Engine overheating issues

I recently purchase a Classic Roadsters Sebring 5000 that was purchased by the builder in 1988, and "finished" a few years ago. The builder never drove the car, as he wanted it to always be "new". As you can imagine, I'm doing a lot of "sorting out", but the main problem is engine overheating. The car has a mild-built 327 Chevy with a THM400 trans. Runs great, but won't stay at a reasonable temp (190 degrees or so). The temp will climb until I get concerned about engine damage and shut it down. The car has the "better" radiator, as supplied by Classic Roadsters. Has a good 6-blade fan and shroud. I replaced the T-stat (180 degree) and verified coolant flow. Engine timing is correct, the radiator cap, which is in the upper hose is good and rated 14 lbs. What am I missing? Or, is the Classic Roadsters "better/upgraded" radiator just too small. I have NO info on the heat rejection rating of the radiator. Anyone have similar problem, or ideas on what the problem is?

Thanks for any help you can give!

Where is the temp sending unit located?

I ask because my car had the same issue and had never been driven much (8000 miles in 16 years).  Turns out that the original builder had put the sending unit behind the carb where it was reading manifold temp.  The exhaust crossover under the carb was heating the manifold, as it is supposed to do, and was reading scary high temps.  This would happen after only a few miles.  I moved the sender to the intake, near the thermostat housing, and the car rarely went over 200.  Never got over 190 after I replaced the fan.  Not saying this is your problem, but I have to wonder why the original builder thought that was where the sender was supposed to go.  The factory put them in the head, but they can sometimes pick up exhaust heat and give a higher reading when located there.  Most hot rodders I know ususally put the sender in the intake coolant passage.

Your cooling system sounds like it should be cooling the car.  If the sender is in the correct location then you could have airflow issues.  All the air entering the engine compartment has to exit too or there will be no cooling.  These cars have issues with restricted air movement around the engine and out of the engine bay.  It's a shame that the fake louvers on most of the Sebring hoods were not made functional.  This would have helped airflow immensely.

When is the car overheating? Idling at a red light, in traffic or on the highway?  Easiest way to prove an airflow issue is to remove the hood and drive the car.  If it doesn't overheat, then you have airflow problems.  There are some cures that have helped others.  Side vents like the Healey Rally cars had and holes cut in the front inner fenders have helped others.

There is is one potential problem that is rare, but has been known to happen.  Up until the 80's, all SBC water pumps turned in the same direction.  When serpentine belt drives came out in the late 80's, they required a reverse rotation water pump.  There is no reliable way to tell from the outside which water pump you have, since the standard rotation and reverse rotation pumps look the same.  If a parts guy gave the builder the wrong pump, the engine WILL overheat.  This applies to the long SBC pumps, as far as I know, there are no reverse rotation short water pumps.

Also, how is your timing set up and what are you running for timing numbers? Retarded timing will cause overheating. I just went through this with the EFI LS engine I'm tuning. It was getting hot idling with 14 degress. I doubled that to 28 degrees and it started cooling better. I have had best results with mild SBC's with the vacuum advance hooked up to straight manifold vacuum. Ported vacuum is a relic of the early smog tuned engines. If you don't have vacuum advance, you should. A lot oif hot rodders won't run it, but a street engine needs it. Retarded timing will not allow all the fuel to be burned in the cylinder. Burning fuel is pumped out into the exhaust and this heats the heads and the puts a lot of extra heat into the manifolds or headers.

Hope some of this helps. Should give you some things to check.

Hotrod had some good suggestions for you. I'll add a few that I noticed on my car. Are you sure that the car is overheating and not that the temperature gauge isn't reading correctly (ie if the temp climbed to over 220 was the radiator puking fluid)? Does your fan shroud completely cover the radiator surface and does it conform closely to the diameter of the fan? Make sure all of the air that hits the front of the car goes through the radiator by sealing up any gaps on the sides or above the radiator. Consider a small 1-2" sheet metal "spoiler" below the radiator. Worst case, you will definitely cool it with a custom radiator and good electric fan and shroud combo. Good luck.

Thanks for the help Hotrod & AHSebring64. Good info.
I verified the ignition timing at 8 degrees BTDC, which is right on spec. Also verified all my temps with an IR heat gun. When i shut it off the engine heads & intake water passages are at 230* and the radiator is at 210* at the top and 170*-175* right at the bottom. Shroud fits the fan well, and temp sender is in the intake manifold right at the t-stat. I haven't pulled the water pump to check rotation, but believe it to be the "short" version which shouldn't have that issue.
The overheat happens when the car is idling, or going down the road. Last night i tried a short drive and as the heat started to build I turned the heater on & temp went right down to 185*, but then slowly started to build again until it hit 215* or so and I pulled in the drive and shut it off.
I'm stumped, but will keep at it. If anything else crosses your minds, please drop me a note. I need all the help I can get so I can enjoy this great car !!

I don't check idle timing because it doesn't matter. Here is a link to good timing management and possible problems.
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