Erratic oil pressure gauge
#1 Erratic oil pressure gauge
The engine in my '69 FHC was completely rebuilt 6000 miles ago and I use 20W/50W Castrol oil, recently changed. The oil pressure gauge reads 30-40 psi at start up, 50-60 psi at 2500 rpms until reaching normal temp, then drops to 20-30 psi. At normal temps under 2000 rpms the gauge shows 20-30 psi but drops to 0-10 psi at idle. The engine sounds normal and there is no loss of performance. What would be the most likely cause of these erratic readings?
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#2 Re: Erratic oil pressure gauge
Cold oil is much thicker (more viscous) than hot oil.
If it is consistently like this, then I wouldn't call it erratic. It's only "erratic" if it keeps flipping between the two at a given temperature. It rather points to the fact that the clearances at the bearings are wider than on a freshly rebuilt engine, but that isn't so here because your engine is new. Typically on such an engine, the cold startup has the pressure relief spring immediately open at ~70psi and then all of the readings drop 20psi as it warms up - just like yours, but all the figures start from a higher number. This means that the likely culprit is that the oil sender reads consistently low or that the supply voltage at the gauge is consistently low.
You should test your gauge/sender using a bicycle track pump or verify the figures using a mechanical gauge. Have these figures changed since the rebuild or have you rewired the sender/gauge?
kind regards
Marek
If it is consistently like this, then I wouldn't call it erratic. It's only "erratic" if it keeps flipping between the two at a given temperature. It rather points to the fact that the clearances at the bearings are wider than on a freshly rebuilt engine, but that isn't so here because your engine is new. Typically on such an engine, the cold startup has the pressure relief spring immediately open at ~70psi and then all of the readings drop 20psi as it warms up - just like yours, but all the figures start from a higher number. This means that the likely culprit is that the oil sender reads consistently low or that the supply voltage at the gauge is consistently low.
You should test your gauge/sender using a bicycle track pump or verify the figures using a mechanical gauge. Have these figures changed since the rebuild or have you rewired the sender/gauge?
kind regards
Marek
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