My roommate has a 1991 W126 350SDL which had the original 3.5 liter OM603 engine replaced with a 3.0 liter OM603 out of a 1987 W124 300D. Most of the glow plugs are bad, so I want to replace them.

I know I can just install the same type that came in the 1987 3.0--right? Or will the relay in the 350SDL body mess them up?

Also, can I install the later plugs that the 3.5 liter engine would have had in it, or are they too long or something? Or would there even be a reason to put them in over the 3.0 type (upgrade)?

I'm just trying to figure out if the new 3.0 plugs my roommate has will work just fine, or if it would be better to get the ones that fit the 3.5 engine because they'll work better with the SDL relay or will give better performance.

Changing out these things is not easy.

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1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles

Which head is on it?

When I did the swap with a friend we used the #20 head off the 3.5 motor and just used 3.5 plugs.

Most people use the 3.5L head they had, not the #14 off the 3.0l.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

If this is an Aluminum Cylinder Head it is common to break the Hex Head off of the Glow Plugs when trying to remove them.

There is some suggestion to reduce the chances of that happening:
Repair Links
Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

http://www.peachparts.com/shopforum/forumdisplay.php?f=82
http://www.peachparts.com/Wikka/DoItYourSelf

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84 300D, 82 Volvo 244Gl Diesel

Well, I don't know what head it is, but the glow plugs that came out are the same part as the new ones my roommate has, so I guess I'll just throw in the new ones.

I had a heck of a time replacing them (not mentioning the fact that the intake manifold has to come off) but found an easy way to remove stuck glow plugs: http://www.peachparts.com/shopforum/diesel-discussion/360891-easy-way-remove-stuck-glow-plugs.html

__________________
Stop paying for animal enslavement, cruelty, and slaughter. Save your health and the planet. Go vegan! I did 18 years ago. https://challenge22.com/

DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles