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Re: what should the temp gauge do? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 15 Nov 2004 05:59:28
In Reply to: what should the temp gauge do?, TML   [Profile/Gallery]
, Sun, 14 Nov 2004 14:45:16
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On a '97, the temp gauge normally goes up to around 8:00 and sits there. The temp gauge on all 9000s is not directly connected to the sensor - it runs through conditioning circuitry in the EDU. In later years (as Bill Davies says), the conditioning was modified to greatly reduce the gauge swings seen on older cars. Basically, it sits around 8 or 9 oclock unless something goes very wrong. This was to reduce the complaints from folks spending more time looking at the gauge wander about than driving.
As to 82 vs 89: There are a lot of good arguments both ways. As to engine efficiency - I'll say that it has no effect on gas mileage due to combustion temps. Fuel burns at very high temperatures; the heat is drawn off into the block and finally to the coolant. 7 deg C of the coolant isn't going to impact the combustion temperatures a whit.
As to speed of warm-up - the engine block is going to warm up, and pass that temperature on to the coolant. The block will warm up to 82C just as fast with a 82C thermostat as a 89; The question is how much warmer it will get. And most of the block runs hotter than the coolant temp; that's how it passes heat out.
The 'advantage' of one temp over the other is oil temp and clearances. The engine was designed to operate at certain operating temperatures, which translates into clearances and oil film thicknesses. However, due to necessary production tolerances, those clearances are pretty much the same at 82 or 89.
As to overheating, a 82 doesn't give you much more headroom. If there is a failure in the cooling system (blockage, etc), the engine will overheat just about as fast with a 82 as an 89.
OK, so what's the advantage? As mentioned before, the block runs at a temperature somewhat above the coolant temp. Certain components run hotter than that. Heat energy flows from hot to cold, and the rate the energy flows is proportional to the temperature difference. And the heat of the engine is also a function of engine load - more load, higher rpm, more heat.
Also, a decent amount of engine heat is removed by airflow through the compartment.
More heat contributes to oil breakdown, and accelerates the bad chemical reactions of the inevitable acids in the oil.
So - in cases where an engine is being run hard - either through spirited driving, heavy uphill loads, A/C on, etc, the engine will produce more heat. With a cooler thermostat, the hot spots of the engine, which run above the thermostat temp, will run cooler. The engine will also be a little cooler, so although the temperature rise during a hard acceleration will be the same as with a hotter thermostat, the end temperature point will be lower. That's the 'more headroom.' The same is true if the engine is in a very hot environment; the US desert Southwest, parts of Australia, etc.
So if you run the engine hard or live in a very hot climate, then the 82C thermostat makes sense. It only makes sense in conjunction with a 82C fan thermoswitch. If you live in a more temperate climate and don't drive the car really hard most of the time, the advantages of the 82C thermostat are less obvious.
And frankly, in a temperate climate and 'normal' driving, there isn't a whole lot of difference between the two. You can argue the pros and cons, but frankly, the effects, either rate of oil breakdown or gas mileage, are miniscule and in the noise of driving. However, I won't let that stand in the way of a good argument.
posted by 192.249....
, Sun, 14 Nov 2004 14:45:16, Mon, 15 Nov 2004 05:59:28 <-- Viewing This Message, Sun, 14 Nov 2004 18:56:43, Sun, 14 Nov 2004 19:46:59, Sun, 14 Nov 2004 22:54:30
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