Starting when warm...

[Big Yellow]

Hi all experts!

I have a small but irritating problem with my 1964 230SL. It runs great and never stalls. When cold it starts immediately and runs steady and without any variation in idle speed. However, after driving the car until working temp, turn it off and leave it for say an hour, it then takes 10-15 seconds of starter motor action to start it. It always starts, but it's irritating to have to "grind" the starter motor for so long, before it starts... Any thoughts? 

Vidar "Big Yellow" Holmdin
230 SL 1964 manual

[Pawel66]

Welcome to the club of owners with hot/warm start problem! All or most of us had it, have it or will have it.

There are hundreds of posts about this topic on this forum. If you type in the search filed "hot start issue" or " warm start issue" or problem instead of issue, you will find all the info you need.

But in summary: hot/warm start situation is about the leanest condition of the engine. In most of the cases it does not want to start because of fuel starvation in this condition. Therefore the fuel supply at that moment needs to be perfect. The cart may run great, bit for that particular moment, it may not have enough fuel. Assuming that the car is in tune (valve clearances, ignition timing, linkage adjustment, idle adjustment, overall mixture adjustment are ok), itis often recommended to look at:
1. Make sure you keep the gas pedal depressed 30-40% when cranking.
2. Check overall fuel supply flow. You should get at least 0.6-0.7liter of gas pumped through the end of the return fuel line during 15 seconds of fuel pump operation. Note: end of return fuel line. It is fairly easy test, just need to be careful as you are working with fuel.
3. Check if your cold start system is working. Cold start system, because you also need it for the warm start. The thermo time switch located near or on the engine block should activate the cold start valve (on the intake manifold) through a relay so that cold start valve injects additional fuel for engine start. The higher the temperature the injection lasts fewer seconds. If the TTS gives it too short time, the engine may have troubles starting. Some owners install a manual switch under dash to prolong this extra injection. Simple test is to check with voltmeter if cold start vale is activated (cold start you say is ok, so I assume it works in essence, but may not work good enough for hot start).

In my opinion also, if your car has too lean mixture overall, it will also have hot start issue despite good fuel supply and despite proper work of CSV.

All the tests are described in detail on the forum or in the Tech Manual.   

[Big Yellow]

Thank you Pawel, I will do more searching in this forum. I appreciate your summary and will report back when/if I get this issue sorted 

/ Vidar

[Nicolas Aristodemou]

3. Check if your cold start system is working. Cold start system, because you also need it for the warm start. The thermo time switch located near or on the engine block should activate the cold start valve (on the intake manifold) through a relay so that cold start valve injects additional fuel for engine start. The higher the temperature the injection lasts fewer seconds. If the TTS gives it too short time, the engine may have troubles starting. Some owners install a manual switch under dash to prolong this extra injection.


In my case the car used to start a little bit flooded during hot starts and it took a few seconds to clear the excess fuel before the engine run smoothly.  I had installed an electronic Bosch TTS and cleaned and checked the operation of the CSV but problem persisted. So I decided to install an additional thermoswitch - in this case a small contact thermostat - fixed on the water thermostat housing which runs in series with the CSV circuit.

If the engine temperature is over 50 deg (contact thermostat de-activation temperature) then the CSV does not activate. At temps lower than 50 deg CSV is controlled as normal by the Bosch TTS. Engine starts first time ever since during hot starts and immediately runs smoothly.