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Event Coverage Just The Facts... Overheating SBCs

Discussion in 'The Hokey Ass Message Board' started by Crazy Steve, Aug 19, 2020.

  1. thomas.parker197
    Joined: Dec 29, 2017
    Posts: 52


    More traffic now? More sitting in traffic idling?

    Sent from my SM-G965U using Tapatalk
  2. I only had one SBF in a '64 Mustang and it over heated all the time in the summer. It even warped the heads and I had to have them machined. I always attributed it to not having a shroud, 4 blade fan and too small of a radiator, from the factory.
    Sold it and bought Chevys ever since.
    Last edited: Aug 21, 2020
    nunattax, ekimneirbo and warbird1 like this.
  3. On my blown .060 over stroker in the '32, I use the 1003 Felpro head gaskets and they recommend drilling the center water holes in the block to 7/16" to allow for better coolant flow between the Siamese exhaust ports on the center cylinders.

    I also use a Stewart water pump without a bypass hole in the right-hand mounting flange, which balances the flow between the banks, so it bypasses from the front of the intake manifold back to the top of the pump.

    I run a 6" water pump pulley, 4 blade fan, 1/2 a shroud, 190* thermostat, 9.5:1 on regular gas @ sea level and 26* total timing and I've not had any issues over heating.

    It will creep up to about 210* sitting in traffic on those 95*+ days though, but it never pukes. I know I'm breaking all the rules, but I'm OK with that.

    partssaloon, Joe Blow and ekimneirbo like this.
  4. Joe Blow
    Joined: Oct 29, 2016
    Posts: 653

    Joe Blow

    I think the bottom line on the OP's observation is that it was just a coinkydink.;) I don't think anyone has ever heard of SBC's en masse having overheating issues in production car configurations.......but as others have stated, the countless variations of how they have been set up in hot rods is another matter altogether.
    Montana1 likes this.
  5. I had a solid fan, no shroud on mine and it overheated quickly if I was stopped or moving slow. Went to a flex fan and added a shroud at the same time, blocked off the sides of the radiator wall next to the radiator (aluminum). Right away it went from 180 to 175 for normal driving. Sitting in traffic, it got much better but still would puke coolant when I parked after a long soak, running temp was 220. Added a pusher Spal 1600 CFM electric fan on a thermostat, nice to hear that come on when I need it to.
  6. And again... ported vacuum PRE-DATES emission controls! It was in use long before the 70's and worked well for years. I would sure like to know where this myth originated.

    Also; I've tried both ported and manifold vacuum on every engine that I've had; never made a bit of difference in engine temperature on any of them. The Cad in my '40 is presently running manifold vacuum and it didn't change a thing when I switched from ported vacuum.

    Though I don't do sbc's so it might work with them...
    jaracer and BamaMav like this.
  7. Where the confusion comes in is there's more than one kind of 'ported' vacuum. The typical type is vacuum that's ported so it's disabled at idle. It's above the throttle blades when the throttle is closed, then becomes 'below' when they open. This works like manifold vacuum; high vacuum at low throttle openings, goes down as the throttle is opened. The vacuum is usually enabled at any throttle opening.

    In the other type, the port is always above the throttle blades, and works opposite of manifold vacuum. Vacuum went up with throttle opening, not down. While this was done on some cars earlier (Ford 'Load-o-matic' comes to mind) by the mid-late '60s this was for done for emissions purposes, and was usually 'switched' by a temperature-controlled vacuum valve, although dual-diaphragm distributors weren't uncommon either . Too much advance would cause pinging, not enough overheating, the valve was supposed to switch back and forth between 'regular' vacuum if/when that happened. I chased an irregularly-occurring pinging on a 351C for a few months before I figured out that was the cause.

    Why this is germane is the first type does retard timing at idle compared to a straight manifold connection. Retarded timing increases engine heat, and if you have an automatic-equipped car idling along under load , it will get hotter than it would with even a small throttle opening or if using a manifold vacuum source. There are valid reasons for using this type vacuum connection, but this is a downside to it. Personally, I almost always use a manifold connection, but that has trade-offs too.

    The other thing to look out for is most aftermarket carbs these day have both types of connections (to retain EPA legality) so you have to pay attention to which one you use.
  8. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,393

    from illinois

    Probably started by some young magazine writer who thought nothing had been invented before his ( short) frame of reference !
    Its like teenagers who think they invented fucking in the back seat !LOL
    texasred and warbird1 like this.
  9. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,998

    from Brooks Ky

    Reverse cooling where coolant flows thru the heads first and then the block......

    Lots going on back at that point in time as far as emissions and trying to get some HP back into factory vehicles. If everyone thinks back you will remember that factories went thru some tough times trying to meet emissions and get some performance. The hottest area (other than exhaust) is an engines head. Blocks actually don't have much problem with heat, and with the coolant flowing thru the block first, it simply warmed the water before the real job of cooling the heads begins. Pumping water thru the heads first resolves a lot of heat issues and can allow even higher compression to be used. Also using aluminum heads from the factory helps even more.
    But then as emission requirements became greater it was determined that higher temps would help control the the benefit of reverse cooling went the way of the dodo bird.
    I think restricted flow caused by smallish coolant holes/passages often keeps engines from cooling better......hence the benefits gained by Montana1 with a few small changes and getting good cooling from a supercharged engine. It doesn't do any good to increase radiator capacity and use a higher volume water pump if there are restricted flow ports to/thru the heads. Like I mentioned once before, the Cadillac (472/500) guys often have problems with too much heat when installing them in other cars. Some started resizing and adding an extra coolant hole at the rear of the engine and it seems to work by keeping temperatures lower.
    Drilling Cad 3.jpg
    Drilling Cad 2.jpg
    Last edited: Aug 21, 2020
    tb33anda3rd likes this.
  10. I've personally not seen that to be true... doesn't mean it it isn't... just my personal experience. Small block Fords, FE's, Y-blocks, Olds, Big block Chryslers, and the above mentioned Cadillacs. Manuals and automatics. All used ported vacuum from the factory with the exception of one of the 440's that had the goofy idle solenoid; if they ran hot, they ran hot and going to manifold vacuum made no difference.

    Just my experience, YMMV
    RmK57 likes this.
  11. belair_54
    Joined: Aug 17, 2010
    Posts: 85

    from australia

    Probably because a SBC produces alot more power than most engines more HP equals more heat.
    On a serious note I had a 34 chevy roadster with a tunnel ram 350 it did run hot but I am sure if it was running a SBF it would run hot also. It came down to the radiator not being adequate there is limited space in those early cars. I also had a high stall convertor 2800 RPM I plumbed this into a seperate cooler this helped. At the end the best solution was running 2 thermo fans offest from each other.
    What I needed was a triple row radiator.
  12. I was never a fan of reverse flow cooling. (Pun intended.)
    It doesn't make sense to push HOT water down into the block, when HOT water naturally rises to the top. :confused: But what do I know, I'm just a painter...
    firstinsteele likes this.
  13. What size is the crank pulley? HRP
  14. Or more square inches area for air

    2OLD2FAST likes this.
  15. cheepsk8
    Joined: Sep 5, 2011
    Posts: 579

    from west ky

    Steve, I've owned over 150 vehicles in my life and off the top of my head, at least 100 of them were pre 1985 sbcs. Many were stock, mind you, but many were higher hp engines. I can only remember one of mine with a chronic case of cooling issues. It belongs to a board member now, but only after I solved the issue. I ran a stock 350 long block with a nice crane cam, 461 heads, regular size valves, aftermarket intake and q jet carb. Walker desert cooler radiator and shroud, clutch fan , no air. Ran hot in traffic at idle every warm day. It was in a 38 chevy. I bought every thermostat you could, played with the timing, changed brands of coolant, even put on a pusher fan. And that is after 2 fan changes. I went to 2 different fixed blade fans. I finally gave in and threw up my hands. So... I was sitting in line ,( letting it cool off), at a show, when this older guy in a 50 olds pulled over to offer help. I told him that this was nothing new, explained to him all that I had tried, and he asked one question. What kind of water pump you got? I answered, with a Summit high volume pump. I had put that on when I built the engine. I expected it to help cool I guess. He said, put your clutch fan back on and ditch the pump for a stock one. I did when I got home and she never went over 190 again. I never used the pusher fan unless it was over 100 degrees outside after that. I don't think that after that experience, cooling is a one size fits all endeavor. I have applied what I have learned to every one I build now. I think there is a recipe for cooling with every vehicle no matter what the make or engine. Sometimes it takes a little longer to figure out what works for you.
    AHotRod, Baumi, 40FORDPU and 5 others like this.
  16. BamaMav
    Joined: Jun 19, 2011
    Posts: 4,979

    from Berry, AL

    I've always heard you use ported vacuum for the distributor advance so the spark can come in earlier as the RPM increases. If you use manifold vacuum on the advance, you have advance all the time except when first cranking the engine before it starts creating vacuum. If you're going to run the advance on full manifold vacuum and have it at full advance all the time, you might as well leave it off and just set it higher with the distributor, you're doing the same thing anyway. The advance curve coming in needs to match the increase of fuel and RPM, with full vacuum all the time it isn't doing that.
    AHotRod likes this.
  17. 1oldtimer
    Joined: Aug 21, 2003
    Posts: 8,033


    My '60 El Co has a lumpy cam in a bone stock 283 engine (with a Performer intake and Qjet), stock rigid fan, stock fan shroud and I did replace the radiator with a junkyard 4 row (after the 3 row was leaking). That thing can sit at idle in Pomona Swapmeet traffic (1 hour) during the height of summer and not get above 1/2 on the gauge.....the only whimper I hear is me sweating my ass off. I really think it has to do with engine bay heat exiting (setting aside bad tune up procedures).
    Stogy likes this.
  18. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,998

    from Brooks Ky

    Think of it another have to overcome gravity to push the water upward into the head even though it's hot. Also if you want to remove the most heat you have to apply the coldest medium to the hottest area first. When I stupidly pick up something I just welded, I put my hand directly directly under the faucet.......not my elbow.:D:p:D
    Blues4U likes this.
  19. 6 3/4" single groove
  20. Ever try swimming up stream?

    Gravity is not a problem. Hot water being less dense, overcomes gravity. When I was a kid, we had a Farmall Cub tractor that didn't have a water pump from the factory. The water circulated by convection. Hot water up and cooler, denser water down. It flows naturally. Gravity is our friend.

    I don't think SBC's have a problem with cooling anyway. As already stated, we harvest these motors and put them in without re-thinking our situations, or worse OVER thinking our situations. Sometimes we get lucky and sometimes we don't.

    Besides that, I like the head to run hot for better combustion efficiency. Think MPG and power. NASCAR engines run at around 290* Fahrenheit, under 75 lbs. pressure. This reduces required airflow through the radiator and therefore, yields less drag. ;)

    On my '32, I noticed a big difference between a 160* thermostat and a 190* as to whether it over heated or not. It likes the 190* a lot better, and maybe even a 200* would be better yet.

    I know we've discussed this topic before, but maybe we need to go back to what already works... :cool:
    AHotRod, warbird1 and Stogy like this.
  21. I was laying in bed early this morning thinking about this overheating problem. The question came to me - Do all these cars run 50/50 antifreeze in them?

    You only need enough antifreeze to keep them from freezing or boiling over. Of coarse, straight water transfers heat the best until it reaches the boiling point. However, again, you only need enough antifreeze to not boil over.

    Sometimes it's it's too easy to top off the radiator with straight antifreeze and when it gets hot out, you got problems. (Ask me how I know.) I like to run just enough antifreeze to cover the freezing and boil over perimeters, because it transfers the most heat away.

    Just a thought... :cool:
    AHotRod likes this.
  22. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 1,998

    from Brooks Ky

    Last edited: Aug 22, 2020
  23. jnaki
    Joined: Jan 1, 2015
    Posts: 5,991



    We have known plenty of our friends that owned SBC powered hot rods and cruised all over So Cal, from the oceanfront elevation at zero to the high elevation of the local ski resorts in the San Gabriel and San Bernardino Mountains. They even drove out to the desert on the other side of the mountain range that you all see when starting the approach to LAX in the comfort of your big jet from any other airport during normal windy days.

    Never once, did any of our Chevy sedans powered with 265, 283 and even a 348 thrown into the mix. There was no overheating issues. Even on hot days cruising to the beach. Or, even when we had to idle through a block long line of hot rods and lowered sedans during Easter Vacation days. (better known these days as Spring Break) there were plenty of times that traffic caused other older cars to pull over and watch the steam coming out of the overflow pipe. Some had the audacity to actually open the radiator cap to the danger and delight of others watching the “Vesuvius of water” shooting up in the air.


    As long as there is a good flow of air coming into the front of the grille, the cooling worked as it should. If anyone had to stay idling a long time for any reason, and experienced an overheating situation, the simple fix was a change of thermostats. Not many of the SBC motors had any long standing, overheating problems
    The 65 El Camino was perfect running in snow, desert, mountains and beach without any problems with the SBC. But after 122k, is started to overheat in town traffic. Changed the thermostat and it was ok for a while. Then the water pump started making some noises. The complete removal of the old pump and installing a new one did the trick. The funny thing was, for 125k miles not a single mishap, repair or replacing anything. Pure good times in driving all over So Cal, dusty deserts, (twice El Mirage), SF Bay Area, Baja and into the Sierra and local mountains.

    We had decided to sell the 65 El Camino and get a new car that had A/C. Our little new guy made driving without A/C somewhat hectic. So, once we made the decision, the 65 El Camino started acting up with the thermostat and water pump.

    Last edited: Nov 6, 2020
    AHotRod likes this.
  24. I have had my best results running a 7 1/4" crank pulley and a 6 1/4" water pump pulley.

    I also use a 17" steel bladed mechanical fan for maximum air flow. HRP

    Montana1 and partssaloon like this.
  25. Well, this is Washington state and it does get below freezing here in the winter often enough to make antifreeze something most owners use, so I'm sure they all have antifreeze in them and more than just a minimal amount. Full-time heated garages here are a luxury few guys I know can afford.

    Again, this just struck me as rather strange. FWIW, all the cars had full hoods, a few had aluminum radiators, and body styles varied from late '30s GM trucks, several '40s Fords, to even a '57 Chevy. A couple had AC but most didn't. Most (if not all) were 350s (except for the lone Mopar).

    I'll make one more comment; talking to the Chevy motor guys one big attraction is how 'simple' they are to use and there's a bit of a 'one size fits all' mentality at work. If I've learned anything over the years, it's that it's rarely as simple as it looks... LOL...
    Montana1 likes this.
  26. Manifold vacuum doesn't give full advance all the time; it varies with engine load. If you've ever owned a car with vacuum wipers, that will be connected to manifold vacuum. When going up a hill and the wipers slow/stop, that's because manifold vacuum dropped under load.

    The only real difference between manifold and ported vacuum in terms of the ignition is ported doesn't add advance at idle. Above idle they both act the same. But ported vacuum will increase engine temps at idle.
  27. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,584


    I'd say that it is not small block near as much as it is coolant capacity and air flow.
    That and the OMG my gauge hit 200 I am going to ruin the engine in my hot rod, nonsense. It's amazing how many engines that run just fine in the original vehicle they are designed for running 195 thermostats and operating around 210 daily for thousands of miles are all the sudden overheating when they are put in a hot rod with a 180 thermostat and hit 200. Was it hot was it just hotter than they thought it should be?

    Still air flow is a serious issue, I went out an dug out the old Ricky racer flex fan I ran on the 48 from 1989 until 2004. That would run down the highway all day at just over 180 with a 180 thermostat but get in traffic and the gauge would shoot up fast. The fan that I thought I needed for clearance just flat didn't pull any air. Comparing it to a fan that I bought at a swap meet last year there is a serious amount of difference in how much air they will pull Same diameter fan but one is designed for low restriction on a race car and the other is designed to pull some serious air. It was totally my screw up there as I probably should have run and electric fan on the top half of the radiator and left the mechanical fan off or gotten a real fan. IMG_0032 (2).JPG IMG_0031 (2).JPG

    During another similar thread I got on the Spal fans page and discovered that not all Spal fans are created equally. There are several CFM ratings for the same size fans and if you go cheap you may not get one that moves enough air. Just because it is a Spal fan doesn't make it the best one for the application.

    I went and checked the "reverse flow" on the LT engines and they use an entirely different cam driven water pump than the other small blocks do and coolant goes in the heads first and down though the block and back to the radiator.
    Borrowed from the Engine builders site:

    Reverse-Flow Cooling System

    One reason why the new
    engine performed better was the reverse-flow cooling system. By routing
    the coolant to the cylinder heads first and then the block, the engine
    could handle a higher compression ratio and maintain more consistent
    cylinder head temperatures.

    The water pump on these engines is driven by a small shaft off the
    camshaft gear. This improved cooling reliability (no belt to slip or
    fail), but it also creates a potential leak path for oil. The water
    pump driveshaft seal typically leaks once the engine has about 60,000
    miles on it. The fix is to replace the seal, which takes about two
    hours and requires a special tool (J39087) to install the seal. The
    tool prevents the lips on the seal from deforming when the seal is
    installed. If you don’t use the tool, chances are the new seal will
    leak — and you’ll have to do the job over again!

    The cooling system on the LT1 tends to trap air when you are
    attempting to refill it, so there’s a small bleeder screw on the
    thermostat housing to help vent air. But even this may not be enough,
    especially on the Camaro. If air gets trapped in the system, the
    temperature sensor for the cooling fan may not be in contact with the
    coolant, preventing the fan(s) from coming on, causing the engine to
    overheat. To get the air out, you may have to raise the front of the
    vehicle up so the radiator becomes the highest point in the system. Add
    as much coolant as the system will take, then lower the vehicle, start
    the engine, let it warm up, then shut it off. After the engine has
    cooled, recheck the coolant level and add more coolant as needed to top
    off the system.

    That was my education for the day.

    It's still comes down to:
    Condition of the whole system.
    capacity of the cooling system matching the engine.
    ability of the whole system to effectively transfer heat from the engine to the air and away from the car.
    Baumi likes this.
  28. Baumi
    Joined: Jan 28, 2003
    Posts: 2,765


    I ´ve only had one SBC overheat on me yet. It was a 350 I put in a 64 Buick Wildcat. The stock radiator was clogged so badly it would overheat over 60 mph. My rule of thumb- experience is : Overheating at idle means not enough airflow through the radiator , overheating at speed means not enough radiator. Usually a clutch fan and a fan shroud are missing when one of my buddies´s complaining about their car´s overheating. But some of them won´t listen and keep buying new Chinese aluminum radiators and water pumps until they finally give in.
    AHotRod likes this.
  29. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,697

    from So Cal

    This is not accurate. First off, using ported vacuum doesn't cause the advance to come in earlier; when it starts to come in as the throttle is opened, the manifold vacuum system is already there. Both will end up the same, but the ported vacuum system does not come in earlier. Second, using manifold vacuum is not the same as leaving the vacuum advance off and setting the static timing more advanced to make up for it, that is a misunderstanding of how it works. During periods of low vacuum the manifold vacuum system will retard the timing. That retarded timing during periods of low vacuum will not occur if you just eliminate the vacuum advance and set the static timing more advanced.

    Here's an article from Super Chevy discussing this (note it contradicts some remarks made earlier in this thread)
  30. donno
    Joined: Feb 28, 2015
    Posts: 424


    Las Vegas here, hot in the Summer. 4 SBC's, 46 Ford, 32 Ford p/u, '48 Merc and a '57 Pontiac. CENTER THE FAN WITHIN THE RADIATOR!!! No shrouds, NO flex fans, have pushers on the '57 and the '48, no over heating issues. Oh yeah, run A/C on 3 of 'em.

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