Hi All,

I have swapped an M113K from an S55 into a 560SEC. My engine oil temp is always 15 to 20 degrees Celsius lower than the coolant temp which ranges from 83 to 90. So mostly my oil temp is around 65 to 75. This has been confirmed with my oil temperature gauge installed in the vehicle as well as heat gun reading on the oil pan. From my experience this seems to low, am I correct? Possible to have a faulty oil thermostat? The engine sat for a couple of years while the swap took place. I have an aftermarket oil cooler but that should be irrelevant with the factory thermostat. Cheers

I'd definitely start with the oil thermostat. On this car and many other makes I've owned, this is especially common on water temp thermostat (especially after 15+ years of usage) staying stuck open and never getting to optimal operating temperature.

Best of Luck

Temp needs to be higher, else you will keep moisture in your oil, leading to the "mayonaise"/sludge

Most oil temps on cars I have stay below the coolant temps until it’s pushed hard. I wouldn’t be concerned at all. Ince the oil gets hot it’s difficult to keep the engine cool.

Have the M113K oil thermostats been known to get stuck?

Curious to know the location of the oil thermostat .., I also did M113k swap into W220 S500 and just connected the oil in/out lets directly to remote oil cooler...my oil temps remain close to coolant temps 85-95C ....I think may the factory oil coolers had temp sensors on them are they same thing a oil thermostat ( my limited knowledge has a thermostat that has some mechanical function to open / close based on different circumstances including temperatures.

Just below the oil filter and the lines to the oil cooler is a little cover with round centre with 3 bolts holding it in. The thermostat lives behind this cover.

So that would be item 107 in the attached exploded pic?

yes that is correct. Do they give a part number for it?

Yep - 113 180 00 75 $50 retail, about $41 online plus shipping.

This question hasnt been answered yet, but for the price of about 50 bucks, I think this is worth replacing as part of preventative maintenance. Especially if you would replace the oil filter housing O-rings etc