Bearings Knock on Startup
jimss454
06-20-2004, 12:23 PM
350 (5.7L) with factory oil cooler, '92 Suburban & '95 Conversion Van.
On startup, main bearings knock until oil pressure rises, which takes a few seconds. My 88 3/4T had no oil cooler, and had 293,000 miles when I sold it. Good oil pressure & power, never knocked & no smoke. The girlfriends 'Burb was bought with 120K miles, knock kept getting worse, finally pulled motor & replaced the crankshaft, bearings, oil pump, and removed the oil cooler adapter & lines. (Installed standard old-style oil filter adapter - new from dealer was about $20). 2 years & 20K miles later, still no knocking! I use Valvoline 10/30 in all of my vehicles. May have to do same mod to the van, but don't even want to try removing the engine from that thing. Why did GM put that darn oil cooler (& oil heater?) setup on a proven engine design that had been working fine without a cooler since 1955? I suspect the government's mandatory fuel economy standards forced GM to go to 5W30 oil to get the fuel mileage, and the 5/30 oil is too thin to stand up to truck use without a cooler? The oil pump has to pressurize about 10 feet of hose, plus cooler, before the bearings get oil pressure, which is what causes the mains to wear out. The anti-drainback valves in the oil filter & the cooler adapter do not usually keep the cooler lines full of oil...
Anyway, someone told me to put 5/30 oil in my van, and the knock will not happen, because the thin oil will flow to the bearings a lot faster. I am concerned that the bearing damage is already done, and that 5/30 won't handle the load. (Van weighs over 6,000#, and I tow my race car with it). Oil pressure seems decent, (close to 40# when warm, at highway speed). Any thoughts or experience on this one? Thanks. -Dan.
On startup, main bearings knock until oil pressure rises, which takes a few seconds. My 88 3/4T had no oil cooler, and had 293,000 miles when I sold it. Good oil pressure & power, never knocked & no smoke. The girlfriends 'Burb was bought with 120K miles, knock kept getting worse, finally pulled motor & replaced the crankshaft, bearings, oil pump, and removed the oil cooler adapter & lines. (Installed standard old-style oil filter adapter - new from dealer was about $20). 2 years & 20K miles later, still no knocking! I use Valvoline 10/30 in all of my vehicles. May have to do same mod to the van, but don't even want to try removing the engine from that thing. Why did GM put that darn oil cooler (& oil heater?) setup on a proven engine design that had been working fine without a cooler since 1955? I suspect the government's mandatory fuel economy standards forced GM to go to 5W30 oil to get the fuel mileage, and the 5/30 oil is too thin to stand up to truck use without a cooler? The oil pump has to pressurize about 10 feet of hose, plus cooler, before the bearings get oil pressure, which is what causes the mains to wear out. The anti-drainback valves in the oil filter & the cooler adapter do not usually keep the cooler lines full of oil...
Anyway, someone told me to put 5/30 oil in my van, and the knock will not happen, because the thin oil will flow to the bearings a lot faster. I am concerned that the bearing damage is already done, and that 5/30 won't handle the load. (Van weighs over 6,000#, and I tow my race car with it). Oil pressure seems decent, (close to 40# when warm, at highway speed). Any thoughts or experience on this one? Thanks. -Dan.
Thunderbolt
06-21-2004, 07:59 AM
If your bearing knock on startup changing the oil probably won't help.If you have an oil cooler then your filter sits sideways and you need to use filters with a good anti drainback valve or it will always make noise on start-up. As far as the oil goes the only difference between 10w- 30 and 5w-30 is that the 5w-30 would be slightly thinner at start up when it is cold. You will not notice any difference between the two unless the temperature is below zero.
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