Oil temp and skid plate, the saga continues

#1

Summary.

  1. Getting good air flow to the oil pan seems to be worth 35deg of oil temp. I know that seems like a helova lot, but I’ve now tested this a couple different ways and it’s hard to come to any other conclusion. That’s about 2.5X as much cooling as I got out of my big aftermarket oil cooler, and prob 10X as much cooling as you get out of the OEM oil cooler.

  2. Oil temps vary significantly depending on where you are measuring it. If the other guy isn’t measuring oil temps exactly the same way you are, you can’t compare info.

Details.
A couple months ago I experimented with oil temps with and without a skid plate. I got 35deg of difference, but because I used a sensor with almost no “probe length”, I figured that some of that was oil pan temp and not oil temp. But over the past couple weekends I ran the same tests again but with a temp sensor that had a nice long probe. And I got the same 35deg difference as measured in the pan.

What I did differently this weekend is I had someone weld some reinforcement on to the skid plate, and then I cut some big holes in it. I ran Friday and Saturday with the skid plate holes covered and today I raced with the cover removed such that air could go thru the pan. 35deg difference.

Re. temp and where you measure it. I also have 2 oil temp sensors on an oil filter sandwich adapter. They read crazy high, like 70deg high. I can’t be sure why that’s occuring, and it wouldn’t necessarily be that bad with all sandwich adapters. My guess is that the engine block is quite hot there, just below the water jacket, and the sandwich adapter gets hot.

#2

Nope still don’t believe it.

#3

Oil filter sandwich measurement?
Scott, is the sandwich still in the stock location? Is not the stock location right next to/below the exhaust header?

There is your 70 degrees.

RP

#4

Patton wrote:

[quote]Oil filter sandwich measurement?
Scott, is the sandwich still in the stock location? Is not the stock location right next to/below the exhaust header?

There is your 70 degrees.

RP[/quote]
Is at the stock location. One temp sensor pointed forward and the other one underneath. Certainly if the car was stationary the hot manifold would affect the sensors, but I think that at speed the convection cooling due to the air blast in the area would overwhelm any heat transfer via radiation.

My theory is that the block just below the water jacket gets pretty hot. That would make the sandwich adapter and oil filter pretty hot.

The two sensors in the sandwich filter read the same, even tho they are different makes and one is digital. Since one of them is at the bottom of the sandwich adapter, that supports the idea that it’s not the exhaust manifold causing the high temps.

Re. non-believers. 35deg’s is a lot, sure. But the data for “no air flow” oil temps is solid. I’ve measured oil temps in a half dozen ways in the past 3yrs and 225 on a hot day under race conditions is right. Now I’ve measured “with air flow” temps in the oil pan 2 different ways and the results agreed.

I’m not selling anything. I encourage everyone to do their own tests to confirm or contradict.

For CMP I’ll move sensors around a bit and see if anything changes. That will exclude the possibility that the 190deg gauge reads low.

#5

What about ambient temperatures? there’s bound to be 25 degree difference from your test a month ago and what it’ll be at CMP. What about surface temp? Are you factoring in the track temp… sunny… overcast… Were you in clean air or were you on someones bumper the whole time? And what if you’re running around on someones bumper and their car is running hot or possibly on fire? What about then?

#6

scottmc wrote:

I log temp and sunlight changes at 40hz as I travel from direct sun to cloud and then back to direct sun. Additionally, each rain drop is recorded and the thermal Ek loss due to it’s energy of evaporation is accounted for. If I lose a drop of oil the thermal Ek it carries away is accounted for. After I pass someone I blow a rasberry, the thermal Ek of which also must be accounted for. Without this degree of accuracy Foushee, and more recently Devinney, turbo329 and kingtut ride my ass.

#7

I agree with scott. i’m running the poore pan with no skid plate (although after i went airborne this weekend maybe that’s not such a good idea) and my oil temp (measured at the pan) never gets over 200 degrees. I’m going to add a skid plate now and check what the temps get upto.

#8

Ranger wrote:

Clearly, you need to rig up a video camera and some old school aero streamers to see that the air flow. Or you could hook up with this guy:

http://www.ricardo.com/Documents/Downloads/pdf/vectis_underhood_airflow.pdf

Air flow under the hood of an E30 makes the car’s body shape look absolutely Adrian-Newey-slippery by comparison.

#9

Ranger wrote:

That hurts. I value your accuracy of course. I still have my Factory3 skid plate sitting in the closest uninstalled on my car. I still have my oil cooler installed though. :laugh:

#10

King Tut wrote:

[quote]Ranger wrote:

That hurts. I value your accuracy of course. I still have my Factory3 skid plate sitting in the closest uninstalled on my car. I still have my oil cooler installed though. :laugh:[/quote]
Might want to install the skid plate before Road Atlanta. The turn 1 exit gators have taken out several oil pans.

#11

I’m not brave enough to get close to the turn 1 exit gators yet, but I know Road Atlanta has taken out multiple pans. It will be December so maybe the oil pan can take no airflow. :smiley:

#12

Ranger wrote:

I decided not to do this. It occured to me today that the gauge and sensor that measured this are the same ones I’ve been using since I got the car. I’ve used them in so many ways that if they were off, I’d know it.

I took the sandwich plate off today, and with it went an analog and a digital oil temp sensor. I’ve learned that measuring oil temp there results in crazy high readings so I don’t see the value of continuing to do it.

Frankly, I’ve now measured oil temp in every way I can think of, with all sorts of sensors and gauges, and often redundantly to check for calibration errors. I think I’ve learned all I’m likely to learn about oil temps.

#13

Ranger wrote:

repent! the end is nigh!

#14

oh noes!! ranger has come to the end of his epic quest to find the meaning of life in motor oils! what exciting adventures lie ahead for our superhero?

#15

jtower wrote:

[quote]Ranger wrote:

repent! the end is nigh![/quote]

bahbahbhabh!!!:lol:

#16

So where, after your in depth research, is the best place to get the oil temp from? And if its the pan, where are you putting the probe, in the drain plug or in the side of the pan?

I want to add the temp gauge but have never installed an oil temp before and want to do it right the first time, thanks for the help!

Your pal, the noob!

#17

The most meaningful point to measure oil temperature is just as the oil enters the oil galleries in the block. If the car has a full time oil cooler that point is the the return line from the cooler.

#18

I wrote a response to this earlier today and it seems to have disappeared.

IMO the best place to measure oil temp is in the flow, and that doesn’t mean a sandwich adapter.

The 2nd best place is the pan. Put a bung low on the driver’s side. The problem with putting a sensor in the oil drain plug is that the sensor will hang down because the plug is pointed down. That makes the sensor vulnerable to getting whacked by something. Would be a bummer to drop your oil load because your OT sensor got whacked out.

#19

I’ve come across a new wrinkle in the oil adventures. I think that high rpm may temporarily reduce oil volume in the pan. That is to say when you rev up to high rpm the pump is pulling more oil, but there is a lag in how fast oil returns. I wouldn’t have thought that the lag would be enough to make any difference in oil level but I can’t come up with a different way to interpret what I’m seeing.

So here’s what is going on. Often, but not always, near the end of the RA back stretch and RR front stretch my oil temp will seem to suddenly jump 40-60deg, and then go back down shortly thereafter. The temp climb and drop rates are ~10deg/sec. The temp doesn’t spend any time up high, it just goes up and than down.

Why it’s happening now. My gauges turn colors and flash at different thresholds. I would not have noticed my OT gauge do this before, but the color changes and flashing gets one’s attention. I normally did not check the OT gauge all that often anyhow, maybe just a couple times towards the end of the session or race.

There is no way that my oil temp is really going up/down like this. The OT sensor is on the driver’s side of the pan behind that baffle that separates the oil level sensor. That baffle would slow oil down a bit, but not a helova lot. The sensor is higher in the pan than the oil pump pickup. There’s 3 layers of sensors that would tell me if the pump sucked air so I’m pretty comfortable that the pump pickup is staying submerged.

I think that what is happening is the oil level is dropping below the sensor. Then the sensor is exposed to the hot air inside of engine which come from combustion blow by past the rings.

Why should I care. Think about the turns that have been historically problematic for OP starvation. Left turns, sure, but not just any left turns…it’s the sweepers. What’s different between a left turn and a sweeping left turn?..Sustained high rpm. So I’m thinking that it’s not just the left turn that causes oil starvation, but the combination of temporary low oil level due to sustained high rpm, and the left turn.

Give the engine a couple seconds and the oil will come down and fill the pan, but there is a brief period when the oil level drops.

Any other theories on why my OT would show this behavior?

#20

Excessive fartknocking…

How was the weekend???

Al