Question:
I purchased one of your nylon relief valves for the C20XE engine (standard) a while back and now have the engine up and running with the nylon relief valve fitted but I'm a little concerned about how high the oil pressure is at warm idle. The directions say it should be 65-75psi at 4000rpm, which it seems to be but sits at 50psi at idle when warm but sometimes a bit higher. The mechanic at my local garage pointed this out to me saying that it seems to be very high for a engine at idle.
The relief valve came with washers to adjust the pressure and I have 3 washers in at the moment. So I was wondering if you could you tell me roughly what the oil pressure should be at idle on a standard engine when warm.
Answer:
Provided your oil pressure is ok at higher rpm, oil pressure at tickover being higher than expect is not a problem. The oil pressure at tickover is controlled by several things; the condition of the oil pump itself, the condition of the engine and how thick the oil is. From the information you have given, this would indicate that everything appears to be in good condition. Oil pressure is very much dependant on clearances within the engine and the oil pump itself, the larger the clearances, the lower the oil pressure would be at tickover.
Also the oil temperature would have a major effect on the oil pressure, for example to give a better indication you would need to monitor the oil temperature at tickover against oil pressure at this will give you the true indication. Also the oil grade has an effect as well, for example if your oil temperature is only say 60°C, I would expect approximately 50psi, at 80°C I would expect approximately 40psi and at 100-deg C, I would expect approximately 25psi.
These are only to give you a guide and you cannot use water temperature as this will be different to oil temperature. Even if you were achieving 50psi at tickover with 100°C and the oil pressure was stable at higher rpm, I would still be happy.
OS-NV-1-K - 2.0L/1.6L/1.4L Vauxhall Oil Pump Nylon Relief Valve Kit