[f35074]

I am the new owner of a 1982 300D. I have driven diesels for years in Japan, just new to the 300D.

Three concerns I have now:
1. No heat, A/C works great. From what I have read I need to replace the Mono-Value?

2. When driving on the Interstate at the flow of traffic 75mph she is taching around 3500. Just want to make sure I can do that without issues.

3. While in drive and I let off the gas pedal she slows down quite a bit like something is dragging the speed down. I understand that the tranny will for account for some of it, but it seems to slow down quite a bit (not like an engine brake, but very noticeable). If I place the car in N she seems to roll quite a bit easier. Should I be concerned?


Thanks

 

[akimball442]

Yes to the monovalve, and the other things are perfectly normal.

Welcome.

Have any pictures?:thumbsup:

 

[f35074]

Thanks.

No pics yet, she is very straight no rush just several chips and fading paint, I need to get some wax on her soon.

 

[GogglesPisano764]

Welcome to the forums! I have an 83 300D and its new to me coming from a 420sel so its all a learning process for me too as I go along!

 

[Rmac58]

I understand a failed mono vale would produce heat all the time.

 

[akimball442]

Back to the  Mercedes Diesel parts for sale

 

[mountainredneck]

negative on the monovalve making constant heat. drove mine to florida last year in jan. and had to pull over every 20 or so miles and tap on the monovalve. heat would return. i took mine out totally and installed a ball valve. unemployed and all...

 

[MBeige]

Hello and welcome.

Speed at 3500rpm sounds about right. When you release the accelerator, the engine compression on diesels is high so it will slow down faster than a comparable gas powered car. It's the high compression in a diesel engine that accounts for it.

 

[Rmac58]

negative on the monovalve making constant heat. drove mine to florida last year in jan. and had to pull over every 20 or so miles and tap on the monovalve. heat would return. i took mine out totally and installed a ball valve. unemployed and all...

I was thinking about a torn diaphragm, vs. one not being told to open.
As a test, simply remove the valve and warm up the engine, see if you get heat..

 

[mrbenz7]

It will be hard to find a "replacement" monovalve because these are just not being made any longer for the W123's. But you can replace it's inner working parts and a stuck piston and diaphragm assembly.

This si a great source for parts: https://www.autohausaz.com/index.html :thumbsup: