I was SO wrong for SO long... egg on face, mouth'o'crow, etc.

[greg]

Today I helped Pong install his UFMotorsport relocated engine air intake temp sensor. But that is another story, one I will post on later (because we did some things differently, including not taking the bumber off.)

However we did remove the R side headlight assembly in preparation to take the bumber off if we needed to. It was the combination of the view this afforded (the end of the air intake duct is visible), combined with a look at where UFMotorosports instructions want you to mount the sensor, that I realized something that really surprised me.

I have always said here that the stock OEM M5 has cold air intake - that is, it got its air from a relatively directly flowing source of unwarmed air. This came from viewing the ducts leading to the air cleaners and following their path out and down to the bumper/front intake area.

I was wrong. The standard M5 air intake is NOT getting cold air.





The ducts snake around to just inside the front bumper and end. Any casual glance would assume they are getting air from the large "M" opening under the bumper.

But when we looked at the recommended mounting location for the UFMotorsport sensor, it became clear: there are baffles on the sides of the intake area, both the kidney grills and the larger opening below, that effectively direct ALL the air that comes in the front to and through the radiator. (UNLIKE the MAF and its associated thermistor) the radiator does a GOOD JOB of transferring its heat to the air. The air entering the engine compartment is therefore warmer than ambient air.

Although the air intake ducts are low and forward, they are on the back side of these baffles, and therefore are not getting cold air.

I am sorry for disseminating incorrect information so far and wide, loudly, I might add.

However this leads me to wonder "why" and sheds further skepticism on the engineering validity of the temp sensor relocation idea. THAT will be the subject of my next post, coming shortly.

The best part of life (and flight training ) is that you never stop learning. I would have expected BMW to try and take advantage of the best induction system they could have, but hey, I am not a part of BMW AG, so I woulnd't know the reasons.

[TCM]

All BMW E39 5 series are desgned this way. Quite amazing and confusing that BMW actually has the intake suck in hot air. Thanks for posting the picturs Greg.

[Need4Spd]

Very interesting. I would guess that BMW purposely routed the intakes to receive warmed air as part of emissions control. Plainly they could have eliminated the baffle and allowed it to receive colder, pre-radiator air, but made this choice on purpose. Is it possible to easily remove the baffles and if so, think it's a good idea? Will doing so badly compromise the radiator's ability to receive enough of a cold air flow?

As for the sensor relocation w/o removing the bumper, I'm all ears! I have a UFM kit but have been putting off the installation b/c I didn't want to get into taking off the bumper and was hoping for an easier location.

[greg]

Need4Speed -

A great question. Check out my next post, which considers the ramifications of these mods. I suspect they ARE safe, especially if you don't live in Phoenix or Saudi Arabia. But I DO have some ideas as to why BMW did what they did, and I explained my thinking in this post.

[Need4Spd]

I just read and responded to your other post. One question that more appropriately belongs in this thread. You mention sensor relocation is probably ok so long as you don't live in a really hot place. But wouldn't it be the other way around? If the car is actually receiving warmed air, and the sensor was out in the cold, wouldn't it be more dangerous for the car to think it was getting really cold air when in fact it was warmed air thru the radiator? IOW, isn't the danger created by the temp differential between actual air received and sensed air, and if so, then living in colder places would be more dangerous. Thus, you'd be saying relocation is probably ok so long as you don't live in a cold climate?

[V-10 4 Me]

I looked and in my install following directions, the sensor was located within the schroud fore of the radiator, and below it. Greg, are you saying that this is not the best spot to put it?

Back part of sensor:


Front part of Sensor located within cold-air schroud:



IMHO, the Bumper was only 2 large screws and to panels under neath that had only 4 bolts. It was easy-peasy.

Sam

[greg]

OceanSide - I'm not passing any judgement. In the location where you put the sensor, it is reading the temperature of air outside the car, not the warmed-by-the-radiator air the engine breathes. Much deeper explanation in the next thread I posted

[ColinM]

I doubt the air directly after the radiator would be *very* warm, just slightly warmer than ambient esp. at higher car speeds. The high volume of air going throught the radiator does the work of cooling the engine not so much each individual 'gallon' of air.
Imagine adding 1gal of 10deg water to 1gal of 100deg water to cool it. The result would be 2gal at 55deg and the cooling water did a lot of 'work'.
In the radiator the temps probably goes from 90-50deg (guess) while the very much larger volume of air going from 20-25deg (guess). Air within the engine bay gets heated by the block etc so gets to be much more than 25deg. So air after the radiator is warmer just not very much.

I would like to see some real measurments. Maybe use three temp probes, one just in front of the radiator, one just behind it, and the last next to the black plastic induction piping between the MAF and plenum to measure engine bay air temp. Then take the car out from cold, warm it up, do a hard run, slower running to cool down a bit then idle for 5 minutes.