ilko

This is just a hypothetical question. Modern water-cooled cars will never warm up if you just start them up and let the engine idle. Is that the case for an air-cooled 911? I'll go even further, is there any danger of overheating?

Irishdriver

,,,duh,,,,of course modern cars will warm up......unless your thermostat is broken....?

and air cooled cars can warm up too - and they should not overheat unless something is wrong.

was this a trick question? have I missed something?

of course you should not just leave a car to idle until it's hot for enginnering and enviromental reasons !!!!

ilko

Duh, the water temp gauge on your Boxster goes up to the middle reading, does that mean your engine is warmed up?

Irishdriver

Go on, I'm curious to know what theory you're working on here.

What does a temperature gauge really measure then?

flashgordon

Coolant temps may come up fairly easily at idle, but oil temps take much longer. Your car may not be warmed up even if the water temp is up to normal.

ilko

The engine is really warmed up when the oil has reached 200 degrees F (around 90C if my math is correct). Coolant warms up much faster as flashgordon pointed out, but that doesn't mean that the engine is warmed up.

On my Audi I have a water (coolant) gauge and an oil temp gauge. The water temp goes to the middle reading pretty quickly if I start the car and let it idle. But the oil temperature won't even go past the low (150 F) reading if the car just idles at 700 RPM and is not being driven. That's how I know that the engine is not warmed up. Modern engines are more efficient and produce less heat at idle. That's why I wanted to know whether an air-cooled 911 is similar in that regard or not.

Irishdriver

now I think I understand what you're on about.........

In the cars with an oil cooler circuit there should be a thermostatic switch as well so the oil does not go through the cooler until it is warm. In racing cars it is comon practice to put an electric heater in the oil to get it up to temperature.

Your oil temperature requirements is dependent of the viscosity of the oil - if you have the right oil in the car then it should be warm enough during tickover. it will not be as warm as under full power hard usage but that is normal. This is why you're told to let your turbo idle for a few minutes after hard driving. If you put gearbox oil in the engine I would recommend that you get it really warm before driving hard.

So your question then comes back to when is a car warm enough - warm enough for what and what is warm enough?

Audi think 150F is warm enough but you obviously don't. Why do you assume 150 is wrong. It is possible that your oil reached maximum viscosity at 150. Modern oils are very good. Audi have designed the system carefully as it is critical to get the car to optimal running temperature for emission control.

Or have I missed the point again...?

ilko

Thanks for the explanation, I didn't know race cars have an oil heater, that's a cool feature! As far as the 150F mark, that's the bottom of the gauge on the Audi. When warmed up and driving on the highway the temp goes to about 200-210F. If I really push it and shift at redline it can go up to 250F (that's the middle reading).

My thinking of normal operating temperature is around 190-220F (90-105C). At that temp any water condenssation in the oil will vaporize. Here's a photo of the temps on an air-cooled 911. The oil temp there goes to the 9 o'clock mark and that's the standard operating temperature.



And here are the explanations from p-car.com:

At 87c/188F (per Bruce Anderson's hi-performance book) for a 964, 83c/181F for a 993 (per manual), the oil cooler thermostat opens and oil starts to flow to the cooler.

At 212For 230F (993), the thermosender—via the control unit—starts the oil cooler fan in slow speed.
At 239F (964), the oil cooler fan switches to fast speed. The 993’s fast-speed set-point is unknown.

Desouza

Originally Posted by Irishdriver
Go on, I'm curious to know what theory you're working on here.

What does a temperature gauge really measure then?

srf506

It measures the temp of whatever fluid is flowing by it. Its not an indication that the motor has "warmed up" to the point it is heat soaked and all components are at or near the same temp. As pointed out, on start-up most fluids are diverted by the thermostat until they are warmed up enough to cause it to open. The thermostat is calibrated with margin to ensure that the engine is not allowed to overheat before the "cooler" fluid is allowed to flow to begin to soak up heat off of it.

I guess I'm still trying to figure out what's the point of all of this? If the car's systems are functioning properly you should just follow the manufactuer's recommendation as to the "warm-up" procedure. If he says let it idle until the temp guages are at some level, or hold it below smoe number of revs for so much time or distance, than just follow those recommnedations.

NeufCentOnze

Hi Ilko,

Your picture of an oil temp gauge starts at zero Fahrenheit (-17.8 Celsius). Are we supposed to park our cars inside a freezer between runs?

VGM911

Regarding what our temperature gauges are telling us:

I've read that coolant system temperature gauges from some car manufacturers are not intended to provide an accurate/precise temperature reading, but instead indicate if your car is operating within a normal operating range of temperatures. These gauges are said to be "buffered."

As I understand it, the needle will move to a certain point on the gauge face (i.e., the middle area), and will stay there as long as the coolant temperature is in within a normal operating range.

It will move significantly to the right only if the coolant exceeds the normal temperature range. In essence, these buffered gauges tend to be little more than warning lights.

It has also been my experience that the best way to warm up a car is not by excessive idling, but by gently driving it once oil pressure builds up, which happens in a matter of seconds. This adage applies both to air-cooled cars and water-cooled cars, both of which I've owned.

VGM911

Well said, srf506!

srf506

Thank you VGM911.