Engine Temperature vs Longevity

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Engine Temperature vs Longevity

Post by Grumpyjohn1957 » Mon Apr 01, 2024 11:27 pm

Stumbled across a web link discussing BMW engine running temperatures and reliability.


In a nutshell the article suggests lower engine temperatures are better for longevity.

I get that higher running temperatures improve emissions and possibly economy but what effect does temperature have on individual components? Plastic chain guides, valve stem seals, O rings, rubber gaskets etc. The article suggests engine temps of 105-108’C or more not only quickly degrade the elastomers and polymer components within the engine but can also affect the transmission.

Checking the running temps on the B5 I observed the following.

In default comfort mode, sitting stationary or moving in slow stop/start traffic the engine consistently runs between 105/108’C. Upon moving off at speeds up to 30mph + it drops fairly quickly to 102/105 before rising back up and stabilising once more at around 105/108’C.
It seems to remain within this band regardless of speed or how much or little hoof is applied.

Cruising at a constant 50mph I tapped the stick into M/S.
To my surprise the engine temp quickly dropped to 85’C and stayed in the range 83/90’C.
Putting the stick back to drive immediately increased the temperature again.
I repeated the experiment using the sport button instead of the stick.
Sure enough the temperature dropped to 83/90’C range again stabilising mid-point at 85/87’C. Switch back to comfort and it rises.
Even sitting on the drive for a prolonged period at tick over the mode dependant behaviour was the same. The fan kicked in briefly for a minute or so at one point but the temps remained steady. This behaviour is something I’d never noticed before.
I think the N63 just uses an electrically controlled thermostat as opposed to a traditional wax job. Therefore temp control must be programmed into the engine control unit.
Alpina say they upgrade the physical cooling system components, do they also program the temperature management differently to other BMW V8 cars like the 550i, M5 and M8?
More importantly, does running cooler really help preserve the engine as the article suggests?
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Re: Engine Temperature vs Longevity

Post by Norrie » Tue Apr 02, 2024 12:58 pm

This is interesting and to perhaps explains why I was told that ALPINA vehicle's should not be left to idle? I dont use the car as a commuter vehicle and naturally try to avoid heavy traffic, at my 132K I think that my individual user style will produce longevity? However, anything can fail at any time.
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Re: Engine Temperature vs Longevity

Post by Henry » Wed Apr 03, 2024 10:02 pm

I changed the thermostat on my 4.6 to a 92c thermostat many years ago and converted to electric fan. Never see temperatures above 96c and never heard the fan cut in while driving, it will cycle a few times after the vehicle is switched off. Presumably normal thermo syphon action taking place. Before changing I was plagued with small coolant leaks, which I put down to age of components especially rubber pipes. The leaks went away due to the reduction in pressure in the system. Still not replaced a coolant pipe at 175k. Had the effect of reducing the gearbox oil temp a little as well. Although I have just had a 3k gearbox rebuild last month. There was a vast difference in the hardness of the coolant pipes and sheer heat coming from the engine. I put a 10 ohm resistor in the map plug to not show faults.
Edit, I also see a drop in temperature if I put my foot down like 96 to 90 I just put that down to more air passing through the rad.
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Re: Engine Temperature vs Longevity

Post by JohnW » Fri Apr 05, 2024 8:53 pm

I know the N54 engines in all the E90 B3’s run very hot. Some tunes run lower temperature plugs and bigger oil coolers.

Not looked into it myself but it must help the plastic parts as you would be bringing the temperatures far under their maximum tolerance level.

I noticed the cooling fan on mine runs readily after around 3-5 mins of standing traffic depending on weather and how I was ‘pushing the loud pedal’ before. I religiously change the coolant according to service schedules. The heater matrix does warm up quickly after a cold start too.
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