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

The Chevy 3.1-liter engine has a flaw 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, before it reach the point of coolant in the oil, at about 40,000 miles. This cost me twelve hundred dollars- most of the cost was in labor charges- and 15,000 miles later the gasket failed again. This time coolant leaked into the oil. The give away was the milky like substance that could be seen on the oil fill cap.

Realizing I was looking at another repair bill over fifteen hundred dollars, I decided to do the job myself and do it right. The reason why I did not do the job the first time was that I didn’t have the time it would take to do the repair properly; 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, change spark plugs and filters, which is a basic tune up then you can do this job.

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 heads. These magazines also have web sites with archived articles. The articles are easy to read and easy to understand. You may find them more informative than the manual. Once you have read as many articles that you can find, you will realize that the job of pulling the heads off of any car is a rather straightforward process.

Now you need to find out 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 needed. Just make sure they are metric, 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. The cost is nominal and in some cases it is free. For some tools there is a hefty deposit, which 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, and a torque wrench, the click type is better than the bar and scale, due to the torque requirements of the head bolts and the lower intake manifold bolts the torque wrench is indispensable. The heads are aluminum 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, necessitating another repair. It is worth the expense.

Once you have read all the car magazines articles and the procedures in the manual. You will think you are ready to begin. Not so fast, a little more prep in the beginning will save you from a major headache later. The scope of this article is not to take you step by step through the process of completing the repairs. This article is to help you avoid some of the common mistakes everyone makes when they work on their car. We learn from our mistakes and believe me I have learned a lot.

Get your digital camera out and start snapping pictures of the engine. Take pictures of every wire connection you can see, what ever you do don’t say, ‘oh that’s so obvious I don’t need to take a picture of it,’ trust me it will save you hours of frustration later if you take the picture in the beginning. Next get a roll of blue painters tape and a red sharpie, this will allow you to label every connection. I use the A to A; B to B; C to C; and so on method. I suggest red because the tape will get dirty and the label will become difficult to read. Take pictures of every part you are removing before you remove it; then take a picture of were the part came off of. The more reference points you have the better.

Zip lock bags are a must, put all the nuts, bolts, small gasket, and the part; if possible, in the bag then label the bag with the name of the particular part. This way you are not looking for a part later on when you are putting the piece back together. Once you have the bag sealed put it in a safe clean area where it will not get lost or moved.

You will need some miscellaneous items: coolant container, an oil container, a floor jack, mechanics magnetic pick up tool, socket extensions, socket adapter ¼ inch and 1/2 inch, a magnetic florescent drop light, two jack stands the auto part store will have these items. Set up a workbench (two saw horses and a couple of board will do the trick) and pick up some kitty. 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 your 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.

The basic steps to 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 coolant container. Make sure you drain enough of the coolant out of the engine so that when you take the heads off the coolant does not spill over into the open cylinders. Here is where the kitty litter comes in handy. Spread it over any spills you have and let it absorb all the fluid then just sweep it up. Spray all bolts that look rusted with WD 40, I do this the night before, it will penetrate and help when you loosen the rusted bolts.

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, depending on your make and model is: air cleaner, plenum, disconnect the PCV valve and push out of the way, disconnect the heater by pass hoses and clamp off, or jam sharpie pens into the hoses, this works just as good as a clamp, disconnect the thermostat by pass pipe and remove. Be careful with the quick disconnect on those hoses they can break if you don’t do it correctly. The good news is a replacement for a quick disconnect is inexpensive maybe five dollars at the most. Then disconnect the thermostat housing

Removing the ignition coil pack is going to be your first area of self-doubt. Don’t worry, disconnect the spark plug wires from the spark plugs label each wire for 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 will notice that there is an electrical connection, this goes to the fuel rail, label it and disconnect it.

You are now ready to remove the upper intake manifold. Depending on the make and model of your car it could be six bolts or eight bolts you will have to take off. Bag the bolts then label the bag.

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 will have to buy a ratchet box wrench, I believe I needed an 8 mil wrench, otherwise you will be fighting the bolt and rounding the edges of the bolt. If that happens, you will never get the bolt out

I choose 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, 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 to release the tension.

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 bolt from the intake manifold. The power steering reservoir is bolted to the block right over one of the angel 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 that when the engine is jacked up they will be easy to turn. Get the floor jack and a short piece of hard wood 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 can gain access to the power steering reservoir attaching bolts. Follow the manual’s direction 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. The bolts are removed in a sequence and each bolt has a number Take a piece of card board, a cardboard box use to ship copy paper is great for this, punch holes in the card board as you take the bolts out, in the order that the manual says, push them into the card board holder. Put the correct sequence number next to each bolt. Once all the bolts are removed the lower intake manifold is ready to be taken off and set aside.

One of the problems with aluminum heads is that they warp very easily. You’ve gone 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 one hundred and forty dollars to have the heads checked, cleaned and milled, they were warped so it was worth the money.

The cylinder heads are not difficult at all to remove, 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 by hand. Remove the bolts and place them in the cardboard hold numbered 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 other wise 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 for each head and they are located on the rear edge of the head. These pins help up properly place the head gasket so don’t loose them.

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 and one tube of Red RTV silicon gasket maker 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 and set the part in the sun for a few hours then wash the part off. The Easy Off dissolves the grease and oil.

A couple of things to do that the manual does not tell you. Make sure you use quality gaskets. One of the reasons for a leaking gasket was the cheap gasket GM used when they 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; such as, leaves, dirt, acorns or pine needles, that get into the engine will reduce the life of your engine considerable. Remember to reinstall the lifter guide plates before you reinstall the lower intake manifold.

Putting the piece back together should not be a problem sense you took it apart and took pictures, just take your time and be patient. Follow the direction in 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 small 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 need be from the gallon bottle you bought. Start the car and check for leaks.

If everything checks out take the car to a quick lube and have them replace the cheap oil and filter with a good grade of oil and a good filter. Have the quick lube shop also drain and replace the coolant. That is why you reused the old coolant.

Why pay some one to change the oil and the coolant. It’s a disposal issue, trying to get a place to take contaminated oil and coolant is difficult. Save your self the hassle and have the quick lube place do it for you. They might even take the original contaminated oil, off your hands, 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. You will have saved your self a lot of money. You 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. On the other hand you can save your self a substantial amount of money if you do it yourself.

A word of caution, this article is meant as reference only. Follow all safety procedures in the repair manual. Never get under a car with out jack stand. Never open the radiator cap of a hot engine.