Custom radiator?

[Aaron S]

Hi guys, I have the yellow 6x6 built by Bob Jones with the first gen Cummins 6BT in it. It appears that I am going to have to have a custom radiator with bigger tubes built for it and I figured it would be a good idea to ask here if anyone has had this done and what your experience was. If anyone has a technical drawing of a flat fender radiator, that would be a big help as well.

The issue I'm having is that it runs hot on the highway, especially with a load on the trailer. I have changed it over to Evans waterless coolant to stop it boiling over, and removed the hood to let the hot air out... both of which have helped. It is now fine bobtailing around town, but it doesn't take long on the highway to hit 235-240 degrees. When I pull up to a stoplight it comes down to 180 by the time the light turns green. This seems to me to be a heat exchange efficiency problem rather than airflow or coolant volume.

I realize the the temperatures I'm running at aren't completely outrageous (i.e. melted pistons, scalded bearings, etc.) but its keeping me from driving the truck as often and as far as I would like, because I'm apprehensive about ruining an engine on a long trip.

Ultimately I would like to get it running cool enough that I can put the hood back on, because I think it looks better that way... though I may need to have the top of the hood louvered to help with heat evacuation from the engine compartment.

[Kevin in Ohio]

I had a custom radiator made for mine and if you want to eliminate most fitment problems I'd suggest doing what I did.

Use your current radiator as a full size guide for who you choose to make it. I took wood, foam and attached all to the radiator to within a 1/2 inch of anything it might hit. Do this when it is in the truck, then remove it and ship it all to them. Mark your outlet/inlets and such if you want any changes. Yes, it costs some money to ship it but you'll avoid most of the issues and problems. The guys I sent mine to were happy with what I did and I've had no issues.

[Desoto61]

The factory radiator in those trucks is huge, I'd wonder if there wasn't a problem with it first. Also I looked long and hard at Evan's coolant, and one of the issues is that any vehicle running it will run hotter because it's not as effective at moving heat as water/anti-freeze mixture, but it can get away with it because it doesn't boil as low, nor does it need to be pressurized to raise that boiling point.

Otherwise I had a custom radiator built for mine, plenty of shops that will do it, but like Kevin said getting them a good template, or the original rad, is key, but honestly not sure you'll get dramatically better performance vs a good factory unit, and there's just no room to make them much bigger.

A better first step might be to have the original radiator inspected/cleaned or potentially even re-cored. Price will probably be similar and they really are big radiators.

[Aaron S]

Thanks for the replies. I had been considering that the best way to do this would be to box up the radiator I have and send it off to a builder. The factory rad I have is in proper working order and, interestingly enough, when I changed the coolant I checked the total coolant volume and found it to be within about a pint of what this engine would have come with in a 1993 Dodge pickup.

So from a coolant capacity standpoint, the factory radiator would appear to be sufficient. Which it is, under low load conditions or when the ambient air temperature is below about 60 degrees F (which is about two or three months out of the year here in central Texas). Given how rapidly the temperature drops when the engine is no longer under load, I am thinking that an aluminum radiator of the same size with larger tubes should make a significant difference. It seems like I read somewhere that a 10 to 15 percent increase in heat exchange efficiency is possible.

If there are flaws in my logic here, please point them out to me. This is not an area in which I have a lot of experience and if I am wrong about something I would much rather find out about it before I throw a wad of money in that direction.

[Tom Petroff]

Is this a new problem or one you inherited?

I can't believe that radiator is insufficient to be the cause.

Can't remember what Bob used for a fan?
I thought it was mechanical, so I would be looking at the clutch,t-stat,
Or adding some type shroud.
Tom

[Aaron S]

Its been like this since I got it. Bob was upfront about it blowing a little coolant on the windshield once in a while. The difference in ambient air temp between Illinois and Texas changed once in a while to every time I take it out on the highway. I'm not complaining, just stating the issue and working towards a solution.

It has the mechanical fan on the engine. If it was a fan or general airflow issue I would expect it to run hot in town and cool on the highway. I've had that before on other vehicles.

I just talked to a fellow at PRC about an aluminum radiator. Apparently they've done a few for flat fenders with 6BTs and have had good luck with them. If I'm lucky this might even save me the trouble of shipping my current radiator off (although that is a lot of ifs).

[Desoto61]

The only other thing that occurs to me is that at speed your pump is moving coolant too fast or not effectively enough for it to have time in the radiator to do it's job.

The only real way to test that would be to get temperatures across the radiator ideally at idle and while moving. That would tell you where the heat is going or not going and how efficiently the radiator is doing it's job. It could be that a multi-pass radiator may help more than just one with bigger tubes, both of which will slow down the fluid and give it more time in the radiator to loose heat.

[im02crazy]

Airflow efficiency thru core

+1 on the radiator shroud. We're working on a similar problem on a 1949 B1-? 3 ton still in commercial use. The shroud makes a significant temperature difference because it forces air draw through almost 100% of the radiator. Doing a few air flow tests on the un-shrouded unit shows very poor pull through most of the core except the central section just in front of the fan. However there's lots of short circuited airflow around the fan (turbulence).

[penski61]

so what did you end up going with? my 47 didnt come with a radiator so i need to find something that will handle 350-400hp . i got quoted $2200 from ron davis with fan and shroud $1600 without and im not sure if a stock radiator (reconditioned ) will cool that hp in az heat

[Aaron S]

I'm having an aluminum radiator built by PRC in Indiana. It will be about $500 (radiator only). They have done a number of flat fender radiators and already have a design to work from. When I talked to them last Friday they mentioned that they have a core support and nose sheet metal in the shop (at least for now) to check fit with. It will be about the same size as the factory radiator with two rows of 1" tubes which should give significantly more efficient heat transfer than the factory radiator. They build shrouds and intercoolers as well, and can provide fans. Very pleasant and knowledgeable folks to talk to. One of my cousins has used them on several projects and been very satisfied with the results. After talking with them myself and looking over the technical drawings and photographs they sent I feel comfortable doing business with them... and the price is less than I was expecting.

[penski61]

awesome thank you , ill give them a call tomorrow

[Charles Talbert]

custom aluminum

We use custom built aluminum rads on all our Cummins trucks. It is far and away more efficient than copper and brass units. I have had only 1 several years back that I had a few reservations about proper cooling. Those of you that know M Series Rebuild know that if I have any shadow of doubt, it ain't leaving until I'm happy. Since this issue stuck in my mind during initial testing of the truck, I can't actually say it would have ever been any real problem, but going to its home several states away, I just couldn't bring myself to release it. We built some air channeling components from sheet metal that funneled air more efficiently to the radiator core area. With an all aluminum rad already in place, improving air flow made a tremendous difference, so much so that it put my mind at ease about it. Sent it to the owner in 2010 I believe it was, never has been a problem at all. Certainly other issues can be the cause of problems with cooling, but bottom line, if all is done right, aluminum and air flow is the ticket to success.

Are you aware that some later RAM Cummins trucks actually are equipped with a second radiator mounted in front of the main radiator? I have a 2014, 2500 Ram Cummins that is equipped that way from the factory. If your problem persist, that is always another option to explore.

[Aaron S]

Thanks Charles, I was not aware of the secondary radiator on the newer Cummins trucks. That is quite interesting, and it makes sense, especially if the truck is equipped with an automatic transmission which shares one of the radiators.

[Charles Talbert]

Thanks Charles, I was not aware of the secondary radiator on the newer Cummins trucks. That is quite interesting, and it makes sense, especially if the truck is equipped with an automatic transmission which shares one of the radiators.

The radiator does not share space with a transmission cooler on the 2014, 2500 models, trans cooler is a totally separate unit. Not sure when this change took place, as you are correct in saying on earlier models the trans cooler was incorporated with the radiator. The 6.7 electronic Cummins like mine has is set up at a considerably higher HP rating than many of the earlier models from years gone by. It isn't hard at all to get more power from an engine, especially when doling up the fuel rates, etc., however when this takes place, whether from the factory as in a new engine or tweaks made on older engines after the fact, heat can and will become an issue super fast, as apparently they found out in later models with the 6.7.