i have an '81 240-D & yesterday thepreglow ind. light failed to operate wheni turned the key to that position usually a good starter, it took several tries, about 40 or 50 cranks to start and seemed to be "flooded" i havent checked the light bulb itself but this is the first time car ever started hard -but runs fine .i fell asleep online looking thru manuals last nite ,need some help

Welcome to the forum.

When the glow plug light fails to illuminate, the problem is usually one or more than one failed glow plug.

You can perform a test with an ohmmeter to see if the plug resistance is proper.

However, on that vehicle, you're at the transition point between pin type and loop type plugs, so, someone will chime in as to which type you have. The testing procedure is different.

i really dont know which type of gloplugs i have but i would like to perform the ohmmeter test if anybody could tell me which type i have.it sounds like maybe a plug is starting to or has failed, but then starts working as soon as the car finally does start.however it would be much easier if someone knew the differance instead of havingto pull a gloplug to find out I do appreciate your previous help!

Seems to be a quiet day today..........

You can just take a look under the hood and determine which type you have.

The older loop style plugs are connected in series and there is a large curved wire that runs between each plug.

The new style pin plugs are connected in parallel and there is a single wire attached to each plug. No wires run from plug to plug.

If you lose one glow plug in the older style, all plugs fail to operate.

If you lose one glow plug in the newer style, only that plug will fail to operate. In this case, the vehicle should start relatively normally. If more than one plug fails, then you'll get into starting issues with this type as well.

thanx for the info 2 day brian i figured i have the newer style gloplugs but i still need to determine which ones gettin' funky on me.it's still starting real hard but will restart easier;after 5 or 8 turns as opposed to immeadetly if anybody knows how to test plugs i sure would appreciate the advice thanx for the help

as cheap as glowplugs are, i would just replace all 4. they are like $10 each, and then you know that you ahve new Bosh glowplugs that might not go out for some time. probably easier to replace all instead of spending time to find the culprit.

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Grey '91 350SDL 214k Dad's car
Beige '81 240D 4 Speed 254k SOLD
Blue '82 300D 225k SOLD
White '95 E300D 46k SOLD
Blue '87 190D 2.5 Turbo 315k SOLD
Brown '80 240D 4 Speed 716k SOLD
Beige '80 300D N/A 119k SOLD
Blue '85 300D Model 186k T-Boned

Testing glow plugs are easy. Follow the wiring from the glow plugs from the front or the engine onto the drivers inner fender. You'll find a plastic cv]over that protects the fuse and plug connector for the glow plugs. If you unplug the connector and turn it over you can measure the resistance from each socket on the connector to ground. You might also replace the glow plug fuse if it doen't look pristine. You are looking for all four glow plugs to be about the same at about 1 ohm each. As someone mentioned above, if in doubt, replace all four, and i'd replace the fuse too. Good Luck, Chuck

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2000 C230 Kompressor "Frosty"

2007 PT Cruiser
2001 VW TDI Beetle
1999 Landrover Discovery II
1971 Corvette

Gone: 97 Cabrio, 83 240D, 93 VW Eurovan, 95 Volvo 850, 93 Chevy Astro Van, 77 VW Bus, 99 VW Jetta, 74 VW Bus

With the newer style plugs, follow the procedure as provided in post #7. The readings should all be between .6 and 1.5 ohms. Anything reading infinity must be replaced. Anything above 1.5 ohms must be replaced.

If one or more glow plugs fail, the LIGHT will not work but the remaining good plugs will still be heated. Unfortunatly, just one glow plug out will make starting more difficult especially if you don't have "like new" compression.

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Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY