At idle my car runs around the half way mark, but when I take it out on the road it heats up past about 3/4. This can't be good? If I am cruising at about 65 with the A/C on it overheats past the H.

In the rain, or at night it stays around 1/2.

Can someone give me a few pointers?

 

check your fan clutch per the FSM or haynes manual. also when was the last time you flushed your radiator? or changed the hoses?

 

more info. Fluid was flushed 2 weeks back.

Fan is electric (pretty much always on).

Hoses are good, inspected 2 weeks back. System was bled for air. I know the radiator is not the stock one. and the E-fan doesn't cover the whole rad.

Could it be the Rad can't keep up? System is good and pressurized so I can't see the waterpump being defective.

 

Have you checked your thermostat to make sure it opens properly?

 

is there a particular way to 'check' the thermostat besides just removing it and checking it that way?

I will have to consult the hayes manual.

Thanks.

 

Check your belt tension, also. It may be that at high rpm your water pump belt is slipping

 

just remove the thermostat anyway your running the e-fans off of an electric thermo unit anyway right? also have you pressure tested the rad caps? most people overlook this but it could cause the same symptoms as bad thermostat.

also, what temp is your switch at? and have you tested it? maybe you got a deffective themo switch.

 

I've always heard to toss it into a pot of boiling water and see if it opens all the way.

 

I know the rad cap is good. It looks like all signs point to the thermostat or the e-fan thermo unit, I'll check those.

Thanks.

 

first off I don't think I would remove thermostat
some efi cars ecu reads engine temp to enrich/lean,
fuel/air mixture at colder readings...
what I am getting at if you remove thermostat
the temp sending unit will read cooler longer
and ecu will add more fuel trying to bring
engine up to proper operating temp..
often refered to as closed loop/open loop
on some efi cars.....maybe not RX-7s though..

 

Overheating – check list

1) Replace the thermostat. Make sure it fits. The spring loaded disc on the stat must close the bypass port, or guess what?
2) Replace the radiator cap. Low pressure = steam bubbles = spit out coolant.
3) Look for leaks. (same symptoms as #2) Some can be very hard to find. You may have to pressure test it. A common failure spot is the 3/8” coolant line that runs from the top of the rear housing (under the intake runners) to the throttle body, to the BAC, to the water pump. Another one is the heater hose under the oil filter.
4) The fan clutch will slowly start slipping as it ages. The fan should pull really hard up to about 4k when the motor is hot. It should maintain about 4k as the motor revs higher. Sometimes you can get more life from it by bending outward the bi-metal strip on the front of the fan clutch. The cut-in for the series 4 fan clutch is gradual – it pulls some even when cold. The series 5 fan clutch is more on/off.

 

Yes I saw you had an electric fan..

So - here is some more stuff to look at.
My 87 was showing overheating symptoms. What finally fixed it? Would you believe the water pump housing? The aluminum casting behind the pump was eroded by the turbulence of the high revving pump and the previous owner using plain water for some time. The bypass valve seat under the thermostat had about a 4mm chamfer eroded away, and there was a 6mm hole eroded through the internal wall between the inlet and outlet side.
All this bypassing gives symptoms like a partially blocked radiator. I fabricated a repair with Bondo Marine Epoxy Putty Stick. It was running cool when I sold it a year later.