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Now it all makes sense!
Posted by EDZ (more from EDZ) on Fri, 23 May 2003 14:54:26
In Reply to: Sorry for confusion..., Micah in NC, Fri, 23 May 2003 14:27:18
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> When cold-starting on a cold day (say, ambient temps below 40-45°F) the
>engine coolant (which acts on the thermoswitch) warms up SLOWER than the
>metal of the exhaust manifold. By the time the coolant reaches 69-77°F
>(black switch threshold), the O2 sensor has already reached operating
>temperature for some time--nothing bad happens when CIS computer starts
>"listening" to the O2 sensor.
Bingo! Now I think I understand! So the design flaw is really not that the switch threshold is low, but that it reads the coolant temp rather than the exhaust manifold temp, and makes an extrapolation (that the manifold is, say, 40 deg hotter than the coolant) which isn't valid when the engine is in a cool-down phase.
I would say this is not really a Sweden-US issue but an outright design error; after all, it gets above 60F pretty often in Sweden. If everything is in equilibrium (i.e. a "cold" start), the coolant-manifold temperature extrapolation is likely to be right even when the weather is fairly warm -- if it's 90 outside the exhaust manifold will hit 100 very quickly. The problem would presumably happen only after a few hours of cooldown with moderate ambient temperatures, when the large, non-conductive coolant reservoir stays warm but the low-mass, metal exhaust manifold cools down faster, leading to a temperature inversion between the manifold and the coolant. The red switch then doesn't fix the problem so much as get around it at the cost of defeating the fuel-saving feature of the CIS for a longer time. OK, so I'll look for a red switch.
posted by 131.225.56...
Posts in this Thread:
- Cool start problem, EDZ, Fri, 23 May 2003 09:21:26
- Radical, but it worked..., MS, Fri, 23 May 2003 21:24:58
- Re: Cool start problem, Todd 83-900T, Fri, 23 May 2003 11:45:26
- A couple of things to mull over... (long), Micah in NC, Fri, 23 May 2003 10:55:40
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