454's and rads

[greg mgm]

I've owned my 78 GMC 3/4 ton PU since '84, and most of its life has been with a 350. I couldnt overheat that engine in the worst conditions (summer heat, towing, AC on, etc). I installed a 454 a couple years back, and had my 27" rad rebuilt as a hi-density 4 row. Now, the engine cooling is only OK, but at freeway speeds, while towing up even a mild grade, the engine runs hot, and forget going up steep grades, it'll overheat. I did all the usual trouble-shooting, rad cleanout, changed thermostats (3 times) fresh coolant, correct timing, fan clutch and shroud, etc, etc. So, my question is, you guys with older trucks and 454's, what size rads are you running, and is this a common problem for older big blocks? Would I be wasting $$ on something like a Ron Davis aluminum rad, or similar? Thanks in advance.

 

[shane74]

Is your 4 core a stock replacement unit? If not, and you had it rebuilt as a 4 core, it still may be a bit too small. You may need to run dual electric fans. Also, I know you mentioned your clutch fan, but if it isn't working (spinning) properly, it won't pull enough air through the rad to cool properly.

 

[greg mgm]

The rebuilt rad looks like a stock rad, but high density. The guy who built it has built rads for many years, and seems to know what he's doing, and said the rad is plenty big enough. I did buy a flex a lite dual fan, which helps at low speeds (in traffic etc) but the cooling seems to suffer when the engine has to work fairly hard. What size rads are in the older trucks that originally came with a 454?

 

[k20]

explain the 'high density' bit. I have a stock 4 core on my 496 and no cooling issues *knock on wood*. I have heard there were stock style that had a lot of 'fins' on them, and that impedes airflow and made em overheat.

 

[BAJA_BLAZER]

One thing that you didn't mention checking was the water pump. They do go "bad" as impellers and pump housings erode. I just put a new 454 in my Class A Motorhome and that was such a PITA that I replace everything else at the time. One of my racing sponsors is the largest Radiator Company in San Diego so I could have any radiator they had. After lots of discussion we decided on a high efficiency aluminum two row unit. The goal is high heat transfer, not a large volume heat sink. Heat transfer requires good airflow and we felt that a "high density" thick 4 row was too restrictive. So far, it is running cooler than it did with the previous 4 row, though that had 40,000 miles on it. If you are going to run the "high density" thick 4 row, make sure you are getting enough air through it by using a good fan or properly installed electric fans. Another important factor is proper shrouding to direct airflow through the whole radiator, not just the middle.

 

[1-ton]

There is a difference between a radiator for a small block and a 454. The radiator for a small block has smaller side tubs than a 454. Are you running a fan shroud, trans cooler, and a oil cooler? You would be surprised at how much the cooling difference between having a fan shroud and not having a fan shroud is. Oil coolers are almost a must for a big block.

 

[rjfguitar]

Your problem sounds similar to mine. Like you, I have replaced everything and installed a nee 4 core and dual electric fans. That is barely enough and if I stay in it hard for longer than a few minutes it shoots up. I haven't been able to control mine either.

Things I have started to check...

Make sure your spring is in the main hose at the bottom of the radiator, that spring keeps the hose from collapsing from the suction.

Make sure you aren't running lean.

Hope that you don't have a head gasket problem.


Do early big block trucks run hot? Well, my dad used to overload his gooseneck trailer behind a 1976 C30 dually with a 454/400 and said it would get hot on steep hills. He then junked the clutch fan and installed a direct drive aftermarket fan that pulls more CFM than the stocker. That pretty much fixed it.

 

[greg mgm]

Thanks for the replies, great info! The fans have a shroud, and its installed xlnt, and when on full, it pulls serious air through the rad. The fan controller is working great, also. At this point I have to believe the "high density" part of the rad, or the thickness may be a problem. The comment about "heat sink" and "heat transfer" make a lot of sence to me, so Im going to be talking with a rad manufacturer. BAJA BLAZER, what's the name of that company in San Diego? Thanks for the great info guys, and keep 'em coming if you have more info.

 

[HarryH3]

If I'm reading your post correctly, you have a 4-row version of a 350 radiator. The 454 radiator is wider than a 350 radiator, so it has a considerably larger surface area. If you want a really big rad, check out the one that came with the diesel engines. Those things are nearly as wide as the truck.

 

[BAJA_BLAZER]

AAA Radiator or The Radiator Store, they are the same company.