You can only apply direct battery voltage to a string of loop type glow plugs at the number five cylinder. This is where the wire from the glow plug relay connects. The individual series glow plugs are only rated at something like 1.2 volts each. Yes 1.2 volts. So a 12 volt shot is about 10 times more individually than they are designed for if applied to an individual plug.

This would be the case if you applied the 12 volts to the number one glow plug at the front of the engine block. Applying power to the number two plug for example would still be too much voltage and one of the two plugs would burn out in my opinion. Applied at the third glow plug the three plugs would go over temperature but might survive. Actually probably would.

This is why a jumper with decent connectors should be in the trunk of all the cars still using series glow plugs. If one plug burns out usually you could bridge it so current would flow to the remaining three glow plugs and hopefully get you going.

They are intended to run in the same fashion as an old set of christmas tree lights. With say five plugs in series using 6 volts. The remaining 6 volts or whatever the actual voltage differance is used or dropped across the squiggly resistance wires that can glow in the dark.

Where the pencil style glow plugs by design each operate at twelve volts. You should recheck with an ohmeter the loop style plugs. Unless you took the effort to burn out them all some may stil be good. If an engine is generally in good shape the loop plugs are quite adaquate for spring,summer, and fall temperatures.

The reason they are less efficient than the pencil plugs primarily is the energy used on those squiggly wires. Someone originally made a simple error in design I suspect those many years ago or a system of dropping more voltage across each glow plug may not have been too practical initially I suspect. So by simple design the pencil plugs are just more efficient with less waste.

For those that read this post since a four cylinder engine has one less glow plug. Either they have a different part number for their resitance wires As they would be recieving 20 percent more voltage than designed for otherwise. Or they have a different part number for the dropping squiggly connecting wires. For example after measuring the voltage under load if you replaced the squiggly wires with those from a five cylinder I think the glow series glow plugs would operate in a slightly higher voltage but safe and hotter fashion.

If the part numbers are different for them between the four and five cylinder engines this could be looked into. Maybe it has already and I just have never seen any mention of it.

Not relavent to this post other than to glow plugs. I used to read all the threads on glow plugs and hard starting a few years ago. I never investigated it as I do not use these cars in really cold weather.

Still it did cross my mind if a pulsed higher voltage than the plugs where designed for might increase the element temperature and stil give a decent glow plug lifespan. Much depends on the temperature that the element plasticizes at. There may be a decent safety factor already engineeered in.

The time constants or frequency could be applied to a modified loop plug system. Doing it with the pencil plugs would require a higher voltage source so not as practical from a cheap perspective. My opinion is you would have to carry a second battery to enable it with the pencil plugs.

The amount of current the pulser would have to handle is substantial. A motorized mechanical device to generate the pulsing perhaps. Any system to generate higher overall temperatures is going to stress the plugs. As long as the melt point of the element was not approached it should generate substantially more heat I suspect.

Metal technologies have also advanced. There might be better materials for glow plug element service already existing. Who knows? In the future a plazma type of glow plug could even become a reality.

A lot of the technology utilized when these diesels where manufactured could be vastly improved today I suspect. There is just no market to justify what might be possible.

We have never even tried tapping and installing a couple of pencil plugs into the intake manifold to preheat the combustion air either. Hard to estimate what the improvement if any would be. A temperature probe into the intake manifold would give indications of what temperatures the air is rising to. If air temperatures in the manifold can be increased faster than they are lost it has to have some upside.

Maybe using the type of glow plug that volkwagon is currently using for this type of issue would do it. The energy used to preheat is offsett by the easier starting if it is workable.

Two plugs on a push button switch might really help even. Until people probe these areas there will be no change. Some of todays diesels and some in the past used pre heated manifold air. Some used heated manifold air as their only starting aid. Since they are still doing so it has to have some advantages. I think volkswagon for example uses more glow plugs than there are cylinders today.

Something like six or seven glow plugs on the four cylinder tdi engine. If nothing else that engine will start in severe cold conditions. I wonder how well it starts in comparison if the manfold air heating glow plug or glow plugs are defective?

Any working volkswagon mechanic should have the answer. I will ask in their back shop the next time I am going past a dealership. I think the time has arrived to find out if improvements in cold starting abilities might be seriously improved on the older engines with no great effort involved to do so.

I was was giving a response to Post #4 "so do i wire these to the original power wire or can i hook them up directly to the battery with a switch in between to turn them off and on? i really dont want to burn up another set its getting expensive quick also im new to this how do i start a new thread? much thanks "

I got the impression that 79benz300d wanted to simplify His system.
I was also trying to show that if He only wanted to install a Switch (no Relay) He had to make sure the Switch could handle the amperage.

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84 300D, 82 Volvo 244Gl Diesel

You basically cannot burn out the twelve volt pencil style plugs. Unless they are left on for extended periods. That may only shorten their lifespan.

This is based on that they operate at twelve volts and you have no higher voltage availble in the car essentially.

The series loop plugs as mentioned are very low voltage plugs in comparison . Depending on what you did you may only have one burnt out loop plug incidently. If one is burnt out no others will be functional until the burnt out one is replaced.

Do not throw them away before checking them with an ohmeter for resistance. They are new plugs and not all that cheap. There is a fair chance that four of them may still be good. Depends on what you did exactly.

Resistance is checked where the two external wires connect on them. Not from any connection point to ground. There should be continuity or a very low ohm reading between those two external wire connection points on each glow plug if it is still good.

If you live in a warmer part of the states you can make this cost what you want. Replacing one glow plug you burnt out is not all that expensive. If you where low on funds you could probably use one of your old ones if the resistance check seems okay. Until you take the time to check each plug you can have no way of knowing how many are burnt out.

Unless you in some fashion applied the effort required to burn them all out. I feel and hope you may still have four new good series plugs out of five.

The new style works great now I need a cam any ideas?

Well I got the car going it has what sounds like a liifter knock if you look in the oil filler hole on the valvecover you can see the one lobe it us scored pretty bad rough feeling where is a good place to get a new cam? It holds 45 psi oil pressure while driving and about 25 at idle when fully warmed up so I think the bottom end is ok it also has a slight miss i did hook the glowplugs upto the relay any ideas on finding a cam would be appreciated