Hello, I have a 1985 Corvette and I've been trying to hunt down an overheating problem. It is highly modified, TPIS Miniram Intake Manifold, Flat Tappet ZZ409 camshaft, 58mm Power Products throttle body, Hedman Longtube 1 5/8th headers, Dynomax true dual exhaust with Dynomax Ultra Flo Mufflers, D.U.I. distributor assemblly, MSD 8.5mm low resistance ignition wires, K&N Air Filter, Cut air cleaner, EGR delete, AIR delete, 3.75:1 rear gears, Speedometer Calibrator, Heated O2 sensor conversion, moates.net computer chip adapter, descreened MAF sensor, AFR 195 Eliminator heads, AFR Gauge and Wideband O2 sensor, Adjustable Fuel Pressure Regulator set at 60 PSI, American Eagle Performance Radiator, Throttle body coolant bypass, maybe some other things I'm forgetting.

Anyway, it started overheating after I installed the new heads. The heads have a 65 CC combustion chamber, I am running 10:1 compression, 0.024" deck height,0.028" compressed head gasket thickness, 0.052" quench, +4 CC valve reliefs in pistons.

The motor is a 350 L98 generation 1 small block Chevy with fuel injection.

I replaced the Thermostat with an OEM Thermostat, new performance radiator, passes compression test, passes cooling system pressure test, passes cooling system evacuate/vacuum test, passes cooling system exhaust gases test. Bled air out multiple ways. Cooling fan comes on when it supposed to. Tried hotwiring the secondary fan, no change. New CTS new Temp Sending Unit.

It only overheats when I take it for a ride, and it is intermittent. I located a misfire on cylinder 1, and cylinder 1 does not pass a power balance test. Ignition wires are about 6 months old and cylinder 1 has about 120 - 130 ohms, same thing as cylinder 3, and cylinder 3 DOES pass a power balance test.

New distributor, ignition module, pick up coil, cap, rotor, coil.

When it misfires, I can feel it, and it doesn't over heat, the temperature climbs slowly and comes back down. Then the other times where it DOESN'T misfire, I feel more power in the pedal, and then it overheats under normal driving, any type of driving actually. I have to pull over, shut it off, wait a minute, then start it up again and then the temp will start dropping down.

I'm am still tuning it by the way. Air/Fuel ratio is all over the place, some times rich, some times lean.

I also tried retarding the timing by 2 degrees, no change.

Any help is appreciated. Asked all around, no one has any ideas. Thanks.

Also water pump was replaced last year by previous owner.

 

Who tuned it? Are you still running a 870 ECM?

 

Solomon at lt1pcmtuning.com tuned it. I only sent him one data log so far and he made a little change but I think it was an inaccurate data log. And yes I am still running the 870.