1987 928 Oil Thermostat
 

I recently installed an engine oil temp sender in the pan drain plug (Lindsay Racing). Now I am wondering if the oil thermostat is:
a) not functioning
b) stuck open
c) not there
When driving at low speed (40 mph) the temp is reading 70 F.
When driving at about 70 mph (2300 RPM) it reads about 140 F
When driving about 80 mph (2800 RPM) it reads about 180 F.
.
If the oil cooler is in the rad tank, shouldn’t it read same as coolant temp?
Looking for some experts here, I am confused.
.

That seems about right.

You're in the coldest area of a well heat dispersing sump...and not much oil is circulating around town and with much less friction load, and a highway temp of 180 way down there is about right. Be hotter at the filter for sure.

Also about 20-50d hotter at the bearing.

The oil cooler in the radiator is very efficient, but not 100% so. I'm also not 100% sure that all pumped oil volume hits the cooler(s) at the same volume that the engine sees oil either..the flow to the cooler may be just a portion of it like some other cars I know to be so. Just not the 928. But..I would not be surprised.

Those oil temperatures are suspect and my first inclination would be whether the engine had fully warmed up when those readings were taken. It takes the engine oil quite a bit longer to warm up compared to the coolant or so I have observed.

Oil temperature should typically be around 100C plus and the oil in the sump is at its hottest temperature. The thermostat reacts to the temperature of the oil it is pumped at - as the temperature increases at some point the plug starts to open- probably about 105C and will be fully open at around 110C or so. At this point some oil still flows directly and some goes to the cooler but I do not know the proportions - the logic being if there is a blockage in the cooler oil flow is still present.

For the cooler to function its temperature must be lower than the media being cooled [obviously] - the coolant temperature as it returns to the engine is about 90C- the temperature you see on the dash panel is the temperature leaving the block and is typically 98C when the system is under control. When the cooler is operating at its design limits it will cool the oil to within a certain number of degrees of the coolant temperature- this is known as the "approach temperature"- the closer the temperature is to the coolant temperature the bigger the cooler has to be and the approach temperature will typically be at least 5C above the coolant temperature so feasible that the target oil temperature will be 95C. This of course is when the engine is at maximum revs [positive displacement oil pump] - at lower rpms the oil flow will be lower and the oil temperature can then creep closer to the coolant temperature. Thus logic says the oil temperature going to the bearings can never be lower than 90C and thus the temperature of the oil going to the sump is going to be higher as it picks up heat in the engine. Therefore if the oil temps you report are corrrect the engine cannot possibly have warmed up.

The other clue is to look at the oil pressure gauge- when the oil is up to temperature idle oil pressure should be 2 barg- if the oil pressure reading is 5 barg at idle the oil is still cold.

The numbers that I posted were after the car had been driven for at least 2 hours, so engine was fully warm - that was what was confusing me.
.
Another question - is there a port on the oil filter or thermostat housing that could be used for a temp sender ?
Looking for a location that would give more accurate readings.

Suggest you calibrate the gauge using boiling water to test for 100C.

What are you trying to learn?

What temp sender are you using? Some of them are very slow making them mostly useless. We typically use these:
https://www.aemelectronics.com/produ...rature-sensors
https://www.milspecwiring.com/Fluid-Temp_c_379.html

I do that with all gauges that I have ever installed.
Again, does anyone know if there an available port on the oil filter housing or the thermostat housing that may accept a temp sender ??
.

.
Speed of gauge reaction is not critical.
As posted, I checked gauge accuracy prior to installation.
From above replies, it appears that it is not a “gauge problem” but a sensor location issue.
if someone has suggestions regarding a better (and simple) sender location, I would love to hear it.
.

Speed is critical if you want an accurate reading. The slow sensors can take minutes to register differences instead of split seconds.

Location of the sensor depends on what you are trying to accomplish. If you are testing the efficiency of the oil cooler then you want a sensor immediately before and after the cooler. If you want to know the temperature of the oil before entering the engine, get an oil filter plate and install it there. If you are simply trying to see the absolute hottest your oil is getting, that's in the pan as that is the oil falling out of suspension after being spit out the bearings or returning from the head. Any other location will require fabrication of some sort versus buying some kind of bolt on adapter.

In theory the oil temp at the location you are using now should be similar to oil after the pump / before the oil cooler since it's only a few inches away from the oil pickup screen.

On some race cars we have oil temp sensors at the bottom of the pan, at the oil filter, before and after the oil cooler and sometimes further up the engine if there's a provision for one. With Motec all those sensors are being monitored with fail safes temps built in.

Not surprising you were confused because those numbers are bullsh*t.

Nothing wrong with the location but for some reason the numbers are being corrupted- a photo of what you have installed would not go amiss.

Temperature sender wiring is not usually susceptible to signal corruption unless you used a thermocouple of some kind- most unlikely but...?

Im guessing the drain plug and mass there is a good heat sink around town???..but the higher speed temps seem just about right. Might see 220-230 "run hard" for "many minutes".

Oh, my. What an eloquent reply.
so . . . which numbers fail to meet your approval ??
it seems that you skipped the part about my testing the gauge/sender for accuracy, prior to installation.
BUT, you are absolutely correct, I did completely neglect to test the installation for ultraviolet, infrared, RF, ultrasonic and magnetic interference at that location . . . . .
I will endeavor to fulfill those requirements as expediently as possible.
.

.
Thank You.
Your explanations make the most sense.
I installed this gauge merely as a monitor. (I have no intentions of beginning an engineering project)
Now that I have a better understanding of the oil pan and oil flow, I will attempt to find a more effective location for the sender.
Again, if anyone has a simple suggestion for sender relocation, I would love to hear it.
.

The numbers being generated are BS not your methodology which is fine. I did the same type of thing a few years ago and got credible results and the kit I used was not expensive - clearly something does not add up

Given your location recorded ambient temperatures of 78F today and thus presumably not much different to when you tested, how could the oil in a hot engine be at a lower temperature than ambient? The average metal temperature in the crankcase of a hot engine is about 80 degrees C, the oil emanating from the bearings is even hotter. The oil in the engine will not go to the oil cooler unless and until it reaches a certain temperature. If the cooling medium is at 90C stands to reason that there is no point sending any oil to the cooler until it is about 95C. Engine manufactuers try to keep the oil temperatures at or above about 105C so that any entrained water in the block as a result of combustion gases passing the rings can vapourise and be expelled thus preventing dew point corrosion.

Thus the first reading of 70F is seemingly impossible unless you happen to be Father Christmas at the North Pole and even then I doubt you could see that kind of temperature in the oil other than during the warm up process which you advised was not the case.

Have you seen any signs that give you cause for concern thus why you fitted a temp gauge?

I merely installed this sender to monitor temp, but was confused by the readings. I picked that as the simplest location. I have no inclination to begin an engineering project, and I am happy if the readings are "close enough"

Permit me to return to Part B of the original question:
- is there a simple way to get the sender into the oil flow ? Is there a port adjacent to the oil filter housing that can be used ? Is there an oil filter adaptor that will take a sender ? Does anyone make such an item ?