[ard5040]

My oil temp has been sitting at 250 for the past two weeks, even with AD Engineering Thermostat. Some background. Car is an '07 e92 335i. At 132k miles developed a leak in the head gasket. Owner of the shop that services it, certified BMW tech, said that he had the motor from an '08 535i with 72k and that it would be much less expensive to essentially rebuild that motor than it would be to drop my motor and replace the head gasket alone (dealer quoted $6000 for head gasket). After pressure testing the 535i motor, all cylinders better than 95%, the head was completely rebuilt, connecting rod bearings replaced, all gaskets and seals replaced. My new oem turbos were transferred with new oil lines. Before motor swap my oil temps with the AD Eng thermostat were in the 210 to 220 range, even with air temps of 90. After the swap, the oil temp sat at 250. I reinstalled the oem thermostat, still 250. I bought a new AD Eng thermostat, still 250. After driving for 30 min today I held my hand next to the oil cooler in the wheel well and it was hot so I'm pretty sure that oil is circulating. Would appreciate any help. Thanks in advance.

[Jeff@TopGearSolutions]

Oil temp sensor on the fritz? Any codes?

[ard5040]

No codes. If sensor was bad I wouldn't think that I would get any reading at all, no?

[Velocity26]

Difference in the oil temperature sending unit ... put the one from your old motor in that one.

[feuer]

Are you using the same engine oil?

[ard5040]

pennzoil to castrol, both 5w30

[Jeff@TopGearSolutions]

Originally Posted by ard5040

No codes. If sensor was bad I wouldn't think that I would get any reading at all, no?

That's not necessarily true.

Originally Posted by Velocity26

Difference in the oil temperature sending unit ... put the one from your old motor in that one.

That was my next response.

[feuer]

Originally Posted by ard5040

pennzoil to castrol, both 5w30

There is a possibility that is the reason. You will know after the next oil change.

[limitdown]

Your previous temp of 210 to 220 in 90F ambient seems very low. I have a CSF radiator, a BMS themostat bypass and I run 240F in 90F+ and 80%+ humidity weather.I run Motul 8100xcess 40 or Red Line 40. I've always had problems with 30 weight shearing. With Mobil1 40, it would shear within 500 miles and my temps shot up to 280 and I limped.
Try changing the oil to see if that helps. Simple and cheap to try.

[ard5040]

So the oil temp sending unit and the oil temp sensor are not the same? I will be changing the oil this weekend to see if that makes a difference.

[Velocity26]

Originally Posted by ard5040

So the oil temp sending unit and the oil temp sensor are not the same? I will be changing the oil this weekend to see if that makes a difference.

There is more than one sensor pertaining to oil, there is also an oil level sensor. But the temp sensor and temp sending unit are two names for the same item.

[BB_cuda]

Put tape on side of oil pan (there is a reason). Use IR thermometer and shoot the beam on the tape. IR thermometer measures by virtue of infrared emittance. Polished aluminum will read lower than real temp. As cast aluminum will do better. A way to see if tape is necessary is to shoot the pan adjacent to the tape and then go to the tape ...back and forth. It would sure be prudent to find out if you have a real problem or an instrumentation problem.

[STR8-6IX]

anything 250+ is a high oil temp. you can try removing your plastic engine cover which traps unecessary heat within the engine bay. with it off, i noted an almost 50F reduction in temps. I only keep it on in cold weather.