If there is no oil temp sender, how does the ECU calculate it?

I have read here that there is no oil temp sender, but those with a Scanguage, or running OBD Fusion as I do, can read it, and the number makes sense (IE it’s not some random gibberish). It has been said here it’s a calculated value based on other factors.

I watched it on a long drive, and it was it’s own number that trended and changed like you would expect it to (IE it’s not just the same number as the AT temps or coolant temp). This screen shot shows the value in the upper left.

Does anyone here know how this number is produced/calculated? Why would they need this calculated value?

 

Somebody who is intimately familiar with the 2gr-fks will know but there's no way there's not an oil temp sensor in this engine. That's gotta be where it comes from. If not, I'll be very intrigued.

 

I would have thought it is a sender, but if you search this forum, there seems to be an opinion expressed that there is no sender and this number is being mathematically derived. I would be happy to find out there is a sender and this number is an actual value, not “fake news”.

 

Link to a good thread? I'd like to read.

 

page 5 or so the discussion starts:

https://www.tacomaworld.com/threads...under-normal-driving-conditions.701501/page-4

There’s another couple threads I read this that I will try to dig up.

 

Look at the engine spec document under sensors. There is no oil temp sensor.
Temp is getting calculated based on coolant temp with correction

 

That may be so, but I am still left with a couple questions after watching it for some time tonight. Maybe you have these answers or someone else does. I’m just curious what I am looking at, for no other reason than I find it interesting.

1- What the point of the ECU calculating a derived oil temp, if it is not displayed anywhere?

2- Why does it not change in step with the coolant temperature? The oil temp trend is much different on my truck than coolant. It doesn’t just follow the coolant with a linear correlation or correction. (IE it’s not just the coolant temp +/- some constant value, or just delayed from what I can tell watching it over time.)

 

Your observation is correct.
I put 3 temps over each other . Looks like AT1 and Oil flow close to each other with a similar pattern .
It seems there is a pattern of the coolant temp to influence the oil temp.
My last thermodynamics class was almost 30 years ago

 

So if that is the answer to my second question, that Toyota is somehow deriving an Oil Temp value from some algorithmic combination of Coolant temp and Transmission temp, the question remains of why they’d bother to do this trickery of it’s not displayed. Like, certainly the ECU can be programmed to react properly to the values that are actually coming in from real-world sensors in the coolant and Transmission, and not have to create derived/imaginary values for itself to operate properly. It would seem an unnecessary step in the software to me.

Anyways…..I don’t expect any hard answers here, I just find the whole situation curious.

Is there a temp sensor in the manual transmission oil bath?

 

As you have found, there is no engine oil temp sensor. Ditto for the manual transmission.

We briefly touched on using the front diff oil temp circuit to measure engine oil temp. The issue that needs to be solved.... at what temperature does the diff overtemp warning ensue, and apparently limit speed.

 

I was gonna tag you, but you're everywhere anyway!

 

Nah, here and there.

 

This very much makes it look like the engine oil temp parameter comes from a/t temp. Wonder what's up on a manual truck.

I also find this interesting that there's no engine oil temp sensor on a modern truck showing an engine oil temp parameter. I'm guessing this parameter is irrelevant to any engine control system and exists for the sake of existing. Calculating this from the other temp parameters makes little sense and wouldn't serve any real purpose that I can think of.

 

Well……I guess we’ll let this remain a bit of a mystery. I still find it strange this active number exists, and displays it’s own changing value. There are lots of unused parameters in the OBD2 register on a Toyota Tacoma that display nothing, or display an irrational number, however this isn’t one. If the active oil temp is created/derived by the software using other parameters, I am left to wonder why Toyota bothered to create it, however little effort it may have taken to write the code.

 

In the patents I've read, from other manufacturers, it's used in the engine oil degradation estimate. Whether or not Toyota does...

 

That could be. Do some Tacoma trims monitor oil conditions and suggest a change based on more that miles travelled and/or time?

My Ford F-150 insists on oil changes based on a large number of factors, idling, engine hours, oil temp, time, duty, etc.

 

You would have to ask an engineer, alot of manufacturers use calculated values for various things some serve an aparent purpose and some don't have an obvious purpose.
Chrysler comes to mind, they have a calculated catyletic converter temp PID that doesn't serve an aparent purpose but it's there.

 

Mine pops up on the regular. I wonder if owners who have done something like a summertime cross country trip while towing, noticed a shorter interval.

 

So I guess the larger question, based on the assumption that all this is true, is whether this displayed oil temp is totally meaningless to the operator of the vehicle, or if it is worth having a glance at?

Toyota, we all know, gives us minimal information on our dash boards, but I would argue the auto transmission temperatures are worth looking at if you are ascending a long grade or towing. I use it as a judge of when to go into 4lo on long off-road climbs in 4WD. You’d be surprised how quickly the transmission temps drop when you switch into 4lo.

I am thinking looking at a derived engine oil temp is mostly meaningless, if it is simply produced from the water and AT temps and some algorithm. I’ll leave it there on my OBD dashboard as a ghee-whiz feature nonetheless.

 

This owner was showing excessive oil temps....

https://www.tacomaworld.com/threads...g-and-under-normal-driving-conditions.701501/