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Prime considerations

oil-pumpsWhen I was a lad, my old dad always used to say, "Change your oil regularly, son, and you'll rarely have any engine problems." Good advice indeed at a time when the statistic that 90% of all engine wear takes place in the first few seconds of engine life wasn't even invented.

So every 2500 or 3000 miles, I forget which, I would dutifully warm the engine of my ten-year-old Triumph TR4 and drain the oil, allowing at least 30 minutes for as much of it as possible to drip into the battered container underneath. Then I'd clean the sump plug and carefully replace it, ensuring that the copper seal was still up to the task, then replace the oil filter with the same fastidiousness and fill up the engine with the required amount of fresh oil. At eight or nine pints if I remember correctly, this was no cheap task even back then!

Subsequently, carefully removing the spark plugs and with the ignition coil disconnected, I would carefully crank the engine until full engine oil pressure was reached. Replacing the plugs and reconnecting the coil, the engine would be fired up and after a few minutes the filter housing and sump plug examined for leaks.

Later on in life, when the TR4 was replaced by the tow wagon, whenever the oil in the racer was changed or the engine fired up after a period of inactivity (usually 24 hours or more) a similar procedure was adopted. Whether I was changing the oil or intending to start the engine after a period of inactivity, the plugs would be removed, electrics disconnected and the engine spun over until at least 40 psi showed on the gauge.

I mention this because rarely do I see this procedure enacted inside the paddock early in the morning when firing engines for the first time. Possibly because roadcar oil-drain periods are much longer these days (up to 20,000 miles in some cases) or possibly because of the difficulties of removing spark plugs and isolating electronic fuelling and ignition systems, the practice of priming the oil pump before firing the engine for the first time or after oil changes seems to me to have been long since forgotten.


On wet-sump engines when the pump is inaccessible, the practice is perhaps excusable. Even so, I have seen production engines with wet sumps that if left for a few weeks without running would quite easily lose their oil pump prime, with catastrophic results. But on dry-sump engines, especially if the oil tank is located some distance away from the engine, it is inexcusable and courts disaster. Of course, there will always be some residual oil left in the feed oil gallery and bearings, but with remote mounted dry-sump oil pumps some or even most of this oil may have drained away once the engine has been stopped.

To fire the engine and introduce combustion loads into the bearings therefore seems to me to be something akin to a lottery. In some cases as well, if the oil tank is mounted higher in the chassis, oil has been known to drain down into the oil pan and cause hydraulic locks when the engine is cranked for the first time after a long lay off. Cranking without the plugs will indicate a problem without the possibility of serious engine damage.

Even cranking without firing or removing the spark plugs is surely better than nothing, but you'll have to disable the fuel injectors or else you might introduce other issues such as fuel entering the oil system and the problems that brings, not to mention the bore wash.

No, I may be old-fashioned or fastidious (or both) but the only way to ensure your oil pump is fully primed without risking any damage is to spin it over without any plugs. At the very least you might discover any issues before any serious damage can occur.

Oh yes, and just listen to your old dad now and again! He's probably been there and learned the hard way - from his mistakes.

Fig. 1 - Simple dry-sump system

Written by John Coxon

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