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  #16  
Old 12-03-2011, 08:08 AM
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Quote:
Originally Posted by t walgamuth View Post

And I don't trust testing them any way except taking a jumper cable and testing the glow right on the battery terminals. If it does not glow immediately or fully it is junk.
There has been a lot of discussion regarding glow plug temperature requirements, with the prevailing notion as you have mentioned. However, has anyone done any analysis of whether these plugs, of reduced performance, actually function adequately?

If the plug glows red instead of the required bright orange, what's the tip temperature? Would that tip temperature be acceptable for ignition if the ambient temperature doesn't get below, say 0 F?

In my specific case, we rarely get down to 10 F.

I have never changed a plug until I get an open reading on the meter.

I have to conclude that I must have one..........or several.........."weak" plugs on the SD. Some have been in there for years.

I never observe the SD start on four and with a subsequent check with the meter and fail to find an open plug.

Although I would never disagree that the performance of five new plugs is certainly better, the cost of them is now close to $75. and, for those with limited funds and limited cold ambients, there might not be such a strong requirement for "brand spanking new".

Food for thought.

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  #17  
Old 12-03-2011, 08:47 AM
t walgamuth's Avatar
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Considering the cost of a starter, replacing glow plugs once or twice in a decade seems like good prevenative maintenance.

Batteries are not cheap either.
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..I also have a 427 Cobra replica with an aluminum chassis.
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  #18  
Old 12-03-2011, 08:51 AM
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Originally Posted by t walgamuth View Post
Considering the cost of a starter, replacing glow plugs once or twice in a decade seems like good prevenative maintenance.

Batteries are not cheap either.

You make the assumption that weaker glow plugs correlate to longer cranking times.

I'm not ready to make that conclusion for ambients of 10F or above on engines with decent compression.

It may be eminently possible to achieve the same starting capability of brand new plugs via longer glow times to heat the air around the plug. You can heat it for a short time with a very hot plug or you can heat it for a longer period with a cooler plug.........same result.
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  #19  
Old 12-03-2011, 08:51 AM
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... that is a good point, autozoo now charges over 15per plug... and they have changed their policy towards aquiring $20.00 points to each $20 purchase must be outside 24 hours to qualify for adding to the card... bean counters must have realized we were breaking up our large purchases to get more credits on the card...
anyway, if you live in an area that gets below 15°F your block heater should be in TIP TOP shape, and it should be used!
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  #20  
Old 12-03-2011, 08:55 AM
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Originally Posted by vstech View Post
anyway, if you live in an area that gets below 15°F your block heater should be in TIP TOP shape, and it should be used!
............i'll see if the Marriott will let me run an extension cord through the lobby entrance.............


Seriously, an engine with good compression doesn't need a block heater down to about -10F. Some folks have started them even lower, which never ceases to amaze me.

The variable of compression is huge in the whole scheme of things. If you have it, all the other players become somewhat moot. If you don't, you need all the other players, including the block heater, and white hot glow plugs, to assist.
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  #21  
Old 12-03-2011, 09:46 AM
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Same weather conditions this morning. Same starting procedure--count to 15 after glow light goes out. Fired right up, no hesitation at all.
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  #22  
Old 12-03-2011, 09:47 AM
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Quote:
Originally Posted by Brian Carlton View Post
There has been a lot of discussion regarding glow plug temperature requirements, with the prevailing notion as you have mentioned. However, has anyone done any analysis of whether these plugs, of reduced performance, actually function adequately?

If the plug glows red instead of the required bright orange, what's the tip temperature? Would that tip temperature be acceptable for ignition if the ambient temperature doesn't get below, say 0 F?

In my specific case, we rarely get down to 10 F.

I have never changed a plug until I get an open reading on the meter.

I have to conclude that I must have one..........or several.........."weak" plugs on the SD. Some have been in there for years.

I never observe the SD start on four and with a subsequent check with the meter and fail to find an open plug.

Although I would never disagree that the performance of five new plugs is certainly better, the cost of them is now close to $75. and, for those with limited funds and limited cold ambients, there might not be such a strong requirement for "brand spanking new".

Food for thought.
Nutritious food too.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #23  
Old 12-03-2011, 09:57 AM
t walgamuth's Avatar
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Quote:
Originally Posted by Brian Carlton View Post
You make the assumption that weaker glow plugs correlate to longer cranking times.

I'm not ready to make that conclusion for ambients of 10F or above on engines with decent compression.

It may be eminently possible to achieve the same starting capability of brand new plugs via longer glow times to heat the air around the plug. You can heat it for a short time with a very hot plug or you can heat it for a longer period with a cooler plug.........same result.
I also make the assumption that a half a$$ glow probably indicates that the plug is in its death throws and will not even glow that much ...much longer.

You apparently have in your past professional experience been involved in some fairly scientific testing proceedures on cars, so you have a professional instinct to do research before making an opinion about something automotive.....myself? I am just a guy trying to keep a 27 year old car on the road and avert an avoidable problem down the road a few months.
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..I also have a 427 Cobra replica with an aluminum chassis.
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  #24  
Old 12-03-2011, 10:39 AM
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Quote:
Originally Posted by t walgamuth View Post
I also make the assumption that a half a$$ glow probably indicates that the plug is in its death throws and will not even glow that much ...much longer.

You apparently have in your past professional experience been involved in some fairly scientific testing proceedures on cars, so you have a professional instinct to do research before making an opinion about something automotive.....myself? I am just a guy trying to keep a 27 year old car on the road and avert an avoidable problem down the road a few months.
I'm not sure about that. Maybe the plug has deteriorated from the performance that it had when new............and will function for years with a reduced tip temperature?

Way back in the day when I worked for Chrysler. However, in this discussion, I'm no different than you are...........just trying to keep the exact same 28 year old car running reliably as the daily driver.

I don't even like taking the devil's advocate in this discussion since I can easily spend the money to change all five. I'm just not fully convinced of the need.............so, I haven't done it.
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  #25  
Old 12-03-2011, 10:46 AM
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And I'm conservative/cheap enough to replace them one at a time, particularly when I've got one spare one sitting in the toolbox and a whole set would require a trip to the parts store. Bosch glow plugs are $7.47 at Rock Auto
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1984 300SD 315k--daughter's car
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  #26  
Old 12-03-2011, 10:52 AM
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Originally Posted by kerry View Post
And I'm conservative/cheap enough to replace them one at a time, particularly when I've got one spare one sitting in the toolbox and a whole set would require a trip to the parts store. Bosch glow plugs are $7.47 at Rock Auto
The question is whether you change them based upon an electrical open condition............or whether you have pulled one or two and changed them on tip temperature?

I have never done the latter. I conclude, with limited data, that tip temperature is not relevant to a good start in my ambients, with my compression.
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  #27  
Old 12-03-2011, 10:59 AM
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Just for experimental purposes I wonder if tip temperature could be inferred from plug temperature when shot with an infrared thermometer from the outside with the plug glowing??
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1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
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  #28  
Old 12-03-2011, 11:02 AM
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Brian has a good point. I'm with Kerry, I also change out glow plugs if they are bad. I feel there is no sense in replacing them all if they are still working. I occasionally change out visually. But most of time I change them out based on an open condition.

Quote:
Originally Posted by kerry View Post
Just for experimental purposes I wonder if tip temperature could be inferred from plug temperature when shot with an infrared thermometer from the outside with the plug glowing??

When I get them time, I'll test some extra glow plugs and see if I can use the laser temperature gun to determine the different tip temperatures.




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  #29  
Old 12-03-2011, 11:02 AM
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Originally Posted by kerry View Post
Just for experimental purposes I wonder if tip temperature could be inferred from plug temperature when shot with an infrared thermometer from the outside with the plug glowing??
Doubt that you'd get much correlation. The tip is a long way from the outside of the plug. The time for the heat to crawl all the way to the outside of the plug would be way more than 35 seconds.

Maybe if you could achieve equilibrium in about an hour.............maybe..............
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  #30  
Old 12-03-2011, 11:02 AM
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To add fuel to the discussion: Last year when I had a weak plug--ohm out high but was not open, engine would still start but run unevenly for about 30 seconds. (maybe the temperatures weren't quite as cold--20's possibly) In this recent event, symptoms were much more severe with a completely open plug.

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1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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