Glow plug removal and how to do a compression test on 2004-2005 Passat TDI

May 12, 2014
Glow plug removal and how to do a compression test on 2004-2005 Passat TDI

  • Glow plug removal, recall information, and how to do a compression test on VW Passat TDI(top)

    This article shows how to remove the glow plugs from a 2004-2005 B5 VW Passat TDI, the recall on Bosch ceramic glow plugs, and how to do an engine compression test.(top)

    difficulty: 1/5


    Glow plug recall information on ceramic glow plug(top)

    - update - the recall has been suspended by VW because I believe it results in hard or no starts in near freezing or colder temperatures. You probably haven't noticed any problem if you live in a warm area but if you had the recall done and live in a cold area, this is probably the cause of your hard starting. See 1000q: post recall cold start problem FAQ for more details. The recalled was later recalled to fix this problem.

    Any chip or tune will be overwritten with the ECU reflash. The reflash will also include other updates to the program. Some known updates to the program result in smoother power delivery and "occasional hesitation from a stop" fix. This is normal since most car models get software updates over the life of the car. Note - a few ECUs have gotten fried during reflashing due to dealer computer problems. The dealer should replace the ECU at no cost to you since it's part of the recall and it's not your fault.

    If you want to put the new steel glow plugs in yourself to minimize any cost, just leave their wires unplugged and drive to the dealer for the reflash. Keep the old ceramic plugs in case the dealer wants them. The recall is free so there should be no cost.

    You may also want to replace the glow plugs yourself because rough handling by a dealership tech could break off the glow plug tip. If this happens the cylinder head may need to come off. There's at least one report of a piston being cracked and a head being damaged from someone at a dealership who cranked the engine after a glow plug tip broke off during the recall service.

    Compression testing the TDI engine(top)

    A compression test will tell you the compression of the engine. It is not to be confused with a leakdown test, which puts air into the cylinders and measures the rate that the air leaks out. A leakdown test is another test to determine the condition of the engine. It's also not a boost leak test which tests for air leaks upstream of the engine.

    VW compression for the 2004 2005 2.0L VW Passat TDI engine (BRM)
    New: 360-450 psi (25-31 bar)
    Minimum limit: 275 psi (19 bar)
    Max difference between cylinders: 73 psi (5 bar)

    This is about the same as the 1.9L TDI engines.

    Note - it's normal to get readings of 450-550 psi on a TDI engine, this is considered normal. The specs above are on a new engine. After the engine is broken in you may see higher compression. Keep in mind that high altitude will also lower compression test readings. Very low compression could be piston/cylinder wear, cracked head/block, warped head, bad head gasket, or bad valve.

    Special tools for TDI engine
    8mm triple square bit for removing the fuel filter

    Glow plug removal procedure(top)

    To do a compression test you must first warm up the engine (engine oil to at least 86oF or 30oC) and then remove the glow plugs. Here is a picture with the engine cover off to get familiar with the area.

    Glow plug removal(top)

    Remove the engine cover (3x 10mm nuts).

    Set aside the fuel filter by loosening the clamp (m8 triple square bolt, yellow arrow). Unclamp the fuel line hoses at the sides to get more play (yellow box).

    Optional step for doing a compression test (top)

    Remove the fuel injector electrical plug (red box below). Pull the red tab out a little and then unscrew the socket.

    Here is a picture with the intake piping removed for clarity. The red tab doesn't have to come all the way out.

    Also move the coolant line aside. You now have room to remove all the glow plug wires.

    Clean the area around the glow plugs.

    The glow plug wiring harness is marked below. The area around the wires tend to collect dirt and sand, things you don't want falling into the engine. You can use compressed air or wad some paper towels and use some carb cleaner on the metal to clean the area. Always wear eye protection!

    Spray a drop of PB Blaster or another penetrating lubricant around the base of the glow plug and let it soak. This will really help them come out. After it's loose, put another drop around the base and let it penetrate.

    Loosen the glow plugs using a 10mm deep socket and extension. You may also need a universal joint or swivel head extension. I strongly suggest removing them by hand instead of using air tools or power tools. This will help avoid any shock which could break the glow plugs in the head.

    Here is a picture with the coolant line/fuel filter removed for illustration.

    Remove all 4 glow plugs before doing a compression test.

    The rest of installation is the reverse of removal. Tighten the glow plugs to 11 ft-lb.

    Do not overtighten them because the cylinder head is aluminum. If they don't go in smoothly for at least a few turns, you may be stripping the threads - STOP and check it. In some cars, the glow plugs do not go straight into the cylinder head, the threads are at an angle, so beware of parallax (viewing error)! Please read 1000q: mechanics tips - parallax for more details on viewing errors. One trick you can try is to turn the screw/adapter/bolt/etc., counterclockwise to loosen it and get the threads seated, and so you can "feel" the threads, then turning clockwise to tighten.

    How to do a compression test TDI engine(top)

    Warm up the engine to operating temperature (engine oil to at least 86oF or 30oC) . The metal parts of an engine expand when they get hot, so warm vs. cold engines will have slightly different compression. The conditions for the test are all glow plugs removed, car in park or neutral, fully charged battery. All the cylinders not being tested to have their glow plugs removed so that they are not building compression. This absorbs the energy of the engine cranking, and can affect the compression readings and unnecessarily drain the battery.

    Remove all the glow plugs. Remove the electrical socket for the fuel injectors as shown above. Take your compression tester and find the correct adapter. Remember: do NOT use a gasoline car compression tester because the ranges are completely different.

    Test by threading the adapter GENTLY into the glow plug hole to about 10 ft-lb.

    With all 4 glow plugs removed and a fully charged battery, with engine in park or neutral, have a helper crank the engine until compression stops rising. Make sure the tester isn't loose and going into the serpentine belt. Note how far and fast the needle moves. Then do it again to double check. Move to the other cylinders and write down the values so you can compare them later.

    Unlike a gasoline engine, adding oil is not recommended due to the high compression in the cylinder. You risk having the compression tester be damaged or personal injury due to the cylinder firing. Remember, a diesel engine can run on oil and the peak compression reached from the combustion process is in the thousands, way beyond the range of the compression tester. In addition, if you do a compression test and the results are bad, you can do the test again. There would be no point in adding oil since you already know there is some problem either with the gauge or engine.

    If the compression tester isn't holding pressure, a common problem is the stem inside the adapter coming loose. Use a valve stem tightening tool or very thin pliers to turn the spring loaded stem inside the adapter clockwise.

    If the readings are still unsatisfactory, replace the glow plugs and start the engine. If the readings are still unsatisfactory, then there may be a problem with the compression tester (may be inaccurate/broken), a poor seal or stripped threads around the glow plug hole, bad fuel injector seals/washers. More serious would be bad valves, rings, pistons, worn cylinders, warped head, bad head gasket, or a cracked engine. At this point, you can be sure that something is wrong with the engine or compression tester.

    Also keep in mind that two different compression testers may show different readings on the same engine. Professional grade testers tend to be more accurate then cheaper gauges which can show slightly higher or lower readings. In this case, don't worry about a slightly low reading as long as it's within the normal range. As long as the compression is consistent across all of the cylinders and the engine idles well, starts in the winter, and isn't pouring smoke, it is acceptable and I wouldn't worry about it. Remember that high altitude will also lower compression test readings.

    For example, VW diesel engines have a spec of 360-450 psi with new engines. It is only considered a bad engine if the reading is below 276 or there is a difference of more than 73 psi between cylinders. That is a lot of allowable variance. To put it in perspective, gasoline engines typically can have no more than 15 psi difference between cylinders on engine compression of about 125-180 psi, depending on the car. If you need more detailed information about the condition of the engine, then a leakdown test or a better compression tester is recommended. Consulting a mechanic would also be a good next step.