Why an oil temp guage instead of pressure?

Let's speculate. Why do you think BMW included an oil temperature gauge in my E46 M3, instead of an oil pressure gauge? And why does my Miata have a real oil pressure gauge, in place of an oil temperature gauge?

What would you rather know . . .

I would say that both are important. On the BMW you also have the oil pressure light.

Oil lubes best in a narrow temp band ~180-240F but depends on oil base and additives etc. Preasure is more important in my mind.

If you want to know if your engine is working at its optimal capacity: oil temperature

If you want to know if your engine's about to blow-up: oil pressure

Would it be wise to add an oil temp gauge for a manual transmission?

Slippery wrote: I would say that both are important. On the BMW you also have the oil pressure light.

I am just waiting for a manufacturer replace most of gauges by a single happy/sad face light, which would translate to "take to dealer!"

Why not both? 4 of 5 cars I drive have both . . . the other will as soon as the motor swap is started.

DavidinDurango wrote: Why not both? 4 of 5 cars I drive have both . . . the other will as soon as the motor swap is started.

It isn't an either or for me . . . I was speculating as to why BMW decided on a temp guage, and Mazda a pressure gauge. There must be a reason behind it.

<<< Starting with these!...BMW folks were clamoring for an oil pressure gauge in the '70s! As far as I'm concerned, the light just tells you you've ruined your engine...but also I think it mostly depends where the sending unit is...at the furthest point from the oil pump or close to it?

If i had to choose between just having a pressure gauge, and having a low-pressure light and a temp gauge, i would take the idiot light and the temp gauge. Just my .02.

I agree both are necessary for cars that are going to have their limits tested. But as the manufacturer is concerned the cars are just commuters for doctors. The gauges are just there to make doctor feel like he's driving the ultimate driving machine at speed limits set for semi-trucks. In that case neither gauges are needed. The doctor wouldn't even know what they meant if both were there

Yeah, i've never met a doctor who knew anything about interpreting instrument readings, or overtemp conditions, or anything like that.

BMW designs cars for enthusiasts. If they did such a mediocre job of it that enthusiasts complained that their instrument panels were just full of meaningless flashing lights and trying to pull one over on us, they would lose the 'ultimate driving machine' credibility that helps them sell to non-enthusiasts (bread & butter yada yada).

I think the point you're making is valid against certain manufacturers and demographics but i wouldnt have picked BMW and doctors to use it on.

I can only add this. Fiat used to have an oil pressure gage in the 124 spiders. in 1979 is vanished for replacement for a light. It was not that the Fiat Twin Cam didn't need the gage.. it was that the TC ran very low oil pressure at idle. Many many many cars were returning to the dealer to have this "fixed" to the point where fiat simply deleted the gage.

Could BMW be the same?

Pressure tells you if the engine is shot, temperature tells you if you're cooking the oil and if its ready to thrash on or not.

mad_machine wrote: I can only add this. Fiat used to have an oil pressure gage in the 124 spiders. in 1979 is vanished for replacement for a light. It was not that the Fiat Twin Cam didn't need the gage.. it was that the TC ran very low oil pressure at idle. Many many many cars were returning to the dealer to have this "fixed" to the point where fiat simply deleted the gage. Could BMW be the same?

I do know that the real gauge in the Miata was replaced with a dummy gauge in 1995 because, allegedly, people were complaining about wildly swinging oil pressure. The first NB I drove made me worried that there was something wrong with my car, since that oil pressure gauge never moved a lick. Then I learned it was essentially an idiot light . . .

ZOO wrote: I do know that the real gauge in the Miata was replaced with a dummy gauge in 1995 because, allegedly, people were complaining about wildly swinging oil pressure. The first NB I drove made me worried that there was something wrong with my car, since that oil pressure gauge never moved a lick. Then I learned it was essentially an idiot light . . .

That's not unusual. I had a 99 ranger with the same idiot light desguised as a gauge.

Any pressure over 5 psi put the needle to the middle of the range.

I have only had one oil pump fail.... it was in a BMW

Kenny_McCormic wrote: [oil] temperature... if its ready to thrash on or not.

^This.

Especially given BMW's issues in the last decade with special oils and bearing failures, I'd say it's pretty important to know when it is safe to really get on the throttle and wring the snot out of the motor.

Hint: it's not when the coolant gets up to temp.

mad_machine wrote: I can only add this. Fiat used to have an oil pressure gage in the 124 spiders. in 1979 is vanished for replacement for a light. It was not that the Fiat Twin Cam didn't need the gage.. it was that the TC ran very low oil pressure at idle. Many many many cars were returning to the dealer to have this "fixed" to the point where fiat simply deleted the gage. Could BMW be the same?

Probably. It's the same reason BMW changed their coolant gauge from reading honest temp changes to staying in one place during a range of temps. people were taking cars back to the dealer and complaining about the gauge moving all the time.

gunner wrote: people were taking cars back to the dealer and complaining about the gauge moving all the time.

Yup.

Oil temp IS a nice thing to know.

Oil pressure.... 10psi at idle is perfectly fine. 10psi at highway speed is not. Many people can't tell the difference, and flip out when it's "got no oil pressure".

I am intending on adding Oil Press, Oil Temp, and Trans Temp to the Landrover.

To a certain degree, you can use an o/p gauge as an o/t gauge. If you're getting higher-than-normal pressure readings, your oil is probably not up to temp yet.

clownkiller wrote: I have only had one oil pump fail.... it was in a BMW

I had one fail also...in a BMW; but it was TOO MUCH pressure! Early 2002s had the relief valves stick. Mine was on the start line at a hillclimb, much to my chagrin and the (ahem) consternation of the start line crew who had to clean up my mess!

They don't want you to have a pressure gauge any more - they just lead to increased numbers of people bothering their dealers, thinking something is wrong and demanding new engines just beacuse the pressure is lower than they think it should be.

Personally, I've never race without both. I had one engine that always had decent pressure, but the temp headed up to 280 F or so - always figured there was a constriction somewhere in the galleries - and it finally blew. Never seen that in any other race engine I've built.

The only car that has both stock is my old Lambo. I still get antsy driving modern cars with no pressure gauge......

In reply to Vigo:

Maybe it's not an accurate representation of the demographic, but I used the doctor as an example for a good reason. I was at a gas station and a guy with a hospital badge and with a newer model BMW asked me how to put oil in his car and what kind he should buy. He said he hadn't changed the oil since he bought it and some warning was on for oil. I told him to look in the book in the glove box. He did and went into the gas station and came back out empty handed. He said I will just take it to the dealer in on Monday... and drove off