i've always wondered what is it that causes most of our cars to run hot without a high dollar alum radiator? these cars were built to run in hot climates with AC's on and now you are lucky to get them to run a nice temp with no AC on in 85 degree weather with a 4 row. does boring an engine cause this? older radiators with deposit buildup? does even a mildly modified motor generate enough extra heat to make the radiator insufficient? i can understand if you've built a 500HP BB that you shouldn't expect the factory radiator to be adequate, but i have personally had and know others who have problems on stock and mild engines.

i've always wondered what is it that causes most of our cars to run hot without a high dollar alum radiator? these cars were built to run in hot climates with AC's on and now you are lucky to get them to run a nice temp with no AC on in 85 degree weather with a 4 row. does boring an engine cause this? older radiators with deposit buildup? does even a mildly modified motor generate enough extra heat to make the radiator insufficient? i can understand if you've built a 500HP BB that you shouldn't expect the factory radiator to be adequate, but i have personally had and know others who have problems on stock and mild engines.

I think high performance goodies just add tons of heat. My old very mild very tired 350/PG combo ran nice and cool with just the ancient clogged up 2-row radiator and stock transmission cooler. Now with the new 350 with a lot more HP and the OD trans it runs way hot in stop and go traffic, and that's with a 3-row radiator and a B&M transmission cooler but still the stock fan and water pump. I need to either install a high volume wp, better/larger radiator, electric fan or a combination of those, I think, to get it to run cool at idle.

Andy

I think high performance goodies just add tons of heat.

Why would they add tons of heat during normal operation? If it takes 25 hp to move your car down the road at 50 mph, what difference does it make if you have 300 hp or 400 hp at WOT? Where does the extra heat come from and why?

Why would they add tons of heat during normal operation? If it takes 25 hp to move your car down the road at 50 mph, what difference does it make if you have 300 hp or 400 hp at WOT? Where does the extra heat come from and why?

Well I would guess if you have an engine that produces more HP that means it breathes better. If it breathes better that means you're sucking in and burning more a/f mixture, which would create more heat. Same thing with higher compression.

Andy

Most over heating problems are caused not so much by High H/P motors as they are by not having the carb correctly jetted for the H/P ... way to many people throw MONEY at all the wrong parts trying to fix a heating problem that isn't any thing more then the jets in the carb ...... this is not to say that substandard raditior or fan/shroud can be or should be overlooked but they are not the end of the problem when facing a heat problem

Well, that much extra heat from modifications? No.

Reduced heat transfer from engine block, heads, manifold to coolant and oil? Probably. Does any cleaning process really remove all of the scale and corrosion from all internal surfaces?

Reduced heat transfer from coolant to radiator core? Probably. See above.

Altered ignition timing? Maybe. You start changing these things from factory and now you are in an experimental mode.

Reduced heat transfer from radiator to air stream? Maybe. Add on extra stuff ahead of the radiator or in the engine compartment reduces flow. That cool air has to get to the radiator core and the hot air has to exit the engine compartment.

Modified components? Maybe. Cobble together some brackets, pulleys, fan, used fan clutch, radiator, shroud, etc. from an old car or junkyard and they may not work together optimally.

Partially collapsed radiator hose. HaHa. They don't even include the spring anymore on new hoses.

Inadequate water pump, They wear out too. Slipping fan belt? Clutch fan that doesn't clutch?

Stock systems worked fine then. They work fine now: provided that the components are matched and in good condition. Radiator cores just need to be replaced when they get degraded. Flushing is just that...$$$ right down the drain.

My $0.02

Yeah, forgot about another possible"performance modification": lean mixture...

i'm with JJ, i think it's a combination of factors. i don't think these cars ran hot when they were new.

speakin' of clutch fans, i have NEVER had one hook up in full on drive mode. except in my '93 gmc pickup. and beleive me, if you are thinking "i don't know if mine does or not", then it hasn't. when they do, it produces a loud roar.

i've always thought that old radiators cannot be made to work like new. they simply can't get that buildup out of there. look at one that comes out of a radiator shop, you can see the mineral buildup still in it. IMO, you are throwing away money getting an older copper/brass radiator fixed when new ones are so reasonable.

that makes sense JJ. A/F ratio has a big effect on heat, as does timing. I suppose a bigger cam would require changes to AF mixture and timing to run right which would in turn affect heat level. Or it could just be that the settings for stock are no longer optimum and need to be modified to fit the cam

Andy

My car is unmodified 350HP, TH400, A/C, with a recored radiator, new fan clutch, timing set at 8* BTDC, and the correct shroud on it. I can drive in stop & go traffic with the A/C on and the temp hovers about 3/4 up the gauge (factory gauge & sending unit in the head) in the Arkansas summer heat & humidity. It'll fall to 1/2 or lower at speed. I do set the idle up a little in the summer because GM didn't install a idle-up solenoid in 68, but that's the only change from stock.
BillL

My car is unmodified 350HP, TH400, A/C, with a recored radiator, new fan clutch, timing set at 8* BTDC, and the correct shroud on it. I can drive in stop & go traffic with the A/C on and the temp hovers about 3/4 up the gauge (factory gauge & sending unit in the head) in the Arkansas summer heat & humidity. It'll fall to 1/2 or lower at speed. I do set the idle up a little in the summer because GM didn't install a idle-up solenoid in 68, but that's the only change from stock.
BillL

now that I'm thinking about this a few things come to mind. The cars were engineered to run a certain way and they had an array of stuff on them to ensure good cooling performance, including I would imagine water pumps, radiators, shrouds, fans, pulleys, thermostats, etc. All that stuff worked together as part of a system designed to keep that particular engine cool under all conditions that might be encountered. Over the years a lot of that stuff gets changed, replaced, removed with something not quite the same like a made in China water pump or an aftermarket flex fan which in turn affects how well the other components, which were designed to operate in conjunction with whatever part got changed, replaced, removed, operate. I guess you have to think about the whole package. The first inclination is to add a bigger radiator but maybe just a more efficient fan or even where the fan is in relation to the shroud or the shape of the shroud itself. Very interesting. I can really wrap my mind around discussions like this.

Andy

THERE ALOT OF GOOD POINTS HERE GUYS .

I get this from customers all the time with stock engines that cant seem to stay cool ... you boys have hit on many of the reasons .
BTU out put should be matched with the radiator .. on a mildly built motor ... more btu = more efficient rad needed

but as some stated ...carb settings .. timming.. water pumps .. fans .. shrouds .. hoses .. all come into play when getting away from stock .

but for the guys with stock motors ,that ran cool back in the day ...and now run hot .. even with a 4 row ...it may be due to lower octan gas ... one thought .. think about this .. in simple terms as one poster stated .. things need to be replaced in time ....like tarter on your teeth ... build up and calsifacation on the tubes can deture heat transfer .. in simple terms ... so if the rad hasent been recored with your original Harrison tanks ...or if it has , and your still running hot ...it might be time to up grade ...as you go after more pony's ...so does the chance your BTU rate will go up also .

Don

Did a frame off on my 70-SS 454 M22---Ran hotter than he!!. Hooked up with a retired G.M. Thermo Eng. First thing he said "What did you do to change what we built"? I got a LESSON on HOT cars. Most important--ALL the rubber items that you car had when it was built--2--Including so called splash guards, They keep underhood air directed.--3--Correct-fan blade -shroud-clutch if so equipped. A 70 Chevelle is designed to have the air enter the grill and exit ONLY- to the rear of both exhaust manifolds. This is why all the rubber items HAVE to be in place, Why a 3947772 fan blade? This blade is designed to pull the correct cu. ft. of air for a 3:31. In other words -if your 70 chevelle has a 3:31 rear then it has to have a 3947772 fan. Why? The 3947772 blade has the correct PITCH to cool an engine with this rear and thats why fan blades have numbers to match needed air flow for said engine cooling. Most of the time on 70s worn out clutch fans cause heating problems. Afterinstalling a new EATON fan clutch doing what this retired GM Eng. said-Start your 454, Turn the air on, kick off the high idle circut, And let it idle for a 1/2-hr. or 45 min. I said the friggen thing will blow up-Well SITTING at idle with the air on Mech gauge 195 would not go higher. HE SAID .Most owners cause heating problems due to mismatched parts. Now my 2 cents, Look at some numbers matching very correct cars and I drive mine They took the time got all the right numbered parts and DA thier cars do not run hot!!!! My home built 70 SS 454 RED wagon runs 195-200 on a 95 degree day with the air on, Excuse me I am just venting, Thanx for your time Bob ACES 2825

Most over heating problems are caused not so much by High H/P motors as they are by not having the carb correctly jetted for the H/P ... way to many people throw MONEY at all the wrong parts trying to fix a heating problem that isn't any thing more then the jets in the carb ...... this is not to say that substandard raditior or fan/shroud can be or should be overlooked but they are not the end of the problem when facing a heat problem
Funny you mention this. Let me ask...would this also cause your headers to glow red?

I too am trying to figure out my heating issues and am stumped.

Thanks,
Dave

Funny you mention this. Let me ask...would this also cause your headers to glow red?

I too am trying to figure out my heating issues and am stumped.

Thanks,
Dave

Glowing headers means that fuel is being burnt in the tube instead of the combustion chamber. If all or most of the tubes are glowing it's probably due too not enough ignition advance. If it's only one or two tubes, it's probably a problem with those ignition wires or plugs. Inadequate advance will also increase coolant temps.

4-row cooling today does not mean the same as 4-row cooling some years ago. Tube count and fin density have both decreased in current radiator cores and as a result, so has cooling capacity.