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Old 05-14-2007, 03:06 AM
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Join Date: May 2007
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Doomed or not?

I purchased a 75 300D this last fall.
Long story shortened
I have had BIG problems getting it to start.
First I came on sites like this and read archives until I was ready to go cross eyed.
heres what I have tried
Its not the fuel tank screen
Its not a leak in the fuel line
Its not glow plugs I replaced them
Its not a glow plug time relay I replaced it.
Its not a fuel filter
Its not a fuel pre-filter
It turns over good and fast and I dont think its the starter.
Its not the short rubber lines between injectors.
I have primed the lines and purged the air.
I do get fuel at the injector if I loosen the nut.
I have adjusted the valves
I have added bio-killer stuff to kill any fuel bugs.
The prefilter is nice and clear.
Let me back up a bit and describe the problem
It starts only if you plug in the block heater and its a good warm day.
It puffs some smoke out the air Intake while trying to start.
Local shop says it has bad compression.
Runs like a champ once its going no smoke and lots of power.
last owner says the odometer is correct at 78,000 miles.
I think maybe timing chain is streched out and allowing compression to drop.
just to make it more confusing it started two times in a row on a 38 degree day out of the blue and then went back to being a booger.
Can anyone help?
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Old 05-14-2007, 05:13 AM
t walgamuth's Avatar
Join Date: Apr 2005
Location: Lafayette Indiana
Posts: 33,454
despite all you have changed it sounds like glow plug function to me.

did you run a compression test?

the compression must not be too bad or it wouldnt have started twice in a row.

what oil do you have in the crankcase?

has it been run on wvo?

still sounds like glow plug function.

tom w
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual. It still needs upholstery redone...I also have a 427 Cobra replica with an aluminum chassis.
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Old 05-14-2007, 11:35 AM
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Location: Dallas
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ream the glow plug holes???

if a glow plug issue, would reaming the glow plug holes help?
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
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Old 05-14-2007, 12:05 PM
John Holmes III
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I had the same problem on my '75 300D, it was the delivery valve seals in the injection pump. They caused the pump to lose it's prime, making it very hard to start.
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Old 05-14-2007, 03:10 PM
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other things I have done

No it has not run WVO
I wondered about the glow plugs also so I reviewed the instalation and they are how they should be.
Well kinda I have never had a light on th dash that says the glow plugs are on.
The routine the fella who had it last did was to turn the key on to the first stop, the plugs get hot and I wait 20 seconds then I crank the engine. if its cold out I do that cycle twice without cranking.
on 20 sec off wait 10 sec on 20 seconds crank.
I wondered if the system was getting hot so i put a very small amount of oil on one of the connecting wires. When the plugs should get hot the oil burns off. My fathers an electrician and says the way they are wired if one fails they should all not work like a string of christmas lights.
Now that I describe that. I can see where it could be glow plugs HE HE
The injector valve seals being the problem sounds interesting. I have noticed after a million tries at getting it to go that the best chance
happens when the batteries are fully charged on a warm day and for good measure I have pumped the primer about 50 times. At this point its just become a voodo ritual I go through that may or may not mean anything.
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Old 05-14-2007, 03:13 PM
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I have reamed the glow plug holes also
my thinking on compression is the timing is off due to a stretched timing chain.
I found a description of a woodruff key that is off set the bigger the offset the more the chancge in timing. I am thinking of doing this or replacing the timing chain. the off sets are 3 5 and 7 degrees.
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Old 05-14-2007, 03:16 PM
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Location: Milford, CT
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Post some compression numbers.

Also adjust the valves and check the timing.

It could be injection pump related to.
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Old 05-14-2007, 03:37 PM
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At home having never done a compression test. I got 150 on all but the back it was 180. This was through the glow plug holes.
I did not trust this, so had it done at a local shop
They got 135 on most and 150 on one.
I dont know if they actually did the test though.
When I picked the car up I tried to start it just to see if it would go.
It almost started. It will get to the point the engine is shaking along like its running and looks like if you were to quit cranking it would continue to run but then it does not.
It occured to me that if this test was done though my injector holes that the injection system would need to be re primed afterward. I got charged for an hour of labor
During that time they did a compression test, reprimed my fuel system and checked the valve adjustment.
I just dont know if I buy that.
I also got the feeling they regarded the car as antique junk and it was easiest to tell me its "BROKE"
I will try to do another compression test and post those numbers.
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Old 05-14-2007, 03:51 PM
John Holmes III
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On my '75 300D, it helped a little if I primed the fuel primer, but it was still very hard to start. As a matter of fact, a shop had condemned the motor. There is a small copper crush washer and an O ring, one each for every cylinder.

The key here is that the engine runs fine once it does start, this points to the injection pump. Or bad glow plugs.
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Old 05-14-2007, 04:40 PM
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Location: Milford, CT
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No wonder it doesn't run, its got no compression.
Well I don't know what the specs are for the natural 617, but here they are for the turbo charged engine. They should be about the same, if anything slightly lower for the turbo engine. I beleive the compression test should be done through the injector holes.

Normal 24-30 approx (350-440 psi)
Minimum 15 (220 psi)
Max difference between cylinders 3 (44 psi)

Test should be done with coolant temperature at 80C, ie engine up to operating temp.

I hate to say it but if the test is done correctly the engine is shot. Do a leak down test and see if its the bottom or top end. You might be able ot get away with a valve job. The cheapest option would be a junk yard engine, but thats a roll of the dice.
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Old 05-14-2007, 04:52 PM
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Location: Mount Holly, NC
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do you know the Original owner personally? 78K is VERY low miles for a 75, heck it's low miles for a 95, what condition is the rest of the car? seats and floormats are good indicators of miles, but they can be changed. steering wheel should be heavily contoured, not smooth at all. smoke exiting the intake as it's cranked could be an indicator of burned intake valves, and it could be indicator of heavily worn rings. hard to know. 20.00 compression tester from is pretty good. test dry, then test with a teaspoon of oil squirted into the pc.
if much higher with the oil, you got bad rings, no diff, it's the valves.
pretty simple to check the timing. but at 78Kmiles, there should be no stretch just line up the cam gear with it's TDC mark, and read the balancer mark. should be dead on 0 anything else, and you have wear/stretch.
check out this upgrade. it's worth it for sure.
******** az has the best price on the plugs alone, but DG's kit comes with the wires cut to length and the fuse upgrade.
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Old 05-14-2007, 04:59 PM
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Your compression is low. Do another compression test with a squirt of oil in the test cylinder and see if the numbers rise. If they rise then the rings are toast. If no change then it's head related.

Also, less then 100,000 miles on a diesel car this old is rare and usually harmful if it was not prepped for long storage. If it is the original miles and it was sitting for a long time prior to you getting it the cylinders could be rusted/pitted.
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Old 05-14-2007, 05:13 PM
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Exclamation Why...????

Originally Posted by ghosttownguy View Post
I purchased a 75 300D this last fall.
Long story shortened
I have had BIG problems getting it to start.

It puffs some smoke out the air Intake while trying to start.
I would investigate this point.....seems to me that the only way that it would have puffs of smoke from the intake would be a overly tight valve....or a burnt valve.....either way it would lower your compression, and cause starting difficulties.....

someone else asked you to do another compression test, with the block warm (from the block heater would be good enough).....and to do each cylinder dry and with a little oil squirted in the combustion chamber.....if the results are similar....look at the valves......


'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
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Old 05-14-2007, 05:52 PM
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Join Date: May 2007
Posts: 10
ok i'll go do another compression test with the oil

I am going to do the compression test and see whats bad
I dont understand how the thing can run and preform fine once its started If its that shot.
I think I'll check timing too.
If the timing is off enough to have a partially open valve on compression Then I would show low compression also correct?
Is the engine temperature enough to make up the compression problem when running?
I guess I'm just hung up on the preformance once its up and going, it doesnt act like any car with engine trouble I have ever owned.
Also I beleive the 78,000 is true its a pretty little car no wear on seats or brake pedal etc.
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Old 05-14-2007, 07:18 PM
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You may be able to run once started with low compression. At this point you may want to do as suggested with a little oil. If compression does not rise on that then inject some air to see if the valves are sealing as well. Less than 200 pounds per cylinder is not really acceptable. Even 200 lbs is poor. A diesel really is not happy starting at 150-180.
All you seem to have is gas engine compression numbers on a diesel. Yes you could line up your bottom pulley at zero and the top cam alignment marks to check the chain. If the low reported milage were true the car would have had to have been sitting out of service a lot. That could cause this problem as well as excess milage. The indicated milage is only in the magnitude of 2,000 per year.
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