JC, here goes:
1. Yes. My 3.4 has no problem staying cool with a 2-row aftermarket radiator. 70 mph on the cruise control in 5th, going up I-5 out of Portland, Ore while pulling a 2000+ lb load, in 85+ deg F summer heat !! And barely nudging the temp gage towards 1/2.
2. You probably have a plugged radiator and the all the water is being blown out the overflow. You can easily lose a ton of water this way if you're running on "H" all the time (which ain't so good for the motor, natch!!). Pull your radiator out and have it flow checked, you'll probably find it's at least 75 percent clogged. Try
www.radiatorbarn.com for decent deals on a new rad. BTW to properly 'burp' the air out of the system, you need to point it uphill and run with the cap off (starting from cold, of course!) for a few minutes. Then top off. Also be sure you use the correct thermostat (190-195 deg). You can verify the fan clutch is working, as when you're quite hot under the hood the fan should be moving like crazy and you'll definitely hear it blowing. If it's just lazily spinning around, the clutch is shot.
3. Same heads as a 3.4, you really don't need to worry about using the old 2.8 heads. If you want to rebuild them for whatever purpose, you should have the machine shop check them for cracks.
4. No! A properly working clutch fan is more than adequate to cool your motor in 'normal' applications. See #2 !
5. Pretty much. You may get a small benefit from the larger-throated TBI but obviously no way you'll ever flow to full potential without boring the intake. Quite easily done once it's off the motor. Just get a base gasket from a GM 4.3 TBI and use as a template to lay out the holes. Take it to your friendly local machinist and you'll get it back all nice and pretty. BTW tell the parts counter guy you've got a '90 S-10 with 4.3 TBI and it'll make it a lot easier. BTW if you don't bore the intake and do use a 4.3 TBI, you'll have to run some kind of spacer as the 4.3's throttle plates will hit the intake when opened. When you order gaskets for the conversion, you can use 2.8 or 3.4 stuff. You may find good deals on 2.8 gasket sets on eBay. The head gaskets are different of course, but everything else will pretty much fit.
And regarding your oil cooler, nice to have but seems to be a real pain if there are problems with the hoses. As long as you have oil pressure on your gage I don't expect blocking them off has harmed anything.
HTH..........ed
