Yes you read it right. Some 396 Big Block motors will NEVER see normal operating temps-Some will always run Hot and overheat alot of the time. There are some odd ball motors out there due to the castings or the way they were made at GM back in the 60's. I can attest to that fact. Sometimes you can try re-building them and using every available aftermarket bolt on component to cool them and it just won't work. There have been 100's of complaints on this site about overheating big blocks but the fact still stands as Wheaton once told me-Any motor changed in the least way will produce heat and sometimes enough heat to run at 230 to 240 temps all the time. All I'm saying is that if you've tried everything under the sun to get yours running at normal temps and nothing ever works getting it to run cool, then I think it's time to think about another complete engine or move on to a small block car. Some guys I know have had success with a new motor but it's a costly venture. Just remember these big blocks are not running on the same gas that there used to so that's always an issue. Anyway-enough said. We all know the drill-Some Big Block's always have some Big Heat issue's.

Bob in CT

So what temp are you running at?

I have a 1968 396 block I been running in different projects for years...and has been freshened several times..the head bolt holes keep striping out this time and and I'm tired of drilling time-serts (as I am on number 4) I was going to use another block and just put my rotating assembly in it after machining it...The friend of mine who has shop I use to do the work has made a few comments of the same on cooling issues on some 396 engines..he has been a machinist here locally for 40 yrs and does consulting and test for the major cam companies here in memphis. Although I want to do another 396 I'm considering a stroker for replacement and this brings me to the question of what is your opinion on the issue for this problem...Is it certain years or what? I'm going to ask my machinist and see what he says and if he doesn't mind me posting his reason or opinion I will. I would like to the answers before I decide. Thanks Robert

I either need a valid reason why or wonder if the right things were tried.

Yes, Big Blocks are known for more overheating than small blocks, but if the right things are done, unless someone can come up with a valid reason, I have to believe that enough heat can be dissipated with the right combination of cooling parts and settings.

Now I do think that each engine is different, and some should run at timing other than the recommended factory settings.

Is this an opinion or do you know something specific about why some would never run normal?

Steve

I have owned probably 20+ big block Chevy powered cars and worked on so many I forgot and never had a problem.Corvettes,full size and Chevelles...Throw in Buicks and Oldsmobiles and that number triples ;)
A 3 or 4 core radiator and a non thermal clutch fan are about all you need. Never came across a "mystery" that couldn't be solved.
In fact,my 10.5 to 1 454 runs at 180-185* with a 3 core on 93 octane with a 772 fan and non thermal clutch. There is no black magic to these cars or their cooling systems.
JMHO and experience.

I may have been misuderstood or whatever but i never said many bbc run 230-240 deg and thats just the way it is and you cant do anything about it.

What i have said in the past is that with more perf mods/hp increase also comes some more heat to be disapated and that some modified bbc's can run 230+ deg esp in traffic with no mods to cooling system like larger radiator or an upgrade to an AL rad along with a hi flow water pump and or hd/ac or severe duty fan clutch etc which may have been misunderstood.

What i have also said in the past is bbc's typically run a little hotter but unless there is some issue with 1 particular block/casting you should be able to get any bbc running at a reasonable temp range on the street even when modified as long as your runing appropriate cooling system mods /upgrades for more cooling capacity depending on setup.

just my 2 cents on that.

scott

I must be lucky.Mine runs an average of 170 and about 180 on real hot days or at idle in traffic.

Y'all are making me worry about the 396 I just purchased. I have had five 454SS trucks, all with stock radiators and some with electric fans, never had any cooling problems in 5:00 traffic in the middle of Dallas in the summer. Also had a '72 455 riviera with no issues. This is my first 396 though, and I have a brand new alumitech about to go in. We shall see.

Yes you read it right. Some 396 Big Block motors will NEVER see normal operating temps-Some will always run Hot and overheat alot of the time. There are some odd ball motors out there due to the castings or the way they were made at GM back in the 60's. I can attest to that fact. Sometimes you can try re-building them and using every available aftermarket bolt on component to cool them and it just won't work. There have been 100's of complaints on this site about overheating big blocks but the fact still stands as Wheaton once told me-Any motor changed in the least way will produce heat and sometimes enough heat to run at 230 to 240 temps all the time. All I'm saying is that if you've tried everything under the sun to get yours running at normal temps and nothing ever works getting it to run cool, then I think it's time to think about another complete engine or move on to a small block car. Some guys I know have had success with a new motor but it's a costly venture. Just remember these big blocks are not running on the same gas that there used to so that's always an issue. Anyway-enough said. We all know the drill-Some Big Block's always have some Big Heat issue's.

Bob in CT


Bob ..as you know every case is different .. it may be a issue of the area of the one lives in .. try Arizona .. hot hot hot ...A lot of the things we need to think about here .. such as ambient air temps we are starting with .. the size of the radiator and its efficiency .. the Btu out put of the engine to begin with .. all these factors come into play .. along with what type of conditions the car is being used for .. drag strip .. road course racing .. city stop and go .. rpm ranges .. a number of things to take into account .
The delta factor ... (in simple terms we can all understand) ..this is the drop in temps from heat going in to temps of what comes out .. in some cases may be low depending on ambient air going in to begin with .. then coolant flow also has to be accounted for .. a bunch of factors come into play ... but back to flow .. in simple terms any restriction is not good .. the higher the coolant flow the better ..if the rad is (efficient enough) to give you a good delta for the conditions .. if you cant go bigger or better... then higher Cfm Is going to have come in to the picture.. not trying to be too technical here ...But as you know 3 keys to cooling .. a good radiator .. be it Aluminum or a fresh 4 row .. plenty of Cfm .. and great flow .

Don

I have owned probably 20+ big block Chevy powered cars and worked on so many I forgot and never had a problem.Corvettes,full size and Chevelles...Throw in Buicks and Oldsmobiles and that number triples ;)
A 3 or 4 core radiator and a non thermal clutch fan are about all you need. Never came across a "mystery" that couldn't be solved.
In fact,my 10.5 to 1 454 runs at 180-185* with a 3 core on 93 octane with a 772 fan and non thermal clutch. There is no black magic to these cars or their cooling systems.
JMHO and experience.

I definitely have to agree with Chris, here.

I also have never come across a BB (Chev, Olds, Pontiac, etc.) over the last 35 years that had a heating issue that could not be traced back to an underlying problem.

Think about this for a minute. Engines convert fuel and air into heat energy to push the piston down. The excess heat is carried away by the cooling system, oil, and exhaust.

At FULL throttle, a high horsepower engine will generate more combustion heat than a low power engine simply because it is converting more fuel and air into heat energy on each power stroke.

At PART throttle like most town driving or highway cruising is done, the horsepower output is MUCH lower. Maybe 50-100 horsepower generated at part throttle while propelling a car down the street generates the same amount of heat whether produced by a small block OR big block.

The cooling system doesn't know or care what size engine is making the heat. All it knows is it has to dissipate the excess heat from whatever horsepower is being generated at that moment.

Look at alot of radiators being sold that are rated for 500 horsepower, 600 horsepower, 700 horsepower, or whatever. How often do you have enough throttle opening to generate that power level? 5% of the time? 2%? Maybe once or twice a week for 10 seconds or so?

Now, long runs with a 650 horsepower engine at wide open throttle and max load would generate more excess heat than a 350 horsepower engine. Here is where the effects of limited radiator size, coolant flow, air flow, etc. would rear their heads.

Simply put, if it takes 50 -100 horsepower to propel your car around town, the radiator doesn't know if it's a six cylinder or a 555 making those ponies. If you're going uphill under load and the engine generates more power than the original one did, the cooling system would have to carry away the extra heat. If the cooling system was designed to be adequate in front of a 175 max horsepower 6-cylinder, it probably won't be adequate for the 300 that may be being generated in that situation.

My 10.7 compression 540 runs 170-180 ALL the time, even on the hottest Dallas day in stop and go traffic. Just a simple two row aluminum radiator, Stewart pump, high flow thermostat, blocked bypass, and a 7 blade clutch fan with a shroud.

As a matter of fact, the slower I drive, the cooler it gets. If I'm just idling around, it'll run 165-170 all day.

My friend's 489 in a Chevelle can sit and idle at 900 rpms for an hour and never get above 180-185 on a 95 degree day. Stock 4-row radiator (new), stock water pump, high-flow thermostat, clutch fan, and shroud.

I may be all wrong with my view, but it's JMHO and experience.:)


Randy

Yes you read it right. Some 396 Big Block motors will NEVER see normal operating temps-Some will always run Hot and overheat alot of the time. There are some odd ball motors out there due to the castings or the way they were made at GM back in the 60's. I can attest to that fact. Sometimes you can try re-building them and using every available aftermarket bolt on component to cool them and it just won't work. There have been 100's of complaints on this site about overheating big blocks but the fact still stands as Wheaton once told me-Any motor changed in the least way will produce heat and sometimes enough heat to run at 230 to 240 temps all the time. All I'm saying is that if you've tried everything under the sun to get yours running at normal temps and nothing ever works getting it to run cool, then I think it's time to think about another complete engine or move on to a small block car. Some guys I know have had success with a new motor but it's a costly venture. Just remember these big blocks are not running on the same gas that there used to so that's always an issue. Anyway-enough said. We all know the drill-Some Big Block's always have some Big Heat issue's.

Bob in CT
That begs the question........
If these are blocks that were actually installed in factory production cars how did they not get repaired and/or replaced while the cars/engines were under the manufactures warranty?

I recall replacing some non-fixable overheated Chevy engines while working at the dealershop back in the 70's. The Zone rep took a sledge and busted the sides out of them to find the issues. It was usually a massive peice of casting slag hung in the water jacket. These blocks/engines never made it to go back in another car. Especially 30+ years later.

jim

Thank's Jim for your input. That's exactly what I was talking about. NON-FIXABLE 396 Chevy engines that would overheat due to a factory problem internally. Even tearing them down and re-building them will not bring a solution to the overheating. I've see it myself as there was no re-course but to buy a new block and start over again. It's just a rare GM flaw on some engines that can never be corrected, except to use it as an anchor.

Bob in CT
90% foliage

reading this makes me feel a little better my 454 runs hot 210 220 in traffic and I start to panic. When cruising it runs fine just when i am at idle and in traffic the temp jumps from 180 185 to the 210 220 range super fast it has never overheated on me just runs hot. I have 2 gauges in mine one in the intake by the thermo and it runs on the cool side when driving and the worst it climbed was aliitle under 3/4 my actual temp gauge is in the head and thats the one that jumps fast. I had a 4 core rad, shroud, 5 blade fan with fan clutch, temps seemed to stay higher purchased a Allum rad from Allumitech and it did lower my cruising temp but same results at idle in traffic temp climbed but seem to cool down quicker with the allum rad and not as hot .. I am now back to the 4 core and a flex fan (temp repair) i unfortualty had an a fender bender and tore up my brand new allum rad and fan blades, Hopefully over the winter I save enough to buy another allum rad with elec fans maybe that will help more. it gets frustrating worring about weather and how hot my BBC runs it limits the amount of time i would like to drive it because I worry about it running to hot an messing things up.. so i guess my question is how hot is to hot should I worry that my temp gauge in the head reads so high ??? sorry about the long post I just wanted to give as much info as I could

Thank's Jim for your input. That's exactly what I was talking about. NON-FIXABLE 396 Chevy engines that would overheat due to a factory problem internally. Even tearing them down and re-building them will not bring a solution to the overheating. I've see it myself as there was no re-course but to buy a new block and start over again. It's just a rare GM flaw on some engines that can never be corrected, except to use it as an anchor.

Bob in CT
90% foliage
What my point was......I honestly don't think that any problematic engines (396 or otherwise) would have made it beyond the warranty period without the owner/customer demanding replacement. Everything that I replaced under warranty had to be tagged and sent back to Chevy...these defective parts never made back out for public use.
If someone has 396 that is overheating now...I'd bet it wasn't overheating when produced (1965 thru 1969)....it wouldn't have never made it (40 yrs later) without cracks and major core shift issues. It's what Scott said....the problems stem from what's been done to them....poor combinations etc. I had an overheating issue on my 396 initial start up....again as Scott pointed out to me..."get a distributor with a vacume advance and get enough timing in the engine to make it run correctly with an aftermarket cam".


jim