[mjposner]

My M235i hits 108c at idle, dropping down to about 80c cruising. That seems awfully hot to me. Is this normal? Outside temp was 83f.

[jadnashuanh]

Most (all?) BMWs temperature gauge shows oil temperature, not coolant, and oil temp is often hotter than coolant. Those temperatures wouldn't both me at all. Coolant often can run above boiling...which is why it has a pressure cap on the system to raise the boiling point sort of like a pressure cooker, to keep things liquid rather than turning into steam.

[one1er]

That's normal! I can't remember the exact explanation, but engine temperature will vary depending on load, and the other way round than people might think. It actually lowers as you load the engine to about 80ºC, and rises when you're just demanding little or no effort from the engine!

I first saw this on a MINI JCW and was really mind boggled...an engineer explained me the process but I really can't remember and reproduce it well...anyway, something to do with consumption and performance!

P.S. The temp is for coolant, not oil.

[pikcachu]

It's cause what cools the engine is the air going through the radiator.... if you are stopped there is only a little air from the fans but if you are going at 40mph there is a lot more air cooling your radiator than when stopped....

also coolant won't boil till around 250F..... that's why you put coolant and not just water

[overcoil]

Originally Posted by pikcachu

It's cause what cools the engine is the air going through the radiator.... if you are stopped there is only a little air from the fans but if you are going at 40mph there is a lot more air cooling your radiator than when stopped....

also coolant won't boil till around 250F..... that's why you put coolant and not just water

I use anti-freeze in the summer for corrosion protection and in the winter so it won't freeze

[pikcachu]

ya it won't boil and won't freeze either....

[Delnari]

During my mountain runs last weekend I was seeing water temps 215-230 degrees F (up to 110 C). Never got any higher no matter how hard I pushed it. The outside air hit a high of 83 degrees F. Seem high but since it never moved any higher I figure that was normal. I was using an OBDII reader for my temp display.

[mjposner]

"Most (all?) BMWs temperature gauge shows oil temperature, not coolant.." Thanks for accusing me of being an idiot...but with all due respect I know the difference. I had both the secret gauge and Torque running to confirm WATER TEMPERATURE.

I had not expected over 100, but it appears that up to about 110-115 is acceptable.

[Meeni]

Coolant temp dropping under 100 is not normal and the sign of a defective T-stat. 108 is perfectly normal operating temperature.

oil temp varies more, 100+ is also normal.

[adrianv]

Originally Posted by pikcachu

It's cause what cools the engine is the air going through the radiator.... if you are stopped there is only a little air from the fans but if you are going at 40mph there is a lot more air cooling your radiator than when stopped....

also coolant won't boil till around 250F..... that's why you put coolant and not just water

That is isn't why you mix antifreeze with water. Water boils at 122C/250F at 2 ATM of pressure. Since most automotive cooling systems are pressurized to at least 15lbs, that is where most of the boilover protection comes from and while it is true that ethylene glycol's boiling point is much higher than water, it's a pretty crappy coolant. The only reason they put it there is for the freeze protection. It is also why you should use as little as you can possibly get away with based on your climate. If it never freezes in your area, straight distilled water is superior.

[Delnari]

+1

I learn from racing that water is king in the radiator. In fact, our track motorcycles are forbidden to run anti-freeze in their bikes as it creates a slippery mess on the track.

Not sure if "Water Wetter" is really better as advertised, but water is in a pressured coolant system is still the best way to run cool.

[overcoil]

Straight ( distiller ) water - dosen't that lead to corrosion issues ?
You can actually use an ohmmeter to check anti-freeze PH - so I was thinking corrosion was a big issue.
As with Water Wetter dosen't anti-freeze reduce cavitation around the head - and in return keep head temps lower?

You

[Spitfi-r]

With a properly sized and functioning cooling system the coolant temp will be determined by your thermostat while moving at speed and by the temperature switch for your electric fan at idle.

On my track car I picked the specific temp thermostat and temperature switch to get the temps that I wanted. For this reason my car runs warmer at idle than it does thrashing it on a race tack on a hot day.

[mjposner]

"Coolant temp dropping under 100 is not normal and the sign of a defective T-stat. 108 is perfectly normal operating temperature."

I see 100-105 at idle, drops to about 80 as I go drive...tstat defective? Can anyone else check and see if they get these numbers?

[Delnari]

Heading back out to the mountains later today for 3 days of fun. Will see what startup (idle) water temperatures are. Monitor off and on for peak temps and average commuting temps.

[scanspeak]

Isn't it true that normally aspirated engines run at around 95 deg C? That would make them about 10 deg cooler than the turbo engines.

[benneyb]

Originally Posted by mjposner

"Coolant temp dropping under 100 is not normal and the sign of a defective T-stat. 108 is perfectly normal operating temperature."

I see 100-105 at idle, drops to about 80 as I go drive...tstat defective? Can anyone else check and see if they get these numbers?

MJPOSNER, I can confirm. I've been riding around during my break-in period using the hidden menu, and I see water temps go from 79 - 108C, and oil from about 88 - 118C, up to 120C for a few seconds. Water temp very much tied to air going through the car, oil temp I'm damned if I can determine the tendency/behavior of. Much more fluctuation than I expected.

[mjposner]

Thanks Bennyb. We recently went through a stuck open tstat on or cayenne. The fake gauge said 185f, but the check engine light was on and the obd-ii port was reporting a steady 165-168 fully warmed up.

[Steven1077]

This is all getting very confusing, can we stick to either c or f? lol

[Delnari]

Startup and idle after 5 minutes was 215 degrees F.

[jeffclev]

Originally Posted by mjposner

"Coolant temp dropping under 100 is not normal and the sign of a defective T-stat. 108 is perfectly normal operating temperature."

I see 100-105 at idle, drops to about 80 as I go drive...tstat defective? Can anyone else check and see if they get these numbers?

I checked my M235i yesterday with the hidden menu, on my commute home. Freeway speeds, low load, coolant was 107-109. Oil kept climbing to about 112C. A couple of quick 0-40 bursts once off the freeway got the oil to 117C but the coolant stayed at 108-109. I would think 80C after the engine is warmed up would be a bad Tstat.