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Chevy 3.1-Liter Engine: Leaking Intake Manifold Gasket and Warped Heads

I enjoy working on DIY projects and giving advice to others to help them with their own projects.

Upper intake manifold, Chevy 3.1-liter engine

Upper intake manifold, Chevy 3.1-liter engine

Once Bitten, Twice Shy

The Chevy 3.1-liter engine has a notorious weakness, a failure mode that GM will not cover after the warranty expires. The lower intake manifold gasket fails and leaks coolant into the engine oil.

I had the dealership replace the manifold gasket the first time at about 40,000 miles before it got to the point of leaking coolant into the oil. This cost me $1,200, mostly for labor. Then, just 15,000 miles later, the gasket failed again. This time coolant leaked into the oil; the giveaway was the milky substance that could be seen on the oil filler cap.

Realizing I was looking at another repair bill of over fifteen hundred dollars, I decided to do the job myself and do it right. The first time, I didn't do the job myself because I didn’t have the time; also, I was a little intimidated by the fuel injection system, two intake manifolds, the special tools I would need to complete the repair, and the manual’s complicated procedures for removing all the different parts of the upper engine. The time element was a reasonable excuse, but the intimidation element was not. If you can change your own oil, replace belts, and change spark plugs and filters—which is a basic tune-up—then you can do this job.

How to Prepare for an Intimidating Repair Job

This article will not take you step-by-step through the process of completing the repairs; you will need a manual for that. But this article will help you avoid some common mistakes everyone makes when they work on their car. We learn from our mistakes and believe me I have learned a lot. A little more preparation in the beginning will save you a major headache later.

Before you begin the tear-down, you will need to do some preliminary research. First, go to the auto parts store and buy the repair manual for your make and model car. Next, pick up a few car magazines. They usually have articles on replacing intake manifold gaskets and rebuilding cylinder heads. The articles are easier to read than the manual. You can find even more articles archived on the websites for these magazines. Once you have read as many articles as you can find, you will realize that pulling the heads off of any car is a rather straightforward process.

Now you need to see if you have all the tools you need to do the job. A basic toolbox with socket wrenches, box wrenches, flare wrenches, and screwdrivers should cover most of your needs. Just make sure they are metric since most cars today have metric nuts and bolts. You will need some specialty tools; however, most auto parts stores have a rent-a-tool program, sometimes at a nominal cost and sometimes for free. For some tools, there is a hefty deposit, but it is credited back to you when you bring the tool back.

I would suggest that you consider buying a breaker bar; it is a must to break (loosen) the head bolts. A torque wrench is also worth the expense; the click type is better than the bar and scale. The torque requirements of the head bolts and the lower intake manifold bolts are specified in the manual, and should be followed, since the head is aluminum and thus a little vulnerable to damage. If you over-torque the bolt you can cause the bolts to break; if you under-torque the bolt it may cause the gasket to leak and you'll need another repair.

Get your digital camera out and start snapping pictures of the engine. Take pictures of every wire connection you can see. Don't say, "Oh that’s so obvious, I don’t need to take a picture of that." Trust me, it will save you hours of frustration later. Next, get a roll of blue painter's tape and a red sharpie; this will allow you to label every connection. I suggest red because the tape will get dirty and make the label hard to read. I label connections as "A to A," "B to B," "C to C," and so on. Take a picture of every part before you remove it, then take a picture of whatever the part came off of. The more reference points you have the better.

Ziploc bags are a must. Put all the nuts, bolts, small gaskets, and small parts you remove into a bag; then label the bag with the name of the particular part. Seal the bag and put it in a safe, clean area where it will not get lost or moved. Following this practice, you won't waste time looking for a part later on when you are putting the pieces back together.

You will need some miscellaneous items, all of which you can get at an auto parts store:

  • container for the coolant
  • container for the oil
  • a floor jack
  • two jack stands
  • mechanic's magnetic pick-up tool
  • socket extensions
  • socket adapters (1/4 inch and 1/2 inch)
  • a magnetic fluorescent drop light

Set up a workbench (two sawhorses and a couple of boards will do the trick) and pick up some kitty litter.

Once you have gathered all the necessary tools, you are now ready to begin the job of fixing your own car. Follow the manual carefully. If you're not sure about a procedure, take a break and re-read the procedure again. After the second or third read, the procedure will make sense.

It looks complicated.  Go slowly and keep checking your manual.

It looks complicated. Go slowly and keep checking your manual.

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Disassembling the Chevy 3.1-Liter Engine

The basic steps in the tear-down are not difficult. With the engine completely cooled, disconnect the negative battery cable, drain the oil out of the block into the oil container, and drain the coolant into the coolant container. Make sure you drain enough of the coolant out of the engine so that when you take the heads off, the coolant will not spill over into the open cylinders. (Here is where the kitty litter comes in handy; spread it over any spills you make, let it absorb all the fluid, then sweep it up and the spill is gone.) Spray all bolts that look rusted with WD-40. I'd do this the night before; it will penetrate the rust and make loosening the bolts easier.

With the car drained of fluids, you are now ready to begin removing parts. Remember to take pictures and follow the manual’s procedures. The order in which you will take off parts will depend on your make and model. As an example, the video below shows the disassembly sequence on an ‘04 Buick Century. On my '02 Chevy Malibu, the sequence begins:

  • Disconnect the air cleaner.
  • Take off the plenum.
  • Disconnect the PCV valve and push it out of the way.
  • Disconnect the heater bypass hoses and clamp them off (or jam sharpie pens into the hoses, this works just as good as a clamp).
  • Disconnect the thermostat by-pass pipe and remove it. Be careful with the quick-disconnects on those hoses, they break easily. (The good news is a replacement quick-disconnect is inexpensive, maybe five dollars at the most).
  • Last, disconnect the thermostat housing.

Removing the Ignition Coil Pack

Removing the ignition coil pack is going to be your first area of self-doubt, but don’t worry. Keep on working and start disconnecting the spark plug wires from the spark plugs. Label each wire with the cylinder number it came off of. If you do one at a time and label each wire, you will not have a problem. Leave the wires connected to the coil pack. The coil pack is connected to a plate which fits over two posts, coming out of the head, and is bolted down with two nuts. Remove the nuts and lift the pack off the posts. You'll see the electrical connection that goes to the fuel rail; label it and disconnect it.

Ignition coil pack.

Ignition coil pack.

Removing Upper Intake Manifold and Valve Covers

You are now ready to remove the upper intake manifold. Depending on the make and model of your car you'll have to remove either six bolts or eight bolts. After you remove each one, bag it and label it.

The next step is to remove the valve covers, four bolts to each cover. The only one that will give you any trouble is the bottom bolt of the rear cover on the driver’s side. Due to the post for the ignition coil pack, you cannot use a regular socket wrench. You’ll have to buy a ratchet box wrench—I think I needed an 8 mm wrench. Otherwise, you’ll be fighting the bolt and rounding its edges. If that happens, you’ll never get the bolt out.

Valve covers after removal.  The yellowish creamy gunk means coolant has gotten into the oil.

Valve covers after removal. The yellowish creamy gunk means coolant has gotten into the oil.

Removing Exhaust Manifolds, Fuel Rail, and Alternator

I decided to take the exhaust manifolds off next because I was a little intimidated by the fuel rail and wanted to leave it for the next day. The exhaust manifolds are not difficult to remove; just follow the directions in the manual and you will have them off in no time.

The fuel rail is actually very easy to remove. Just relieve the fuel pressure in the line (with the pressure relief gauge you rented), disconnect the inlet line and the regulator line, and pull up on the rail; all six fuel injectors will pop out. Replace all the O-rings when you reassemble the fuel rail.

You will have to remove the alternator. The manual is very straightforward on removal and installation. The tensioner pulley is released by using a ¼ inch ratchet (no socket attached) with a short length of pipe on the end to give you enough leverage to release the tension. Don’t try to release the tension without a short-handled extension on the ratchet; you will not have enough leverage.

Removing the Lower Intake Manifold

The lower intake manifold is the tricky part. You have to jack up the motor and remove the passenger-side motor mount in order to remove one of the bolts from the intake manifold. The power steering reservoir is bolted to the block right over one of the bolts to the lower intake manifold. To take the reservoir off you need to remove the motor mount.

First, loosen the motor mount bolts with the breaker bar just enough so they'll be easy to turn when the engine is jacked up. Get the floor jack and a short piece of hardwood. Place the wood across the bottom of the oil pan towards the edge of the passenger side. Slowly jack the engine to take the weight off the mount. You can now remove the mount completely. Once the mount is removed, you will have access to the power steering reservoir attaching bolts. Follow the manual’s directions to remove the bolts and move the reservoir out of the way. DO NOT disconnect any hoses. Re-attach the motor mount and remove the jack.

You now have access to all the lower intake manifold bolts; just follow the directions in the manual. Remove the bolts in the numbered order given in the manual. Take a piece of cardboard (for example a cardboard box used to ship copy paper), and each time you take out a bolt, punch a hole in the cardboard, push the bolt into the hole, and label the hole with its number in the sequence. Once all the bolts are removed, the lower intake manifold is ready to be taken off and set aside.

The source of the problem:  bad intake gaskets

The source of the problem: bad intake gaskets

Removing Cylinder Heads

One of the problems with aluminum heads is that they warp very easily. If you have gotten this far, you might as well remove the heads and send them out to a shop for reconditioning. At the time of this writing, it cost me $140 to have the heads checked, cleaned, and milled. Since they were in fact warped, it was worth the money.

The cylinder heads are not difficult to remove at all. First, remove the valve springs so you can pull out the push rods. Next, loosen the bolts, in sequence, a quarter of a turn, until you can turn them by hand. Remove the bolts and place them in the cardboard holder. Make sure you number the bolts in the right sequence. You will need to remove the lifter retaining guides. Each one is held in place by two screws. DO NOT forget to put them back in, or you are going to have major problems.

The heads are ready to be removed. A word of caution here: these aluminum heads have locator pins that can be lost very easily, so be careful when taking the heads off. There are two on the rear edge of each head. These pins help to properly place the head gasket, so don’t lose them.

Preparing for Reassembly

You have completed the tear-down. Now send the heads to the shop to be reconditioned. While they’re at the shop, go to the auto parts store and pick up a gasket kit for a valve job, cheap oil and filter, one gallon of anti-freeze, a can of gasket remover, one tube of Black RTV silicone gasket maker, one tube of Red RTV, and a new thermostat. While you are waiting for the heads to come back from the shop, clean off all the mating surfaces with gasket cleaner, being careful not to gouge any of the surfaces. Clean up the valve covers and the two intake manifolds with Easy-Off Oven Cleaner. Spray it on the surface of the part, set the part in the sun for a few hours, and then wash the part off. The Easy-Off dissolves the grease and oil.

Here are a few things the manual does not tell you.

  • Make sure you use quality gaskets. This whole hassle is caused by the cheap gasket GM used when they originally put this engine together.
  • Your push rods are two different lengths: the short push rods are for the intake valves and the long push rods are for the exhaust valves. If you mix these up, your heads will be destroyed.
  • While you’re waiting for the heads to come back from the shop, cover the opening to the engine with shop rags or a plastic garbage bag. Any debris—leaves, dirt, acorns, pine needles—that gets into the engine will reduce the life of your engine considerably.
  • Remember to reinstall the lifter guide plates before you reinstall the lower intake manifold.
The heads.  Don't forget to reinstall the plastic lifter guides. The coil pack installation post can be seen on the head to the right.

The heads. Don't forget to reinstall the plastic lifter guides. The coil pack installation post can be seen on the head to the right.

Reassembly of the Chevy 3.1-L Engine

Putting the pieces back together should not be a problem since you took it apart and took pictures. just take your time and be patient. Follow the manual carefully. Reinstall the parts in the reverse order that you took them out. The black RTV is used on the front and rear mating surface of the engine block; also, put a little bead of black RTV around the water jacket openings. The red RTV is used on the thermostat gasket. Once everything is bolted back on and the electrical connections are made, refill the engine with fluids. You might want to use the same coolant you drained from the engine; just top it off if you need to from the gallon bottle you bought. Start the car and check for leaks.

If everything checks out, take the car to a quick-lube shop and have them replace the cheap oil and filter with a good grade of oil and a good filter. Also, have the shop drain and replace the old coolant. I recommend paying someone else to change the oil and coolant because of the disposal issue. Trying to get a place to dispose of contaminated oil and coolant is difficult. Save yourself the hassle and have the quick lube place do it for you. They might even take the original contaminated oil off your hands. Just ask them—all they can do is say no.

When this project is completed, you will have successfully rebuilt the top end of your engine yourself, and you will know the job was done right because you did it. Try to fix it yourself first before you call in a professional. The worst you can do is break it some more, and if you succeed, you will save a lot of money.

A word of caution: This article is meant as a reference only. Follow all the safety procedures as well as the repair procedures. For example, never get under a car without using a jack stand, and never open the radiator cap of a hot engine.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

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