Dependant on the vehicle totally. GPs aren't much fun...

I would have to go with glow plugs. My 82 240 d is alot more user friendly than my 87 T-Bird.:sword2:

69 microbus w/ porsche flat 6...remove engine to replace plugs.
mitsu gt3000...rear 3 are in undisclosed location.
vw and subie flat4s....can be done in situ but easier to kidnap 7 year old hands.
Acura Legend...looks easy but must remove strutbar to replace one closest driver.
BMW L6...right there and can be done in 3 mins.
Ford 302 in 1971 F100...climb up and sit on fender to do...easy.
Glow Plugs....I have yet to change one.

Depends on the vehicle, but in general, I'd rather change Glow Plugs. Remember that while SPs are cheaper, you have to replace the wires too! My GP wires have 260k on them, and work fine. :)

Plus, you don't have to gap them (even though many come gapped correctly already these days).

Peace,
sam

Well unless you have a MB. The newer ones have a coil on each plug so no plug wires. With the older cars the wires last an extremly long time usually you only have to change the ends. I would expect a 10+ year lifespan for MB plug wires.

I would have to vote for spark plugs. Although that is considering any gasser MB versus a diesel MB.

There are some gassers that can be a royal PITA such as a Ferrari 3 litre V8. It's not hard, just that it helps to be a contortionist to reach the rear bank. Oh, and Porsche 911s are fun too. :rolleyes:

Depends on the car we are talking about. On my firebird you would need to be a professional contortionist to get at the #6 & #8 plugs because of the way things are and the headers. Easier to take the starter out to get to it. On the Benz a plug froze in the head and had to be drilled out with the head off the engine. So, if we are comparing the vette and the benz, the vette came out real easy so I would say spark plugs. If we were considering the benz the way it is now with the anti-sieze vs my vette, it would be a toss up.

I had a FRAUD Ranger that got about 2 mpg more when I changed the spark plugs at 70000 miles. The dealership said it wasn't necessary tho. I suppose they were right when I took out the plugs and found that the gap was twice what it should be. Maybe not twice but at least 50% more

Spark Plugs
 

Like so many have stated, it does depend on the car but overall I'd go with Spark Plugs. Why? Well, I've only changed spark plugs on one car: my 1990 Honda Civic. I'm not expert wrencher, but it took less than 10 minutes to change the plugs and the wires. I've never done glow plugs but I've heard many negatives stories related to changing glow plugs - I know a guy who had to get a new head for his 1995 E300D after he somehow accidentally broke one glow plug while attempting to change it, and this guy is no stranger when it comes to working on cars. Plus, no glow plugs last for 100,000 miles like the Platinum spark plugs that you can get for nearly any car today.

Well, if I were willing to ignore the GP light, I'll bet I could still have started the car to this day and I ahve 100K on the clock. Don't believe the 100K lie. It will work but your mileage will suffer because wear and tear does occure on the plugs which are firing all day long. GPs only have to work for 5 mins a day

Well you'll need to show me some hard scientifically obtained evidence for me to go with your belief as opposed to what the automakers / auto parts makers say.

I am saying that it will work to 100K like they say. However, whether it will work well is a different story. Just like towing stuff. You can go with what the books say it will tow but your parts just wear out that much faster. The question is, will it hold a decent gap at that mileage and under what conditions will it take to hold the mileage. They are correct that it will do it but from the gas cars I have worked on and used their parts, it works but won't work as good.

Glow plugs...can't run WVO on a gasser, so why own one?:D

But if someone can't get enough WVO, why own a diesel?:P
I had Mercedes in mind with the GP to SP comparison. Other cars can be easier or more difficult when it comes to either.

Glow plugs on the older cars seem to last a very long time though. I got stuck with changing them on both my cars and all of the old glow plugs seemed very old or original. I am pretty sure the rear glow plug on my 617 was original.:rolleyes:

The M103 in the S-Class. The configuration layout says it all.

http://images.andale.com/f2/106/104/...3_MVC_010L.JPG