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Low Oil Pressure

By Doug McPherson

Austin Healeys have several characteristic problems (what an understatement), one of which is low oil pressure. It is usually most noticeable after the engine is hot. The pressure initially is quite reasonable when the oil is cold but deteriorates quickly as the engine warms up. Most people will tell you that your bearings are worn which is often the case. As detailed in a previous "Technical Hints," one place that is easy to check is the rocker shaft. Spouts of oil coming from the hole in the top of the rocker is usually a good indication of a problem in this area. The majority of this repair can be accomplished with no special tools.

If there is no oil sprouting from these points or if you have affected that repair with little change In the oil pressure, then there are other possibilities. The oil pump is one but is unlikely. Another which can be easily checked is the pressure relief valve which is what I found to be my problem.

In all six cylinder engines, the pressure valve is located just above the oil pan flange in the centre of the right side of the engine block. A 1-1/8” wrench is required to remove it, a socket is best. Note: You do not have to drain your oil to do this job. Removal of the nut (watch it doesn't spring out at you!) reveals a spring and a tapered nose cone. The cone may remain inside but it is easily drawn out with a screwdriver.

As the engine gets older, the relief spring becomes softer thus allowing the pressure to drop off. Higher pressures will be noted initially when the engine is cold due to the higher oil viscosity. (e.g. The spring must compress further to allow the thicker oil through.) As the engine warms-up the oil thins and the pressure drops.

A simple solution to this problem is to insert shims at either end of the spring to revive its strength. I found that a 1/8" shim (1/2" in diameter) raised the pressure about 3 PSI, this will vary with the condition of the spring. Steel shims are the best if they are available but an excellent and inexpensive source of suitable shims is faucet washers. If you purchase a 'Flat Faucet Washer Assortment' in the plumbing department at Canadian Tire you will find that the small 1/2" diameter washers fit perfectly. These seals are Buna-N which is compatible with engine oil and normal engine temperatures.

Putting in one or two of these shims should produce a noticeable change in the oil pressure both at start-up and after the engine is warm. If no change takes place then you might as well remove the shims and prepare yourself for some bearing work.

This repair of course assumes that the actual springs are not readily available. It also allows you to determine if the problem is in the relief valve before starting more serious engine work. If the shims do work, add enough to keep the pressure above 40 PSI when the engine speed is above 1500RPM. Don't add more than 1/2 an inch of shim material.

Not what you were looking for? Don't forget you can check our back issues using the AHCUSA Magazine Index.

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