What could the problem be?

Busted Knuckles · 07-09-2008, 03:41 AM

mkiiisupra, I beg to differ on a few points.

Point 1: 20W50 is a recommended oil for the 7M-GE and 7M-GTE for ambient temperatures above 40 deg F, according to the owner's manual. So, the oil journals, including the cam journals, are sufficient for this viscosity. I live in Atlanta, and we only see temps below 40 for a couple of weeks in the dead of winter.

Point 2: Oil is pushed through the engine by pressure. The higher the pressure, the more oil is being delivered to all parts of the engine, especially to the top of the cylinder head. At idle pressures of 5 psi, less oil makes it to the cams, and more is running through the main bearings due to widened clearances due to wear. A heavier oil will push less through the mains, and force more towards the cams, as monitored by increased oil pressure.

Point 3: Since 20W50 is a recommended oil, you do not have problems within the oil delivery journals of 'choke points' where the oil delivery hole prevents the oil pressure from being delivered. Thus, the oil pressure is the same at the cam bearings as it is at the main bearings.

Point 4: Bearings get most of their protection from film thickness. Higher viscosity oils provide higher film thicknesses than lighter oils. Pure and simple. And as the bearings wear, and clearances widen, that film thickness may prevent a bearing from getting smoked.

I've read link after link from sites like Bob Is The Oil Guy and discussions that link to studies, like Technical Journal: R&D Review of Toyota CRDL

that specifically links light viscosity oils to increased wear in piston rings over higher weight oil specifically because of the lighter oil running off the cylinder walls faster. They also show increased wear in connecting rod bearings, cam bearings, and main journals.

07-09-2008, 03:41 AM	#23
Busted Knuckles 12psi boost Join Date: Dec 2007 Location: Atlanta Posts: 300	mkiiisupra, I beg to differ on a few points. Point 1: 20W50 is a recommended oil for the 7M-GE and 7M-GTE for ambient temperatures above 40 deg F, according to the owner's manual. So, the oil journals, including the cam journals, are sufficient for this viscosity. I live in Atlanta, and we only see temps below 40 for a couple of weeks in the dead of winter. Point 2: Oil is pushed through the engine by pressure. The higher the pressure, the more oil is being delivered to all parts of the engine, especially to the top of the cylinder head. At idle pressures of 5 psi, less oil makes it to the cams, and more is running through the main bearings due to widened clearances due to wear. A heavier oil will push less through the mains, and force more towards the cams, as monitored by increased oil pressure. Point 3: Since 20W50 is a recommended oil, you do not have problems within the oil delivery journals of 'choke points' where the oil delivery hole prevents the oil pressure from being delivered. Thus, the oil pressure is the same at the cam bearings as it is at the main bearings. Point 4: Bearings get most of their protection from film thickness. Higher viscosity oils provide higher film thicknesses than lighter oils. Pure and simple. And as the bearings wear, and clearances widen, that film thickness may prevent a bearing from getting smoked. I've read link after link from sites like Bob Is The Oil Guy and discussions that link to studies, like Technical Journal: R&D Review of Toyota CRDL that specifically links light viscosity oils to increased wear in piston rings over higher weight oil specifically because of the lighter oil running off the cylinder walls faster. They also show increased wear in connecting rod bearings, cam bearings, and main journals.