Resolved the difficulty in getting appropriate auto-operation of the electric radiator fan.

('93 964 fan + relay installed in '89 245 NA, auto tranny)

Changing from a 92ºC thermostat to an 88ºC Vernet did the trick. Theories re. clogged radiators didn't pan out; they both "passed water" very well with the "turn-on-end" garden hose test. Currently using a newish Blackstone, has metal sleeves in the hose necks.

Current setup uses a 93º/88º switch in the upper hose and an 82º/77º in the lower hose. Either of these alone will switch to keep the temp gauge needle near center. The upper hose switch comes on a little earlier and so keeps the needle centered a bit better. Either fan speed seems OK for traffic lights + idling type situations.

Why did this solution work?

Problem: When idling with a 92º t'stat, the hot coolant (93º-96º or more) running via the bypass channel lets the engine get hotter (gauge needle goes up) before the lower hose switch kicks in. With the t'stat opening gradually + slowly, some pretty hot water is going through there before the no-airflow radiator output is hot enough to trip the lower hose switch.

Solution: 88º thermostat passes cooler fluid, notably via the bypass channel. T'stat and bypass channel rarely reached 93º in today's road test. This doesn't cause the temp gauge to go up. At idle, upper and lower hose switches both tripped before the gauge needle rose. Lower hose switch did let needle go up about 1/8 inch or less.

Using a switch in the upper hose with a 92 t'stat was a partial solution. Works OK for idling, but not on the highway. Coolant through a partially open t'stat is over 92º, probably often 95-97º, and so trips an upper hose switch even at moderate throttle. I saw that often, right after getting on a highway, and it generally stayed on in warm weather.

Even with an 88º thermostat, the upper hose switch (93º/88º) does come on occasionally during hard accelleration at highway speeds. I can live with that. It happened 3 times on the 78 mile drive to work, always on hills. Twice on highway accellerating hard uphill (testing to see if I could trip it), and once on a small road after a short stop at a light where the idling hadn't yet tripped the fan. If I wanted to cool the engine during hard highway accelleration, I'd run the fan on high speed. Maybe if I had a turbo or a 6-cyl. I think that for the 2.3L NA, low speed fan controlled by the upper hose will work well, as many have suggested. What these folks missed was the interference from my 92º thermostat and the bypass channel.

I'm concerned that the lower thermostat will cost me in fuel economy. I was getting 26.5-28.5 mpg (US gallons) with 92º t'stat and manually-assisted fan switching. Looks like I can go to full auto fan switching with the 88º t'stat, but it's only a truly good deal if the mpg's stay up there. If not, I'll be looking for a way to switch via temps read off the pump housing, which will give the temp of the coolant mix going into the engine. That's what a fan clutch seems to be reading. Or possibly via the temp-gauge sender, but it's "busy" supporting the gauge.

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[aka Sophie's Maintainer] Sven: '89 245, IPD sways, E-fan conversion, 28+ mpg - auto tranny. 850 mi/week commute.