Radiator Core Thickness?

I am having overheating problems with my 1009, and would appreciate any help.

It has a new badger diesel rebuilt IP, new injectors, and starts right up even in sub-freezing weather. The engine runs great, sounds great, and makes good power. But if its hot outside (>90F) or if I try to pull long highway grades the engine coolant rapidly warms to 220F and would probably continue to rise if I didnt get out of the throttle. EGTs are 500-800 cruising and eventually climb to 1000F or so on long steep grades.

If its warm out then I hit 215F coolant temp long before 1000F EGT and I need to slow down or sometimes pull over. If its cold like it has been recently (60F air temp) then I hit the EGT limit and water temps stay around 210F or just a bit under. But even that seems too hot to me and it wont stay winter forever...

I have temperature gauges in the radiator inlet and outlet and maintain a 20-30F delta at all engine operating conditions. Around town and on flat sections of highway when it is cold the radiator inlet temp is 195-205F and the outlet is 170-180F. When climbing steep grades, or even cruising 70mph on flat ground when its hot out the inlet temp rises to 210-220F and the outlet temp goes to 195-205F if I stay on the throttle. With the water coming out of the radiator already at the maximum 205F operating temperature, there is obviously no hope of keeping the engine at a safe temperature. Based on this data I am assuming the engine is creating more heat than the radiator can shed.

The radiator was installed new by me a couple years ago, and the truck has this problem whenever I drive on highways in the summer. I usually just drive around town and have been careful to slow down and not overheat when on the highway, but I really want to get it fixed now. Do I just need a bigger radiator? The stock mechanical fan and shroud are installed and in good condition, and the engine runs at thermostat temp (195-205F) at idle and at low throttle. It only overheats under heavy load on the highway or off road.


My current radiator is a 2 row 1.75" thick aluminum core, from rockauto (https://www.rockauto.com/en/moreinfo.php?pk=3606795&cc=1050589&pt=2172&jsn=1)

I have seen many posts on here about a copper/brass "CU850" radiator, but when I search that part number all I find is a Spectra Premium CU850, which is a 2 row plastic/aluminum radiator with a 2.375" thick core

I really dislike Jegs, but they also carry a radiator that looks like it would be a direct fit for the stock rubber insulators/brackets and has a 2.5" thick 2-row core (https://www.jegs.com/i/JEGS/555/511457/10002/-1)


What radiators are folks on here using successfully? Will going from a 1.75" to 2.375 or 2.5" thick core in my truck increase cooling capacity significantly? It seems like it would?

Your 2 row (core) sounds like the issue to me.
The original is 4 row.

The 2 row simply doesn’t have the capacity to get rid of the extra heat.

The original design brass/copper radiator is still available.
Expensive, but available.
My radiator shop had it within a few days.
Was an exact replacement and dropped right in without issues.
That was 7 years ago and not a single issue.

I agree with Tinstar, your problem is with your 2 row radiator. Get yourself a 4 row and you should be good. Good luck.

Still listed in their catalog

Does anyone know the core thickness of the original radiator, or have one you could measure at some point? I dont have one to measure unfortunately.

My current radiator is a 1.75" core, which I agree is probably too small. That said, a 2 row radiator with 1" tubes (granted not what I have) has more cooling surface than a 4 row with 3/8" tubes. I'm curious how much smaller mine is than the factory original and would like to compare the actual core sizes before buying a new radiator. I recognize I probably need to buy one, but want to at least do the math on tube surface area before I spend $600-800.

Your knowledge of aluminum 2 core compared to stock 4 core in post #5 is good to read. I have a stock radiator that I will try and measure later this evening. I can’t right now.

I have vehicles on both sides of the copper-aluminum debate. I will let others keep arguing that but state I think the biggest aluminum unit you can fit is the correct path. Due to cool down time after a pull and it is all 1 alloy instead of several.

You mention EGT. Do you have a turbo? If so, which turbo? As in Banks, GM, or other.

I only have experience with a Banks set up. I went through the same issues you are on one of my trucks. I wrote about it over and over for years. That thread is linked in my signature below.

My biggest adjustment needed was between my ears. Growing up anything over 200° was bad and anything over 212° was shut down the engine time. The 6.2/6.5 is just different. A stock 195° thermostat starts to open at 192° and is fully open at 204°. That means by design it is engineered to be above 200°. The same engine in a HMMWV has a fan that doesn’t even turn on until 225° or 228° is reached. Which again means by design running 220° for extended periods of time is expected and designed in.

Just because those are design facts doesn’t mean I like them. I have learned that higher RPM as in above 2250 rpm to 2500 rpm when climbing keeps the water pump working good enough and the EGT’s down enough to stay below 1000° EGT and 215° coolant. I added water injection which actually keeps me below 800° EGT.

Barrman said:

Your knowledge of aluminum 2 core compared to stock 4 core in post #5 is good to read. I have a stock radiator that I will try and measure later this evening. I can’t right now.

I have vehicles on both sides of the copper-aluminum debate. I will let others keep arguing that but state I think the biggest aluminum unit you can fit is the correct path. Due to cool down time after a pull and it is all 1 alloy instead of several.

You mention EGT. Do you have a turbo? If so, which turbo? As in Banks, GM, or other.

I only have experience with a Banks set up. I went through the same issues you are on one of my trucks. I wrote about it over and over for years. That thread is linked in my signature below.

My biggest adjustment needed was between my ears. Growing up anything over 200° was bad and anything over 212° was shut down the engine time. The 6.2/6.5 is just different. A stock 195° thermostat starts to open at 192° and is fully open at 204°. That means by design it is engineered to be above 200°. The same engine in a HMMWV has a fan that doesn’t even turn on until 225° or 228° is reached. Which again means by design running 220° for extended periods of time is expected and designed in.

Just because those are design facts doesn’t mean I like them. I have learned that higher RPM as in above 2250 rpm to 2500 rpm when climbing keeps the water pump working good enough and the EGT’s down enough to stay below 1000° EGT and 215° coolant. I added water injection which actually keeps me below 800° EGT.

Click to expand...

Yes, I have a GM1 turbo. Not the most efficient thing, I know. I will read your thread and see if there is anything I can apply to my situation.

I've read on here and elsewhere on the Internet that 210 is the upper limit, and 220+ can lead to cracking the heads and block. I agree that with a thermostat which opens by 204-205, staying under 210 seems like a challenge. But other posters claim to be able to do it.

The one time my factory coolant light came on the engine was over 230F when the fan clutch failed in stop and go traffic. If I just let the engine run 220-230F as it probably did for years before I installed temperature gauges, that might be fine and it would probably get noticably better MPG. But it's hard to know what the actual safe limits are and with as expensive and hard to find as these engines are becoming I would prefer to keep it a bit cooler if I can...

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As far as copper and brass vs aluminum radiators, that's a debate I usually like to stay out of haha. Both can work well if properly designed and sized for the application or both can work poorly if used incorrectly.

I'd like the focus of the thread to stay on specifications or the stock radiator and selection of a suitable replacement however, and to that end there are some things to keep in mind.

With copper/brass radiatos, the tubes are limited to about 5/8" wide due to the strength of the material, so more rows virtually always means more cooling capacity. With aluminum the material has far higher mechanical strength and tubes can be 1", 1.25", or even 1.5" wide. A smaller number of wider tubes gives the same surface area with fewer gaps between them. Gaps waste space in the core where the tubes are not touching the fins, so a 4 row core with the same thickness as a 2 row core actually has less functional surface area to transfer heat from tubes to fins. This site has a good diagram explaining this:

It is true that copper has a higher thermal conductivity than aluminum, but that only matters for getting heat out of the coolant in the tubes and into the fins. The zinc solder used to connect the fins to the tubes has much lower conductivity than pure copper, which limits the conductivity advantage. The surface area where the tubes contact the fins is also smaller for a given core thickness as discussed above. Both of these facts reduce but may not completely eliminate the advantage of coppers higher conductivity.

The convention coefficient, or the ability of the fins to reject head into the air, is not a material property at all but a product of the working fluid (air) and the boundary layer across the fin surface.

All this to say any radiator material can work in any application. But just looking at the number of rows in the core, or the material, or any other specification in isolation misses the rest of the picture.

I love seeing threads like this, tons of excellent information!

My experience in this department have faired well with a 4-row brass/copper or 2-row all aluminum.

I have had fantastic experience with Champion Radiators in SoCal. They build a quality all-aluminum piece, and I know many Squarebody trucks in the Desert Southwest running their hardware with great success. Note: they build to spec by year/make/model unless you're doing a one-off custom build.

Other severe heat options are a Flow-cooler high-flow water pump, Robertshaw high-flow t-stat, and desert heat-beater multi-flow radiator. I emphasize severe on these items.

The one thing I haven't seen mentioned yet is the fan clutch, a very critical item in the cooling system. If you have no leaks, and you've recently cleaned your rad from the inside out with degreaser and low pressure water...replace your fan clutch before you do anything further, then proceed if symptoms remain.

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