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Discussion Starter · #1 ·
Hello all. I've got a 78 with a 355. Nothing crazy on hp but I've run into an issue with cooling. Yesterday was a nice 75 degree day and I was doing a lot of in town driving. Hit me than a few stop lights. Anyway the car was far too warm for my liking. Running bergen 210 and 215. Hitting 220 once. The car does run a lot better when it's in the 195-200 range but I'm not real comfortable with it being higher than that I run an alloyworks set up. Aluminum radiator and electric fans which I believe are around 800cfm per fan. Now I could just spend the money to invest in larger fans but I know someone running the same radiator and fans and he apparently has no issues. Anyway my question is could my problem be thermostat and fan switch related? How should you choose what temp to use? I've also read that the fan switch should be a higher temp than the thermostat. Is this correct? Why would that be?

I really appreciate any help I can get.
Thank you
 

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1973 Pontiac Ventura - 489ci BBC swap
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If the fan switch matches, or is lower, than the thermostat opening temp, the fans will never shut off. A thermostat's rated temp is when it begins to open, and often won't be fully open until 10-15 degrees higher.

Contrary to popular belief, a thermostat does NOT limit an engines max temp, rather it sets the minimum operating temp. Thus going to a lower temp thermostat will not fix an over heating issue.

Now, if a 180 thermostat begins to open at 180, and a fan switch turns on at 180... The fan will never pull the coolant temp below the thermostat's set minimum temp. Thus, once the fans switch on, they will never turn off until you shut the engine down.

Generally, you want the fans to switch on around 15-20 degrees over the thermostat temp. Keep in mind that the fans really are there only for slow speed cooling, such as when you're in traffic, or cruising slowly through the neighborhood. Once you're above around 40mph, the motion of the car moving is pushing more air through the radiator than the fans can pull anyways. Which is a good reason you don't want fans running non stop - you're effectively limiting your airflow to the fans CFM. I've had several cars that, during my rolling pennies for gas broke days, I ran without a fan at all. As long as I didn't sit still for more than a few minutes, it was fine.
 

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1970 Nova, 4 DR, 307, Powerglide
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Increasing your cooling system capacity can have a significant impact on keeping it cooler as well. If you have a 2-core radiator you can entertain a 3-core if you don’t already have one in there. I once had issues with a big block running hot at slower speeds and in traffic. I was able to remedy by going to a triple core radiator and a mechanical fan with more blades. Problem solved.

I was still a broke teenager at the time and didn’t have the money for the electric fans or I may have opted for those as well.

Capacity, air movement and circulation are all the key ingredients to keeping an engine at proper temperature.
 

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Discussion Starter · #4 ·
If the fan switch matches, or is lower, than the thermostat opening temp, the fans will never shut off. A thermostat's rated temp is when it begins to open, and often won't be fully open until 10-15 degrees higher.

Contrary to popular belief, a thermostat does NOT limit an engines max temp, rather it sets the minimum operating temp. Thus going to a lower temp thermostat will not fix an over heating issue.

Now, if a 180 thermostat begins to open at 180, and a fan switch turns on at 180... The fan will never pull the coolant temp below the thermostat's set minimum temp. Thus, once the fans switch on, they will never turn off until you shut the engine down.

Generally, you want the fans to switch on around 15-20 degrees over the thermostat temp. Keep in mind that the fans really are there only for slow speed cooling, such as when you're in traffic, or cruising slowly through the neighborhood. Once you're above around 40mph, the motion of the car moving is pushing more air through the radiator than the fans can pull anyways. Which is a good reason you don't want fans running non stop - you're effectively limiting your airflow to the fans CFM. I've had several cars that, during my rolling pennies for gas broke days, I ran without a fan at all. As long as I didn't sit still for more than a few minutes, it was fine.
Okay so if that's the case then I should definitely change the fan turn on switch. Assuming my gauge is correct the fans turn in at 160 and I believe my stat is 180. So I should put in a 195 fan switch? I thought that if the fans turned on before the thermostat opened it would be already cooling the fluid to be ready for when the stat opens.
 

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Discussion Starter · #5 ·
Increasing your cooling system capacity can have a significant impact on keeping it cooler as well. If you have a 2-core radiator you can entertain a 3-core if you don’t already have one in there. I once had issues with a big block running hot at slower speeds and in traffic. I was able to remedy by going to a triple core radiator and a mechanical fan with more blades. Problem solved.

I was still a broke teenager at the time and didn’t have the money for the electric fans or I may have opted for those as well.

Capacity, air movement and circulation are all the key ingredients to keeping an engine at proper temperature.
I am running a 3 core radiator from a place called alloyworks. I am running their fans and shroud as well. They said their fan switch was 180 but they come on at 160 according to my temp gauge. I believe the fans are 800cfm each
 

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Oh yeah, 160 is way too cold on the fan switch. Keep in mind too that a motor needs heat in it to run effectively. Trying to keep the motor down that cold is going to rapidly increase sludge formations in the motor, and lead to increased wear. It's one thing on an all out race motor where ultimate life span comes behind ultimate power production, but on the vast majority of our motors you want it running around 185-195.

Modern motors often run in the 220 range, and that's part of how they can routinely go 200K+ miles, though computer control plays a large part too. I wouldn't recommend running a carb motor that high.

Over cooling the coolant in the radiator isn't doing you any good. The thermostat regulates water flow through it by adjusting how far it opens, based on the temp of the coolant running through it. If it starts to open, and gets hit by water at 100*, it will just close right back up again.
Also keep in mind that a well working radiator is only going to see a 15-20 degree difference between the hot and cold sides. So if you have 200* water going in, at best you're only going to see 180* water coming out, but that cold side will be going down as the hot side cools down as well. Even if you get the coolant sitting in the radiator down below that 160 (which won't be hard just by driving the car), it will be displaced by hot coolant VERY quickly anyways.

Ultimately, all you're accomplishing is wearing out the fans faster. Based on the 800cfm rating on them, I'm guessing you have eBay specials for fans, and their lifespan is going to be considerably shorter than a Spal, Derale, etc to begin with too.

Actually, just checked Alloyworks website, and yep...cheap imported fans. That 12V 80W sticker is a dead giveaway. My bet is that 800cfm rating is much like the knockoff companies rate stereos - something like 1000watts from a $30 amp being fed by a 10 amp fuse...where it's physically impossible to get 1000 watts of output from 150 watts of input.

I had the same thing on one of my C10 radiators..worked fine on the freeway, but got hot quick in slow traffic...fans just didn't pull enough air.
 
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If it runs between 215 and 220 deg at its hottest is it really an issue? If the absolute hottest it has ever or will ever get is 225 deg that doesn’t seem insane. While a little cooler might be nice, if it NEVER gets hotter than that I’m sure it would live a long happy life. The only reason I don’t like to see that temp on my Nova is with my old crap once it gets up to that temp it tends to keep going…
 

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Discussion Starter · #8 ·
Oh yeah, 160 is way too cold on the fan switch. Keep in mind too that a motor needs heat in it to run effectively. Trying to keep the motor down that cold is going to rapidly increase sludge formations in the motor, and lead to increased wear. It's one thing on an all out race motor where ultimate life span comes behind ultimate power production, but on the vast majority of our motors you want it running around 185-195.

Modern motors often run in the 220 range, and that's part of how they can routinely go 200K+ miles, though computer control plays a large part too. I wouldn't recommend running a carb motor that high.

Over cooling the coolant in the radiator isn't doing you any good. The thermostat regulates water flow through it by adjusting how far it opens, based on the temp of the coolant running through it. If it starts to open, and gets hit by water at 100*, it will just close right back up again.
Also keep in mind that a well working radiator is only going to see a 15-20 degree difference between the hot and cold sides. So if you have 200* water going in, at best you're only going to see 180* water coming out, but that cold side will be going down as the hot side cools down as well. Even if you get the coolant sitting in the radiator down below that 160 (which won't be hard just by driving the car), it will be displaced by hot coolant VERY quickly anyways.

Ultimately, all you're accomplishing is wearing out the fans faster. Based on the 800cfm rating on them, I'm guessing you have eBay specials for fans, and their lifespan is going to be considerably shorter than a Spal, Derale, etc to begin with too.

Actually, just checked Alloyworks website, and yep...cheap imported fans. That 12V 80W sticker is a dead giveaway. My bet is that 800cfm rating is much like the knockoff companies rate stereos - something like 1000watts from a $30 amp being fed by a 10 amp fuse...where it's physically impossible to get 1000 watts of output from 150 watts of input.

I had the same thing on one of my C10 radiators..worked fine on the freeway, but got hot quick in slow traffic...fans just didn't pull enough air.
Thank you for the help. That was an awesome explanation. So I'm gathering that I not only should be running a hotter switch but invest in some better fans as well.
Thank you.
 

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Discussion Starter · #9 ·
If it runs between 215 and 220 deg at its hottest is it really an issue? If the absolute hottest it has ever or will ever get is 225 deg that doesn’t seem insane. While a little cooler might be nice, if it NEVER gets hotter than that I’m sure it would live a long happy life. The only reason I don’t like to see that temp on my Nova is with my old crap once it gets up to that temp it tends to keep going…
I'm worried because if it will get that high in my small town after a half hour of driving, what will happen if I tried to drive it to work which is an hour drive one way with road construction routinely making it stop and go traffic turning an hour drive into 1.5 or more hours.
 

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Is there room to install the stock mechanical fan and fan clutch in an appropriate fan shroud? The stock mechanical fan will move way more air than any electric fan. Electric fans can have a small advantage when you're sitting still. To put actual numbers on it, the mechanical fan on my S10 pickup (4.3L Vortec V6) moves about 1800cfm at idle. As the fan speed increases (you take off from a stop light), the CFM increases. On a hot summer day, it'll peak around 7,000cfm at an engine speed around 3,000 RPMs. By then, even on the hottest day with the AC running, the air at the fan clutch is cool enough that the clutch is already in the process of disengaging.

Check into an aluminum fan shroud kit. All the major online "speed shops" have them. Here's one from Speedway motors:


Summit Racing, Jegs, etc. all offer similar products.

If you must have an electric fan setup, get a good quality fan (or two). I use Spal fans (and no substitutes) where I install electric fans as primary cooling, and I prefer them for auxilliary cooling (like a fan mounted to an AC condenser or to a transmission cooler). Spal tends to give honest CFM ratings on their products. The ones I've measured always slightly exceed the rated CFM.

For a high quality fan, a general rule of thumb is 1A of current draw ~= 100CFM at best. 80W at 13.4V = 6A, +/-, and I'd expect no more than 600CFM from those fans you have, maybe less.

For switches to turn the fans on, I always use relays, and I generally use a thermal switch for the ground for the relay coil. Select your on and off temperatures so that it turns off about 10°F above thermostat temperature (any lower and it might never shut off), and so it turns on 10°F to 15°F above the turn off temperature.

For a 180°F thermostat, I've used Standard Motor Products TS244 or an equivalent. It turns on about 205°F-210°F, and turns off between 190°F and 195°F. Original application was Mazda 4 cylinder engines from early 1990's (tell the parts guy you have a 1991 Miata and he will get you the right part). The one disadvantage to this one is it's metric threads, so you'll need an adapter bushing or you'll need to drill and tap your own hole for it. For a 195°F thermostat, I use something that cross references to GM 14043275. AC Delco D1855B or Standard Motor Products TS85 are common (although I think the AC Delco may now be discontinued). That one turns on around 215°F and turns off around 205°F, which matches up with a 195°F thermostat well.
 

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Also, make sure the rest of the car is in tune as well, especially in the ignition department. Particularly, correct ignition timing, and make sure you're using the vacuum advance with manifold vacuum (as opposed to ported).

While it's not quite an apples to apples comparison, my 489 will consistently run around 15* hotter with the vacuum advance disconnected. Running mechanical only or locked out timing as some do has it's advantages in a race motor, but tends to cause more problems in a street motor. I know a lot of guys will freak out when they see 30*+ of timing at idle, but it really does help keep temps down at idle and low speeds. It also helps to lighten up the mechanical advance springs in a stock distributor, especially so in the mid 70s and newer units, as many of them were calibrated for emissions reductions at the cost of power and drivability, and you may not see full mechanical advance until 4500rpm or so. Some of the early emissions era stuff through to mid 80s stuff was atrocious from the factory, and this is also where ported vacuum came in to play. There was a number of things I had to do to my Fiero to get it through emissions, which made the car run like crap, but it paased every time. Set it back to run right, and it consistently failed, lol
 
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Also, make sure the rest of the car is in tune as well, especially in the ignition department. Particularly, correct ignition timing
I completely agree with this as well. Running insufficient advance (total) will make it run hot. Set the static timing with vacuum disconnected. With a stock (ish) cam, I generally like between 2° and 5° more advance than the stock setting, depending on carburetion upgrades. A few extra degrees can drop the operating temperature significantly. 8° to 10° BTDC is usually a good starting point for most SBC engines.

Then, with vacuum advance still disconnected, test and measure centrifugal timing advance. I don't have the specs in front of me for OP's 1978, but there should be no additional advance at 1,000 RPMs, and it should be something in the neighborhood of 12° at 1500 RPM, somewhere between 15° and 18° at 2500 RPM and 22° when it's all in, somewhere north of 4000 RPM for those 1978 smogged up engines. Weaker springs will get you all in sooner (generally a good thing), but "all in" should be about 22° to maybe 25° of centrifugal advance (on top of the 8° static, that's 30° to 33° total).

and make sure you're using the vacuum advance with manifold vacuum (as opposed to ported).
I have to disagree with this as general advice.

First, using vacuum advance depends a whole lot on the cam profile being used. With a stock cam, up to around 225° at 0.050" lift, or 275°-280° "advertised duration" (at valve seat contact), ported vacuum is the way to go. Manifold vacuum will give you a big stumble on sudden acceleration, as all the vacuum advance is lost when the throttle is suddenly opened.

Over that on the cam specs, when the idle vacuum level is low (below 10" Hg) and no-load mid range (2000-2500 RPM) vacuum is also low (below 14" Hg), it's better to just plug the vacuum pot and run another 5° to 15° (or more) static timing.

Testing the vacuum advance, you really need a MityVac or similar hand operated vacuum pump. IIRC, You're looking for no advance at 4" to 5" Hg vacuum, and 20° (ish) advance with 10" Hg vacuum.

Sometimes if you get too much total advance, you have to limit the movement of the vacuum advance lever. This can be done with a block off piece in the dizzy to prevent it from pulling too much advance.
 

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I have to disagree with this as general advice.
This is one of those few times where it's probably going to be a "we'll agree to disagree" situation, lol.

Ported vacuum came about as strictly an early attempt at controlling emissions. The whole idea was to retard the timing at idle, inject additional air into the exhaust via the A.I.R pump/smog pump which intentionally raises the exhaust gas temps to get the hydrocarbons and NoX to burn off in the now much hotter exhaust, as catalytic converters hadn't yet been well developed to handle this duty. This brought along with it - higher coolant temps. This is also why a number of vehicles from the late 60s into the 70s had a factory initial timing spec near 0, and even sometimes a couple degrees after top dead center - the more you retard timing, the hotter the exhaust gets. This is also a part of why some of those early emissions era engines had such dismal power outputs. As catalytic converters became more advanced and commonplace, this method of controlling emissions via ignition timing disappeared.

You're going to lose that vacuum advance momentarily on sudden heavy throttle application regardless of whether you're using ported or manifold vacuum, as intake air velocity is directly related to vacuum levels. Snap open the throttle, you lose vacuum, and thus you also lose air velocity - which then kills your ported vacuum signal. Along with this, you WANT that drop in advance on sudden acceleration, as the accelerator pump tosses a heavy shot of fuel down the intake, and a large amount of ignition advance at that point is a good path to detonation city....which also would bring higher coolant temps with it.
 
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Discussion Starter · #14 ·
Wow those are some very thorough answers. Thank you guys for taking the time.
The timing I believe is dialed in pretty well. It's a 355 with a comp cam 262h so it's pretty mild I believe but I will say that when it's running around 195- 200 degrees it seems to run extremely well. So I'm thinking I should change both the thermostat and switch them moving on to sidebar fans. I'm sure I could get a mechanical fan back in there but not sure I want to do that.
 

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If you want to keep the shroud you have and get better fans, I'd recommend 2 of the Spal 30101522 fans. Be sure to get the little mounting brackets, Spal # 30130010(you need 8, 4 per fan).

Also, I don't really like those slots/louvers in the shroud. I'd cut that area out to a rectangular opening (maybe leaving a vertical piece up the center with the edges folded forward to make a "support beam" and use the Spal rubber flaps (Spal # 30130012) in those locations. The slots you have will let the fans suck air in through the openings when you're stopped and there's no air flow from the moving car. Air that comes in those slots won't cool the radiator, it just recirculates into the engine bay through the fan. The flaps open when the car is moving, allowing air flow at higher speeds, but close when you stop, allowing the fans to draw air only through the radiator.

Each Spal fan needs it's own relay, it's own 25A fuse, and works best with it's own power wire going to the alternator charge post, the starter battery cable post, or to the battery, whatever is most convenient. I generally power the coils with a short jumper from the main power wire at the relay socket. And both coil trigger grounds can go to a single switch on the head or manifold.
 

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Discussion Starter · #16 ·
If you want to keep the shroud you have and get better fans, I'd recommend 2 of the Spal 30101522 fans. Be sure to get the little mounting brackets, Spal # 30130010(you need 8, 4 per fan).

Also, I don't really like those slots/louvers in the shroud. I'd cut that area out to a rectangular opening (maybe leaving a vertical piece up the center with the edges folded forward to make a "support beam" and use the Spal rubber flaps (Spal # 30130012) in those locations. The slots you have will let the fans suck air in through the openings when you're stopped and there's no air flow from the moving car. Air that comes in those slots won't cool the radiator, it just recirculates into the engine bay through the fan. The flaps open when the car is moving, allowing air flow at higher speeds, but close when you stop, allowing the fans to draw air only through the radiator.

Each Spal fan needs it's own relay, it's own 25A fuse, and works best with it's own power wire going to the alternator charge post, the starter battery cable post, or to the battery, whatever is most convenient. I generally power the coils with a short jumper from the main power wire at the relay socket. And both coil trigger grounds can go to a single switch on the head or manifold.
I'll look at those now. Thank you
 

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What thermostat and fan switch would you guys recommend then if I want to keep the engine around the 195-200 range?
I'd go with a Stant SuperStat thermostat. Either stock 195°F or maybe down to a 180°F one.

I know this isn't an apples to apples comparison, but in my 1997 S10 pickup truck with the 4.3L Vortec V6, I run a Stant "SuperStat" 195°F. When I run Torque Pro gauges on my phone in that truck, the engine coolant temp gauge (from OBD-II data) reads 200°F +/- 2°F regardless of what I have loaded in the bed (up to 1,000 pounds, I don't overload) or where I drive.

If I'm towing a trailer (up to 5,500 pounds, although my truck and my hitch are rated for 6,000 pounds), it'll creep up a little higher, but that's more because I'll shift down out of overdrive, and the tune I have for the transmission won't engage the TCC clutch in drive, only in overdrive. The extra heat from the plate cooler for the transmission fluid seems to boost the ECT as much as 10°F.

I do run two auxiliary pusher fans on a shroud in front of the AC Condenser. One is a 12 inch Spal pusher like the one I recommended above on the driver's side which is triggered by the AC refrigerant pressure and has an additional trigger at 215°F coolant temp by a sensor in the passenger side head. When that one comes on for engine coolant temperature, I know my fan clutch has crapped out, and it's time for a new fan clutch and probably water pump. The other is a smaller 9 inch (maybe 8 inch) Spal fan that's mounted in the front shroud right in front of the transmission cooler. It's triggered by a temperature sensor in the transmission fluid line. There's also a few of those flaps in the front shroud to let more air through at highway speeds.
 

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One other thing that hasn't been mentioned. On many vehicles, there are "air deflectors" or bulkheads that force all the air that comes through the grill opening(s) to go through the radiator rather than around, over or under the radiator. If you have these in your Nova, make sure they're well sealed to keep all the incoming air routed through your new radiator. You may even have to fab some additional deflector pieces for your aftermarket radiator if it isn't a perfect fit where the stock radiator was. You may also need some foam or rubber "seals" around the edges where the radiator sits to seal it off to the deflectors.

If too much air goes around the radiator instead of through the radiator, the symptom is generally that the engine will run hot at highway speeds. This is a common issue on older Corvettes (C3 and C2 generations especially). They had foam seals around the radiator that age and degrade, or completely disintegrate, and the radiators in those cars are rather small for the weight of the car and the size of the engines.
 
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