Missionary

Hi folks, I like to cold crank after oil changes to prime the system before a hot start.

http://www.mercedesmedic.com/c-class...ayout-diagram/

It looks like there are a number of fuses related to engine electronics and fuel pump.

Anyone know which to pull to get a cold crank?

QWKSNKE

Need to unplug the injector or ignition harness. Fuel is still in in the lines and the car could briefly fire off even with the pump fuses pulled.

Also, you do realize that the oil system is still primed after oil change, right? Oil changes do not drain all the passage ways, coolers, lifters, bearing journals, etc. Oil change only drains the pan. So, you really are not accomplishing anything.

Now if it was a new engine that had never been fired, then you would prime the system manually with the pump without rotating engine.

roadtalontsi

just unplug the crankshaft position sensor

Jasonoff

What if you dump the cooler? If you do it's probably better to crank it with the starter first. I didn't bother since I did mine hot so there wasn't much time for any bleed down.

QWKSNKE

IMO, even if you do the cooler, priming isn't necessary since bearings, journals, lifters, have not been drained. The whole jest of priming is to get oil in these items.

Think of it this way, you do not want to rotate the motor by cranking or by hand if there isn't oil in the bearings. These are the wear items that get damaged when starved for oil.

Does that make sense?

Jasonoff

If you dump the cooler, the pump will push an initial air pocket through. Doing that at 2-300RPM instead of a full cold start RPM could be beneficial.