Best location for oil temp sender on e30

[AlarmedBread]

Hm, I guess the boys at TMS are a bunch of hacks who don't know what they're doing too eh?

http://www.turnermotorsport.com/html/detail.asp?PRODUCT_ID=TEN9990001

[nando]

Hey Nando, I don't know about this one, I've read a few things to suggest that oil pan IS the best place to get a stable oil temp. Sure the oil pan will act as a heat sink a bit, but I can't think of a better place where these is more oil, and less heat from other components then the pan it's self.

Can you convince me otherwise?

yes, because of exactly what you said - the oil pan acts like a heat sink, and the oil in your pan is much cooler than is what is running through your engine.

It takes about 2 miles to get a temp reading (starting at 120f) and about 5 miles to get up to ~160f with the temp sensor in the pressure switch location. In the oilpan, it could take *hours* to get a meaningful reading, and many, many miles to get any reading at all. I literally sat in stop and go traffic for 5 hours and had a temp reading of 150f. there is no way it was that cool, hell I could feel the transmission through the shifter console. Last track session I was seeing temps close to 250f. the oil pan is probably 100 degrees cooler.

also, name me one OEM that puts the temp probe in the oil pan. BMW certainly doesn't, nor does Porsche.

[nando]

Hm, I guess the boys at TMS are a bunch of hacks who don't know what they're doing too eh?
http://www.turnermotorsport.com/html..._ID=TEN9990001

they reccomend what sells and what's easy. you don't have to listen to me. I'll take BMW's word for it. ;)

[george graves]

yes, because of exactly what you said - the oil pan acts like a heat sink, and the oil in your pan is much cooler than is what is running through your engine.

Ok. I can see your point there. And your point of what the factory does is not to be underestimated too.

But just as the oil pan is acting as a heat sink to draw heat away from the sensor, don't you think that attaching the sensor to a hot part of the block will cause heat to transfer into the sensor? How do you know you are not measuring block temperature?

I can't believe that it would take *hours* as you said, for the oil in the pan to heat up. For example, I could dunk my hand in 120 F Degree oil no prolbem, but no way would I let someone drain motor oil onto my hand from a car that has just driven 10 miles. Way too hot, we all know that.

I have a book on designing engines. I'll see if I can't see if it has a reference in.

[kishg]

not sure about hours. i have temp from the oil pan and it heats up pretty quick.. not sure if its more or less accurate than getting it off the filter assembly.

[reelizmpro]

ahhh the great debate. I've been studying this the past 2 weeks. Many people say the oil pan is best and it makes sense. Plenty of oil there just coming out of the engine. However, a temp sensor mounted lets say on the side of the pan is going to sample cooler temps than the hotter oil in the middle of the pan that immediately gets sucked up by the oil pump. The pan is a large heatsink by design that is cooled by airflow. VDO sensors lag, so it makes sense to put them where this is more oil flow instead of stagnant oil for the gauge to be useful. BMW put the oil temp sender on the oil filter housing on the E30 M3, so I did the same on my old M20 tapping the hollow bolt for the housing and routinely saw temps of 170-175 degrees. I was satisfied with the readings as they made sense. On my convertible with the sensor in the pan, I (like Nando) have only encounted 150 degree MAX oil temps and this is with a fully warmed up Turbo engine. Doesn't matter how hard I get on it...it will never exceed 150 degrees and I put some duct tape over part of the cooler. I thought it was the gauge wiring but I wired it with it's own dedicated ground. I do have an aftermarket oil cooler that isn't thermostatically controlled so I'm putting a thermostat (opens at 160 and fully opened at 180) on it tomorrow. Shouldn't make a difference but at least I can rule out the cooler and have another way of measuring the actual temp.

[kishg]

i've seen the temp rising to 180+ on the track.

[reelizmpro]

We don't know much about VDO sensors except they are thermistor based so they are slow reacting. The sensor is supposed to be grounded to whatever it's mounted to but I don't know if that means the temp of the pan is also being measured. It probably is but then again the pan is being cooled by the airflow underneath, a potential cause of false readings. All I know is my turbo M20 never gets hotter than 150 degrees, which I do not buy. Especially since I saw temps of 175 in my old naturally aspirated M20 with sensor in the oil filter housing and now Nando has the same experience. He did nothing but move the sensor and saw a jump in temperatures. Hard to argue with that.

[reelizmpro]

i've seen the temp rising to 180+ on the track.

Where exactly on the oil pan is it? drain plug? tapped on side? on top?

I'd bet your temps are down about 20 degrees from the actual temp. We're talking about your 325i right? 180 isn't hot at all for a car driven hard on the track. I would expect to see closer to 200 degrees even on an M20.

Another thought: Anyone see a coolant temp sensor in the reservoir? instead, it is right in the thermostat housing right there in the flow path.

[kishg]

drain plug.. stock m20.

[nando]

i've seen the temp rising to 180+ on the track.

put it in the block and you'll see how much higher it really is

[fporro]

Can someone please illustrate how oil flow?
so we can argue where at is it more important to know temp and press off.

Our tranis run lot hotter than engines do, right ?

[AlarmedBread]

Maybe I don't understand how an engine works, but I thought all the hot oil drains back into the pan, and then it is sucked up by the pump, spat at bearings and dumped back into the pan again. The reason I'd choose the pan as a reference point is because that is where I want to know the oil is warm. Yes it takes a while to warm up. Compare your pressure drop to when a sensor in the block says it is warm. As already stated, we want precision, not accuracy. All you need is some base to compare with so you know when something is off.

Obviously the ideal thing to do is have a remote sender unit which is not skewed by hot parts around it, puts no stress on the mounting threads and minimizes potential failure points. Mechanical gauges are great!

[nando]

if you think "a while" is basically never, then okay. have fun reading a gauge that won't even show a reading.

a remote sender is probably a good idea though, I can see how the block could heat soak the sensor. but you can't really have a "mecanical" temperature reading, they're all going to use a thermistor.

[reelizmpro]

Well what happens is the hot oil goes down into the pan where it's pooled and continuously being picked up by the oil pump into the oil filter or filter housing (and oil cooler if temps are high enough) and back to the engine bearings, etc.