What's Your Oil Temperature? - PeachParts Mercedes-Benz Forum

mach4 · #1 07-31-2015, 02:20 AM

It appears that "normal oil temperature" should be around 212 degrees F (100C). This seems to be true for most engines, the reason being that this temperature drives off any moisture that might build up due to combustion and condensation and is also a temperature where the oil functions the best and has good longevity. The upper limit for oil is generally in the 240 to 250F range.

Some thus far pretty sketchy data points toward the potential for high failure rates of the oil cooler thermostat in the open position, allowing the cooler to be open at all times resulting in abnormally low temperatures.

The purpose of this thread is to gather actual data on oil temperatures in our diesels in normal use and to identify how to determine if there are thermostat or cooling issues.

Please state your actual readings on oil temperature along with where and how the readings were taken and conditions present. Include type engine and whether turbo/oil cooler equipped.

mach4 · #2 07-31-2015, 02:32 AM

I'll start...

OM617.952 in a 85 380SL, 722.3 auto trans, 2:47 rear end.

Normal operating oil temperature is around 150F with ambient temps of 70-80F and level highway speeds. Temperatures increase to 180F or so with higher ambient temps and 1-2000ft climbs.

Temps are consistent when taken at the oil drain plug (sensor in the plug), in the cooler line to the cooler (hot side) and a probe dropped down the dipstick tube. In all cases the temp probe is a DS18B20 digital sensor read with an Arduino processor.

I believe my thermostat is stuck open allowing the cooler to always be in cooling mode resulting in abnormally low temps.

ambush276 · #3 07-31-2015, 03:01 AM

in freeway traffic i am hovering around 90-95C. Around town i am usually in the range of 95-100c

82' 240d

dieselbenz1 · #4 07-31-2015, 08:26 AM

Quote:

Originally Posted by mach4

It appears that "normal oil temperature" should be around 212 degrees F (100C). This seems to be true for most engines, the reason being that this temperature drives off any moisture that might build up due to combustion and condensation and is also a temperature where the oil functions the best and has good longevity. The upper limit for oil is generally in the 240 to 250F range.

Some thus far pretty sketchy data points toward the potential for high failure rates of the oil cooler thermostat in the open position, allowing the cooler to be open at all times resulting in abnormally low temperatures.

The purpose of this thread is to gather actual data on oil temperatures in our diesels in normal use and to identify how to determine if there are thermostat or cooling issues.

Please state your actual readings on oil temperature along with where and how the readings were taken and conditions present. Include type engine and whether turbo/oil cooler equipped.

I did a quick Internet search for add on external oil thermostats. I could not find any that were not fully opened higher than 185 degrees F. On the low side I found one fully opened at 170 degrees. I'm not certain what this means but I follow your thoughts on getting up to 212 but now I'm not certain if I ever get close to 212 during the 10 months of cooler weather. Maybe that's why in the older days we always bypassed the oil coolers and only connected through the oil coolers on longer highway runs during the couple of hot months.

Shortsguy1 · #5 07-31-2015, 08:49 AM

Quote:

Originally Posted by ambush276

in freeway traffic i am hovering around 90-95C. Around town i am usually in the range of 95-100c

82' 240d

Am I correct in thinking these may be coolant temperatures, and not oil temperatures?

Benzman53 · #6 07-31-2015, 09:21 AM

1980 300SD with VDO gage and drainplug mounted sensor; highway @ 75 mph 210F, around 200 in town. These temps are consistent thru range of ambient temperatures.

Mxfrank · #7 07-31-2015, 09:59 AM

I have plastic temperature strips applied to the top of my oil filter housing. When I check after a hot run, I'm usually at 170F.

CoolCat Express Corp.: LCD Thermometer 140F-194F (60C-90C)

CoolCat Express Corp.: LCD Thermometers 194F-248F (90C-120C)

Dan Stokes · #8 07-31-2015, 10:32 AM

I need to add an oil temp gage so I don't have data yet but I'm guessing it's pretty cool after a 1 mile run at WOR. I can put my hand on the front sump and, while warm, no burning occurs. I do not run a cooler.

Dan

funola · #9 07-31-2015, 10:46 AM

Engine oil temp measurements are measured at the sump, that is what is widely accepted and the standard location. The oil is hottest coming out of the main bearings but that is not an easy place to measure. Sure it's easy to measure on the outside of the filter housing or at the oil cooler but that is not a standard location and results can vary greatly from sump temp and thus not meaningful for comparison purposes.

85 300D:
45 min drive avg 55 mph, pulled over, insert dipstick thermocouple probe = 181F

funola · #10 07-31-2015, 11:02 AM

Quote:

Originally Posted by Benzman53

1980 300SD with VDO gage and drainplug mounted sensor; highway @ 75 mph 210F, around 200 in town. These temps are consistent thru range of ambient temperatures.

Is this stock instrumentation or aftermarket?

VT220D · #11 07-31-2015, 11:20 AM

I have a VDO gauge and sender that replaces the oil drain plug in my 220D. My average oil temp is between 120F and 140F. The highest I've ever seen is 180F cruising at 75mph on a hot day. The 220D has an oil cooler without a thermostat by design. .

funola · #12 07-31-2015, 11:36 AM

I'd guess the 220D has a 3,000 mile oil change interval?

Mxfrank · #13 07-31-2015, 02:13 PM

Quote:

Originally Posted by funola

Engine oil temp measurements are measured at the sump, that is what is widely accepted and the standard location ... Sure it's easy to measure on the outside of the filter housing or at the oil cooler but that is not a standard location and results can vary greatly from sump temp and thus not meaningful for comparison purposes.

Really? You should inform Mercedes that they don't know what they're doing. They stupidly put the oil cooler thermostat in the oil filter housing. Come to think of it, Jaguar did it the same way, you had better correct them too.

funola · #14 07-31-2015, 02:29 PM

Quote:

Originally Posted by Mxfrank

Really? You should inform Mercedes that they don't know what they're doing. They stupidly put the oil cooler thermostat in the oil filter housing. Come to think of it, Jaguar did it the same way, you had better correct them too.

I called up Shell tech support and asked them where engine oil temp is usually measured and was told in the sump.

Here's a good discussion on it.
Engine Oil Temp Measuring Points | Passenger Car Motor Oil (PCMO) - Gasoline Cars/Pickups/Vans/SUVs | Bob Is The Oil Guy

Edit: Where the oil T-stat is placed has nothing to do with where oil temp should be measured.

ah-kay · #15 07-31-2015, 02:38 PM

Shouldn't engine block, coolant, oil temperature are all of the same? The temperature may differ with hot spots but it should track the coolant temperature pretty much. Am I right, wrong or full of it?