Yeah- Rod’s Radiator in SoCal is who we all recommend for rebuilding Hummer/hmmwv radiators. There is some other shops guys used around the country but prices are all similar. Factory is all copper and it has huge support brackets. Has to be built well because of the ridiculous angle the thing rides at then all the offroad abuse. About a grand to rebuild one is normal.
But brand new price is $1600-1800 depending where you get it.
Many of the guys jump to the cheaper aluminum options - they aren’t cheap made, just lower price. And they hold up for onroad use ok for about a decade. But even ones from Ron Davis and Griffin who both are crazy well known for off road racing radiators dont hold up to 100,000 milesof use when doing a lot of it off road. Just a matter of material strength.
As to 3 core vs 4 core- I spoke to an engineer from the original company who used to make all the hmmwv hummer ones- as well as they make them for several auto brands like USA made Toyotas. He said the idea of 25% more cores = 25% more cooling is off because another row of cores restricting the airflow going through limits it. He was one of the original engineers for hmmwv cooling stack and said when they designed it and AM General decided to save $$ and go 3 core- they knew future problems would happen. Remember it started with the 6.2 n/a engine. So they built the tanks, brackets, etc to fit a 4 core from day one. My 95 had 3 core factory but by 2004 they were 4 core. Early 2000ish era hmmwvs with uparmor packages were getting 4 core.
He said for Hummer/hmmwv the 4th core adds 23% more cooling when on a test bench- but the restriction in airflow at certain airflow speeds actually helps more energy transfer. He explains it like the cold air spends longer in contact with the fins between the cores so it then becomes a far greater ability to extract the heat because of the unique redirecting of air in a “Z” pattern across hummer radiator and through the shroud across the fan blade. So we actually get a 25% increase for the majority of its cooling.
I asked about regular pickups- he referred to the CUCV (we know as a square body from the 80’s) and he said they are more on the 23% down to 21% as they go faster and faster head wind speed for being 4 core. They built the radiators for GM back then.
Interesting enough- he asked me if I ever heard of a coating company called Techline- haha. They don’t use it stock but would get special orders from AM General once in a while… haha.
When I had mine rebuilt I went from 3 core to 4 core. But also had them use dimple cores. They are like little dents in the cores that stop linear flow. Type in linear flow on YouTube if you don’t know it. But basically the water going through the core after a few inches just builds a wall of water around it and has water in the middle that stays insulated from touching the metal.
So the dents or dimples in the core cause turbulence in the water and makes it all come into better contact with the metal to help shed the heat from the water to the metal core by eliminating laminar flow, increasing surface area contact and more surface area of airflow. This also causes a greater pressure differential which impacts more cooling.
Some of the studies like this one:
https://ijsrd.com/articles/IJSRDV3I30024.pdf
Show that gains of 210% are possible. In reality what we can get in automotive applications and survive the abuse tends to be 25% gains. The longer the cores are the more they increase. Getting 2.1 gain is when used in heat exchangers that are 25 feet long.
Aluminum vs copper- copper is stronger and better conductor for heat. So thinner core walls mean better heat exchange along with better conductivity.
The larger cross sectional area of the cores used in aluminum radiators are required for strength. The tubes are thicker wall but more importantly larger sized core itself. Basically a 2x4 cant span as far as a 4x6 without bending under its own weight. An advantage of larger core is it can hold more water to get more water cooled off faster. But laminar flow happens much easier so it’s a two edged sword. The specific shape of the cores makes a huge difference in the performance of it because one might have 5% flow while the other is 95% laminar.
So comparing 2 radiators of “exact” size isn’t always identical performance.
We would see this in the fleet when we hadn’t yet abandoned dexcool and radiators failed fast. I had 3 trucks in for new rads, all got same flush & treatment except 1 was a factory new radiator, and the other 2 got aftermarket from different brands because no one had more than 1 in stock so 3 different suppliers.
The difference was immediately noticeable upon test drives. All were aluminum, same size, identical trucks, near identical mileage, coolant came from same 55 gallon drum. We actually swapped twice and used a camcorder to record the difference. It was like a good, better, best example. The factory one did best the one from napa did ok and one from a Checker auto parts did absolutely horrible. We had outside salesman for the checker & napa. I had them come over and watch the tape. Both took the radiators back for full refund as soon as the 2 factory units arrived the next week. Spending tons of money they don’t mind eating it once in a while.
It was kinda funny because we took out my custom all copper (even tanks were copper ones I made & gave to the radiator shop) one from my truck and ran it in a truck for comparison. HUGE gains. But was twice the cost back then and was a cirle dimple rather than the now used rectangular dimple. It was also a two pass where there are dividers in the tanks.
Anyways- don’t ever assume that two similar looking radiators will perform the same. Subtle differences in how the tubes are made or if it is 100% aluminum tubes or an aluminum alloy makes big difference.
www.summitracing.com
