Just Bought 1985 300D Turbo, need help with some problems - PeachParts Mercedes-Benz Forum

trooper.hughes · #1 02-23-2009, 10:24 PM

Got a deal on a great running car, but I do have a few problems. I have a few issues I need help with. Anything is appreciated

1. heat dont work well. at idle it blows luke warm air and the faster you drive the hotter the air gets.

2. tachometer does not work

3. glow plug light, lights intermittenly

Thats about it. I live in VA and gets quite cold here, so if i dont plug it in for a few hours will not start so I am glad at least it works fine

Thanks

jim16671836 · #2 02-23-2009, 11:08 PM

Is your coolant level low?

Pull your cluster and see if you are getting any signal from the sending unit at the rear of the engine(older engines had the sending unit above the harmonic balancer.

Check your connections on the back of the cluster and in your glow plug relay.

shadetree77 · #3 02-23-2009, 11:25 PM

1. could be stuck open thermostat (normal op. temp should be 80 C)
2. there's a sensor above the harmonic balancer; on my 83 it was bad, i don't think it's that expensive...i believe the wire runs from above the harmonic balancer to the big round looking thing with a screw on cover on near the driver's side fender (that was on a SD; yours might be different)
3. do you mean it lights intermittently when the engine is cold (i.e. when trying to pre-glow?) if so it's probably bad (mine was)...the new and "improved" glowplug relay is only about $100...i would check the the glowplugs first thought (ohm meter) before replacing the relay...there's a fuse in that relay too...kinda big if i remember ...

hope this helps,

p.s. i would get a factory manual, they usually have them on ebay

vstech · #4 02-24-2009, 08:38 AM

it's an 85, the tach is totally different from earlier models. sometimes it's the ovp relay... not sure how to troubleshoot one.
heat problem sounds like a torn monovalve diaphram, click buy parts above and order a repair kit.
glow light could simply be a few bad plugs, go to www.dieselgiant.com and dig in there for the mercedes maintenance page and go to the glow plug repair page... pretty simple testing instructions there, also, you will need a digital volt ohm meter.

charmalu · #5 02-24-2009, 11:45 AM

The 85 gets it`s tach signal off the flywheel. there is a plug that fits into the adapter plate, left side about the 10 or 11 o`clock position.

There is the black box behind the passenger side kick panel the sig goes into. think it also has something to do with the EGR also. not sure where it goes from there.

As VSTECH said could be the OVP relay, believe it is under the dash by the glove box.

The heat problem could be the auxillary water pump on the passenger side inner fender. It supplys hot coolant to the heater when the engine is idling to keep the cabin warm.

the 85 has a few changes from the earlier W123`s.

Charlie

::matthew · #6 02-24-2009, 11:49 AM

I believe my tach was fixed by replacing a fuse that was near the OVP relay...I say I think, because the mechanic did this the first week I owned the car. IIRC, the A/C was affected by the same fuse.

Jeremy5848 · #7 02-24-2009, 11:50 AM

The mono valve repair kit is on sale for only $40. Might be a good idea to get one. I suspect that they may become NLA soon.

ImBroke · #8 02-24-2009, 11:59 AM

Also, where in VA? I'm southeast, and would be willing to help.

jim16671836 · #9 02-24-2009, 11:59 AM

The tach pickup is no longer in the front of the engine. It is located inside the rear of the engine just a inch or so from the transmission and it gets the signal from the flywheel. Some of the late 84's are also this way.. Jim

muleears · #10 02-24-2009, 12:07 PM

I don't own an 85 and never have so ignore this if I'm way off base. Does this car have an auxilary coolant pump? If that were bad, during low flow situations (idling) he would get little heat. Just a thought.

I'm in SE VA. also.

jim16671836 · #11 02-24-2009, 12:20 PM

If the monovalve goes bad the default position should allow hot defrost. Do you have hot defrost at idle and low speeds??? Jim

vstech · #12 02-24-2009, 12:33 PM

most likely the "fuse" the mechanic changed was the relay... can't quite recall the name of it, that controls the ac and the tach... Brian Carlton will know what I'm talking about... OVP is another option. All I can come up with is K1, but I know that's in the transmission... grrrr. kilma relay...

AMH · #13 02-24-2009, 01:35 PM

Quote:

Originally Posted by trooper.hughes

Got a deal on a great running car, but I do have a few problems. I have a few issues I need help with. Anything is appreciated

1. heat dont work well. at idle it blows luke warm air and the faster you drive the hotter the air gets.

2. tachometer does not work

3. glow plug light, lights intermittenly

Thats about it. I live in VA and gets quite cold here, so if i dont plug it in for a few hours will not start so I am glad at least it works fine

Thanks

Where in VA are you?

Low coolant could be the problem, easy enough to check look at the overflow tank. Or the movovalve insert could be torn. Also an easy fix. This car does have an aux water pump, if the 1 amp fuse mod has not been done, do it. Do a search under my username and write down the procedure. It will save your pushbutton climate control unit from a seized aux water pump. Where does the temp gauge sit when the car is warmed up? Are the heater hoses warm/hot?

On the '85 models the tach pick-up is located on the bell housing and will rarely fail. Usually the OVP (overvoltage protection relay) fails, it's located underneath the glove box and will be a silver box with a red cap and 15?? amp fuse. About 2 inches by one inch. Check the fuse on top or go ahead and replace it, very common problem. If the OVP fails, the tach will not operate, and if the tach will not operate the A/C compressor will not engage.

Check you glow plug relay connections and the flat 80a fuse.

ImBroke · #14 02-24-2009, 05:12 PM

You've definitely come to the right place. We're here to help. Time to post again, to see if we've found your problems.

trooper.hughes · #15 02-24-2009, 07:22 PM

Thanks to everyone for your help. I really appreciate it.

The vehicle had sit for 6+ months w/o being started b4 I got it. All I did is
charge the battery and it fired right up!

- The temp stays about 40-60. Even if its been driven for a while.
- When I got the vehicle the the CCU didnt work at all. I replaced
the fuse and then it worked, however it blew a few fuses shortly
after putting new ones in. For some reason this last fuse has worked
fine. I dont know if it was just a few bad fuses I had or a short
somewhere. I checked all the wires thinking it mights of been a short.
- I checked the glow plugs. I think i have 1 bad one, but the others
work right. If I am right my glow plugs are not wired in series. I think
the relay might be bad. Some said there is a fuse inside the relay. Is
that correct and can it be replaced? BTW the light was working fine
when i got it then, it just stopped coming on. I use the engine heater,
so not sure if the are even heating up
- I spoke with the previous owner and he said he dont remember the last
time the tach ever worked.

Also, I live in SW VA, near Va Tech.

I am working alot these last few days so really haven been able to get dirty yet.

Again, Thanks for everyones help. I am sure glad I stumbled upon this forum!!