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Old 07-19-2002, 10:13 PM
Michael B
Posts: n/a
560sl hard to start when hot... HELP

I've searched the archives for a posting I vaguely remember. It concerned a 560sl that was very hard to start when the engine was warm.

The posting mentioned some kind of a relief valve for the gas tank. I cannot for the life of me find that posting.

Can someone refresh my memory? "IS" there a relief valve that's very cheap that will solve my problem. At time... I have to try three times (cranking 8-10 seconds) before my '88 560sl will start. Yes... this happens when it's warm.

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Old 07-20-2002, 12:11 AM
Registered User
Join Date: Jul 2002
Location: gray ga
Posts: 105
I had the same problem a couple of years ago, I think the relief value you need to replace is on the fuel storage reservoir.
Not sure, I will check my maintinance records and let you know.
I paid $19 for relief value 1979 450 SL
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Old 07-20-2002, 01:46 AM
Registered User
Join Date: Jan 2001
Location: oregon
Posts: 2,013
have hard start problem with my Euro 500 SE nearly the same engine as 560 SL ,would sedan share this part? if so where is it?
william Rogers......
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Old 07-20-2002, 10:31 AM
Registered User
Join Date: Jul 2002
Location: gray ga
Posts: 105
Try 800-252-6877 ext 306

I have the same problem, my 79 450SL got to be very hard to start after it warmed up.

I call Tom and he told how to fix it & sold me relief value, I believe cost was $19. It was delivered to my dooor step next day

Tom works for MB dealer in Calif.
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Old 07-20-2002, 11:09 AM
Deltacom's Avatar
Join Date: Dec 2001
Location: Edge of the Abyss
Posts: 335
Check Valve

There are many reasons why the engine would be difficult to start, the fuel filter and fuel accumulator may be at fault or the pump may be the cause.

The problem occurs particularly after the engine has been running due to the pressure relief valve located at the back of the pump inside. It is activated by a small spring and a metal cone which in time it sticks and do not allow pressure to be relieved.

As the pump is driven by a permanently excited electric motor the pressure is reduced. After stopping, the fuel accumulator maintains pressure in the system to facilitate starting and with this pressure if the valve is stuck it develops an inner leak.

If you tap the pump firmly it releases the pressure valve and the engine starts again. When the tapping becomes frequent, is time to replace the pump.

Mercedes know this and they provide a Check Valve which to be installed by replacing the existing hollow screw to the pipe connection to the pump, effectively providing a secondary pressure relief valve and avoiding having to buy a new pump.
(Check valve $12.98, cap nut $1.49 - pic attached)
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560sl hard to start when hot... HELP-check-valve-e303027620bos.jpg  
Deltacom ~ Absit Iniuria Verbis ~
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Old 07-20-2002, 11:20 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
I'm curious, do magic elixers work for all problems or do they just get used like antibiotics because they are cheap?
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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