High Oil Temps, normal KTMP - BMW M5 Forum and M6 Forums
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post #1 of 29 Old 22nd May 2019, 09:54 PM Thread Starter
LordSaladbar
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High Oil Temps, normal KTMP

I've been running hot under normal conditions (it was 72 and beautiful today) with OELTEMP averaging around 101. KTMPs are normal and I haven't run into any issues except the fact that the needle is to the right of 210 bothers me. When I'm driving on the highway and not stopping at all, it's 97-99, but even that seems higher than what research on the board tells me.



I checked behind the radiator and while there's crap there, it doesn't seem substantial enough to block airflow. What other things can I check before throwing money at the car? Once I get an air compressor handy, I'll try blasting the crap out of the space behind the radiator.



Aux fan works with a/c on max blast... but it seems quiet to me. It doesn't spin up to that "jet engine" level of noise. Oil is very very slightly above the "max" oil mark on the dipstick, should I try and siphon oil out to be below that?
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post #2 of 29 Old 22nd May 2019, 10:51 PM
josiahg52
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I'm assuming that 72 and 210 is 72F and 210F and 101 and 97-99 is 101C and 97-99C? And these are oil temperatures as read from the cluster meter?

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post #3 of 29 Old 22nd May 2019, 11:07 PM
Jayson
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I'm having a similar issue after the oil level sender and valve gaskets got replaced. Makes me very nervous.

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post #4 of 29 Old 22nd May 2019, 11:27 PM
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Quote:
Originally Posted by Jayson View Post
I'm having a similar issue after the oil level sender and valve gaskets got replaced. Makes me very nervous.

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I believe the oil sender controls temp. And suspicious it happened right after you changed it.

What brand? Perhaps a cheaper version is bad. Can't remember what OEM is, but check the usual sources for parts (Pelican, FCEuro, Turner, Rock Auto, Autohaus, etc.) and you can figure out OEM.

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post #5 of 29 Old 23rd May 2019, 01:04 AM
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I'm fairly confident it's Hella, as I just received this:





With the BMW and part number dremel'd off.





(I too am hunting down why my oil temperatures are a little, well, concerning. I installed a Zionsville oil cooler a while ago, and have a CSF radiator ready to go in. I had read that the cluster oil temperature gets it's readings from this sensor, and I'm all bout the dremel'd OEM parts for less scheme.)
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post #6 of 29 Old 23rd May 2019, 01:14 AM Thread Starter
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Quote:
Originally Posted by josiahg52 View Post
I'm assuming that 72 and 210 is 72F and 210F and 101 and 97-99 is 101C and 97-99C? And these are oil temperatures as read from the cluster meter?

Ah yeah, sorry for being a confusing American. 72F outside and breezy, 97-101C from the secret menu test 16.
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post #7 of 29 Old 23rd May 2019, 01:29 AM
mgdmb
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There's really nothing wrong with those temps, but if it makes you feel better you can check the fan clutch. At temp, you shouldn't be able to stop it with a rolled up newspaper... if you can, fan clutch is toast...
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post #8 of 29 Old 23rd May 2019, 03:26 AM Thread Starter
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Originally Posted by mgdmb View Post
There's really nothing wrong with those temps, but if it makes you feel better you can check the fan clutch. At temp, you shouldn't be able to stop it with a rolled up newspaper... if you can, fan clutch is toast...

Hang on, isn't it the other way around? If you can stop it, then it's fine? Well, either way I'll try it tomorrow.
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post #9 of 29 Old 23rd May 2019, 03:30 AM
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Depends on the Ktmp. At full lock up (95-96C) it should be near impossible to stop. As Ktmp goes down, it will be easier to stop. So, both are correct depending on your Ktmp.

If you can't stop it and your Ktmp is low, yes it's also bad. But presumably if it's fully locked up all the time, oil temp would be lower...
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post #10 of 29 Old 23rd May 2019, 07:53 AM
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The lockup for the mechanical fan is based on the air temp surrounding it. IIRC it is 110C but my memory sucks so search.
This is general, but if your oil temp is up but just by a bit it likely has something to do with the coolant cooling not being 100%. This is how the system works in short and simple terms there are lots of things that can do other things but I have already read some likely candidates so lets start here.
The oil temp in normal driving is effected by the heat exchanger in a major way. I have put a few oil coolers on peoples stock cars because they wanted them and there was no change to the oil temp through normal driving, that is because the heat exchanger that comes with the car is very powerful and the oil will become the temp of the coolant that it is changing heat with.
First we need to take a look at a best guess for the coolant temp going into the exchanger. The exchanger is not right after the rad, the coolant flows through the block first so the temp will be higher than the outlet hose temp. If the oil is really hot the heat flows from the oil to the coolant, but if it is cooler than the coolant the heat flows from the coolant to raise the temp of the oil.
More than likely the issue is the coolant flowing into the exchanger is higher than it was when the car was new.
It could be the rad is not working well and the coolant output temp is higher than it should be, way cooler than the inlet temp but not as cool as it should be. If it comes out 10 degrees hotter from the bottom hose it will likely be 9 degrees hotter when it enters the exchanger which will make the oil temp 9 degrees hotter.


Crud on the rad making it less efficient could definitely be a cause. It does not have to be plugged to be 10% less efficient. Also crud inside the rad is a likely cause. These cars are old and if they have original rads there will be a ton of crud in them. What that crud does is block passages basically making the rad smaller. Smaller rad will be less efficient.
The few times I have had to deal with this issue of raised oil temp. I replaced the rads for people, and when the rads came out they were much heavier than the new one going in. Some of that weight could be a little coolant, but the majority was all crud blocking passages.


Now that is for a car with a constant higher temp and one that is moving. Moving because the aux fan turns completely off at 80KPH and starts slowing at 20 KPH so between 20 and 80 it will have its duty cycle reduced compared to less than 20. Although the mechanical fan works without the magic of sensors it works the same way to a degree. As the volume of air flowing through the rad increases each unit of air absorbs less heat so the overall air temp is less. If your mechanical fan is heard at 80 KPH it is toast and locked in the on position.
If your oil temp is normal while driving at say 50KPH but rises as soon as you slow to less than 20 you likely have a fan issue. Even if you are not seeing it in the coolant temp and you won't because that is the hot temp. It is easy for a rad to get rid of the hot temps, but hard for it to drop the bottom degrees down a little more, you first see these symptoms in the oil temp.

Last edited by Sailor24; 23rd May 2019 at 08:03 AM.
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