In my 86 190D 2.5 NA I bypassed the fuel thermostat. I first tried to repair the thermostat with the o ring, but it wouldn't stop leaking maybe it has a hairline crack in the plastic elbow. I sure couldn't find any reason for it to leak. Any way after bypassing it no leaks what so ever.

My question dose anyone know what the down fall of leaving it bypassed is?

One thing I did notice is sometimes when I stop and put in park the idle goes up to about 1k-1200 rpm. This could just be sticking linkage though. I am going to put some pb on the linkage and see if it happens again.

In this forum the guy says it is ok I would just like to know if anyone has done it with non-biodiesel.
http://mercedes-190.co.uk/topic/224886/1/

Funny, I just got my 190d back on the road and when I put mine in neutral or park my idel will go up also.

Does it go up that high? I am assuming you still have your fuel thermostat to right?

To give you advice on the fuel pre-heater I need to know where you live

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

How cold does it need to get for it to be useful and why don't w123s have to worry about it?

It's something the 60x engines have.

Yes, it goes that high and still have the thermostat.

hmm, My Preheater is bypassed and my Idle RPM's are never that high.....

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

I dont think the high idel has anything to do with the fuel heater.

it dosnt... only thing i can think of that is cause for high idle is a Electronic failure or sticky linkages.

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

I am located just out side of Reno in Nevada. It does get vary cold in the winters here and somewhat hot in the summers to. So knowing that what do you think?

First of all, bypassing the thermo fuel heater is generally OK unless in a really cold climate or you plan on being there someday. Out here we don't get freezing on the coast so I bypassed mine, even a new one started leaking a few years after I replaced it - more than a nuisance if coolant gets into the fuel!

I haven't seen sticky linkages on the 190D but on the 603 engine they do tend to break because MB went to plastic ends. Solution in that case is use metal 617 ends (still available relatively cheap or wrecking yard freebies).

I am assuming the 190D is similar to the 300D on the following:
First thing I'd check on the 603 when the idle is unstable is the connection where the pugs fits the control module. Moisture in the pins on the ECU (electronic control unit) will definitely cause the ELR feedback to act unreliably.
Remove the plug (lift it from one end) and if you see any moisture in there blow it out then use a hair dryer on the pins and reconnect it. A thin smear of silicone grease into the area around the outside edges of the connector will help keep moisture out.
Also unplug and replug the idle speed selector knob by raising then lowering it, not turning it to a new position. This will wipe the contacts in case they are dirty or wet and has been known to fix an idling problem.
The ELR is a sensitive system that works fine most of the time but a little crud can make it unstable.
DDH

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

you should be fine I think. unless your car spends a fair amount of time buried in snow.

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

No I didnt bypass the fuel heater. I bypassed the fuel thermostat so that the fuel heater is always running the fuel throw it.

Check the link out

http://mercedes-190.co.uk/topic/224886/1/