I have been down the ROAD you are on. Same over heating. It over heated everytime I went on HWY. I changed out radiator to a new one and it stopped the problem about 80% of the time. The remaining issue was the timing. I had no vac advance at idle, the vac canister on the dizzy was dead. Then the issue was timing was off at higher speeds, not getting the 32-34 degree of timing at higher rpm's. I had all that set and fixed. My last issue was that my carb was old as hell, prob never touched. It was running lean which I am told can make a car run hot. So that is currently out being rebuilt.
Not really. If the radiator is removing heat from the coolant, of course the inlet tank will be hotter than the outlet tank. The coolant is giving up heat as it passes through the tubes. OTOH, if one or more tubes are "cold", there's no flow of heated coolant keeping them warm. Those tubes are plugged or heavily restricted. Sounds to me like there's a timing advance problem, (30 degrees "all in", but we don't know the RPM, and no mention of how the vacuum advance is working) along with a potential radiator problem...but we don't have enough data to be sure. And, as always, missing or defective air ducting in the engine area, including but not limited to any air dams and the seal at the back of the hood; improper air/fuel ratio, dragging brakes, excessive exhaust heating of the intake manifold...there's plenty of other stuff to consider.
I had similar issues this guy is. My main issues were clogged radiator and a bad vac adv and timing was off. Waiting for carb to get back from a rebuild to see how she does after that fix. When I am done, all in, TC, TC Cover with oil pump from TA, WP, Tstat, Radiator, New electronic distrib, coil, radiator, all the hoses, clutch on the fan, alternator. I know some of that is not needed to fix my overheating, but since this car has been sitting around a lot through the years I just went ahead and did a lot of stuff.
Dizzy is brand new and yes my vacuum advance works. When it showed 30 on the gun the engine was rev up. I know timing not the issue....My carb was rebuilt a few months ago so i ruled that out. Once my radiator gets here im install it and update this post. Im also going switch out the 195 thermostat for a 160 thermostat just to have a lower temp
I had the EXACT same problem with my 455; only began to overheat at freeway speeds. After much troubleshooting it turned out to be the stock Quadrajet carb. As the engine rpm's increased the fuel mixture leaned out causing her to run hot (we put a tester on her in the garage to verify). We tried to adjust it but it would never stay stable. I ran a test with a Summit carb and had no issues; so that carb is still on her today. Once I have the time to rebuild the Q-carb I'll look at putting it back on. Good Luck! -MIG
If you have seen me around you know I have had over heat issues also, most of the time HWY related or right after a HWY run. After all I did to the car, the last thing looked at was the carb. Just a little 2 barrel but the shop told me it was running lean and could benefit from a rebld. I should be getting it back next week and hope it is the last step to a car that I can drive. I started out with a leaky TC cover, so replaced that. New TC, new oil pump, water pump all from TA perf while I had it apart. New hoses, new tstat, new rad cap, radiator, new dizzy, and final refurb carb, plugs and wires, new heater control valve. Throw all new vac lines on it and hope I can finally run her on the hwy and have no issues.
My qjet was just rebuilt a few months ago. So i hope thats not the issue..My radiator will be here monday and i will install it asap. Hopefully that fixes the problem..
Qjet's are finicky. I've rebuilt them myself in the past, but at the time I was just returning from a deployment and preparing to move and didn't have the time. My mechanic has had enough issue in the past with them he won't touch them anymore; hence the good deal he made me on the summit. Be sure to let us know how it turns out. -MIG
Ok update. The radiator came today and i installed it. Took it on freeway for almost 45 minutes and never got above 176 on my gauges and 120 on radiator cap temperature. So i should be good. I will drive it more tonight and its hot and humid out today 89 degrees.
