Oil temp from oil pan

#1

2 ways to do it.

2 5/8th gauge solution:

Sender http://www.summitracing.com/parts/ATM-2259

Adapter http://www.egauges.com/vdo_indS.asp?Sender=Adapter_Bushings&PN=R7962

Gauge http://www.egauges.com/eg_typeI.asp?Type=Elec_Engine_Temp&Face=All&Lighting=All&Letter=All&Bezel=All&Needle=All&Diameter=All&Manf=Auto Meter
(this link isn’t working right because the “meter” isn’t being added to the URL. Either pick an Autometer oil temp gauge that appeals to you, or edit the URL in your web browser such that the end of it has the phrase “Auto Meter” (no quotes"

Autometer gauges usually come with the sender, but in this case the sender won’t fit into the adapter. The solution is to get the cylinder head sensor that the link points to.

2 1/8th gauge solution:

Gauge (Be sure to choose “VDO range”) http://www.egauges.com/eg_typeI.asp?Type=Elec_Engine_Temp&Face=All&Lighting=All&Letter=All&Bezel=All&Needle=All&Diameter=All&Manf=VDO

Sender http://www.egauges.com/vdo_indS.asp?Sender=250F_120C_VDO&PN=323-416

#2

RANGER!!! [color=#FF0000]K.I.S.S[/color]. Use the 2 5/8" MECHANICAL Gauge and forget about all the cumbersome wiring, etc. Paul puts a 1/2" bung in the driver’s side of the pan just for this purpose. The simpler you can keep things, the more reliable. CB

#3

Agreed. If I had it to do all over again, I’d get mechanical gauges.

#4

I’ve always been hesitant about mechanical gauges. If you crack a line, you’re down. Electrical isn’t a problem on failure and not too hard to install. But that’s just a preference thing. I once compared an electric H20 gauge/sender to a thermocouple in a pot of hot H2O and was dead on. :slight_smile:

The link you gave isn’t to a specific gauge, it’s like a can’t find search result.

Make sure what ever gauge you get scales to 300+ F. The bigger diameter you get the easier to read at a glance.

I could never figure out why, but my oil temps were always way higher when measuring from the exit point from the block to the cooler (on SC’d Miata), 285-290, compared to the oil pan temps (sender in drilled out drain plug) @ 240.

#5

rrroadster wrote:

The Autometer link was correct, it’s just that the space in the URL is creating problems. I edited the origonal post to give some guidance.

I assume that the Miata’s oiling system was similar to ours in that oil went pan>block>cooler>block>galley? If that’s the case, that is interesting.

Aluminum dumps heat pretty rapidly. I could imagine the exterior surface of the aluminum oil pan, exposed to significant convection cooling even if it doesn’t have much surface area, being cooler then the oil it contains. This would create a significant temp gradient inside of the aluminum. The exterior of the aluminum, directly in the air flow under the car, could be at 200deg. Meanwhile the interior surface of the pan, in contact with the hot oil, could be at 290deg.

The cooler pan exterior surface would impact the oil temp reading of the sensor that is screwed into the pan. Exactly how the sensor was affected would depend on the geometry of the situation.

#6

Hi Ranger,

Thanks for the links…Does it matter that the adapter is for mechanical gauges?

(Somewhat tangential to the original post–oops) Sorry if this is ignorance on my part, but is it possible to use the existing port in the engine block for the OEM oil pressure sender to the dashboard idiotlight as a site to attach an aftermarket sender for an OP or OT gauge?

#7

Steve C wrote:

[quote]Hi Ranger,

Thanks for the links…Does it matter that the adapter is for mechanical gauges?

(Somewhat tangential to the original post–oops) Sorry if this is ignorance on my part, but is it possible to use the existing port in the engine block for the OEM oil pressure sender to the dashboard idiotlight as a site to attach an aftermarket sender for an OP or OT gauge?[/quote]

Using an adapter for mechanical gauges is fine. I say that having heard good things about mechanical gauges, but I’ve no actual experience with them.

The OEM oil pressure port is a good location for an aftermarket OP sender. The best solution tho is to connect a hose to it, remote it up to the fender and put in an OP sensor and an adjustable OP switch. That allows you to put a big red light on your dash if your OP hits some problem threshold. Mine is set to 20psi.

Some gauges have an integrated warning light and programmable threshold. SPA is one. I suppose the right way to do that is to have it trigger an external warning light. The integrated light is too subtle.
The OEM OP port is not a good place for getting oil temp because it’s a dead end off of the galley. There’s no oil flow past it.

#8

The thing I dislike most about electric gauges is that the sending units fail if not mounted correctly (that would mean “not on the motor”). So the expense you go to to remote mount the sensors is more than plumbing a mechanical gauge. In addition, it is easy to burn the wires, especially around the exhaust. That is why I asked Paul to add the 1/2" bung on the driver’s side of the pan. He not puts a bung on each side, but I shy away from anything close to the exhaust.

If you have problems with the capillary tube, it is your fault…you can’t kink the line or make unusual sharp bends.

Oil temp from the pan.With a mechanical gauge, the probe sticks into the pan about an inch…therefore, you are measuring the temp of the oil, not the sides of the pan. I doubt the heat transfer one inch into the constantly moving oil in the pan is what would be considered significant. In addition, you want to know what the oil temp is in the pan because it is a direct reflection of the temp of your bearings. Good information to have.Chuck

#9

cwbaader wrote:

[quote]
Oil temp from the pan.With a mechanical gauge, the probe sticks into the pan about an inch…therefore, you are measuring the temp of the oil, not the sides of the pan. I doubt the heat transfer one inch into the constantly moving oil in the pan is what would be considered significant. [/quote]
This is a good point that Chuck is making re. the probe length. My cylinder head temp sensor arrived last night so I put it into the pan’s 14mm adapter. The sensor has, for all practical purposes, no probe length. This makes it fit well, but it also means that the temp that it sees will be heavily influenced by the temp of the oil pan. Because of the air flow past the oil pan, and because aluminum moves heat well, the exterior surface of the pan will be cooler then the interior surface. Therefore the temp that the sender sees will be lower then the temp of the oil. How much lower, remains to be seen.

If I have to mentally add 10deg to the oil gauges indicated temp, that’s no big deal, but this is a good example of measuring things can be tricky.

Chuck, how does a mechanical temp gauge work anyhow? How does the sensor transmit the info to the gauge?

Later edit. Just found this…
The mechanical gauge is filled with ether in the thin copper line, and sending unit.

When the sending unit heats up the ether expands.

In the gauge there is a halfmoon shaped copper pipe, that tries to straighten when the ether expands in it , causing the needle to move.

#10

I didn’t feel like dropping the pan or tapping it on the car so I mounted a mech temp gauge in the end tank of the factory oil cooler. Which end is the ‘cooled’ end?

Still need to wire the pressure gauge.

#11

wsl wrote:

Can you elaborate on that? I don’t understand.

#12

Ranger wrote:

http://www.msprotege.com/members/wscottl/oil1.JPG

#13

Are you using the OE oil filter adapter? I guessing that is the case with the OE cooler. In case you don’t know, the OE filter adapter includes a thermostat for the cooler. By moving the spring to the other side of the thermostat you can convert the filter adapter for full time flow through the cooler.

#14

jlevie wrote:

Your oil temp pickup in the picture is well done.

I’m keeping the oil thermostat. I’m concerned about the oiling system being able to rapidly recover from the oil pump running dry in a left turn. If the oil tstat can help shorten the oil route under some conditions, I’m ok with it.

I’m not all that convinced that we even need an oil cooler. I’m going to collect data on it for a couple months and then remove it and see what happens to oil temp.

My peak oil temp racing at Roebling this weekend was 190 as measured in the pan. I’d estimate that if I was measuring it in the flow like I used to, I’d a seen 225-230deg.

#15

jlevie wrote:

[quote]Are you using the OE oil filter adapter?
the OE filter adapter includes a thermostat for the cooler.[/quote]

Yes, OEM housing.

What temp does the oil t-stat ‘open’?

#16

wsl wrote:

[quote]
What temp does the oil t-stat ‘open’?[/quote]
I think it’s 170deg.

#17

The reason your sump temp is 190 is because the oil cooler works. If you bypass the cooler your sump temp should then be the same as your cooler inlet temp (mol). If that indeed is 225-230 you are correct in assuming that is ok. Less efficient, but still OK.

#18

donstevens wrote:

I dunno.

I used to measure oil temp in the flow just before and after my big oil cooler. Hot oil temps during Summer were 210-220deg, IIRC. I got ~ 14deg of cooling from the big oil cooler. I think that’s a good baseline for hot oil temps.

Fast forward to a couple weeks ago when I had a temp sender with a short probe in the oil pan and temps were far lower. That indicates that that the sender in the pan was getting an innacurately low reading. I don’t think that it has anything to do with the oil cooling.

The missing piece is heat flow. If one charted the temp profile of the oil pan at the drain plug, exposed to 80mph air flow, one would find a sharp temp difference between the temp of the outer surface and the temp of the inner surface. The outer surface is exposed to convective cooling and the inner surface is exposed to conventive heating.

If the outer surface was at 160deg and the inner surface at 220deg the temp graph of the 6mm of aluminum wall thickness would be a smooth line connecting the two temps. The average temp inside the wall would be 190deg. If one put a temp sensor in the aluminum wall that had no probe length to speak of, then the sensor would read the average wall temp.

The way to make the temp sensor in the oil pan accurate is to ensure that the sensor’s temp probe extends well beyond the aluminum wall such that it’s bathed in moving oil.

#19

An oil pan shield seems to make my “probeless” oil temp sensor accurate.

The above posts were after racing at Roebling with no oil pan shield. This past weekend I was at RA and I had the oil pan shield on. Oil temps were ~225deg. I think that the oil pan shield stops much of the air flow past the oil pan. This would significantly reduce the convective cooling of the pan, and as a result it would be closer to equilibrium temp with the oil inside of it. Therefore the temp read by the probeless sensor would be relatively undistorted.

Lessons learned:

  1. You can, with reasonable accuracy, measure oil temp in the pan with a probeless sensor if air flow past the pan is reduced.

  2. Oil pan shields interfere with oil cooling because they reduce air flow past the pan. An oil pan shield that allows some air flow is worth thinking about. Aluminum can flow a lot of heat, and there’s a fair amount of surface area there that could be cooling your oil.