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Thread: Glow plug test

  1. #1
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    Glow plug test

    Had some difficulty starting my Universal M25XP and I suspect the glow plugs. It took a very long while to start, battery cranked the starter motor just fine and after the engine ran for a few minutes (and probably heated up), it would restart just fine. Maybe the glow plugs were not operational and the cold weather (maybe 50 degrees) made starting difficult. Can I just remove them one at a time and press the glow plug button and see if they light up? I would keep the power wire connected and ground the plug housing with a clamp.

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    never mind, I found great threads on this site.

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    Too late I already pecked out this reply. That idea might work. Do you have a voltmeter in the circuit for the start battery? Or put a voltmeter across the battery while you activate the glow plugs. You're looking for a significant voltage drop with good plugs. Maybe as much as 0.5 to 1 volt. If you take one out and power it, let us know if it actually glows.

    How long did you apply the glow plugs? Did you activate the glow plugs while you cranked? I struggled with occasional cold starting problems for several years. I began to use plenty of glow even when air temps were warm. Keeping the plugs glowing when cranking really helped reduce crank time and now I don't have any starting problems. I replaced the battery, too, but that alone didn't solve the hard starting on my 4 cyl. 5432.
    Craig Davis & Ellen Le Vita

    1980 E38 "Pilot Project"
    Hull #20
    Seattle, WA



    Somebody once said "It's an old boat and therefore resistant to change."

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    thanks for the suggestion about the voltage drop on the battery. Not sure if the glow plugs are fed off the starting battery or the house battery but I suspect it is the starting battery. I do have a voltmeter reading the voltage at the alternator (as well as a shunt for an ammeter reading) but I can easily put my voltmeter on the either battery, just need an extra pair of hands to push the glow plug switch. It could also be the relay but I am not sure how that is wired, I need to check.

    My first plan is to push the glow plug switch for say 10sec and then feel each one of the glow plugs to see if they are hot. If all are cold, then it should be a wiring or relay problem, if only one or two are cold then it probably is the glow plugs themselves. I see no record in the previous owner's notes of any glow plug replacement and since this the original engine circa 1987, I may need new glow plugs.

    A previous thread identified the glow plugs as NGK Y103K, available on Amazon for about $10 each or directly from Universal at about $80 each. Imagine that!!!

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    I have some questions concerning the removal of the glow plugs. I just bought three NGK Y103K and plan to replace the old, probably original ones. Christian reported that although the middle one was hard to remove (only 1/8 turn with an open end wrench) it was possible to remove all three without removing the exhaust manifold. Other threads said you must remove the exhaust manifold. Can anyone clarify this point?

    Also Christian reported that he moved a water hose, removed the air filter and removed the return fuel hose for better access. Do you have to bleed the engine if you remove the return fuel hose?

    From the photo of the glow plug, the 12mm wrench goes on the body of the glow plug. I dont understand Christian's comment about the knurled nut. Is this nut just to secure the jumper wires? And if so, with no flats does one just hand tighten the nut and ust eh slot for a screw driver blade to tighten just a little more than hand tight?

    Is there any sealant, like Permatex Aircraft grade, needed on the threads or just the crush surface below the flats to make seal, in much the same manner as a spark plug on a gasoline engine?

    I plan on doing the touch test and the voltage test but I suspect that since the engine has always started easily, that the wiring is OK but glow plugs do burn out.

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    The glow plug switch (the push button) at the instrument panel has twice failed in the four years since I bought this boat. Check the switch before doing the glow plug change.
    Bob Morrison
    1987 E-34 Hull #15
    "Terra Nova"

  7. #7
    Moderator Christian Williams's Avatar
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    Recall that my glow plugs turned out to be fine and new ones were unnecessary. They're as sophisticated as a toaster, not much to go wrong.

    More likely it's the switch or the grounds or the wiring.
    Thelonious II, E381 hull 513 (1984) Universal 5432
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    "Alone Together--the Book" trailer here

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    Principal Partner footrope's Avatar
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    Quote Originally Posted by HerbertFriedman View Post
    I have some questions concerning the removal of the glow plugs. I just bought three NGK Y103K and plan to replace the old, probably original ones. Christian reported that although the middle one was hard to remove (only 1/8 turn with an open end wrench) it was possible to remove all three without removing the exhaust manifold. Other threads said you must remove the exhaust manifold. Can anyone clarify this point?

    Also Christian reported that he moved a water hose, removed the air filter and removed the return fuel hose for better access. Do you have to bleed the engine if you remove the return fuel hose?

    From the photo of the glow plug, the 12mm wrench goes on the body of the glow plug. I dont understand Christian's comment about the knurled nut. Is this nut just to secure the jumper wires? And if so, with no flats does one just hand tighten the nut and ust eh slot for a screw driver blade to tighten just a little more than hand tight?

    Is there any sealant, like Permatex Aircraft grade, needed on the threads or just the crush surface below the flats to make seal, in much the same manner as a spark plug on a gasoline engine?

    I plan on doing the touch test and the voltage test but I suspect that since the engine has always started easily, that the wiring is OK but glow plugs do burn out.
    Maybe I can help a little. It is the intake manifold that may get in the way of getting a wrench on the glow plugs, isn't it? It's much less involved to remove than the exhaust manifold, but on the 5432 it's tough to get to all of the bolts.

    You may have problems with the metal injector lines getting in the way of the glow plug removal and the intake manifold removal. If you remove one or more injector lines, then bleeding will be required. Removing a rubber return line from an injector doesn't require bleeding. The picture shows a couple injector lines removed and the knurled nut on top of the plug. There may be tiny lock washers under the nuts, too.

    The knurled nuts. It may be hard to get to one or more of them with fingers. You have to be careful not to torque them excessively, whatever tool you use, so the answer is 'yes' it just secures the jumper wires and should only be hand tight.

    I wouldn't use any sealant. The plugs are meant to seal metal to metal and that provides a ground, just like a spark plug. I put a tiny bit of copper-based anti-seize on the threads of each plug. Make sure the hole in the cylinder head is as clean as possible where the plugs seat.

    I think you have a good plan. Definitely check wiring and relays before tackling the removal of the plugs. My plugs were old and ugly but worked great. If you can get the wires off each plug you can easily test continuity and resistance with an ohmmeter, too.

    Click image for larger version. 

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    Craig Davis & Ellen Le Vita

    1980 E38 "Pilot Project"
    Hull #20
    Seattle, WA



    Somebody once said "It's an old boat and therefore resistant to change."

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    Craig, thanks for the clarification, I will look carefully to see what the physical situation is before I try to remove any plugs.

    Bob and Christian, concerning the glow plug switch, first, I have not done the re-wire job to separate the glow plug switch from the starter switch. So I need to press both the glow plug switch AND the starter switch in order to start the engine. When I do press both, the engine cranks over but does not start, at least easily. If the glow plug switch were bad, the I would expect that the starter switch would not crank the engine, but probably I dont understand the wiring.

    There is a small part next to the engine that looks like it could be a relay for the glow plugs, but again, in a normal relay, there are two low current wires to operate the relay coil, then two high current contacts to power the glow plugs. I do see the high current wires going to the glow plugs but I dont see any low current wires. But I will look tomorrow and take some photos.

    I will try to remove the jumper wires and do a resistance check tomorrow, let you all know.

    Again thanks, this is a great site with lots of mavens.

  10. #10
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    just another thought, I guess the easiest test to do is to see if I get 12VDC at the glow plugs with the glow plug switch on and the input wire disconnected ? Or use my DC clamp on ammeter to see if there is current in those jumpers? That and the hot touch test.

  11. #11
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    Quote Originally Posted by Christian Williams View Post
    Recall that my glow plugs turned out to be fine and new ones were unnecessary. They're as sophisticated as a toaster, not much to go wrong.

    More likely it's the switch or the grounds or the wiring.

    Christian, just a question on your very nice 2014 thread showing glow plug replacement: You say that initially one glow plug was hot while the other two were cold. Then after replacement you found that all three old plugs were good and that the problem was probably wiring related. I am a bit confused, if one plug was hot then the wiring problem must have been with the jumper wires connecting all three plugs in parallel, and that the feed to the plugs was probably not the problem. I know you must have changed the entire wiring but was it the jumper wires that was the main problem?

    And in case the plugs are my problem (and not the switch, wiring or relay, if there is one), am I correct that you were able to replace all three without removing the intake manifold. It may have been difficult and time consuming, but was it indeed possible?

    Again thanks, Herb

  12. #12
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    Good analysis on the glow plug switch. You should be able to put the meter on the end of any of the glow plugs you can get to, leaving the wiring intact. They're in parallel so the reading will be the same regardless of which one you connect your positive lead to. It also won't matter if you have a bad plug, you should see voltage regardless. You're looking for about 12 volts or so with the plugs activated.

    If you need an extra "hand" to be able to see your meter you can extend the leads of your voltmeter so that you can place it in the companionway and watch it. I have also used my phone camera in the movie mode to record what happens when I can't see the indicator during tests. Worked great when I was doing compression tests.

    I hope it's an easy troubleshooting process and a quick fix.
    Craig Davis & Ellen Le Vita

    1980 E38 "Pilot Project"
    Hull #20
    Seattle, WA



    Somebody once said "It's an old boat and therefore resistant to change."

  13. #13
    Moderator Christian Williams's Avatar
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    Herbert,

    I think I concluded that the finger test for glow plug heat is just unreliable. One seemed hot , the others weren't. It was unreliable data.

    I believe you have an Ericson 34? I had a 32-3, which has an M25 engine with very good access, especially compared to an E381.

    On that model, the glow plugs were just an awkward reach, typical of engine stuff. You could get a 12mm spanner on the plugs, but the angle had to be right and patience was required. On that installation there was no need to remove anything big, just whatever hoses are in the way for convenience.

    Might be quite different on your model.

    An easy way to test the glow plugs, when you get them out, is to run a heavy wire from the battery pos terminal to the glow plug top, then hold the base against the engine block. No need for anybody else to push the cockpit buttons.

    FWIW, I'm not a mechanic. My approach is just plunge in, figure things out, go off an buy the right tool, and expect a lot of first-time head scratching. If you do screw something up completely, then just call in a real mechanic to clean up the mess.

    You do have to get dirty just to understand the issue. It helps to remember that if they put it on, it should be possible to take it off.
    Thelonious II, E381 hull 513 (1984) Universal 5432
    Table of Contents for Thelonious Blog here
    "Alone Together--the Book" trailer here

  14. #14
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    On my M-25...

    On the knurled nuts: You'll probably need a screw-driver to loosen them if you haven't had them off before. The slots in the nuts look odd because they're so far off-center. Find a wide-blade screwdriver that fits the slots and you'll be surprised how they rotate just like normal screws. As for re-tightening, I think you have the right idea--finger tight then maybe another 1/8 to 1/4 turn with the screwdriver. I haven't changed glow plugs, but I did remove and polish all the contacts on the jumper wires.

    As to removing the intake manifold: It seems I recall a previous post where an owner said the glow plugs "almost" went in/out without removing the manifold. The problem was the overall length of the plugs--the top threaded posts (that accept the knurled nuts) were hitting the manifold during removal/re-installation. The owner suggested that snipping or grinding off any unneeded extra threads on the posts might have helped the installation.

    As to possible wiring problems: I have not yet re-wired my starting circuit either. I do know that when I hold the glow plug switch in, the panel lights and the oil pressure light both dim slightly and the clicking noise from the fuel pump changes noticeably. All these are signs of both 1) inadequate wiring, but also 2) that the glow plugs are in fact drawing a lot of amperage (I believe they draw 7 amps each). My engine (M-25 with 2100 hrs) was impossible to cold-start when I held the glow-plugs for the recommended 20 seconds. I decided to energize the plugs for a whole minute, then wait two minutes for the cylinder heads to absorb the heat, then hold the plugs for another full minute. It worked so well that I now do the routine as 45 sec--2 min--45 sec for cold-starting. Again, this works for my set-up which I know has inadequate wiring (the glow plugs are likely getting much less than the recommended power). As someone (MaineSail, perhaps) suggested in a re-wiring post, if you install a solenoid for the glow-plugs (along with the proper wiring), you'll need to energize them for much shorter times or you'll burn them out.

    Best of luck.
    Last edited by Kenneth K; 12-08-2017 at 02:49 PM.
    Ken
    '85 E32-3 "Mariah" #641

    "Saltwater is the cure; sweat, tears, or the sea......"

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    Herb,

    I was able to remove and replace the glow plugs with only removing the air filter on my M25XP. I would check the voltage at the glow plugs with them still hooked up and a helper pressing the button. This will give you the voltage drop. My reading was 9.7 volts. My glow plugs weren't acting as red hot diesel igniters. They were acting more like baby bottle warmers. After my rewiring, they read 11+ volts at the glow plugs. The engine now starts with 10 seconds of glow in the coldest weather (28 degrees and lower). On the original wiring, the path of juice was through the ammeter to the ignition switch then to the glow plug switch then through that god awful trailer harness to the glow plugs. My harness went forward to the front of the cockpit locker then doubled back to the back then went forward to the engine and glow plugs. All in all about 30' of undersized wire running through an ignition switch that was maxed out amperage wise. The plugs on the harness got quite hot during this little exercise. No surprise as a slide together plug does not have the positive contact that a screwed down terminal has. Main Sail has an excellent article on this subject and the current Good Old Boat online has just got one on how to cook a wiring harness.

    These trailer plugs were never a great idea and I consider them to be outright dangerous in a 20+year old installation. It is smart to go over the wiring harness with an infrared temperature gauge. The temp readings at the plugs can be shocking. I used a heavy duty relay so the heavy duty current only goes three feet from the batteries to the glow plugs. The voltage drop is minimized and the fire starting high current isn't running all over the boat.


    Oh and I also threw away that air filter and put a K&N on. It didn't seem bright to have all those metal shavings sitting right on top of the intake manifold.
    Bob Morrison
    1987 E-34 Hull #15
    "Terra Nova"

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