can I hurt the engine with low temps?

[kamotors]

in slow driving in traffic my car can get to halfway, but in normal traffic or on freeway my temp is usually just a little out of the blue or about at 3/4. if it below 38* my engine temp stays in the blue. my cars cold blooded

[alpinaclone]

Uhm, a question if I may: are we positive that M20s with stock thermostats are supposed to read lower than the middle and to fluctuate? I ask because it's the first time I hear anything of the sort. As to coolant moving too fast, I wouldn't be worried. That's not how heat transfer works.

That is exactly the problem, the coolant moves by the hot parts too fast, thereby not absorbing as much heat as it could. The converse is also true when the coolant is in the radiator and we are trying to shed heat. Think hot potato, if you catch the potato and quickly throw it, it is not so bad, but catch the potato and hold on to it for a while, it will burn the shit out of you.

[nmlss2006]

Unless I strongly misremember my heat transfer classes - it's been a while - faster coolant speeds never *decrease* the heat transfer capabilities of a system. As a matter of fact, increasing coolant speed means that you have higher deltaT between coolant and surface on the hot side, which means *higher* not *lower* heat transfer.
On the cold side, since you have an actual radiator, I'd think you'd compensate amply for disadvantages.
As to engine temperature, as DaveSmed said, I realise how engines work and that was precisely the nature of my question: while I realise that newer cars have 'normalised' gauges, I also realise that BMW generally dimensioned their coolant loops correctly and had the gauges indicate the correct running temperature at halfway: there is a thermostat in the system for a reason, that is to keep the engine running at its designed operating temperature... constantly. It's the first time that I hear gauge fluctuations in a BMW being called 'normal'. Now, were these english cars from the 1960s, it would be different, but they aren't.

[kamotors]

well its not normal but lots of E30's(from what i've been told) do it and ive been driving my car for 2 years in all weather(20*-100*)and have had no problems at all.

[alpinaclone]

Unless I strongly misremember my heat transfer classes - it's been a while - faster coolant speeds never *decrease* the heat transfer capabilities of a system. As a matter of fact, increasing coolant speed means that you have higher deltaT between coolant and surface on the hot side, which means *higher* not *lower* heat transfer.
On the cold side, since you have an actual radiator, I'd think you'd compensate amply for disadvantages.
.

From Keeping Your Cool
How It Works: Cooling Systems
By Bob Mehlhoff

"If the water pump turns too fast, there are cooling losses because the water travels too quickly through the system."

Also

"Without a thermostat, the water would simply circulate too quickly and possibly even reduce power partly because more horsepower is required to drive the water pump when the restriction of the thermostat is removed."

I know it's a simple article in a chevy magazine but it backs up my theory. I have been looking for an hour for anything that even mentions how the speed of coolant affects anything, I even dusted off some old text books with no avail. But it's almost 2 in the mornig here so an article from Chevy High Performance will have to do.:D

[bwanac]

Well with greater speed you have to deal with turbulence and more friction. I am not sure how fast the coolant actually flows in their. It also might have to do with how fast the coolant can take in the heat and then give it off, too fast meaning not optimal. There are many a factors.

[DaveSmed]

As to engine temperature, as DaveSmed said, I realise how engines work and that was precisely the nature of my question: while I realise that newer cars have 'normalised' gauges, I also realise that BMW generally dimensioned their coolant loops correctly and had the gauges indicate the correct running temperature at halfway: there is a thermostat in the system for a reason, that is to keep the engine running at its designed operating temperature... constantly. It's the first time that I hear gauge fluctuations in a BMW being called 'normal'. Now, were these english cars from the 1960s, it would be different, but they aren't.

Most of the time it's that goddamn SI board coated in battery acid. The traces get a little bit of corrosion, so it bumps up the resistance a bit. Theres two additional connectors in the gauge cluster, some age bumps up the resistance a bit, etc. That and the ground nut on the back is infamous for being a trouble item, further screwing with the gauge reading. Bypassing the SI board if the option is available to you (early cars only) will result in a much more stable and accurate gauge reading.

[nmlss2006]

Alpinaclone, Dave, thanks. I'll play with the dashboard to see what I can do. And I'll see if I can bug a friend who's an expert in heat transfer to get some kind of authoritative reply.

[alpinaclone]

Alpinaclone, Dave, thanks. I'll play with the dashboard to see what I can do. And I'll see if I can bug a friend who's an expert in heat transfer to get some kind of authoritative reply.

;)

[DaveSmed]

I reread some of this thread, and I think I might have an idea....

Without that restriction that the thermostat provides, its harder for the centrifugal waterpump to keep a certain amount of pressure differential within the cooling system, leaving to cavitation which would drastically reduce system efficiency.

[nmlss2006]

And talk to someone I did. The short version is: in a normal automotive sealed circuit, removal of obstructions will always improve efficiency. Cavitation is not going to be a problem in a sealed circuit, neither is turbulence, within normal automotive sealed circuits, again.
I have to say that his wording was somewhat more vulgar, but this is the short version.