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Low Oil Pressure During Idle On
General Motors (Buick) 3.8L (231 CID) Engines
Hot idle low oil pressure is a common complaint directed to General Motors' (Buick-built) 3.8L (231 CID) V6 engines. Some AERA members report hot idle oil pressure as low as 7 pounds, and oil pressure of 25 pounds or more when above idle. Changing the pressure relief spring affects oil pressure at higher RPMs, but
not the idle oil pressure.
General Motors (Buick) advises that a low or no oil pressure condition at idle may be caused by a sticking pressure relief valve. Forcing the relief valve into the bore as far as possible several times will usually free it up. A small chamfer should be formed on the outer edge of the valve (Figure 1) to help it remain free. General Motors (Buick) further advises that the oil filter adaptor gasket covers an oil channel port in the timing cover and it may have a tear in it. Pieces of the gasket may be sticking the relief valve. General Motors (Buick) claims that
replacing the gasket with newly designed GM gasket #25529916 eliminates this problem.
However, field reports from AERA members indicate that this is not the problem in most cases since it primarily occurs in newly rebuilt engines. The problem seems to be centered around two areas: the oil pump and the cam bearings.
AERA members are using several methods to improve the oiling system. The feed line to the oil pump on pre-1980 blocks is being enlarged 1/2 (.005) as General Motors (Buick) has done with blocks since 1980. General Motors (Buick) also increased the size of the oil pick-up tube. Some aftermarket suppliers are
using the larger diameter tubes for the pre-1980 engines. Be sure that the pickup tube you use has a 1/2 ID to adequately supply this enlarged gallery. Sharp edges and 90 degree turns must be deburred and radiused.
The oil pump housing and gear thrust plate must be checked very closely for wear and scratching. Housings within specifications but are scratched should be replaced, and thrust plates should be resurfaced or replaced. Most aftermarket suppliers have a cast iron plate to replace the OE aluminum plate.
A high-volume oil pump kit has been developed by the Melling Tool Company and is available through most aftermarket suppliers. The kit requires drilling two holes to install alignment pins for a plate that increases the height of the housing. This increased height allows the use of taller oil pump gears, and the kit can usually be installed on an engine that's still in the chassis.
It is believed that another cause of dropped oil pressure is that the cam bearings spill too much oil back to the crankcase. General Motors (Buick) engineers increased the size of the oil hole in the bearing because of lengthened oil change intervals. Thicker, contaminated oil had difficulty flowing through the original small holes, but the larger holes allow too much oil to
spill when clean oil is circulating.
Some AERA members drill new, smaller oiling holes to reduce this spill and increase oil pressure. Caution is urged because of the potential problems that thick, contaminated oil will cause. Another alternative is the use of a new camshaft bearing that is grooved on the backside. This allows you to install the oiling hole opposite the supply hole. The oil is then fed to the camshaft at the thrust side. Reduced wear and increased oil pressure over the life of the engine is the result since the cam bearing is no longer receiving oil at the point of maximum clearance.
Other AERA members increase idle oil pressure by just reworking the supply line in the block and using the high volume kit. All members stress the importance of resurfacing or replacing the gear thrust plate. AERA members using these methods are reporting hot idle oil pressure in the 15 to 20 pound range.
Since the housing is a part of the timing cover, many customers are reluctant to replace this costly part. Educate your customers to the consequences of using a worn oil pump housing and urge them to have it thoroughly checked.
The AERA Technical Committee
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