135i owners: idle engine before off after highway use...

[Sindarin]

Originally Posted by Dackelone

This is WHY bmw says to let the engine idle for a few minutes before shutting the engine off after spirited driving.

Where does BMW say that?

Originally Posted by Dackelone

Also... this might also explain why a lot of 135i's just go thru some coolant and oil between OCI's.

All BMW's go through coolant and oil between services. Some more, some less. Depends on how it is driven.

Originally Posted by Dackelone

It would be BEST to "drive like a grand-ma" before arriving at your destination. AND also let the engine idle a few minutes to stabilize the turbo(s) heat temperature before switching the engine off. This is just common sense. But like the saying goes... common sense ain't so common.

How many 135i, 335i, 535i, X5 35i, X6 35i, 740i are out there being driven by some doctor/lawyer who know nothing of cars, beat the shit out of it in morning/evening rush hour with A/C on full blast in 90F heat and yet turbos aren't failing like crazy. I somehow doubt they are letting their engine idle to cool the turbo.

[WINDman]

BITD we used turbo timers, but I understand they are a bitch to install with the alarm system.. so now I just let it idle for 1 - 3 mins depending on use.

[Bill B.]

Here is an informative paper by Garrett (not BorgWarner, but concepts are the same) about water cooled turbos, and how even passive water-siphoning cooling is beneficial.

http://www.turbobygarrett.com/turbob...er_Cooling.pdf

[jkoral]

Reprint (without permission) from Mike Miller's Old School Maintenance Schedule:

----------------------------
Old school turbocharger warm-up and cool-down procedures

Many of my readers who own BMWs powered by the wonderfully powerful but notoriously problematic N54 twin-turbo engine ask how they can help the turbochargers last longer. They are concerned, and rightly so, with the cost of post-warranty ownership of the modern BMW and want to know how to approach it.

Well, you can approach it by not owning the car that long. But if you want to keep it, the best way to prolong turbocharger bearing life is to do two things:

First, use a very high quality full synthetic oil in a viscosity that can withstand tremendous heat, and change it at an interval appropriate to the product, verified by oil analysis. If I had an N54 that I wanted to keep for the long haul it would get Red Line 10W-40.

Second, practice traditional turbocharger warm up and cool down procedures. This means allowing the engine oil to reach operating temperature before spooling up the turbos (keep the rpms low), and allowing the turbos to cool down before shutting off the engine by driving gently at low rpm for several miles before reaching the destination.

Now, anticipating your follow up question, "Why doesn't BMW recommend this?" Here is why:

Back in the olden days, every car manufacturer with a turbocharged engine (BMW, Ford, GM, Mercedes Benz, Porsche, SAAB, Renault, etc.) detailed this warm up and cool down procedure. But those cars were bought and driven exclusively by driving enthusiasts who knew their way around cars. Car buyers have changed and today’s oil is better, but engine oil lubricated turbocharger bearings have not changed. The nature of turbocharged cars has changed as well. Back then, only sports cars, executive limousines like BMW’s E23 745i, and diesel-powered sedans had turbochargers. People who owned those cars could be counted upon to have a certain degree of automotive knowledge.

Nowadays, the family sedan has two turbos to go along with the automatic transmission and the baby seat. If BMW told today’s turbo car buyers they had to follow warm up and cool down procedures first off few would understand it, secondly few would do it, and third-wise a lot of them just wouldn't buy the car.

All that being said, every turbocharged engine shares one thing in common, which is that if it is in service long enough it will eventually need a new turbocharger -- two in the case of the N54.

[jkoral]

Originally Posted by Sindarin

How many 135i, 335i, 535i, X5 35i, X6 35i, 740i are out there being driven by some doctor/lawyer who know nothing of cars, beat the shit out of it in morning/evening rush hour with A/C on full blast in 90F heat and yet turbos aren't failing like crazy. I somehow doubt they are letting their engine idle to cool the turbo.

Lots. But how many of these folks are keeping their cars for 10+ years and well over 100K miles? Few if any I would guess.

And as Mike Miller wrote above, "if BMW told today’s turbo car buyers they had to follow warm up and cool down procedures first off few would understand it, secondly few would do it, and third-wise a lot of them just wouldn't buy the car".

[Bill B.]

Originally Posted by jkoral

Lots. But how many of these folks are keeping their cars for 10+ years and well over 100K miles? Few if any I would guess.

And as Mike Miller wrote above, "if BMW told today’s turbo car buyers they had to follow warm up and cool down procedures first off few would understand it, secondly few would do it, and third-wise a lot of them just wouldn't buy the car".

Good grief! Precisely because of the hordes of ignorant drivers who just get in and turn the key, BMW is using a water cooled turbo with and electric coolant pump.

Look, I would suspect that BMW probably put a little thought into their migration to turbo-driven engines, and understand their target demographic pretty well. While I'm sure they would love for their customers to buy new vehicles every 5 years, I don't think they are going to risk the brand reputation by designing an engine that is only going to last 100k miles.

Geezers who grew up on dino oil wailed when BMW went to synthetic and a 15k service interval. They gasped when they went to a 100k mile transmission fluid and coolant, and they are doing the same with the turbos.

I have not seen BMW's resale value plummet as a result.

[sochermit]

All I do with mine is when I pull into the garage I open the hood and place a fan in front of the grill and let it run. Temp outside is usually around 90 deg.

[pkimM3r]

how about getting a JDM goodness turbo timer? lol

[shah269]

=>This means allowing the engine oil to reach operating temperature before spooling up the turbos (keep the rpms low)<=
See this kind of hurts my head as an engineer...what RPM do our turbos start kicking in power?
The mornings are the worst! The evening ride home yeah i have shit to take out of the car so she will sit for a min or two with the engine on....and then cool down slowly in a heated garage.
But the cold morning shocks...what to do what to do.
With the old VW I use to pull her out, give her 1 min in the summer and 5 min in the winter to warm up and then slide her into first and puts out in second for about a mile.
She lasted 130k miles and i only got rid of her due to it being my x wifes car...that BITCH1

[RPM90]

Originally Posted by Dackelone

You SHOULD if you love your engine. In fact this is what people at the Welt tell new owners when on ED and back home.

When you go WOT the turbos can become red(orange) hot... the engine needs time to cool down at idle before shutting things off. Ever here that: Tick-TICK-Tick sound when you turn your engine off? Try running the engine at idle a bit before next time.

In the new N20 2.0 turbo, you do not have to idle down to cool the turbo.
The cooling system is designed to flow coolant to the turbo on shut down, using thermo readings. Thus if the engine is hot or very hot the electric water pump continues to flow coolant to cool the turbo. Very nice.
I can't confirm this for the N55, but the tech specs for the N20 do reference the N55 as the basis design for the N20, and both engines use electric oil and water pumps, which run as needed instead varying with engine speed.

The N54 is different altogether and I haven't found tech spec confirmation that either the oil or coolant continues to circulate to cool down the turbo's.
I do recall that there is some mechanism by which either oil and/or coolant circulate via convection to provide some cooling effect for the turbo's, thus, there is something in place to help prevent heat damage on the bearings.

As another poster commented, synthetic has 0 to extremely low ash content, thus it's not prone to "coking", which is a carbon residue that results from oil burning away and leaving behind the residue on bearings that can destroy them over time. If regular oil is left to sit on very hot bearings it will "cook/burn" and leave behind solids, called "coking".

For regular running I wouldn't be concerned about letting the turbo's cool. BUT, if you're doing a hard 1/4 mile run a few minutes before entering your garage, then it's always best to let the engine idle at least a couple of minutes, then let the systems in place do their thing.

[RPM90]

Originally Posted by Bill B.

The N55 turbo is a BorgWarner B series which is water cooled.

All modern turbo's are water cooled.
Even my 1990 Mits/Chrysler Eclipse/Laser turbo had water cooling.
But, those engines didn't run on synthetic from the factory. Most of us ran non synth and later switched to synthetic.
But, unlike modern turbo's there was no active circulation of the water once the engine was shut down. So if you ran non synth oil it made sense to let the engine idle down and cool a bit if you had been running hard, before shut down. Some even installed 'turbo timers', which simply let the engine idle for a few minutes after you shut the car off, the timer will keep the engine running and then shut down after a few minutes.

[RPM90]

Originally Posted by Dackelone

The electric water pump MIGHT be able to cool down the turbos(after a hard drive)... but HOW will that prevent oil from "coking" in the oil feed line to the turbos?

By circulating water/coolant, that is providing cooling to the whole turbo, which in turn provide cooling to the oil. So once the engine is shut down residual heat built up is being quelled by the circulating water/coolant.

Also, synthetic oils have 0 to very little ash content, and that's the material the leaves a residue (coking) behind once the oil is burned away.

The only time I'd be concerned to let the engine idle down before shut down is if I were racing the engine right up to the point of shut down. So, if you're on the track running hard and you pull in, then let the engine idle down and cool a bit before shut down for some added protection.
Other than that, if I'm doing some spirited driving, I don't do that right up to the garage, so the engine and oil has had plenty of cooling before shut down, no reason to idle.

As for the OP question, there is quite a bit of cooling going on during a highway run. You're not using a lot of power at normal highway speeds and thus the turbo's aren't that hot. As long as your oil and water feeds are working properly there is no need to idle down when coming off a highway.

[RPM90]

Originally Posted by ErvGotti

I agree with your first statement but not you second. The car will produce full boost at 1800RPM only if you're going WOT. But say cruising in third at 2400RPM with very light throttle you will not be in full boost. How do I know this? Boost guage feature on the Cobb and logs.

Correct. Turbo boost is dependent on load. Light throttle even up to 5k rpm won't result in much boost. That's why normal highway speeds don't create much turbo demand and boost, and that results in better highway MPG, because you don't need as much power to keep a vehicle moving as it takes to get a vehicle moving.

[RPM90]

Originally Posted by shah269

=>This means allowing the engine oil to reach operating temperature before spooling up the turbos (keep the rpms low)<=
See this kind of hurts my head as an engineer...what RPM do our turbos start kicking in power?
The mornings are the worst! The evening ride home yeah i have shit to take out of the car so she will sit for a min or two with the engine on....and then cool down slowly in a heated garage.
But the cold morning shocks...what to do what to do.
With the old VW I use to pull her out, give her 1 min in the summer and 5 min in the winter to warm up and then slide her into first and puts out in second for about a mile.
She lasted 130k miles and i only got rid of her due to it being my x wifes car...that BITCH1

Nothing wrong with doing what you're doing by warming it up.
But consider that the whole car, engine, trans, tires, brakes, heater, and very importantly the catalytic converter will heat up much quicker if you start to drive right away. This leads to better efficiency as you're not wasting fuel by idling. And, by driving you heat up the cat con much quicker, which allows the system to go into a leaner drive mode thus reducing emissions and fuel consumption much quicker vs idling.