E63 Tony

was driving on a highway with the car fully warmed up, oil temps at 199 and coolant around 195-199 and after a few mins of driving i look down and saw my coolant at 183 degrees i tried to take a photo but by time i realized the coolant temps at 183 it started to climb back to the normal 195-199 range.. this is the second time this month I've seen this happen at highway speeds... I've never seen it cool down this fast... and its not even that cold outside(45 degrees)

TMC M5

I don't think it is that unusual. If you are going highway speeds and not dipping into the throttle, these engines run fairly cool when the outside temps are below 50 degrees. Did you also notice if the oil temps came down as well. I have noticed on longer highway trips, when not getting into the throttle (creating boost) I have seen the oil temps drop from 200 down below 185 degrees over time. I didn't pay particular attention to the coolant, as I think the oil temps are more relevant.

Shadow5501

How long had you been driving the car? I have noticed on various MBs that when the coolant temp first comes up to normal, the thermostat opens and you start mixing 45 degree (or whatever) coolant that has been sitting in the radiator into the engine. At that point the engine temp drops and the thermostat starts to close a bit. The indicated temp oscillates up and down a bit until the radiator is warmed and the system settles into stasis. Perhaps this is what you noticed.

E63 Tony

Well the oil temp I've seen drop back into the blue zone on highway drives(normal, my Audi did this as well.) . Although on this car I Never seen the coolant drop below 195 on a highway drive for the last year I've owned the car.

arcticfox

I have not owned my E63 for long, but I have been monitoring coolant and oil temps to see what is "normal" for this car. I noticed the coolant gets to temp quickly, but the oil takes forever to get to temp (probably because there is so much of it). This is in contrast to my E90 M3 which would get fluids to temp pretty quickly.

I noticed the coolant runs at about 200 and is very steady. I have not noticed any drops in coolant temp like you have seen.

cadeca

Are you concerned it's an instrumentation glitch? Otherwise it doesn't seem alarming.

E63 Tony

Not sure. Who knows. Play by ear. Thread junk, has anyone ever noticed that launch control is sometimes much louder than normal? If I park my car hot for 10 mins then drive for about 5 mins then try launch control, it sounds extremely loud haha. Launches the same when loud or when at a normal noise level. But just one of those things I've noticed

6G Schnell

Saw something similar last weekend: driving at constant speed and similar outside temp (avg for the trip was showing 82mph) coolant was at about 199, or less, and oil went all the way down to 176 and turned blue..... guess hi speed in C mode and low rpm cools the engine even though oil level was at 25% above the minimum

E63 Tony

Yea that's very normal for oil to do that.

6G Schnell

Quick update: driving with cold engine for extended time did not seem normal to me, so went to the dealer for checkup.... turns out it was due to the oil temp regulator ... got it replaced, engine runs happily now and oil temp stays in the normal operating range.