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Old 11-04-2021, 09:54   #1
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Smart glow plugs

The glow plugs on my Pathfinder diesel are controlled by a simple on/off relay. I turn the key on, then hold a toggle switch for 10 seconds or so depending on how cold the engine is, then release the toggle switch and hit the starter button. I think this is a pretty standard setup from what I have read. Here in the PNW I definitely need the glow plugs in the winter, not so much in the summer.
Diesel cars apparently have a much more sophisticated system where the glow plugs are turned on automatically, either by the ignition key, by opening the door or some other means, and then stay on after the engine has started until the water temp. reaches some pre set level. This post-start assistance apparently makes for a much smoother cold start idle and much less smoky unburnt fuel on startup. I am thinking my engine would benefit from this feature and probably new computer controlled marine diesels already have it.

Has anybody added the post-start heating feature to an existing "dumb" glow plug system like mine? I am thinking it would be pretty easy to wire the glow plugs to come on automatically when the ignition key is turned on. The tricky bit is to add a relay that will switch the plugs off after the earlier of, say, 30 seconds or the water temp reaching 70 degrees or so. I suppose they would also have to cut out briefly while the starter is cranking so there is full power to the starter. Alternatively, I suppose I could try just holding the glow plugs on for another 10 seconds or so after the engine has started. Does anybody do this? Anybody have any ideas?
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Old 11-04-2021, 10:08   #2
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Re: Smart glow plugs

Hmmm. You can achieve a better initial burn as well by holding the glow plugs on longer before you switch on the starter. I use 30 seconds on my genset just to make sure that I will get a nice smooth start and not wear down the starter motor. My big old DD-453 engine doesn't have glowplugs.

Rigging a timer based glow plug switch would not be difficult; I found several cheap circuits for it on Amazon. My only reservation would be whether you can achieve most of what you want by simply holding down the switch longer before starting.
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Old 11-04-2021, 10:17   #3
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Re: Smart glow plugs

This sort of very familiar mechanical switch usually used to delay turning off lights in AC (home) circuits would do the job. The timing motor spring is wound by turning the knob to the delay you want.
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Old 11-04-2021, 10:36   #4
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Re: Smart glow plugs

Despite all the YouTube videos, I think automobile drivers as a group have many many more users to the far left of the bell curve than cruisers. Hence the automated cold start systems on cars.

Why add another system to fail (with consequences) when you can just use the glow plugs a few seconds longer?
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Old 11-04-2021, 15:36   #5
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Re: Smart glow plugs

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Originally Posted by Nord Sal View Post
Despite all the YouTube videos, I think automobile drivers as a group have many many more users to the far left of the bell curve than cruisers. Hence the automated cold start systems on cars.

Why add another system to fail (with consequences) when you can just use the glow plugs a few seconds longer?
I like the idea of a system that automatically meters the temp and keeps the plugs on for the optimal period, both before and after the engine has started. The thumb on the button for ten seconds or so is pretty hit and miss. However, if there’s no simple and reliable solution, then I guess there’s not much choice
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Old 11-04-2021, 18:27   #6
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Smart glow plugs

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Originally Posted by osprey877 View Post
I like the idea of a system that automatically meters the temp and keeps the plugs on for the optimal period, both before and after the engine has started. The thumb on the button for ten seconds or so is pretty hit and miss. However, if there’s no simple and reliable solution, then I guess there’s not much choice


You could try a heat riser, from exhaust manifold to intake. Also electric grid intake heater, like Cummins Diesel. Red Glowing plugs don’t last long, with combustion strokes.
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Old 11-04-2021, 19:10   #7
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Re: Smart glow plugs

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Originally Posted by osprey877 View Post
The glow plugs on my Pathfinder diesel are controlled by a simple on/off relay. I turn the key on, then hold a toggle switch for 10 seconds or so depending on how cold the engine is, then release the toggle switch and hit the starter button. I think this is a pretty standard setup from what I have read. Here in the PNW I definitely need the glow plugs in the winter, not so much in the summer.
Diesel cars apparently have a much more sophisticated system where the glow plugs are turned on automatically, either by the ignition key, by opening the door or some other means, and then stay on after the engine has started until the water temp. reaches some pre set level. This post-start assistance apparently makes for a much smoother cold start idle and much less smoky unburnt fuel on startup. I am thinking my engine would benefit from this feature and probably new computer controlled marine diesels already have it.

Has anybody added the post-start heating feature to an existing "dumb" glow plug system like mine? I am thinking it would be pretty easy to wire the glow plugs to come on automatically when the ignition key is turned on. The tricky bit is to add a relay that will switch the plugs off after the earlier of, say, 30 seconds or the water temp reaching 70 degrees or so. I suppose they would also have to cut out briefly while the starter is cranking so there is full power to the starter. Alternatively, I suppose I could try just holding the glow plugs on for another 10 seconds or so after the engine has started. Does anybody do this? Anybody have any ideas?
I am confused...

What PROBLEM are you trying to solve?

Your engine seems to start when you want it to and run as it should, or at least you have no specific complaints about the way it functions. Other than being the "cool kid on the block" what's the point of automating such a stupidly simple system? It just adds a bunch of complexity and things to break.
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Old 11-04-2021, 19:31   #8
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Re: Smart glow plugs

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I am confused...

What PROBLEM are you trying to solve?

Your engine seems to start when you want it to and run as it should, or at least you have no specific complaints about the way it functions. Other than being the "cool kid on the block" what's the point of automating such a stupidly simple system? It just adds a bunch of complexity and things to break.
The “problem “ is rough, smokey, noisy idling until the engine warms up, which in winter can be at least a couple of minutes. Diesel autos don’t have this problem and I am wondering if there is some simple solution I haven’t heard of. Apparently not.
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Old 11-04-2021, 19:39   #9
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Re: Smart glow plugs

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You could try a heat riser, from exhaust manifold to intake. Also electric grid intake heater, like Cummins Diesel. Red Glowing plugs don’t last long, with combustion strokes.
Are you saying it is a bad idea to energize the glow plugs once the engine has started? I had never tried it but when I looked into the auto systems they appear to routinely run the glow plugs after the engine has started in order to smooth out the idle and prevent unburnt fuel smoke. As I understand it, They don’t shut off till, in the case of VW’s at least, the coolant reaches 70 degrees F. Are they using different glow plugs?
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Old 11-04-2021, 22:07   #10
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Re: Smart glow plugs

Youll kill the battery quick if you run the glow plugs and starter simultaneously.
My Kubota tractor requires turning the key to the left to activate glow plugs, then to the right to activate the starter. Foolproof!
My old Ford truck has an automated system, and has set itself on fire twice now, to the tune of big bucks to replace the poorly engineered controller. Not Foolproof!
The Cummins in my boat does not have glow plugs, and starts instantly without them.
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Old 12-04-2021, 05:38   #11
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Re: Smart glow plugs

I also have an old Pathfinder diesel with glow plugs on my boat. I suspect the glow plugs will burn out very quickly if you tried to keep them on until the coolant reached 70 degrees. My engine is the 4 cylinder 1.6L which is based on a late 1970’s Rabbit engine - it is not sophisticated at all - which has great appeal to me in terms of reliability and ease of maintenance.
If you have the same Pathfinder, the exhaust manifold is directly below the intake manifold - and so heats it up quickly.
If you are concerned about emissions on cold starts, I don’t think messing with these old, simple glow plugs is going to provide a solution. If anything, you might even make your engine inoperable - the glowplugs are a little delicate in this engine, they readily corrode in, and so are difficult to change without snapping them off still partially in the combustion chamber. If you burn them up with your “solution” and snap off a glow plug in replacement, just how are you going to start your Pathfinder on a cold day? My Pathfinder doesn’t like cold starts without glow plug use even on warm days.
Why don’t you try pre-heating the air going into the air intake with a hair drier or something as an experiment to see if this solves the 30 seconds or so of rough idle. Also, there used to be diesel fuel pre-heat modules available to heat the fuel prior to injection that helped diesels (with no glow plugs) start in cold weather.

I would stay away from any tinkering with a Pathfinder’s glow plugs as once damaged, they might prove extremely difficult to remove to replace.
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Old 12-04-2021, 07:25   #12
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Re: Smart glow plugs

Sounds like a challenge for a dedicated techie. An Arduino (or RPi mini) with a couple of sensors (engine and air temp for example) could control a relay nicely. A bit of software fiddling could have it control the on time to meet the current conditions.
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Old 12-04-2021, 07:37   #13
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Re: Smart glow plugs

Is your current setup such that you can manually energize the glow plugs for 10 (or 30, or whatever) seconds after startup? Sounds like it is? Then try it, does it smooth out your cold idle? If it does then maybe there’s a place for a discussion about automating the process. But first I’d want to (cheaply) prove that it resolves the cold idle problem(s).
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Old 12-04-2021, 07:50   #14
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Re: Smart glow plugs

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Originally Posted by Dsanduril View Post
Is your current setup such that you can manually energize the glow plugs for 10 (or 30, or whatever) seconds after startup? Sounds like it is? Then try it, does it smooth out your cold idle? If it does then maybe there’s a place for a discussion about automating the process. But first I’d want to (cheaply) prove that it resolves the cold idle problem(s).

Agreed. If that works, you could probably rig something easily with a delay-off relay and an indicator light for glow plugs on. It wouldn't be hard to have the glow plugs run for 30 seconds (or whatever time you choose) with a push of the button. So on a cold start, you'd do something like push the button, wait for the light to turn off. Crank engine, as soon as it fires, push button again for another glow cycle during the first bit of running.
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Old 12-04-2021, 08:36   #15
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Re: Smart glow plugs

It sounds like you have a bad fuel injectors or poor compression problem. Not a glow plug problem. If you operate the glow plugs after the engine is running you will create a glow plug problem in a short time.
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