overheating problems

[evilzee28]

 I've got a rebuilt 406 cu in small block '69 Camaro with some overheating problems. It's got a 4 core rad on it from a big block car, an electric fan which comes on at 212 deg or manually if you want. The car seems to run around the 200-210 deg mark on an average temperature day. It has a new Weiand Hi Flow ali water pump & the rad seems to be clear after flushing water through it with a hose. The car seems to be running very hot & when a laser temperature gun is pointed at the hoses it has a temperature of 200 deg going into the rad & around 205 deg coming out on tickover!!! The fan pulls warm air through the rad but doesn't seem to lower the temperature. The car has been run without a grille fitted to it, so plenty of air can enter the front of the rad as well. When the cam was being run in, in the garage it actually burst a top hose (it was a second hand one thought of undeterminate age). When I took it out the other day the top hose blew off the rad

The rad is 530mm wide, by 430 mm deep & 70 mm thick. The tank with the rad cap on is 100mm X 430mm X 70mm. The other tank is 40mm X 430mm X 70mm. It's got a 14lb rad cap. The thermostat has A180 & 8.023 stamped on it (it's an American made one) I assume that the 180 stands for degrees?? It has a 7 blade, 14" dia, Bosch thermostatically controlled fan which comes on at 212 deg. I can also turn it on manually.

I drove the car today ( a distance of about 8 miles) & it boiled over. It was running around the 215-220 deg mark, but I don't think that the fan cut in. (There was no grille or front bumper on it so I would have assumed it should have stayed cooler just with the airflow as the radiator had no obstructions really to the airflow)

Once it cooled down & was topped back up again, I turned on the fan manually & it ran at just under 210 deg constant, but it's not been a warm day.

Any thoughts would be appreciated. It's got a manual trans & has around the 500hp mark, maybe a bit more. It has a circle track race cam, 11.1 comp, ali heads, single 4bbl. To all intents & purposes it's a street legal circuit racer. My friend has a "historic circuit race mustang" built to a similar spec & has no problems & runs around the 180 deg mark. We swapped his rad into mine & it still ran hot.

Could it be the thermostat?? what temperature one should I be using?? Is it the right rad cap at 14lb's?? Should it run an expansion tank?? Any help or advice would be appreciated as this is driving me nuts. Many thanks in advance, .....Nige
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[JohnZ]

The coolant should be 25*-30* cooler coming out of the radiator than it is going in if the radiator is doing its job and has adequate airflow going through it. Most aftermarket electric fans are hopelessly inadequate, especially if they're the round type - they only pull air through the portion of the radiator enclosed within the circle, so at least half of the radiator core surface isn't seeing any airflow at all, thus no cooling is taking place.

They didn't overheat when they were new, because they had a full fan shroud (which pulls air through the entire core, all the way out to the corners), a big fan, and a clutch. Most attempts at "re-engineering" the cooling system with Summit catalog junk are dismal failures. The production cooling components were designed and developed as a complete "system", and they do the job if all the pieces are present and in good working condition.

Put the factory clutch, fan, and shroud back on (and seal the radiator to the support and the shroud to the radiator with foam seals so all the air is forced through the radiator instead of around it), and your cooling issues will disappear.

[evilzee28]

Thanks for the advice John, it's appreciated. I've been told that just with airflow (the car has no grille on it at the moment) at speed, (55mph plus) the engine should run around the 180 deg mark without a fan. Right or wrong I don't know. I just can't understand why after the water's been through the rad it's no cooler but hotter, thanks.....Nige

The coolant should be 25*-30* cooler coming out of the radiator than it is going in if the radiator is doing its job and has adequate airflow going through it. Most aftermarket electric fans are hopelessly inadequate, especially if they're the round type - they only pull air through the portion of the radiator enclosed within the circle, so at least half of the radiator core surface isn't seeing any airflow at all, thus no cooling is taking place.

They didn't overheat when they were new, because they had a full fan shroud (which pulls air through the entire core, all the way out to the corners), a big fan, and a clutch. Most attempts at "re-engineering" the cooling system with Summit catalog junk are dismal failures. The production cooling components were designed and developed as a complete "system", and they do the job if all the pieces are present and in good working condition.

Put the factory clutch, fan, and shroud back on (and seal the radiator to the support and the shroud to the radiator with foam seals so all the air is forced through the radiator instead of around it), and your cooling issues will disappear.

[Sauron327]

Naturally John is right. Except for his Z, a friend always runs BBs. Never had an issue with the stock cooling set up, even when running a stock or hipo motor. Usually the same story heard: electric fan without a shroud. Performance catalogs love pushing those things.

[JohnZ]

Thanks for the advice John, it's appreciated. I've been told that just with airflow (the car has no grille on it at the moment) at speed, (55mph plus) the engine should run around the 180 deg mark without a fan. Right or wrong I don't know. I just can't understand why after the water's been through the rad it's no cooler but hotter, thanks.....Nige

The fan isn't necessary for cooling except at idle and very low speed traffic; over 25-30 mph, ram airflow is more than adequate for cooling. Your temp measurement that shows radiator outlet temp the same or higher than the inlet says either the radiator is internally restricted or there's a coolant flow issue. Make sure the water pump is the one made for clockwise rotation - they're also available in counter-clockwise rotation versions for cars using serpentine belt accessory drives, which turn the water pump CCW.

[tom]

Could there also be a problem with the air recirculating? If there is no shroud to direct the air flow, at a stop the same air can recirculate. As the air heats up, this would greatly reduce the cooling efficiency.