TECHNICAL Q&A

ANSWERS TO YOUR BURNING DIESEL QUESTIONS

Does anyone know of a source for a lower pressure relief coolant cap for a 2006 Chevy? The truck may have a head gasket in the early stages of failure.

I need the truck for my busy season and was thinking that a coolant surge tank cap with a lower pressure vent might help save what’s left of the season for my work truck. This is the time of the year that I cannot sideline the truck. I hope to limp it through, and worry about the repair when scheduling isn’t a problem. I had several episodes of coolant appearing on the ground beneath the truck, and first thought “bad head gasket” but have not found the upper radiator hose to be overly stiff or hard, as has been reported for most head gasket problems. I could smell a hot coolant odor after driving the truck for a while and then shutting it off.

My mechanic thought that there was a leak somewhere in the engine valley. He checked it out and found that the coolant was coming out between the block and transmission. Not wanting the labor charge of pulling the engine, we opted for a shot of stop leak. After the stop leak did its job the upper radiator hose is now somewhat stiff, but nowhere near as hard as my 2001 was when it had a head gasket problem.

There is also evidence of oil seeping and baking around the number 7 cylinder. Mark Via Email There is never a good time for a cooling system problem. However, without further checking, what you’re describing doesn’t sound like a failing head gasket that creates excessive cooling system pressure. In general, a hard upper radiator hose that stays hard even after an overnight shutdown is a sure indication of excessive cooling system pressure due to a combustion pressure leak(s) in a head gasket. For a short-term attempted “get home” fix, we’ve run a diesel with a loose coolant surge tank cap, thinking that less pressure would help with a head gasket problem that resulted in over-pressurizing the cooling system. It didn’t. A loose cap (or likely a lower rated pressure cap as well) just makes the problem worse, causing more combustion gasses to work through the cooling system and force more coolant out through/ around the loosened cap. One easy-to-see indication of a head gasket problem is soot will begin smudging the inside of the coolant surge tank as combustion gasses work their way through the cooling system. The Dex-cool coolant used in these engines just doesn’t deteriorate over time like the older coolant types did. So, if you’re seeing dark discoloration on the inside surfaces of the coolant surge tank, you’ve got a head gasket problem. There is an aluminum transmission adapter sandwiched between the cast-iron engine block and the Allison transmission. Aside from allowing the Allison to bolt on, the adapter also contains a coolant passage that passes coolant from the driver’s bank of cylinders to the passenger-side bank. If the coolant leak your mechanic spotted isn’t originating somewhere in the engine valley, you may need to reseal that transmission adapter. The oil seep you’re seeing is not likely related to the cooling system problem, and would be farther down the list of importance. Good luck with your truck.

The 5.2L 4-cylinder 4HK1-TC diesel engine is turbocharged and intercooled and is 50-state emissionscertified for on-road vehicles having a GVW of between 12,000 and 14,500 pounds. This is an overhead cam engine with four valves per cylinder, a bore/stroke ratio of 115mm (4.53”) x 125mm (4.92”), and rated 210 hp at 2,550 rpm and 441 lb-ft at 1,850 rpm. One unique feature of the engine is its use of dry cylinder sleeves, which simplifies overhaul and further indicates the engine’s commercial nature. The 4H Isuzu diesel utilizes an electronically controlled Denso common-rail type fuel injection system, which will require all of the original wiring, sensors and electronic modules for a successful conversion. How difficult a transplant like you propose largely depends on you. If you’re somewhat comfortable with automotive wiring and have a reasonable understanding of how everything works together, then the conversion shouldn’t be all that difficult. The size, weight and general layout of the engine should fit the K10 (half-ton pickup) engine bay quite well. Even the 4HK1-TC oil pan appears to be shaped correctly to fit over the front axle/frame cross member. This sounds like a fun project. However, depending on where you live, getting the vehicle registered could be a problem. The 4H Isuzu is emissions-certified for a heavier class of vehicle than your K10. California and several Northeast states have much stricter regulations regarding “engine switching” (as the EPA calls it). As of May 2018, the following EPA web links were available for emissions regulation information, including diesel conversions. https://www.epa.gov/state-and-local-transportation https://www.epa.gov/sites/production/files/documents/ engswitch_0.pdf Good luck. run out. I will change the valve and see what develops. Look forward to hearing back from you.

Rob Grenfel Hinton, Alberta, Canada The first generation LB7 Duramax, like yours, was produced from the 2001 to the 2004.5 model years. The LB7 Duramax utilizes a crankcase vent system that ultimately vents to the atmosphere. There is an oil separator box in the system that allows any accumulated condensed oil to drain back into the crankcase. Theoretically, just gasses and vapors exit the engine—no liquids. This all works very well, and we’ve yet to hear of a failed crankcase ventilation valve. Two valves are used in the system, each located center-top of a valve cover. They allow gas pressure to vent to a T’ed hose, which then connects to the oil separator box. According to the GM service manual, the following are possibilities for an external engine oil leak: 1. Plugged or kinked crankcase ventilation system hoses.