket failure, but on rare occasions you might see a cracked intake.

Cracked Chevy Intake ManifoldCracked Chevy Intake Manifold

This usually results from extreme overheating. A cracked manifold leaks coolant into the combustion chamber. Failed gaskets leak coolant into the crankcase.

Therefore, the symptoms between the two situations become different. With a cracked manifold you see white smoke from the tailpipe and the engine runs rough. These often crack on the inside making it hard to see. 

Finally, the last symptom to discuss requiring the removal of the intake manifold is the knock sensor problem. The check engine light comes on and usually sets a code P0327. Long story short, General Motors installed plastic connectors that don't hold up over time. As the connector weakens so does the connection and an intermittent signal to the PCM triggers the P0327 trouble code.

Chevrolet Intake Manifold Parts

Chevrolet intake manifold gasket setChevrolet Intake Manifold Gasket Set

There are a couple of things I want to talk about in this section. After performing the repair over and over again, I learned a few tricks that make the job easier. With that said, an important part of this repair is getting the right parts for the job.

When I removed the plastic and silicone gaskets installed from the factory, I felt a little nauseous. You clearly see how profoundly the gaskets failed. The last thing I wanted to do was buy another plastic composite piece of junk. These gaskets get sandwiched between two major engine parts. At first Delco was the only game in town, but now Fel-Pro stepped up and provides better parts.

I don't usually go throwing around the word better on the FixMyOldRide.com website, but to me, that's what they are. Fel-Pro replaced the plastic with a stainless steel metal gasket using heavy-duty rubber inserts. The part alone reduces the chances of repeat failures because of its construction. This is fantastic news for people who try to perform this repair without an inch pound torque wrench.

On the old plastic gaskets if you over tighten the intake manifold bolts you will crack the new gasket and it will leak badly. This leads me into the next section where we'll discuss the intake manifold bolts themselves.

When you remove the factory installed bolts you find that the threads have a liberal amount of thread locking compound on them. You can reuse these bolts, but you must clean all of the old glue off and then reinstall fresh thread locking compound. In some cases people take a shortcut and skip these steps.

The old glue stops you from smoothly torquing the intake manifold bolts on reassembly. The torque specification is critical in this operation. The tightening pattern and torque specification are in the repair section below. The bolts have a tendency to back out if you don't install fresh thread locking compound.

For this reason I now include the replacement bolts in the estimate. This means I don't have to wire wheel, eight individual bolts and then apply messy thread locker. I'm not saying that you have to do this, but if you don't you leave the opportunity open of a repeat failure.

The next thing to talk about is the knock sensors and the wiring harness replacement parts. This is a tough one because the AC Delco knock sensor parts are about $45 apiece. The wiring harness goes for about another $25. Aftermarket companies have bundled these components together that carry a very attractive price tag.

Here's my problem with saving money in this area. On several occasions I‘ve used an off brand replacement knock sensor and it didn't work. This becomes a big deal, because now you have to take everything apart again. I'm not saying you won't ever come across a bad Delco knock sensor, but in my opinion it would seem less likely.

Chevrolet V8 Intake Manifold Repair Procedure

Since I mentioned the torque of the intake manifold bolts several times in this article already, let's tackle this issue first. The tightening pattern is a typical spread pattern that starts in the center and works its way out by alternating sides.

You can see a video of how it's done on YouTube. With that said, the important part of the procedure is to torque the bolts to 44 inch pounds on the first pass and then 89 inch pounds on the second pass.

This is time-consuming and people often look to take a shortcut. This is not a good idea because a shortcut on this step of the operation becomes one of the leading causes of repeat failures. The Second cause of having to pull the Chevrolet V8 intake manifold again is failure to use a thread locking compound during the installation.

People don't often realize, when you install a thread locker, it provides a smooth even torque lubricant. The compound only locks the bolt in place when it’s fully dry in about an hour or two.

You can find an inch pound torque wrench for 25 bucks at the freight place or borrow one from the local parts store. Don’t try to guess what 89 inch pounds feel like. I’ve been doing this 30 years and I can’t do it without the tool.

We filed this Chevrolet V8 intake manifold article in the maintenance and tune-up section. If you own one of these Chevrolet trucks we have additional diagnostic and repair procedures you're sure to find helpful. Take a look at the Chevrolet truck ignition switch issue and then have a look at the oil pressure switch story. Finally, learn about the plastic Vortec V8 engine distributor problem.