Pressure Problems

Robert U’Ren from Willys Jeep UK shares some of his helpful fixes and tips on buying, selling, repairing and recommissioning World War Two and Hotchkiss

Robert U’Ren is a self-taught mechanic with more than 40 years of experience working on everything from vintage motorbikes to combine harvesters. His passion is military Jeeps, which he has bought, sold, and restored since 2014

I have often experienced low oil pressure on the old World War Two Jeep engines, not so much on the Hotchkiss engines as they have an uprated oil pump, but they are sadly not interchangeable.

The old World War Two Jeeps’ oil pump design generally gives a good high oil pressure at start up, but this will reduce quickly when the engine gets to operating temperature, and the oil becomes thinner. The pressure often settles at 15 to 20 on idle, this is common on the World War Two Jeeps.

If your Jeep has an oil pressure reading as low as 10 on idle it’s generally a sign of engine wear. Low oil pressure can mean a worn engine and pressure being lost through the bearings and bushes. Engine wear can be detected by removing the dipstick when the engine is idling and it’s up to working temperature. If vapour is emanating from the dipstick tube like a simmering kettle this shows engine wear, but if you think your engine is good, but still suffers low oil pressure, there are a few other things that can be a cause of low oil pressure. Once an engine is running too hot it will cause the oil to get thinner and show a low reading. A hightemperature thermostat will make the engine run too hot. It should be 71ºC or 160F, showing a little hotter on the temperature gauge. A blocked radiator or internal waterways will also cause a hot running engine.

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