Warm Running Device still drawing air.

[Raymond]

I think I have tried everything at least twice.  I'm still trying to work out a slightly rough idle and poor fuel mileage.  I have no shims under the WRD.  The rod on the WRD thermo is threaded with the two lock nuts and I have them exteded fully.  I checked the thermostat in a cup of hot water and the rod still extends.  

No matter what I do, the WRD still draws air through the filter on the side.  I thought the WRD would stop drawing air when the engine is at 180 degrees F.  

The timing is right and advances properly to 3,000 RPM. Yet, my guage doesn't read more than 14 inches of vacuum at idle.  The car idles at about 700 RPM.  I would be happier if it was 850 to handle the air conditioner.

Any thoughts?



Ray
'68 280SL 4-spd Coupe

[al_lieffring]

It sounds like you may have an obstruction in the warm water loop for the air slide thermostat. Possibly not enough warm water is circulating and it's cooling down to a lower temp than the rest of the engine coolant.

Al

66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket

[jeffc280sl]

The thermostat rod extension may be too weak to push the control slide into position to choke off the air supply.  It's also possible the control slide mechanism is binding in the slide housing.  A cleaning and very fine wet/dry sand paper can be used to remove any burrs.

Jeff C.
1970 280SL 4-speed

[Shvegel]

The first question is did this just happen or is that the way you found it? If it happened while you owned it I would not add or remove any shims. Fix the problem. Don't adjust around it.

I would consider doing the following in this order.

First I would replace the injection thermostat.

Then go with Al's suggestion and check the flow of water to the injection thermostat. I would replace the hoses and check the fittings into the head just to be sure.

Also if your main radiator thermostat is stuck open the coolant may not warm up enough to close the injection thermostat completly.

If this is a problem that has been around since you bought the car then all bets are off. the one thing to keep in mind is that there are shims under the thermostat pin AND under the housing the thermostat is installed in. Unfortunatly it's been 5 years since I touched my Injection system and I can't remember which shims control the beginning point and which control duration.

Hope that helps,
Pat

[Shvegel]

I just thought of something. If the rod extends when it gets hot then a longer rod is what is needed not a shorter one. I am not suggesting you alter the rod but it would seem you need more shims if you want more projection on the rod.

A word of advice: If you need to shim buy a new thermostat and shim to that Instead of spending time and effort shimming to a thermostat that might fail tomorrow. Ask me how I know.

[rwmastel]

quote:Originally posted by Raymond

The car idles at about 700 RPM.  I would be happier if it was 850 to handle the air conditioner.

Ray,

You should have a device (constant speed solenoid?) that increases your idle when you engage your A/C unit.  Don't adjust your idle too high to compensate for a failed CSS.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[hands_aus]

My understanding is
If you remove shims it affects the whole temperature range.
If you remove the washers in the top of the slide valve of the WRD it will change the temperature that the air is shut off.

Also, The replacement Inj pump thermostats have a different arrangement to the original ones. This requires the spacer ring hole to be enlarged.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[Raymond]

Thanks guys.
I rebuilt the engine last year, so all the hoses and the coolant thermostat have about 2,000 miles.  The engine comes to temperature quickly and sits squarely on 180 degrees. So, I think that thermostat and circulation are fine.  

The FI pump was rebuilt by H&R just over two years ago.  The FI WRD thermostat is the style with locking nuts on the bottom of the shaft and they are adjusted all the way out.  

I bought a new thermostat but the base is 13mm and the guide ring hole is about 10mm. It would have to be drilled out to accommodate it and then I would need compensating washers. I guess that is my only option.  Too bad because adjusting the locking nuts is so easy.

I am familiar with the oval shaped three hole shims that go under the whole WRD where it mates to the FI pump body.  The BBB Figure 07-13/1 calls them compensating washers (#11). Are there supposed to be shims somewhere else?  If I add shims under the housing as shown in the book, it would raise the unit making the effective length of the thrust rod shorter, not longer.  

Rodd, my car is a 1968 280, engine serial #000096 and was never equipped with a constant speed or "Lifting" solenoid.  It just has a passive return damper on the linkage.  However, I have installed a Sanden rotary compressor.  Perhaps when I get it charged and fire it up, it won't drag the engine like the old York compressor. Still I'd like the idle to be higher.



Ray
'68 280SL 4-spd Coupe

[Ricardo]

Raymond
These photos shows the small thin shim(s) that go with the aluminum cylinder to increase the travel of the plunger below the thermostat (WRD).
You have to pull/pry out the small clip spring to access the shims in the aluminum cylinder. The thicker washer goes after the shim(s) and under the clip spring. I think there can be up to four shims here as well as the four oval shims.
Hope this helps

Download Attachment: plunger pieces.JPG
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Download Attachment: WRD parts.JPG
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[hands_aus]

quote:Originally posted by Raymond

I bought a new thermostat but the base is 13mm and the guide ring hole is about 10mm. It would have to be drilled out to accommodate it and then I would need compensating washers. I guess that is my only option.  Too bad because adjusting the locking nuts is so easy.

Raymond,
If you don't drill the collar the thermostat does not sit in the correct position. This will reduce the amount of travel of the 'pin' and make it almost impossible to achieve optimal engine tuning.
It will also mean that you will need to add shims but that will give you adjustment which you seem to be missing now.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[rwmastel]

quote:Originally posted by hands_aus

If you don't drill the collar the thermostat does not sit in the correct position.

Bob and others,

I thought I read that all the 280SL FI WRD parts were still available new and only 230SL owners had to drill/modify new parts to get them to work.  I'm surprised Raymond has new parts that don't fit his existing system.  Am I off base?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Ricardo]

Rodd
I had to drill out the collar on my 250, which has the later type of WRD. I think it's only the early 230's that had the odd thermostat, that costs much more than the later ones. Not sure if all the later types had the same collar or used a slightly different thermostat and the current replacement thermostat is the only one available, so cars with the smaller collar need to be drilled out. It could be that the available thermo is used on different cars and MB just decided that 113 owners would have to adapt to the one style they are willing to stock?

[Raymond]

Nice work Ricardo! Thanks.

As soon as I can pick up some shims, I'll convert it.  The photo will help a lot.  

It's interesting that your 250 and my very early 280 have this issue.  Could it be that the Germans tried the newer style WRD with the existing threaded thermostat?  Then as the they transitioned to the the 280, they shifted to the shim design.  Or, is it just that when good ol' H&R rebuilt my pump, they used the older style?

No matter.  It's one more thing with which to tinker.  

Ray
'68 280SL 4-spd Coupe

[Ricardo]

Raymond
I actually have the non threaded type thermostat... the attached picture shows the old and new versions of the thermo and why drilling out the collar is necessary. I'm wondering if your WRD is the same as mine?

Download Attachment: old one and spacer.JPG
34.59 KB

[hands_aus]

quote:Originally posted by rwmastel

quote:Originally posted by hands_aus

If you don't drill the collar the thermostat does not sit in the correct position.

Bob and others,

I thought I read that all the 280SL FI WRD parts were still available new and only 230SL owners had to drill/modify new parts to get them to work.  I'm surprised Raymond has new parts that don't fit his existing system.  Am I off base?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

Hey Rodd,
When I replaced the inj pump thermostat on my 250sl I had to drill out the collar because whoever is making the new thermostats has made them different to the original.

On Ricardos' picture you can see the brass centre section on the NEW thermostat is way bigger than the original black plastic section of the old thermostat.

The collar must be drilled so the thermostat can sit in the correct position and allow the pin to travel its full length and allow for adjustment of the air/fuel mixture.

The 230sl had a completely different thermostat which has very little travel of its plunger.
I re-read Raymonds statement quote 'The FI WRD thermostat is the style with locking nuts on the bottom of the shaft and they are adjusted all the way out.' unquote
and I am a bit confused.
Download Attachment: IPWarmUpDeviceParts_1.jpg
50.91 KB

This is a JoeA picture which shows my configuration. There are no adjustments to be made on the plunger but they can be made on the air valve by removing washers from the top.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[Raymond]

Bob,
In an earlier post, I pointed out that the brass base of the new thermostats is larger than the rubber or plastic old ones.  The old one is 10.25mm in diameter, and I think I recall that the brass one is 13mm.

If you look at Ricardo's photo of two thermostats, the one on the right, "old style" is like mine.  However, on mine where the small brass bushing is affixed on the thermostat shaft, the shaft is threaded and there are two locking nuts that you can adjust with a 6mm wrench.  That way, you can lengthen or shorten the stroke of the thermostat by adjusting the nuts.  (I'll shoot a photo when I pull it out again.)

Alas, it appears that I have to replace it and go the shim route.  Not as elegant, but nonetheless effective, I'm sure.

Ray
'68 280SL 4-spd Coupe

[George Des]

The thermostats on the older 113 models such as the 230SL are competely different from those used on the 250sls and later. The housing for them is also different as well.  The 230SL thermostat is a long brass, wax filled cylinder with a small pin sticking out on the end. This same thermostat is found on other pre-67 MB FI models and as owners of these models no doubt know they are VERY expensive.

George Des

[hands_aus]

Raymond
That thermostat must have been threaded by someone in the past. I wonder if they removed the pin from the housing and re-inserted it. Not recommended.

When the collar is drilled out the length of the new thermostat pin will be correct and yes you will need to add the oblong shims that fit under the WRD housing.
The best part of that will be that you will get back the adjustability of the fuel mixture on the Inj Pump.


Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto