Mark Houlahan
Brand Manager, Mustang Monthly
September 10, 2000
Photos By: Mike Johnson

Step By Step

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Fixing a blown head gasket is 90 percent labor and 10 percent parts. Since we don't want to be doing the 90 percent part ever again, we opted to reseal our small-block with the tough gaskets from ROL Manufacturing. The company carries a full line of gaskets to reseal the 5.0, including one-piece rubber oil pan gaskets, several types of cork, rubber, and combination valve cover gaskets, and of course high-temperature head gaskets.
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You can perform a compression test of all cylinders to check for a failed head gasket. If the gasket has failed between two adjacent cylinders, those two cylinders will have low numbers. You also can use the compression tester hose (with the Shrader valve removed) to apply compressed air to each cylinder. When the air enters the cylinder, a leak to the cooling system or oil passages will produce pressurized air in those systems as well (check for bubbles in the radiator or air escaping the valve covers or oil dipstick).
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A cooling system tester is another good tool for checking cylinder head gasket integrity as well as your cooling system. The style used here connects to the radiator overflow hose and checks the radiator cap at the same time (with compressed air). Other models connect in place of the radiator cap and are pumped by hand. Drain the coolant when you have completed the testing.
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Getting down to the cylinder heads is a dirty task. Remove any aftermarket items, such as nitrous, blower, or strut brace, that are in the way. The upper intake is held by six bolts (two under the ID plate). Be mindful of an intake bracket at the back on some model years, and don't just start prying in a he-man fashion. Once the upper intake is off, the valve cover bolts are easily reached. Don't forget to disconnect your battery.
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To remove the lower intake, you will need to remove the distributor. Index the rotor to the edge of the distributor with a permanent marker and pull the distributor free. This will allow you to insert the distributor back in the same place (providing the engine isn't turned). Remove the intake manifold's 12 bolts and pry the manifold free of the heads. Loosen the bolt holding the heater tube last. Sometimes you can pull the intake and tube together.
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All front-end accessories will need to be removed to free the heads. The A/C compressor can be carefully rolled over to the passenger-side fender to prevent opening the system. This GT's air isn't working, so we simply pulled the lines off for more working room. Remove the alternator and Thermactor air pump together and let the power steering pump hang from the framerail, using a wire hanger.
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Remove the rockers and pushrods from the heads, keeping them in order. You might be able to simply unbolt the headers from the heads (if there is clearance for your tools); otherwise, you will have to completely remove the headers. Unbolt the heads and carefully pull them free of the block. You might notice here that the timing cover is missing--well, we decided to put a hotter cam in at the same time. Our sister magazine, 5.0 Mustang, wanted to throw on a Holley Systemax I (lower intake, cam, and timing set) for some grins and more low end.
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The lifters were removed from their bores (soak them in clean oil to prevent them from "bleeding" down) and the stock H.O. grind cam was pulled from its home. If you opt to do a similar upgrade, work slowly to prevent nicking a cam bearing in the block. You will have to unbolt the A/C condenser mounting brackets and flip the condenser out of the way for cam removal clearance.
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The problem was evident after the driver-side head was removed. Cylinder No. 6 had breached between a coolant passage and the combustion chamber (screwdriver tip pointing). You can also see the water stains in the top edge of the cylinder bore where the coolant had been seeping into the chamber (between my two fingers).
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Once we are down to our short-block, the messy job of cleanup work starts. Begin with a large gasket scraper or razor blade and remove the large sections of gasket from the block surfaces, intake, heads, and timing cover (if removed).
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Once the large, easy sections of gasket have been removed, step up to a high-speed tool (air or electric driven) with a surface-conditioning disc attached to make quick work of the gasket surfaces. Be careful on any aluminum surfaces to not create low spots that will allow leaks.
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The cylinder heads are cleaned in the same manner. If your Mustang has excessive mileage, you may want to have the heads professionally inspected for new valve stem seals and guides. If you have a friend who is a decent head porter, you can have the stock castings tweaked some, but don't go crazy fixing them up. Why spend $800 on seals, guides, exhaust valves, and porting when you can install a great set of performance aluminum heads right out of the box for $1,200, not to mention that they'll make more power.
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The new Holley Systemax camshaft is cleaned and a coating of the included assembly lube is applied as the cam is installed. Use a bolt or the old cam gear as a handle to aid in installation.
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Using the included Holley instructions or your shop manual, index the camshaft and crankshaft, and install the timing chain set with more assembly lube.
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The timing cover and water pump assembly are reinstalled once the timing chain is secured. Don't forget a dab of silicone where the old rubber pan gasket meets the new cork end gaskets (arrow).
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When installing the new high-temp ROL head gaskets, make sure they are oriented the correct way. The gaskets are stamped "FRONT" (arrow) and should be installed with identification at the front of the block. If you install the head gaskets backward, you will have severe overheating problems. Notice we decarboned the piston surfaces to remove hot spots.
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The cleaned and prepped heads can now be laid into place on the short-block. Make sure the dowels in the lower corner head bolt holes are installed and in good shape, as they locate the head to the block and prevent gasket damage caused by the head sliding around.
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On late-model 5.0 blocks, the lower row of head bolts (the short ones) actually enter the water jacket, unlike early 302 blocks where the holes are closed. Use a quality thread sealer to prevent coolant leakage. I've found the best choice is Permatex Form-A-Gasket 2 sealant. It remains sticky and doesn't harden. Other thread sealers have caused me problems, so you've been warned.
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Reinstall the lifters, pushrods, and rocker arms in their original locations. Using a shop manual, check lifter preload and adjust as necessary with pedestal shims. If you retained the stock cam, you should be OK with just tightening the rocker arm bolts to the specified torque rating.
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Use Felco-Bond or other gasket adhesive to hold the intake gaskets and cork end rails in place. Some people use all silicone for end rails. I have had good luck using glue-down or adhesive-backed cork end rails (with sufficient drying time) and dabs of silicone in each corner where the side and end gaskets meet. Note how the intake gaskets interlock with the head gaskets (arrow).
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Reinstall the lower intake (our Holley Systemax is shown here), taking care not to get any wires or hoses caught under the intake itself. If you don't have steady hands, use threaded rod as locating dowels to help install the manifold.
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Since we had to swap everything over to the Holley manifold, the heater tube was separately reinstalled. If you pulled your intake with the tube intact, remember to start that one bolt first to prevent misalignment of the intake to the heads.
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If you didn't swap cams, you can easily drop your distributor back in by lowering it into place and aligning the rotor with the mark you made. If you installed a cam as we did or the engine was accidentally rotated, you will need to locate top dead center on the No. 1 cylinder. Rotate the engine until the timing pointer is at zero on the damper and both the intake and exhaust valves are closed on the compression stroke of cylinder No. 1. Install the distributor with the rotor pointing toward the No. 1 terminal, and you'll be set.
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Reinstall your headers using new header gaskets, which we also obtained from ROL. Don't forget to retighten the header bolts after a few engine-running cycles.
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Though the A/C and power steering had been started earlier, the remainder of the front-end accessories are bolted home now, including the pulleys, fan, hoses, and wiring.
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Take one last look at the valvetrain to make sure everything is fine, and then button up the engine by installing the valve covers with new gaskets. Don't overtighten the bolts and damage the gaskets. You also may wish to use a little Loctite 242 (the blue variety) to keep the valve cover bolts tight, as they are infamous for loosening and causing leaks.
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The stock upper intake (which already had a BBK 65mm throttle body and EGR spacer) is placed onto the Holley lower with a new gasket. If you want to maintain a stock look, you can get the upper intake Extrude Honed. Start all the bolts before tightening them.
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The Holley Systemax nameplate replaces the stock H.O. cover and gives everyone a hint of what lies underneath the stock-looking components. Top off the coolant, change the oil, and recheck your work before starting your Mustang. We now return you to your regularly scheduled weekend, without the overheating problems.

No one enjoys having car problems--even those of us who claim to enjoy working on cars and repairing them. The last thing we want to do is be forced into working on our cars. We can schedule upgrades and maintenance at our convenience, but a car problem means having to drop everything and change your plans to make repairs. Sometimes a car problem can be as simple as replacing a burned out headlight bulb. A quick trip to the parts store or even Wal-Mart and you have part in hand and the job done in a relatively short amount of time. No muss, no fuss, and your weekend of holding the hammock down with your backside is spared. But sometimes a car problem arises that just can't be accomplished this quickly, and though the job has to be done, it is dreaded every minute until the car is running again. Head gasket replacements are right at the top of the list when it comes to dreaded repairs.

A head gasket is no easy problem to diagnose to begin with, and the repair in itself is lengthy, laborious, and quite boring. There's not much you can do but roll up your sleeves and dig in, leaving yourself plenty of time to complete the work.

How do you know if you have a bad head gasket in the first place? Some of the telltale signs of a bad head gasket make it extremely easy to diagnose, while other signs make you get out special tools for testing. Depending upon where the gasket failure occurs on the gasket, you can have a large amount of coolant entering the combustion chamber, which causes billowing white smoke to exit the tailpipe, along with raw coolant (if the failure is severe enough).

Another easy diagnosis is when the gasket failure is between a coolant passage, the combustion chamber, and an oil passage. When this occurs, the cooling system and engine crankcase oil mix, creating a beige soupy substance throughout the engine and cooling system. Removing the oil fill cap, dipstick, or radiator cap, and visually inspecting the contents should immediately tell you if this situation has occurred.

Sometimes, though, the reason behind a bad head gasket is not evident and testing needs to be done to detect the problem. If a head gasket failure is minor, then it may be hard to get to the bottom of things. Small failures can cause overheating and/or coolant loss as well as poor driveability. Testing each cylinder for compression, testing cylinder leakdown, and pressure-testing the cooling system are necessary for an accurate diagnosis.

Our Mustang in ailing health is a '90 GT hatchback. Internally, the 5.0 is bone stock, but the GT does wear a 100hp nitrous kit. The owner isn't sure if the nitrous or a recent high-rpm chassis dyno pull caused the head gasket failure, but we'll tear into the GT and get the owner back on the road in a weekend. All that is needed is a typical set of handtools (which you already should own), fuel line disconnect tools, and the proper shop manual to fill in the blanks.