WRD removal

[Mqueretin]

Hi there,

I will check the WRD as suggested by a number of the very knowledgeable members on this forum to try fixing the cold running of my '67 250 SL. I have what may sound as a stupid question but being a firm believer in Confucious' principle of "ask a question and be a fool for a minute, or never ask it and remain one for the rest of your life", so i'm asking it:

what's the best way to remove the WRD to check the plunger: should it take the entire WRD off (ie starting from the lower screws, or should I limit myself to removing the plunger housing (top screws). When removing it, is there any specific caution when doing it (ie spings jumping etc .). Many thanks

I have now joined as a full member and could enjoy all the great stuff from the technical/restricted site of the forum. A very good decision of the New Year !

cheers

Marc.

[Jordan]

Marc, before you start taking it apart have you checked the vacuum yet by removing the air filter?  If you have a hard time keeping the engine running at first you can get a second person to keep it running until you can use the throttle linkage to do it yourself.  You should be getting suction from the opening where you removed the air filter when cold and it should diminish to no suction when the engine has reached operating temp.  If this is the case you know your WRD is working and no need to take it apart. If you haven't done so already check that first.  Also a good time to see if your filter is plugged or not.

The upper screws remove the thermostat housing.  There should be a washer between the housing and the lower body.  When you lift it make sure the thermostat stays in the housing until you can safely remove it.  It sits freely within the housing so it will drop out if you just lift the housing.  Once this is removed you should see the plunger in the WRD and you can push on it to see if it moves.  You can also check to make sure the plunger within the thermostat is working by putting it into boiling water.  Don't recall how much it should move but do a search.  Start with the air filter and see where you sit.

[Mike K]

Very good advice from Jordan. I recently undertook the same exercise and checked the thermostat in boiling water, all was working fine.
It turned out to be the small air filter, which I replaced.

http://www.everythingbenz.com/z/part/0000751132-mercedes-air-filter

Best
Mike

[Jordan]

Marc, forgot to mention that those are coolant lines running into and out of your thermostat housing so expect to lose some coolant when you remove this housing.

[Benz Dr.]

You will loose a bit of coolant but since it's so high in the water column it won't be a significant amount. If you loose any coolant that drips on to the sliding valve you should clean it up right away. I use a bit of high temperature grease in the valve housing so that it helps to lubricate the sliding valve.
 The main reason for the valve sticking or seizure is from antifreeze residue in the housing. To prevent this from happening, I always use a bit of sealing compound on the seat of the thermostat. Under no condition should you ever have any antifreeze leaking into the slide valve housing!

[jonb]

I am a complete novice but a full Pagoda fan, an owner of a few, and I have a son that is smarter than I am about the mechanics and serves as my partner in the collector car business (as well as my real business).  Is the "WRD" connected to or a part of the thermostat assembly?  My question is a result of my car having a problem with idle control, losing power at low RPM, and the fix being to rotate the thermostat so that the car runs at way too high RPM after start up, then returns to normal RPM after about two minutes of driving.  I don't really like that "fix" and would like to correct the entire problem, although this problem is better than the previous one.

jonb

[Benz Dr.]

I am a complete novice but a full Pagoda fan, an owner of a few, and I have a son that is smarter than I am about the mechanics and serves as my partner in the collector car business (as well as my real business).  Is the "WRD" connected to or a part of the thermostat assembly?  My question is a result of my car having a problem with idle control, losing power at low RPM, and the fix being to rotate the thermostat so that the car runs at way too high RPM after start up, then returns to normal RPM after about two minutes of driving.  I don't really like that "fix" and would like to correct the entire problem, although this problem is better than the previous one.

jonb

There is a thermostat which controls the movement of the sliding valve; all within the WRD. I can't say I understand the second part of your question though. What exactly, are you turning that makes your engine run differently?

[Mqueretin]

Thanks All for the advise and caution: very useful. I should be back to the car this week end and will report if/how it worked !

Cheers,

Marc

[Mqueretin]

I am now on the car and I have removed the thermostat on the WRD - one of the screws holding the housing was very loose actually, the other was very tight.

I tested the thermostat: in boiling water, the needle got out, but does not retract event if plunged into water with ice cubes.

I've taken the plunger out and it moves, but you need to push quite hard to make it move. I'be used some WD40 to clean it and will use high temp grease as suggested on the plunger and on the needle to lubricate before putting it back.

I'm changing all spark plugs and will make a try. Hope it works and finger crossed !

Cheers,

Marc.

[Mqueretin]

Hi there,

there is some substantial improvement, but I'm not quite there yet.

I checked the air filter and could feel some air flow , but it was weak and it seems it was in the wrong direction (i.e. looked like being blown rather than sucked). the car started very well and, contrary to what has happens systematically in the past, it  did not stall when the accelerator was released, but within a minute of two, idle started to be erratic again and decreasing to a point where it would finally stall.

I removed the air filter and then it worked very well ( and there was a strong suction into the WRD) and idle was stable (though rather low at +/- 600-700 rpm) for a good three to four minutes, and then started decreasing again (at a slower pace than with the filter) and would finally stall. The filter definitely needs to be changed.

Is the issue with the idle setting which is too low (also when the engine is warm, it's around 700/800 rpm) or what else do you think it might be ?

Thanks a lot.

Marc.

[Cees Klumper]

It could be that you need an extra, or thicker, shim under the 'tower' in which the thermostat sits. This has the effect of lengthening the time the WRD enriches the mixture to allow the engine to warm up longer. Just make sure it does in the end close off completely.

[alchemist]

A bit of advice, when you test the temperature feeler (thermostat) as you did with hot and ice water, you should not push it in or pull it out mechanically. That will spoil the feeler. That may possibly happen in your case.

[twistedtree]

Maybe you already understand this, but just in case....

With the engine cold, the WRD should be open.  With the engine running, you will be able to feel/hear air rushing in through the filter.

As the engine warms up, the WRD plunger moves and closes off the air passage.  That's probably the change in operation that your hear.

Once the engine is fully warm, the WRD plunger should completely close off the air passage, and you should feel/hear no air going in the filter opening.

It's essential that this all works correctly, and only after it's working correctly can you adjust idle speed, mixture, etc.  Otherwise you will just be chasing your tail.

One trick, if your WRD isn't closing all the way when warm, is to just plug the air pipe from the WRD to the manifold.  I bought an assortment of rubber bottle stoppers that work great for this.  With the engine fully warmed up, and the pipe plugged, you are simulating a correctly operating WRD in the warmed-up position.  But you will still need to go back and get the WRD working correctly, which is usually nothing more than taking it apart, cleaning it, and reassembly.

[Tyler S]

One more thing to check with the WRD is proper coolant flow. The lines near the water pump and at the banjo bolt can become plugged and restrict coolant flow to the WRD. This causes a continuous rich condition mostly at idle but can also occur at speed if the restriction is big enough. The metal top of the WRD where the coolant lines are should be engine temp or very close to it.