If your Oil pressure at a Hot Idle is 40Psi when the engine is fully warmed and then?

Question

it goes to 65 or 70Psi which is Relief pressure (65Psi) and above when the throttle is applied and at anything over 1500RPM, which is every speed basically above 20Mph, is everything OK or is something wrong?

My 1985 Jaguar XJ6 has a 4,2L. I get to let it sit for awhile. i wonder some causes of "High Oil Pressure" and sometimes it has been at 75psi, or indicating 80. And while thats not horribly high, the Relief IS 65Psi, and the high mark on gauge is 80, and even the Fuel system in this car is a Low pressure 40Psi or so.

Im tempted to take the VC off, clean everything, heat the Oil Pan, use a Gunk flush, then proceed with using a 15W-50. This AFTER the "Oil Sending Unit" and New Gauge are put in place.

My Oil pressure at Hot, fully warmed Idle with all Oils that go in whether its 10W-40 or 15W-50 or 20W-50 with Lucas Stabilizer, is 40Psi.

Take on whats going on? And yes i have a great desire to keep my Oil pressure UNDER RELIEF?

3 months ago, if i put all 10W-40 in it, Oil Pressure would be 60Psi while driving on the Highway. THATS the Oil pressure i want back. And it didnt waver or anything. I see a slight waver of a few psi sometimes, on the gauge. Factory dash gauge.

Answer 1

You seem to have a basic misapprehension about how engine oil systems work. There is no "fixed" pressure that they operate at. There is a minimum pressure necessary for proper operation, and normally a minimum specified operating pressure for reasonable engine longevity. Actual pressure varies depending on a lot of factors. I suspect you are thinking that if the bypass is not active, then all the oil goes through the filter. It doesn't work that way on this car. Oil is bypassed to maintain the correct pressure. Bypassed oil goes to the oil cooler. The filter has a separate bypass system in case of clogging. There is no such thing as as car that has no bypass for oil flow, as it's not fail-safe. They would never design a system that can self destruct. In any event, in these cars, you can not have "too much pressure". Also, using 15-50 oil will tend to raise the pressure, not lower it, as it is a thicker oil.

Answer 2

ST3V3N, He said "Mercruiser engine" That would be in a boat. First, if not done already, check the gauge that is on the engine. Those are more prone to failure than in an auto. It is possible that the head gaskets are wrong or were installed wrong, or the new or re-worked heads developed an oil leak. It may be coincidence that the pressure dropped after the head job, but it could also mean it's time to build the bottom end! As an edit to a post further down, the heads DO have pressure passages in them, that is how the valve train is oiled, and the hydraulic lash adjusters fed. It is possible that the drop is there, but I would still verify the pressure gauge. If you have any pressure at idle, you should be OK for a good while if it is going up to a normal range as you run.

Answer 3

First off if your using 15W-50 or 20W-50 that's the problem you should be using 10W-40 you can use Lucas if you want I use it at every oil change in my car.As far as using engine flush I wouldn't because it is a waste of money and if your oil hasn't been changed on a regular basis there is a chance that all the stuff it flushes out will clog up the oil pump and you will have bigger problems.Switch back to 10W-40 and it should be back to normal