Starting when warm

[Malcolm Johnson]

A question re the SL, when the starter Battery is holding 12.55 volts after several days of non driving. Starts perfectly from cold (instantly) but if started when warm, Starter motor turns at same speed as cold then eventually starts with a tap of the go pedal. But if cooled down say 45 mins, Starts fine. This is very reminiscent of my two pot mottoguzzi which did not like warm starting and eventually I tracked it down to the solenoid not pulling in within the starter motor. Guzzi stealership took the money for investigation and alleged bad connection at a relay base. Totally wrong. Sorted myself for £29.75, fiat solenoid. My thoughts at the moment is possible resistance temperature issue. Any thoughts much appreciated a i don't think this is a specific SL issue. More a aging circuitry/part issue.
As I say any thoughts are helpful.

 

[Bay Leaf]

Hi MKJ Unfortunately I can't help you as I don't know the answer. You mentioned a Fiat solenoid which sparked my interest in your post. I have a Fiat panda which I use as a daily run about and the same condition applies to that. When starting from cold it' fine but sometimes when hot it's as though the battery is flailing.
Sorry to hijack your post but there could be a common denominator here.

 

[Malcolm Johnson]

my 1100 cc motoguzzi would start fine if the battery was fully charged and cold. Although when hot the solenoid would not pull in the circuit to get the starter motor to work, I recall guzzi had fiat starter motor. The motor was fine, the solenoid failed. I replaced it with a Cargo solenoid which i bought from a local factor of electrical items. My thoughts at the moment is the SL is going the same way as my Guzzi. Toys !!!!!

 

[Blobcat]

911’s can suffer a similar issue with hot starting - the issue (on 911’s) is the main lead to the battery being corroded - water wicks through it and it goes black with corrosion, this gives high resistance when hot so starter can’t get enough juice.

Worth a check of the battery cables

 

[Botus]

crank speed declines or no crank with higher temps = electrics / dodgy wires

I'd think about changing the crank position sensor

 

[Malcolm Johnson]

I'm thinking as a start i will replace the starter battery. Recently replaced auxiliary, maybe holding volts but cranking is different. My S tank Held Volts but cranking not. Will look at the crank position sensor as the next port of call if this makes little difference.

 

[Malcolm Johnson]

Replaced the starter battery on the SL this morning, night and day re starting even when warm. Literally rips the starter motor out the engine.
Bought from Mercedes Edinburgh ebay site. (what i did notice was the battery tray was heavily corroded on half of the tray and below the tray.
Looks like a battery leak, cleaned and prepped area)

 

[Wighty]

Replaced the starter battery on the SL this morning, night and day re starting even when warm. Literally rips the starter motor out the engine.
Bought from Mercedes Edinburgh ebay site. (what i did notice was the battery tray was heavily corroded on half of the tray and below the tray.
Looks like a battery leak, cleaned and prepped area)

Boom ! Back in the game buddy ….good fix .