Glow Plug Question

[scgunner]

I'm in the middle of my 100hr service and took note of my glow plugs, with over 1500 hours on the motor it occurred to me that I have never done a thing to them. Maybe because for 30+ years I've never had a problem, I push the glow plug button for 20 to 25 seconds and the motor fires right up every time.

A fellow C34 owner had recently replaced his glow plugs(not sure why)which got me thinking should I replace them or not, I don't know. That's why I'm posing this question to the collective wisdom of the C34 herd.

[KWKloeber]

Kevin

If while you heat them the tops are too hot to hang onto, they're fine.  You could check their resistance from tip to ground to see if they're about the same (same idea as cylinders' compression). I don't recall but could look up the spec on the resistance but the finger test says it all and is most reliable.

Now that said, for the measly cost new ones are cheap insurance.

Yours may just last forever cuz you haven't drunk the Koolaid re: the stupid glow plug relay mod!  I don't know how you've endured that hardship, preheating for 20-25 seconds instead of 10-15 seconds. 

Ken
(I couldn't resist given that opportunity)

[Stu Jackson]

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Yours may just last forever cuz you haven't drunk the Koolaid re: the stupid glow plug relay mod!  I don't know how you've endured that hardship, preheating for 20-25 seconds instead of 10-15 seconds. 

Ken
(I couldn't resist given that opportunity)

Kevin, sometimes Ken just can't help himself.  That'd be most of the time.  He tends to uselessly repeat himself, too, and too often.

It's your CHOICE to install the glow plug solenoid.  The advantage is that you can start a cold engine in half the time.  Ken thinks that's unnecessary, and has explained why maybe once before, followed by his repeated dissing of the concept.

The only disadvantage I can recall is that one could possibly burn out the glow plugs if, WITH a solenoid installed, you keep them energized too long, because the voltage that gets to them is higher because the current doesn't have to run up to the cockpit panel and back down to the engine.

But that would mean that YOU, as the boat owner, just plumb forgot (!!!) that you actually installed the solenoid.  How could that be?!?

In response to one of Ken's earlier solenoid diss comments, I related my actual real life experience where it came in very handy: 

We'd sailed across SF Bay from the Oakland Estuary to Sausalito, and by then our engine was cold.  Sausalito has Hurricane Gulch, with high winds over a break in the hills to the west, but also, just to the north of it, a band of light breeze.  We were right at that point, furling our jib and dropping our main.  There was a Big Boat Race going on, and there was a large group of large sailboats bearing down on us from the north and east - one of their turning marks was a since removed yellow buoy off Hurricane Gulch. 

When we tried to start the engine, nothing happened.  I knew exactly what it was, because ten years earlier I had replaced the start button to starter solenoid fuse holder, and had since relocated it to a more accessible spot (see Critical Upgrades).  I hopped down below, opened the engine compartment and messed with the fuse holder, and asked Morgan to try to start the engine.  It turned over this time, but didn't start because it was cold.  By then those large racing sailboats were bearing down on us, having slid out of the dead zone and hit the breeze.  We could see the bones in their teeth, a few heading right for us.

I told Morgan to hit the glow plug button for 12-15 seconds, and then the engine started right up.  And we motored out of their way, close call.

Do I mind being able to start my engine faster?  No.
Do I need it all the time?  No.
Do I appreciate having it.  You betcha.

We all recognize the help Ken's given us over the years and applaud him for that assistance.  But sometimes his rants get tiresome.  Perhaps he should have resisted.  Sometimes those few seconds can be a real help, in the real world.

Look, it's Your Boat, your choice , to install one or not.  Always has been, always will be.   But faster starting can sometimes be necessary, and eliminating the power run up to the cockpit panel can't hurt.

Plus, I used to like KoolAid.  :D:D

[scgunner]

Wow, I feel like I just stumbled into a dark room and lit a torch to get my bearings only to discover it's a room full of dynamite. Sorry guys I didn't realize I was ripping a scab off, just curious about the longevity of glow plugs.

I have to say I've been coming to this board for a few years now and this is the first I've heard about the great glow plug/solenoid debate. With regard to that debate I think I'll stick with the old saw, YBYC.

One more thing I was wondering about, when I start the motor(after glow plug warm up) I hold both the glow plug button and the starter button until the motor fires, does anybody release the glow plug button first then push the starter button?

[Stu Jackson]

...................................


One more thing I was wondering about, when I start the motor(after glow plug warm up) I hold both the glow plug button and the starter button until the motor fires, does anybody release the glow plug button first then push the starter button?

Earliest input has always been to release the glow plug button before the start button.  Why?  Because the plugs have already heated the chambers; no need to have simultaneous draws on the battery.

[scgunner]

Stu,

I like that idea, those glow plugs pull a lot of juice which can be freed up to crank the motor. I'll give it a try see how it works.

[mark_53]

Stu,

I like that idea, those glow plugs pull a lot of juice which can be freed up to crank the motor. I'll give it a try see how it works.

That's exactly right.  Glow plugs draw a lot of power.  I release the glow plug momentary switch then wait about 3 seconds to let the start battery recover then hit the start button.

[Jim Hardesty]

Kevin,
Do you really need to use the glow plugs to start?  Shamrock starts right up till the temps are in the 40s.  Rarely on a restart.  I don't use the glow plugs a half dozen times a year.
Jim

[ewengstrom]

Jim,
Maybe that M35BC just has better compression than our old M25XP's. Mine takes a good 15+ seconds before it's warm enough to fire....and I just had the injectors rebuilt this year too.
But she's old and I do believe I'm getting a good bit of blow by on the rings, (reduced compression) I installed a catch can in between the crank case vent and and air filter and it's about ready to be emptied after only moderate use this year. 
Kevin,
When I pulled the motor out this past winter I gave it a major servicing (not rebuild....yet) and replaced the glow plugs at that time. Given our boats uncared for past I felt it couldn't hurt. The original glow plugs showed some wear so since the replacements were actually pretty inexpensive, it was easiest to replace them.

[Ron Hill]

Guys : I believe that the glow plug solenoid relay is one of the best and smartest mods for the M25/M25XP engine that I've seen!!

Look at what you have with out it -  To turn the key switch/glow plug button to energize the glow plugs the current must travel in a #16 gage wire from the common starter solenoid post, up to the key switch and then back to the #3 cylinder glow plug about a distance of 15-16 ft!! Then it is gang wired in series to the other 2 glow plugs.  I've have never measured the voltage at #3 cylinder, but it must be only a dribble.  Then that dribble must also has to energize the next 2 plugs!!  Why energize that circuit for 30 some seconds (dragging down the battery/s starting power) when the Ford truck solenoid mod. will allow you to just open a circuit (for 2/3seconds) from the starter common post thru a #8 wire just around the corner only 2/3 ft away to the #3 glow plug????  Why NOT!?! 

Ken : I've been in an anchorage when the wind (T storm) has changed the wind 180 degrees @ 03:00 AM and suddenly awaken by the smell and noise of diesel engines because Anchors are dragging!!  Believe me it sure is nice to be able to hit that glow plug switch for 2/3 seconds and get that engine running while I figure out what all is happening!!
Also it nice when the spinnaker is up and flying and there is TOOO much wind!!  You are on the bow trying to hold things together and you call back (never yell!!) to the 1st Mate to start the engine.  One hand on the wheel and only 2/3 seconds of glow plugs!!

Jim : The glow plugs are there for a reason and I always figured that lighting the glow plugs lessen the strain (# of rpm) that the starter needed to turn and start the engine!  Also to replace glow plugs is alot cheaper $$ - than starters!! Restart seldom/never needs the plugs.

Ken : I found that Kool aide is a cheap drink to fill up kids, but it stains every thing when spilled, gives the drinker an energy hi and is a Dentists delight for making $$. 

If the old original charging circuit thru the gummy plugs was bad i.e. from the alternator to the key switch and back to the battery bank was bad and inefficient (15-16ft) - then why would you do the same with the glow plugs? when you can install a simple mod????

A few thoughts

[Noah]

Anything that shortens the cranking/starting time of the engine is a plus in my book. If you crank it too long you risk filling the muffler with seawater and back-flowing into the engine. Caveat: I am not a mechanic.😎

[mark_53]

Anything that shortens the cranking/starting time of the engine is a plus in my book. If you crank it too long you risk filling the muffler with seawater and back-flowing into the engine. Caveat: I am not a mechanic.😎

It wouldn't shorten the cranking time just the preheat time on a cold engine.  Once the glow plugs are up to temperature, the engine should fire right up.  I seem to recall the glow plugs were 10v so maybe some voltage drop is ok but I'm no mechanic either.

[Stu Jackson]

Ron, thanks for explaining a couple of other good reasons it wouldn't hurt to shorten the glow plug time.  I know, I know, it was so completely wrong of me to be an imprudent skipper to even think of getting myself in the way of racing sailboats on SF Bay, who woulda thunk?     I'm so irresponsible...

[scgunner]

Well let's see here, we've got one opinion that the solenoid install is the best thing ever, we've another which says it's the dumbest thing you can do, and someone else saying what do you even need glow plugs for anyway! I think one thing we can all agree on is this is definitely a YBYC kind of a thread.

As for me I'm reluctant to monkey around with a system that works great especially when I have other fish to fry. Right now I'm dealing with a persnickety heat exchanger that doesn't want to exchange heat.

Stu, releasing the glow plug before cranking works great, thanks for the tip. Only took 32 years to get it right!

[Robert Mann]

I think the issue of the solenoid is also interesting in that without it the circuit runs through the panel, this has to cause some voltage drop due to wire length.  Perhaps if that were combined with lower battery voltage then the:

Watts (Glowplug power requirement) = Volts x Amps, if the power requirement stays the same and the voltage dips  the amps go up.  Could be the wiring might not handle that so well. Solenoid stops that amperage draw through the panel wiring.  Plus, believe me, if an engine manufacturer added a solenoid to this circuit there was a potential (no pun intended) problem.  It certainly wasn't done for our convenience!

There are some interesting trade offs in the engine world.  Indirect injected engines push fuel at a lower pressure into a combustion chamber in the cylinder head, which is surrounded by coolant.  On cold days this chamber is cold and stays cold during cranking, hence the need for artificial heat in the form of glow plugs, to reach the light off temp for a single stream of fuel.  In a direct injected engine where the fuel, at much higher pressure, is sprayed into the combustion chamber on top of the piston, through 4, 5 or 6 very small holes in the injectors, the chamber heats up quicker and retains heat due to the piston mass.
This type of engine does not need glowplugs, until emission compliance becomes the primary driver of engine design, and that is mainly due to timing requirements and the need to avoid white smoke, not steam, at start-up.

Some of the advantages of indirect injected engines are;

1) the combustion noise is better damped in this type of engine than the alternative, making the combustion noise "softer" and the engine inherently quieter.
2) the single stream of fuel through the indirect injection injector is extremely tolerant to water in the fuel.  Typically if you ingest water you get a cloud of white steam and the engine stops.  As long as the oh
s--t moment occurs soon after this happens, one can clean the system and put clean fuel though it and save it from rusting.  Try this on a direct injected engine and the tips will be blown off the injectors due to water expanding into steam in the tip (anyone run 4-108 Perkins??) and you are stuck in some odd port waiting for new expensive injectors or tips.

The main disadvantage of indirect over direct is that it shows somewhere around 12% higher fuel consumption, mostly due to lower thermal efficiency, typically who cares?

I glow my M35B for a few seconds each start, as Ron says it takes the strain off the starter.  Mine is running in very few turns of the engine.