C220 CDi Cold Running

C220 Cdi 2003 (W203)
Winter's approaching and I'm not prepared to put up with the cold running of the C220 anymore, and before everyone chimes in with, "it must be the stat"; it aint.

I thought it must be the stat too, so at the last service I got the garage to replace it, but it made no difference. Took it back, they scratched their heads and changed it again, but it still made no difference. I began to think that maybe the garage fouled up something when refitting it, so I got it out and tested it in a saucepan on the cooker. It opened and closed repeatedly at around the 92C mark, and sealed perfectly in the housing.

I can run 50 miles up the motorway at 70mph and the temp only just manages to reach 80C after about 15 miles and that's without the cabin heater on. Also when the engine temp is at an indicated 60-70C I can feel heat in the radiator, so I've also changed the temp sender unit in case that was playing up.

The stat has been tested so I know it's working correctly but the radiator is still warm long before it should be, so there's only way this can happen as I can see it, and that's by getting back flow through the fuel heater. Trouble is I can't find any information on this device, no schematics of the flow paths or any temperature controls. Does anyone have any details??

I think I might try clamping the rubber hose between the stat and the fuel heater to see if this will encourage a faster warm-up.

 

Do you have the diesel powered Webasto heater?

 

No, nothing fancy like that.

 

The thing you say is the fuel heater is actually a fuel cooler. This cools the fuel before it is returned to the plastic fuel tank.

Do you know if genuine parts were used? The genuine part comes with a new housing and temperature sensor.

The only way that the radiator can get hot when the engine is cool is by the thermostat opening and coolant passing through into the radiator. It has to go through the top hose. So something is opening it this could be the water pressure from the pump if a substandard stat. is fitted or very unlikely the bypass is blocked.

 

Yep, there could be also second thermostat, in fuel line like said.

Here are instructions how to change that, sorry about finnish language (try google translator): http://www.mese.fi/forum/viewtopic.php?t=24396 At least you can find some useful pics

 

You do well with your English considering that the Finish language does not have 1 international word, but there again you probably speak very good English and German too

 

Check water pump had vw with the same problom turned out vains spinning on back of water pump ,car didn't over heat as well was running like that for over 6 months. Dan

 

Thanks for the responses everyone, but I clamped the rubber hose between the stat housing and the fuel cooler (I stand corrected), and wow what a difference that makes!

Just tootling round local roads at 30-40mph and with the cabin heater on too, the temp soon rose to 90C and stayed there.

So now I know how the temperature is being kept low, by flow through the radiator, fuel cooler and beyond. What I don't understand is why it's happening?? Where does it go before/after the fuel cooler?

Also, just how hot does the fuel get that it requires cooling by water coming out of the block?

The other stat mentioned in the Finnish webpages, located in front of the Aircon condenser is associated with the automatic transmission, so that doesn't really help with my situation.

 

hmmmm... nope, that should be fuel heat exchanger, and the stat of the fuel cooler part number A 005 203 3975. It's not found in every car, dunno if its meant only for northern climates...?

 

I'll see if I can follow the pipework around the engine bay, but it will probably mean removing things because everything is so cramped in that area. The Haynes manual says the little radiator that is inline with this other stat is for the automatic transmission. But I must say it did seem very strange to me, to have a stat in an oil circuit like that.

 

cooler of the tranny is under the main radiator

 

Now, not sure if this will help but hear me out! On the Jaguar diesel I had before the Merc there was a problem of cool running even when the thermostat was changed for a genuine unit. It transpired after a lot of digging and arguments with Jaguar that there was an additional thermostat built in the flow line to the oil cooler that should have opened at 90c or more. The original units fitted in maufacture were opening far too early and allowing coolant to circulate the oil cooler radiator thereby causing the cool running! A tech bulletin was issued on this problem and lo and behold a new oil cooler thermostat with a part no ending in /2 was found to be in parts departments and duly fitted as it had a higher opening temp. Needless to say I never had another problem with cool running again!!! Now, I am not sure if we have these fitted in Mercs or not but I am sure Alex or Colin or Steve will come up with that answer.

 

I have a DEC2002 w203 220 diesel.

Mine has always taken a long time to warm up. At least 15 miles. I believe this is normal for this model. A piece of something in front of the radiator will make a little differene but not a lot. Diesel engines are more efficient hence generate less waste heat, they also have more metal in them so take longer to warm up than petrol ones.

Mine has the diesel powered Water Heater which operates if the outside temp is below 7degC. I thought all cars of this age had this heater. It can be disabled in the menus. It will exist in the menu settings if you have it.

Later models without this heater had modifications to the cooling system to enable faster warm up, I do not know when the change was made.

Alec

 

Martin got me thining here! Think I know what it is...

The extra cooler mounted on the front of the rad, also has an extra inline thermostat - have a look at the front of the rad and all will become clear.

 

... number 22 in the 1st pic in the link I posted above...

 

Yes, Mersum1es pointed this out earlier on, and I will get it replaced. For now though, I'm happily running around with a warm (90C) engine, simply by clamping the hose between the fuel cooler and main stat housing.

I tried to trace the hoses from the the front mounted fuel cooler rad, but one of them just disappears under the inlet manifold, I can't see where it goes, the other one feeds into the base of the fuel cooler.

Looks like the fuel cooler was only fitted to CDI 2 units, so probably had a short production run, but I'm still surprised just how little information there is about it.

To answer the other questions:-
Now it gets up to 90C after about 10 miles of commuting, whereas before it would never get above 80C, even on a long motorway trip, and last winter I was lucky if it exceeded 60-65 on the commute.

I just have the heater booster, not the diesel fired heater.

Thanks everyone for your help, I'd love to see a schematic of the setup.

 

No, it is actually part number 70 in the 3rd pic, and it is not in the fuel line, but the coolant line.....

Teacup, did you look for this small inline thermostat on the front of the rad?
It clips in a plastic holder in the same way the low temp cooler does.

 

Yes, part 70 was the item I was looking at in the link, and the seaky little thing is there hiding behind the horns. My problem was that I just assumed the fuel cooler rad was the automatic transmission oil cooler, so totally ignored it. I'd never heard of a fuel cooler until this weekend.

 

Yes, the stat is 70 but extra cooler is 22... (I replied on that ) but problems solved now!

That really seems to be rather rare component, those russian epc sites are not recognizing it either. It's a bit unclear for me is the cooler is meant cool the fuel or heat the water (that finnish guy who started the finnish thread is calling the cooler as 'cooler of the cold zones'...) and because it's so rare I would believe that it's meant for colder environments, otherwise it should be installed more wider. Or MB engineers noticed that fuel is not heating too much in the tank, and part was removed in later models.

 

The little rad on the front is standard equipment on the earlier 220 cdi and 270 cdi W203 cars here in the UK - not sure about elsewhere.
It is known as something like the 'low temperature radiator', and is used for gearbox oil and/or fuel cooling.
If it is stuck it stands to reason that engine temps could run cool, even with a new main system thermostat.