Excerpted from Vol. 27, No. 9 November 1999

Editor's Note: Radiator Reporter's investigation of GM 34-inch crossflow radiator failures is ongoing. If you have comments or field experience to share on this subject, please submit your experiences to RR by e-mail or by fax (708/485-4237). We also welcome your phone calls on this subject. You can reach our tech desk by calling 708-485-6768. Thank you.

Stress Failures on GM 34-Inch Crossflows
Copyright 1999, 2001 by the National Automotive Radiator Service Association. All rights reserved.

Subtitle: GM's Pickup Rads Just Aren't Big Enough

Rad shop owners across the U.S. have been fighting a losing battle with GM's 34-inch crossflow radiators, found in many Chevy/GMC pickups, Blazers and Suburban models built since 1988. That's a lot of trucks, and a lot of unhappy truck owners.

In countless calls toRadiator Reporter's RadHotline, readers tell the same sad story of recurring radiator leaks caused by thermal stresses and sudden pressure surges. It is a chronic, nationwide problem presumably affecting thousands upon thousands of vehicles. Exact figures are hard to come by, but GM sold over a half-million C/K pickups last year alone, and when you throw in the Blazers and Suburbans, the sales number approaches one million vehicles annually.

Not all C/K trucks are affected by the problem, which seems to plague big-block models with 34-inch crossflow radiators with 17-inch or 19-inch headers. It's a decade-old problem that spans both copper/brass and PTR designs. To date, RR is unaware of any published bulletins or advisories from GM addressing the problem. Attempts to contact GM officials for comment have so far been unsuccessful.

Based on field reports and calls to RR, GM's 34-inch crossflow radiators are tearing themselves apart because the inlet tank and header—indeed the entire radiator—is simply too small to withstand the pressures and thermal stresses generated by GM's big-block cooling systems. Depending on driving habits, large amounts of coolant can rush into and overwhelm the inlet side of the radiator during heavy acceleration.

Because of the relatively short profile of the 34-inch crossflow, which has a core measuring only 17 or 19 inches high, coolant and pressure surges slam against the inlet side of the radiator and have nowhere to go. There simply aren't enough core tubes to accommodate the surge of coolant, a problem exasperated by the flow resistance caused by 34-inch long tubes. Consequently, radiator tanks bulge outward and headers flex to the point of cracking. One California reader says he recored or replaced 10 of GM's 34-inch crossflows in a single month. On older copper/brass styles, he has seen the inlet tank blown off the header from solder shear. Hairline header cracks reportedly are common, whether the radiator is copper/brass or plastic and aluminum.

Radiator benchmen have tried in vain to solve the problem on their own. They've switched from cu/br to PTRs and back again. They've recored and replaced with every available brand, from OEM product to beefed-up aftermarket cores and all-metal completes. When those efforts failed, they have attempted to reinforce the inlet tanks with internal braces and brackets, along with silver-soldered tank-to-header seams. Sometimes the efforts pay off, or at least buy a little more time between comebacks, but in many cases these extraordinary approaches fail as quickly as the factory-original radiators.

Don't expect GM to do anything about this problem because it would cost them a fortune, provided GM's engineers could even devise an answer. In our view the solution is to increase the height of the grill opening to accommodate a radiator with larger headers. This, of course, cannot be done without a total redesign of the vehicle's body. Never mind.

GM truck owners who have been subjected to this engineering nightmare have limited options. Because aggressive driving and towing heavy loads are believed to trigger the surges in coolant pressure and volume that tear the radiators apart, a lighter foot on the accelerator pedal will delay the incidence of radiator failure. But for many GM/GMC truck owners, who bought their trucks for work instead of cruising to Blockbuster, changing their driving habits may not be possible. For them, the best solution may be to buy a Ford or Dodge. That's a pretty radical solution sure to raise eyebrows at GM, and sure to anger and disappoint those GM truck owners who have been forced to replace their radiators time after time.

Radiator repair shop owners need to protect themselves from the financial liability and loss of customer goodwill that GM's 34-inch fiasco has wrought. Many benchmen now know that even their best repair techniques are no match for the pressure and volume surges that characterize the 34-inch crossflow problem. But shop owners have given away a lot of replacement radiators in the mistaken belief that 34-inch comebacks were somehow their fault. On the supply side, radiator and core manufacturers have eaten far too many warranty claims that had nothing to do with defective manufacturing or materials.

GM's 34-inch crossflow problem isn't the radiator industry's fault, and it is important to educate the consumer on this point. Start by describing the problem and how driving habits affect the problem. Provide them with a copy of this article or other items published in past issues of RR. Let them know that this is a nationwide problem with no known solution, short of changing driving habits or changing vehicles.

To limit your warranty exposure, include a warranty disclaimer on your repair orders stating that your normal warranty policy does not apply to GM 34-inch crossflow repairs or replacements. To preserve customer goodwill, along with your sanity, don't promise to fix something that field experience suggests cannot be fixed. The truth of the matter is, we work on vehicles, we don't build or engineer them.