I just got a 81 300SD and i took it to the shop and the mechanic said a few things i wasnt to sure about. He said there was a lot of oil in the airfilter probably from a bad ring on one of the pistons? He also claimed that i needed a thermostat replacement even though my car doesnt run any more than a click over the 80C mark. I figured a thermostat is either good or bad right ? and wouldnt need replacing if it was keeping cool. My glow plug light does not come on and he said that i needed to replace the glowplug relay. It starts easy though so im thinking it really could be the relay and not a glow plug. Could anyone tell me if these things are really the problem and that im not being misled. Thank You for your help!

 

I don't own a SD; I have a 300D the air filter housing gets a tad of oil residue in it.

The thermostat appears to be holding the correct engine temp.

I doubt the relay is bad more likely a bad glow plug,or the flat blade80A fuse in the relay box.

I believe if you left the hood, cycle the glow plugs and stand beside the driver’s front wheel in 45 seconds to a minute you should hear the relay click off

 

The fact that he suggested replacing the Glow System Relay without further diagnoses
tells me you need to find a competant Independant Mechanic FAST!

 

So today i did test all the glow plugs on the car and all seem to be working fine. I also heard the little click that the glow plug relay does after about 30 seconds or so. Assuming that im hearing the right clicking sound from the relay wouldnt that mean its infact ok and could possibly be just my glow plug light on my dash that is inoperative?

 

I don't trust any mechanics, period. I do my own maintanence on my 1983 300TD. My takes on the issues

1) Clean out the airfilter assembly and replace the air filter if it is clogged up bad. Then leave it alone until the next oil change. If the rings or piston is shot then you would see a lot of white smoke.
2) Glow plug light will fail to come on when 1 or 2 plugs are bad. This is a MBZ thing to indicate bad plugs. I normally unplug the socket from the glow plug relay assemby and ohm them our one by one. I think it is a 5 or 6 plugs connector with thick cables. Ohm them out to ground with a multi-meter. They should all measure < 2 ohms. Any one with high reading means bad glow plug.
3) Thermostat should be fine unlessthe engineoverheat. If the temperature stays low then it is stuck open. 80C is fine for me.

As other have said, I would not go back to him. Ever again.

 

Did you take out the 80a blade fuse to inspect it?

 

You did NOT need to take out any fuses. It should be the same in your car. You remove the connector from the glow plugs assembly to the relay circuit. It should be a 2" x 1" connector with very round thick legs. I cannot remember whether it is a female or male plug. Just follow the wires from the glow plug to the relay box.

After you remove it then measure the ohm from theconnector pinto ground ( chassis ) and every wire should measure < 2 ohm. The plug provides the current to the glow plugs. You are measuring the resistance of each glow plugs, that is all. Good glow plug has very low resistance.

One thing I forgot is that someold MBZglow plugsare arranged in series, i.e. they are chained together one by one. My car is a star type, each one is connected to the relay individually. That means you need to find out but it should be quite simple. I do not have access to my book now but I think if it is in series then 1 bad plug would make the car very difficult to start as no plug would come on.

Good luck.

 

l o tanner as above replies mentioned oily a/f is normal for 617s that have been in service with 100k+ miles g/p issue: your pro dosent mention area [climate] im in so fla. & 1 non working g/p gives a short term rough idle 30-60sec if your ambient overnite is freezing or below &veh. still fires off after 8hrs outside glow plug system is all there, possibly 1 dosent heat ohm out by pulling con. off controller [drivers side fenderwell ]the no heat culprit will be open as a short will fry the fuse link visually .other than that service, change filters & fliuds & drive it!i bought a 81 sd 100k drove for 15yrs put her out to pasture at 450k jumped time[ lo comp all cyls] present ride 85 td 175k regards butch

1 MORE THING DONT RUN HER HOT