Perplexing; 2006 Sierra 1500 5.3 cooling system issues

Nanotech Environmental · February 7, 2017

I should update this since I started this thread. It turns out my intermittent overheating issue was caused by the spring clamp on the lower rad hose where it attaches to the rad. It had partially rusted thru, allowing pressure to blow past it. Because of it's location, it couldn't get a visual on it. The rad had been replaced a year or two earlier due to a deer strike, so I had assumed that maybe the replacement rad was defective. ( it was still under warranty)

When the body shop pulled the rad, they found the problem clamp & replaced it. Problem solved.

Not sure what is going on with VickK's truck, seems like it could be heads, or head gasket. Could be something else going on as well.

VickK · February 8, 2017

Thanks for the quick replies. I have been at this gearhead stuff since 1974. While I've only been working with the LS platform for the last 10 years the principles are the same. I have owned this silverado ecsb 4wd 4.8 automatic for several months and have been plagued with coolant leaks. Chevy Tech77 you say head/head gasket which the symptoms point to in my opinion as well. The strange thing is/are; no coolant in oil, no oil in coolant, holds pressure under cap for days without being used, no vapor from exhaust, changed spark plugs and old plugs looked textbook definition of normal, no gurgling when after shut down, no mil or ses codes. I admit I haven't performed the NECESSARY tests yet as far as compression, cooling system pressure test or dye test for combustion gas in coolant. Engine runs strong, oil pressure normal, fuel economy on par. It's making me a little crazy. Well thanks again guys. One more thing-to Chevy Tech77-I have available to me a 5.3 vin t code from a 1999 same exact truck aside from displacement. From the research I've done so far it seems to be a direct bolt in swap(same fuel and timing maps, pcm, DBC throttle body, sensors, pigtails, crank flange to flex plate, torque converter, bell housing, etc...) Please give me your professional input when you have time. Thanks in advance, Vick K.

SafetyGuy · February 8, 2017

I should update this since I started this thread. It turns out my intermittent overheating issue was caused by the spring clamp on the lower rad hose where is attaches to the rad. It had partially rusted thru, allowing pressure to blow past it. Because of it's location, it couldn't get a visual on it. The rad had been replaced a year or two earlier due to a deer strike, so I had assumed that maybe the replacement rad was defective. ( it was still under warranty)

When the body shop pulled the rad, they found the problem clamp & replaced it. Problem solved.

Not sure what is going on with VickK's truck, seems like it could be heads, or head gasket. Could be something else going on as well.

I just recently had the same thing happen to me. Truck started over heating on the way home one evening, I stopped and it took a whole jug of coolant. Managed to get it to the part store and picked a rad and a lower coolant hose up( had a hunch it was the hose). Started into and found that it wouldn't leak unless it got hot and had was under load. Looked at the clamp and it had rusted through. Changed the clamp no more issues!

redvett · February 9, 2017

"I have re-tightened hose clamps several times but pressure is forcing small leaks at hose connections" How are you tightening the clamps? they are spring clamps. If you changed to screw clamps you have most likely ruined the inlet/outlet tubes. They are composite and you MUST use spring clamps. Spring clamps keep a constant equal clamping force on the hose regardless of hot or cold.

I have a 99 Silverado with the 4.8 with cooling system issues. Bought it used with 227,000 on it. Engine runs strong and sounds great with the exceptions; 1. Lifter tick on start up for several seconds to a minute. 2. Excessive pressure in cooling system-new belt and all new hoses, new thermostat and housing, new radiator, new pressure cap on reservoir and flushed and filled with proper Dex-cool/water mix. Losing coolant-1 pint every 200 miles or so. I have re-tightened hose clamps several times but pressure is forcing small leaks at hose connections. Heater temp is barely warm. Return hose warm, hose to heater normal(hot). I believe previous owner used stop leak as there is telltale signs of crud formations. My belief is head gasket or small crack in head/block. System holds pressure overnight which kind of perplexes me. No sign of coolant in oil or vice verse. I have read several similar posts on symptoms but none with actual diagnosis and successful repair. Any help is appreciated. Vick.

ChevyTech77 · February 9, 2017

Thanks for the quick replies. I have been at this gearhead stuff since 1974. While I've only been working with the LS platform for the last 10 years the principles are the same. I have owned this silverado ecsb 4wd 4.8 automatic for several months and have been plagued with coolant leaks. Chevy Tech77 you say head/head gasket which the symptoms point to in my opinion as well. The strange thing is/are; no coolant in oil, no oil in coolant, holds pressure under cap for days without being used, no vapor from exhaust, changed spark plugs and old plugs looked textbook definition of normal, no gurgling when after shut down, no mil or ses codes. I admit I haven't performed the NECESSARY tests yet as far as compression, cooling system pressure test or dye test for combustion gas in coolant. Engine runs strong, oil pressure normal, fuel economy on par. It's making me a little crazy. Well thanks again guys. One more thing-to Chevy Tech77-I have available to me a 5.3 vin t code from a 1999 same exact truck aside from displacement. From the research I've done so far it seems to be a direct bolt in swap(same fuel and timing maps, pcm, DBC throttle body, sensors, pigtails, crank flange to flex plate, torque converter, bell housing, etc...) Please give me your professional input when you have time. Thanks in advance, Vick K.

Sorry, can't comment on the swap. Never researched it or done it but I would be willing to bet that the ecm cals are not exactly the same. Physically it should bolt/plug in to the truck though.

VickK · February 21, 2017

"I have re-tightened hose clamps several times but pressure is forcing small leaks at hose connections" How are you tightening the clamps? they are spring clamps. If you changed to screw clamps you have most likely ruined the inlet/outlet tubes. They are composite and you MUST use spring clamps. Spring clamps keep a constant equal clamping force on the hose regardless of hot or cold.

I have a 99 Silverado with the 4.8 with cooling system issues. Bought it used with 227,000 on it. Engine runs strong and sounds great with the exceptions; 1. Lifter tick on start up for several seconds to a minute. 2. Excessive pressure in cooling system-new belt and all new hoses, new thermostat and housing, new radiator, new pressure cap on reservoir and flushed and filled with proper Dex-cool/water mix. Losing coolant-1 pint every 200 miles or so. I have re-tightened hose clamps several times but pressure is forcing small leaks at hose connections. Heater temp is barely warm. Return hose warm, hose to heater normal(hot). I believe previous owner used stop leak as there is telltale signs of crud formations. My belief is head gasket or small crack in head/block. System holds pressure overnight which kind of perplexes me. No sign of coolant in oil or vice verse. I have read several similar posts on symptoms but none with actual diagnosis and successful repair. Any help is appreciated. Vick.

Dam Red, you were right about those spring clamps. I've been using worm clamps on EVERYTHING for the last 40+ years without this kind of leak issue. Seems to be a combination of the clamps combined with Advance Auto hoses. I was connecting the steadily dropping oil pressure-still at 30psi @ 2000 rpm but was at 50psi right after oil and filter change-and the low heater temp along with the leaks and I shouldn't have. 1,000 miles later and still going strong but still very small leakage. I'll get to the clamps when the weather warms up. I did get much better heat out of her by blowing out the heater core yet again with compressed air and water. The weird thing is I blew it out really well when I first got the truck(did it like 10 times in both directions) but I guess it wasn't enough. As far as the oil pressure dropping I believe it may be the screen behind the sending unit.