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upgrade radiator on '74 K5

my kids took the truck

my kids took the truck

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Problem: My nearly 45 year old 2-core radiator developed a pinhole about halfway up on a seam. I last had this radiator 'rodded' back in 1993. This radiator has no aluminum - it is the old style brass.

Background: During the past 23 years I have had this blazer the cooling has been marginal at best. This is a 2-core and I think it is 17" high. On hot days on a long incline I sometimes have to turn on the heater to keep from overheating. At idle it seems to hold the temperature ok. During normal driving on a warm day the temperature fluctuates between 180 and 200 deg F. In offroad conditions, high power, low forward speed, hot day, it is less than marginal.

Solutions:
  • Have someone 'rod out' and reseam the 2-core radiator and keep my marginal cooling.
  • Back in highschool guys were putting 4-core radiators in with the higher top mounting bracket. I heard that the 4-core did not help; the first two rows do all the cooling anyways.
  • I have seen custom aluminum radiators advertised that improve cooling. https://en.wikipedia.org/wiki/List_of_thermal_conductivities All hugely dependent on specific alloy and I have seen some report this as reversed, depends on copper components.
    • Brass thermal coefficient 125 + copper thermal coefficient 400
    • Aluminum thermal coefficient 235
Based on thermodynamics, there are three variables for cooling, surface area, heat transfer, and crossflow. My crossflow is fixed by my fan so that is not changing. The heat transfer between brass and aluminum looks like an opportunity. So that leaves surface area, length x width x depth. I don't know how much depth helps in this case, so that leaves width and height. On the K5, the radiator already does a good job of covering from headlight to headlight and hood latch to bumper. So, I don't see more surface area either.

Here are a few relevant threads
Has anyone found a solution to cooling the K5 over the OEM? With a 4spd manual and no a/c.
  • Has anyone measured the real difference between the brass 2-core and 4-core?
  • Has anyone measured the real difference between the brass and aluminum?
If the 4-core helps I can change the top bracket. In the best case I would like to work with the OEM (17") bracket, 2-core radiator mounts, and fan shroud. I want to keep the truck downtime to a minimum.
 
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I've not measured the difference, but I was running around with a stock 2 core, then "upgraded" to a 3(?) core aftermarket copper/brass. The 2 core seemed to do fine, never saw anything crazy temp-wise. Temp swings I see with the newer radiator appears tied mainly to the thermostat being an aftermarket one that doesn't operate very smoothly. I get noticeable (but not dangerous) temp swings at higher vehicle speeds when load changes. 19" IIRC is the most common height radiator, sounds like you have the shorter one. Don't know as it's a real limitation, I believe those still completely cover the core openings.

My *thought* based on GM's various radiator setups in the trucks, is that increasing coolant capacity was a large part of the strategy of cooling these trucks as cooling became marginal with big blocks and diesels. The way the core support is designed, strictly in terms of efficiency, you can't cool any better than what is going to flow through the cutouts in the core support. Yet GM used radiators in certain apps that extended well beyond those cutouts. Obviously SOME air will still go through the "shrouded" area due to the fan setup, and pressure as the vehicle moves forward, but there is no efficiency there.

IMO a thicker radiator that is the "standard" radiator width/height, is about optimum. The majority of cooling is done there, the larger ones I'm guessing are about having some reserve, through heat capacity of more coolant. if the engine load increases, it will take longer to heat more coolant up. Still not a "solution", it's a band-aid, but we don't have a lot of options.

I think the factory fan is an unknown quantity. It's flow is tied directly to engine speed (assuming the clutch is locked up) but at what RPM is the fan most efficient? Is it designed to flow as much as possible at idle, at high RPM, or some compromise? Improvement is probably likely with REAL electric fans (like the windstars) as their flow isn't based on engine RPM.
 
I think you're right on w/ your thoughts. Usually by the time the air has gotten to the 3rd core it's not pulling much more heat out. 4 cores may give more mass of the water to hold a slightly more stable temp but they're not going to shed anymore heat.

Newer designs of cores come w/ higher fins per inch and therefore have more surface area to shed off heat. They also have thinner more oblong tubes than older cores. You may be able to gain some there - there's always a point where too many fins just blocks up air but I doubt any reputable mfg would hit that.

As for fans - everything I've ever read shows that mechanical fans pull MUCH more air across the core - esp when there's resistance to the flow. Such as when you're drawing across a rad core. V8 powered fan vs small electric motor. But your clutch would need to be locked for that to happen. Be sure to check that.
Many of the electric fans only pull max cfm when the flow is unimpeded.
 
The only problem with the factory fans is that there are no measured flow numbers that I'm aware of. I personally have no doubt that they move air very, very well, but it's just impossible to accurately compare to the electric setups with no real numbers.

Obviously the mechanical fans were up to the task, if they don't still use them, they did for a long time after our truck line was done, when cooling was even more critical. You know they can get the job done. It would be interesting to know what the newer RWD applications are using for fans, and how they are controlled. I know the '04 Duramax trucks were not electrics.

I'm thinking mainly for low vehicle speed/RPM conditions, a stout electric fan setup is *likely* more effective than the mechanical fan. But still complete conjecture, since we don't have any numbers for the stock fan. If an electric swap is not going to be considered here, not really worth hashing it out I suppose.
 
Man... I wish I had saved that info when I ran across it. Was on the Corvair forums, and they were discussing various fans to replace the one on those - the fanbelts are hated on them. Many guys have used electric, but it doesn't hold up on the fwy when you start needing power.. It was about 15 years ago and I remember the numbers being vastly different once the airflow was blocked....

Lots of old GM engineers on that forum and they'd posted some graphs.

FYI, I'm not being a douche - just got me thinking now...
 
Crud, just lost my post.

Definitely not taking the banter as negative. :) I like numbers, it's all learning.

I'm just going to be brief, I don't feel like typing it all up again. I found a post stating the Windstars are rated at ~4400CFM, and from all accounts that is more than enough for any small block I've known them to be put up against, so that might be a decent number to shoot for. I'm seeing aftermarket fans at 6000+CFM now.

Too bad we don't have access to all the old engineering and test data. You just know we are reinventing the wheel many times. However we also have the luxury of decades of technology, and don't have the overhead GM did. Our wrecking yard parts are probably pennies on the dollar compared to what the part cost GM new. At least if we had the historical data, we'd have a better idea of what to angle for, and if something isn't working, a better idea of why.
 
I have a 4 core from an '89 that I am considering having re-cored. I kinda been wondering if an aluminum unit would be better. The only time I've had a square body run hot was when the coolant level was low. All my square bodies have hit at least 100k miles.

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For the cost, I don't think you can really go wrong with the plastic/aluminum replacements. I'm still not real keen on believing our trucks are solid enough to not stress the tank/core bonds, but they certainly work fine in pretty much every OEM application out there today.

Even re-coring is probably more expensive than getting a new plastic/AL radiator. :(
 
After thinking a bit I decided to recore my original radiator from two core to three core.

The single biggest factor was that I know it will fit; I wanted this to be a guaranteed 15 min radiator swap. I read that the aluminum radiators cool just as well as the brass/copper radiators so there went that idea. I found an old timer a few towns over that did recores http://www.howardaveradiator.com/. He gets the cores made here in the same area. It was not cheap, $500. The two core tanks are wide enough for three cores so it was not a problem. The radiator is noticeably heavier and the cores are wall to wall now. He says all he does are these old radiators, his sons do other work in the garage. Turns out these radiator shops are getting hard to find, the old guys that do this work are not being replaced.

It has not been hot but the temps seem to hold steady at 185 to 190. The next hot day I will update this post. Anyways, the leak is fixed; he said my core was leaking from a few spots.

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Nice! I had a radiator recored I couldn't replace years back (from an Olds 350 diesel, I just HAD to have an integral oil cooler) and it was pricey at that time. Place even had a machine that would measure the flow through the radiator, so they could show you right there before/after the flow numbers, and could tell you roughly how bad the cores were just by flow testing your original when you brought in. Bad enough and they would tell you not to waste money trying to rod it.

The plastic/AL ones are so cheap, no one is going to recore anything anymore. All that will remain are places that cater to restorations.

I'm going to cut 4" off the width of the radiator in my truck (putting it where the AC condenser was), will be interesting to see if it can still cool.
 
Wonder if the new core was anymore efficient in it's design than the old one. More fins, or thinner tubes for more surface area.
 
JoshHefnerX said:
Wonder if the new core was anymore efficient in it's design than the old one. More fins, or thinner tubes for more surface area.
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They didn't say anything about it and the design looks similar to the original. The fins might be a little tighter together but I think it is just my imagination. The tubes look the exact same. In my first post in this thread I have a link to a new 4 core radiator that has the option for 'fins,' 'more fins' and 'a lot more fins,' for quite a bit more money. The old timer said three cores would be fine and a big improvement over two cores; he might or might not know what he is talking about. From the workmanship it looks like he knows how to put a radiator together. He had it done in two days too.
 
Update on the radiator: I just returned from a longer drive on the highway in warmer temperatures as well as slow country drive. It was 80 deg F today, not the hottest but warmer than anything I have seen for awhile. The temperature does not fluctuate as much as it used to - seems to stay pegged at 188 deg F no matter what, highway or country road, uphill and downhill. At idle the temps drop a bit to just under 185 deg F. So far the three core seems to be an improvement over the 2 core. Once it gets warmer out (100 deg F +) then I can give this a better test.
 
dyeager535 said:
Awesome, sounds like you made the right call!
Click to expand...

Another test case for the new radiator.

Today was warm, 80 deg F; not 110 deg F central valley summer heat but still it was warm.

I had an hour drive and had to rush to give a presentation and then get back the hour in time to take my daughter to dance. It made a good test of the cooling. I pulled 2,500 rpm each way (my speedo gear went out - by the numbers 75mph), I kept pace with traffic and still got passed. Usually I cruise 60 mph (2,000 rpm) in the slow lane. The point is the engine was under load and it used to be that highway scenario would consistently get 200 deg F on a day like this.

The temperature never went higher than 188 deg F.

Seems to drive more consistently without the temperature swing. Towards the end it sounded like it might have been leaning out a bit and on the edge of pinging but I suspect that is back to my fuel line paralleling my exhaust and heating up the fuel on the longer drive. I only heard a very very light pinging once underload on a winding road; might not have even been pinging, maybe a bird or something.

Next post will be an update after a long drive through the central valley on a hot day (100 deg F+) and up the grade into the mountains - the real test.
 
Another test case (hot 95 deg F day and steep highway grades)
  • Over the HWY 17 pass it was mid to upper 80s (hot) there was traffic so I was stuck at maybe 1,800 rpm (50 ~ 55 mph) and right about there the engine has plenty of torque (can accelerate) but seems a little on the low side. In the past on this particular stretch of grade this has caused pinging on warm days followed by 205 ~ 210 deg F engine temps. Last time, with a two core radiator, I had to pull over and richen the idle to eliminate the ping and lower temperatures. This time with the three core and the engine leaned back out, the temperatures began to rise and went to 190 deg F, I might have heard a slight ping for an instant reflected off the center highway barrier.
  • On the way back from the coast we came up highway 101 and it was 94 deg in the south valley. The engine temps went up to 200 deg F cruising at 65 mph. As soon as we got out of the valley the outside air temperatures dropped and the engine temps quickly went back to 185 deg F.
This is not what I wanted to see. My goal is no engine temp rise no matter what.

In the same situations in the past with a two core radiator the temperatures would have been 10 deg higher. I assume with a four core radiator I might get the temperatures down another 5 degrees assuming diminishing returns.

The highest outside air temperatures I see are 105 deg F (maybe a rare 110 deg F) so my max engine temp is probably going to be 215 deg F. In the past I had to turn on the heater to keep temps at 215 deg F on a 105 deg day.

This tells me the hole the chevy engineers put in the radiator support is too narrow. The grill on the K5 goes from headlights to headlights but a good two feet of that is just solid radiator support. I am starting to think the original design was for a super wide radiator.

I have a mild 350, how are higher HP 350s cooled? Particularly in camaros and other applications with small radiators?

My goal is my temperatures do not change. Once I get that then I plan to use a higher temp thermostat but without the cooling stable I don't want to mess around with higher temperatures. Will the temperatures stabilize if the engine temp is raised due to the increased delta between air temp and water temp? At 185 deg F water and 100 deg air there is an 85 deg difference. If I use a 205 deg thermostat then the difference is 105 degrees and should transfer quite a bit more heat - meaning the engine stays 205 deg F no matter what while trying to keep a lower temp like 185 deg F with the same cooling system will not happen.
 
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GM had a really high fan turn on with the injected setups in cars. I'd have to go back and check, but pretty sure the primary fan on the TPI cars came on at 220* (this is ignoring AC requests) and the secondary fan for those controlled with a switch, was 240*. It may have been an impossibility, those cars had even smaller radiators...GM may have just decided what the heck, and let the engine run quite hot when conditions dictated. Obviously though, the advantage there is that they could control timing based on temp, not to mention running it richer as temps start to go high, and a knock sensor as a failsafe. Not an apples to apples comparison, the only portion I think valid to compare is that they were still small blocks, and GM felt 220* was not terrible to run them at.

I started looking up data to see what sort of inlet air temp I was seeing vs. coolant temp and ambient, and the speed of coolant temp climb, but didn't have a lot of luck...most of my testing so far has ignored ambient temps. I noticed that about 205* as reported by the CTS, was as hot as the truck got, unloaded, freeway driving without traffic, on fairly flat ground. It would dip to ~196* when throttle was light (195* rated t-stat) then bounce up to 205* or so and stop climbing. I suspect the thermostat needed the extra heat to open fully. I was trying to figure out what sort of advantage running a lower t-stat might give you for something like a hill climb, where that 15-35* temp cushion might be enough. I'd suspect that carbed though, you may run into similar issues with timing/fueling...at lower temps you can run it quite a bit leaner, but if the engine gets up to 195* on a climb, then that lean at 160* will start to cause issues.

More aggressive vac advance, more fuel on the secondary side?

When I go with the smaller radiator, if I have cooling issues, I plan to run a high flow water pump. There isn't going to be a downside to doing so, except cost. Hard part will be testing under similar conditions to see if the expense was worth it.
 
I see where this is going:

With a 210 deg tune I could find that without an automated loop for fuel and timing control then I will have a finicky tune with a narrow band of operation. That rare occasion I get outside that temperature band then things will go bad fast (as well as being the least opportune time to go bad and at temperatures that could cause severe damage).

A tune at the mid range 180 deg has a broad band of drivability and why it is popular for carbed engines

A tune at 160 deg, while nice and lean and tolerant of lots of timing curve (I tried this maybe 20 years ago but went back to 180 deg thermostats), also has a narrow band of operation

I have never tried a 195 deg thermostat simply due to the need for a buffer to allow for my poor cooling capacity. After reading a few threads, the consensus seems that if you have a 180 deg, then keep it, if you have a 195 then keep it, you won't notice a difference between the two. True, it took me a few tries and some flat filing/sanding to get my housing to seal - no need to screw that up just to test different temps.
Based on the lack of threads that state "hey, I used a 210 deg thermostat with my q-jet and got great gas mileage, drivability, and better power" probably means it does not. Most of the threads say, if you try a higher temp thermostat you will get into detonation problems. A few guys that tried 160 deg thermostats said when they tried a 180 deg thermostat they got a smoother idle and the engine quieted down; they were happy with the 180 deg. Most everyone agrees there is no noticeable difference between 180 and 195, whichever you happen to have in now, just stay with it.

I guess I will stay with my 180 deg and on most days stay steady at 185, on hot days fluctuate from 180 to 200, and on the hottest days (100+) get up to 210. I will just have to find (I think I have it now with a qtr turn richen of idle on hottest days with steep grade) a timing curve and fuel curve that stays happy in that range under acceleration and on steep grades.
 
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You may be running into the point where mechanical control doesn't have enough control or sensitivity. You can run at a higher temp but need more conservative tuning. qjets and mechanical distributors were fine in square bodies even w/ the narrower rads that they have. People here in phx don't have problems... Just have to realize there's a reason fuel injection came about. Not flexible or sensitive enough for all driving circumstances.
 
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