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Jim
03-25-2011, 09:01 AM
The 500E has a fuel cooler on the return line to the tank. I have had various fuel injected cars and they ran without fuel cooling. I have only seen one example for fuel vapour lock in UK and that was on a carburetor engine. I have worked a lot in the Middle East and never had or seen problems or benefits.

There are many threads on the Internet, I found two as follows..

http://www.freshalloy.com/forums/archiv ... 57989.html (http://www.freshalloy.com/forums/archive/index.php/t-157989.html)

http://www.eng-tips.com/viewthread.cfm? ... 415&page=9 (http://www.eng-tips.com/viewthread.cfm?qid=189415&page=9)

Does the 124.036 M119 really need a fuel cooler on the return to the tank as per OEM design?

Jim

Paul64
03-25-2011, 11:12 AM
I must admit, I haven't checked it out on the 500 but certainly, it's nothing new - I had a couple of Jaguar XJ12 saloons from the 70's that had a chiller unit on the return to the tanks.
I guess with the heat of the engine bay of the V12 and the tight space around the V8, temperature must get up there when the fuel is under the bonnet.
The Triumph TR6 didn't have a cooler and was notorious for gassing up the fuel circ system in hot weather, even in the UK(!), and this system ran at 7 or 8 bar I seem to remember which you'd think would be enough to control the problem....

I guess another advantage of a chiller on the return fuel would be to reduce the chance of getting liquid refrigerent back into the A/C compressor when it doesn't have too much cooling load from the car interior.


Paul
Paul

gerryvz
03-25-2011, 11:57 AM
Fuel cooling is an important development that was first introduced in Benzes with the advent of CIS cars in the 1970s and 1980s. Under conditions where the car is driven and there are high outside (ambient) temperatures, you will find that underhood temperatures may get higher than 250F (120C). This situation is often called "hot soak" and the subsequent attempts at starting the car (a so-called "hot start") can be unsuccessful because fuel is literally overheated in the fuel lines. Remember that fuel-injected cars not only have fuel feed and return lines, but also individual hard or soft lines underhood to each injector. This presents quite a lot of fuel-line surface area exposure to underhood temperatures, increasing the likelihood of hot-soak and hard-starting when the engine is hot.

Elevated fuel temperatures associated with a hot-soak condition can easily cause vapor-lock -- which is essentially vaporized fuel sitting in the fuel lines. Vapor, unlike liquid fuel, is compressible, and thus can create a condition where the fuel pumps cannot generate enough pressure to move the vapor down the lines by pushing fresh, colder, liquified fuel down the fuel lines to displace the vapor.

MB (and Bosch) has done several things through the past few generations of fuel injection systems to overcome this situation. First is the use of a fuel accumulator and fuel pump check valves in CIS (K, KE-Jet) systems to maintain fuel pressure in the system for a period of time (usually a few hours) while the underhood temps cool down, thus helping prevent a hot-soak condition from vaporizing fuel in the lines. Second is the use of the A/C refrigerant system to "jacket" the fuel return line, thereby cooling the fuel as it exits the engine compartment.

Our LH-Jetronic systems as used in the E500E do have the fuel-pump check valves, but do not have the separate fuel accumulator that the CIS systems do.

For warmer climates with high ambient summer temperatures, a fuel cooler circuit is almost a necessity.

Cheers,
Gerry

gerryvz
03-26-2011, 11:50 PM
Here's an MB doc that you may find interesting, on the topic of fuel cooling. This pertains to the W126, but is certainly (in principle) applicable to our E500Es.

Cheers,
Gerry

Jim
03-27-2011, 01:13 PM
Thank-you Gerry.

That 126 design has a little more length than the one on the 500E; to allow more heat transfer to take place. Either way the contact length seems short.

Jim.

samiam44
07-08-2012, 10:34 PM
Counter flow heat exchangers are quite efficient.

johan h
01-07-2013, 03:29 PM
I donīt know if i am thinking wrong now but if you run the AC on a hot day the engine temperature tends to rise. When the engine temperatur rice the fue ltemperature gets higher. So the cooler cools of the gas with help from the AC? But arent they working against eachothers? I mean if you donīt run the AC so hard, the enginete mperature donīt rice the temperature of the fuel?

Does this cooler exist on the 400E/E420s?

gsxr
01-07-2013, 03:38 PM
The fuel cooler exists on all 124.034/.036 chassis. The idea is to prevent vapor lock in high ambient temps. More info is in the FSM.

:mushroom:

johan h
01-07-2013, 03:48 PM
The fuel cooler exists on all 124.034/.036 chassis. The idea is to prevent vapor lock in high ambient temps. More info is in the FSM.

:mushroom:

Thanks! Where is it situated?

So with AC on the fuel gets cooler? If the AC is running the engine temperature gets higher and the result should be bigger risk for vapor locks due to hotter fuel? I talk about
realy hot weather (not swedish summer ;)

samiam44
01-07-2013, 08:15 PM
Common on all benz's of the era: M104 and M103's have them also..



Probably overkill-but not a bad design.

gsxr
01-07-2013, 08:23 PM
Thanks! Where is it situated?
In the engine compartment next to the ASR/ABS unit. Follow the fuel lines from the engine fuel rail.



So with AC on the fuel gets cooler?
Yes.



If the AC is running the engine temperature gets higher and the result should be bigger risk for vapor locks due to hotter fuel?
The AC does not increase the engine temp enough to make vapor lock more of a problem. Bottom line, the fuel cooler is a good thing, and in general vapor lock won't be an issue unless it's an absolutely extreme climate (i.e., Death Valley in the middle of summer).


:mushroom:

johan h
01-08-2013, 06:25 AM
In the engine compartment next to the ASR/ABS unit. Follow the fuel lines from the engine fuel rail.



Yes.



The AC does not increase the engine temp enough to make vapor lock more of a problem. Bottom line, the fuel cooler is a good thing, and in general vapor lock won't be an issue unless it's an absolutely extreme climate (i.e., Death Valley in the middle of summer).


:mushroom:

Thanks for the interesting facts. In the swedish sold versions of the 400, 420 and 500s we have another addition to cool the fuel of even more. This is a bulletproof system :)

Jelmer
01-08-2013, 07:34 AM
In the swedish sold versions of the 400, 420 and 500s we have another addition to cool the fuel of even more


Which is?

johan h
01-08-2013, 08:19 AM
Which is?

Frikking cold and rainy summers :p

gerryvz
01-08-2013, 08:35 AM
So, to clarify: a car that is sold into a "frikking cold" and "rainy summers" climate would require additional fuel cooling over cars that live in extremely hot climates such as the Middle East, or the American Southern/Southwestern states?

I'm very curious/intrigued !! Please do tell more !

Cheers,
Gerry

johan h
01-08-2013, 08:47 AM
So, to clarify: a car that is sold into a "frikking cold" and "rainy summers" climate would require additional fuel cooling over cars that live in extremely hot climates such as the Middle East, or the American Southern/Southwestern states?

I'm very curious/intrigued !! Please do tell more !

Cheers,
Gerry

Hehe Gerry. It was the frikking cold summers that was the extra and bulletproof coolingsystem ;)

gerryvz
01-08-2013, 08:55 AM
Ohh, I get it. The 036 has a boosted & rather fail-safe fuel cooling system supplied courtesy of Mother Nature. :hehehe:

johan h
01-08-2013, 09:15 AM
Ohh, I get it. The 036 has a boosted & rather fail-safe fuel cooling system supplied courtesy of Mother Nature. :hehehe:

yea! Maybe i can convert my cooler to a heatexchanger so the fuel dosenīt freeze? ;)

Jelmer
01-08-2013, 09:15 AM
Yer, and a fail-safe system to mess up the cooling system, called a frikking huge engine...

johan h
01-08-2013, 09:16 AM
Yer, and a fail-safe system to mess up the cooling system, called a frikking huge engine...

I like that :D

Taxi Driver
01-20-2013, 02:55 PM
I say, with a late reply, not to forget, the fuel going back to the tank will be heated so in extreme conditions there can be accumulated heat
and as the container lives safely inside the shell, hot fuel radiating into the cabin/trunk maybe an advatage in the winter but not really needed
in the summer, also too hot fuel does no good for performance, density may cause a problem. I remember how many race cars used to have a fairly large fuel cooler up front,,Roger