WRD hose goes around the air intake - why?

[Miloslav Maun]

May I ask a silly question? The lower hose from the Warm Running Device goes to the air intake (close to the venturi), around it and then to the termostat. Why is it like this? What is the point? And what happens if I simply delete the air intake part and route the hose directly?

[Tomnistuff]

I`ll take a chance on stepping in it, but since I`m an old carburetor guy (old carburetors and old guy), there`s probably not too big a risk.

Since idle air flow mostly bypasses the throttle plate and passes through the idle air flow system directly into the intake ports, that leaves a very tight fit of the throttle plate to the throttle bore.  The air that leaks past refrigerates the throttle plate and the bore.  Depending on the dew point, that can lead to throttle plate icing at idle, even with the engine warm - the throttle plate is far from the heat of the engine.  Routing warm coolant around the throttle plate area can keep the plate from icing.  Carbureted airplanes had carburetor heat systems for that purpose.  It must have been a field problem.  My 67 230SL doesn`t have that routing.
Tom Kizer

[twistedtree]

I think that's the coolant hose that you are talking about.  The coolant line loops through the first part of the throttle body to help pre-heat the intake air, then loops through the WRD heat feeler and back to the engine (or it might take another detour - I don't remember for sure).  The air path enters the WRD through the attached mini-filter right on the WRD body, the follows the hose/metal pipe around the back side of the engine up to the Cold Start Valve.  Bypass air admitted by the WRD enters through the CSV, not through the throttle body.

[DaveB]

Wouldn't it be better to keep intake air cool (dense)?

to help pre-heat the intake air

[twistedtree]

Wouldn't it be better to keep intake air cool (dense)?

Good point.  I'd guess it's related to emissions to keep the temperature just right.  The early 230s (maybe all 230s - I'm not sure) didn't have any pre-heater at all.  Then it was an additional apparatus in front of the throttle body, then ultimately integrated into the throttle body.

[stickandrudderman]

Tomnistuff has it.
The purpose is to avoid icing on the throttle valve in the same way that aircraft have carb heat (even modern ones!).
There will be little pre-heating of the incoming air so any performance degradation from modified air density will be very small, if any.
Some cars have it and some don't. I'm sure someone will pop up with the definitive figures that determine which models had it.

[Jordan]

The coolant line around the throttle body was added to the 230SL in 1966, late September or early October.  Mine has it and it was produced in mid October.  If memory serves they added it to the 230SL maybe 50 or 100 cars before mine was made.

[glenn]

Ah, yes.  MB fuel management systems.   That coolant coming off the head to the WRD(willnot run, dummy) wandered around many paths over the years - back to the thermostat, pipe around the venturi, built in around the venturi, round and round, etc.  Don't know how they did it on the ME 109s. ..   

[Tomnistuff]

Twistedtree, The line around the throttle body is indeed coolant.  My idle air flow comment was simply to explain why the throttle plate is so tight in the bore and is easier to freeze due to the refrigeration effect of the throttle.  The idle air line I mentioned is the air line from the air filter to the adjustable fitting on the intake manifold.  I`m sorry I wasn`t clearer.  Stickandrudderman is right.  That isn`t a good enough heat exchanger to heat the inlet air.  It would perhaps be enough just to warm the bore so ice doesn`t collect.  

It would be theoretically better for performance to keep the air cold, but throttle plate icing can ruin your day when you bend something trying to open an iced-up throttle.  Also the idle speed tends to drop due to the minimal loss of air flow.

It was in about 1970 or 1971 when the American auto industry "invented" the zip-tube that takes air from the front of the car and ducts it directly to the engine to keep hot engine compartment air out of the carburetors.  The result of the colder air on normal day with a fully warmed-up engine was lower NOX, due to lower peak combustion temperatures.  The air heater worked only when the engine was cold and helped vaporization, but shut off when the engine warmed up.

The word "invented" is in quotes since the mercedes had an equivalent cold air supply since 1963, or before maybe?  I don`t know when they put the air filter just beside the radiator to take in fresh cold air.

By the way, Jordan, my 67 Italian 230SL was built on 11 August 1966 and does not have the heated throttle body.  It's S/N 017590.

Tom Kizer
 

[Jordan]

Tom, I decided to check and it was 14 October, 1966 that the coolant tube was added for warming the intake air ahead of the venturi control, starting with chassis 018563.  My memory wasn't far off as it was exactly 50 cars before mine was built.
Marcus

[ja17]

Yes, I have seen the non-coolant tube venturi units ice up under just the right conditions.

[Benz Dr.]

The 300SL Gullwing of 1954 had the air filter right at the front of the engine bay where cold air would be found. Early 111 coupes ( 1961 ) had an air filter not unlike those found on 113's but with a long snorkle that ended in front of the rad. I suppose they were looking for colder air back then. Niether of these cars had a warming device on the throttle valve.

It would be possible to fit a throttle warmer to any early 113. If you drive in cooler weather it's a good idea to run with one. And, they do get very hot - probably up around 150 F.

[Miloslav Maun]

Thank you all for your explanations.

Tom, I decided to check and it was 14 October, 1966 that the coolant tube was added for warming the intake air ahead of the venturi control, starting with chassis 018563.  My memory wasn't far off as it was exactly 50 cars before mine was built.
Marcus

Below I send a picture of my first pagoda engine and you can clearly see the intake loop. The car was a 1965 230 SL, VIN 11163.

[twistedtree]

Twistedtree, The line around the throttle body is indeed coolant.  My idle air flow comment.......

Yes, I see now.  Your post was clear - I just didn't read it carefully and got a few things mixed up.

[mbzse]

Thank you all for your explanations.
Below I send a picture of my first pagoda engine and you can clearly see the intake loop. The car was a 1965 230 SL, VIN 11163

Due to the cold ambient temperature running difficulties, the water heated inlet was frequently retrofitted. There was a technical change document issued by M-B describing this retrofit.
/Hans in Sweden

.

[stickandrudderman]

Niether of these cars had a warming device on the throttle valve.

Not sure about that. I've seen a couple of 111 with it fitted.