I would go with pressure first, temp second. Sure you'd think if the oil is really hot the pressure would be low, but without the pressure you just don't know. If you are running an oil cooler then temp should be added as you can run too cold temp also.
OIL temp (not water temp) is a much better indicator of whether your engine is up to operating temperature. You can get a similar indication, however, from oil pressure. When oil pressure drops from the typically high morning/cold level, you can tell the oil's thinned as it warms. Once the engine is up to temperature and the oil's getting all nice and flowy and lubricious and comfy in the little oil passages, you can put more load on the engine without fear of increased wear or overly stressing the engine internals. (there's a more technical explanation, and someone will likely give it, but that's the gist of the situation!) Oil Pressure, however, is the more important gauge. You can run a cold engine, but if you've lost oil pressure the engine will seize. Too-low oil pressure is also an indication of the improper oil grade being used, or (in extreme cases) an indicator that the oil level itself has dropped to critically low levels.
Oil pressure, if the engine is operating normally, is rather static. It doesn't change much from hot to cold BUT if something stops working the pressure will drop rather fast. If it does drop to low the oil pressure light will come on and give you plenty of warning/time to get the car stopped. With todays oils you could run the car w/o oil pressure for a much longer time than you used to. The temp gauge on the other hand will give you a lot more info on the engine performance.
Running thin synthetic oil like newer engines do I wouldn't think there'd be a big change in oil pressure just due to getting to normal operating temps, unlike when we used thick straight grade oils in years past. I'd rather have an oil pressure gauge, about the only time I ever looked at the oil temp gauge on my '03 JCW was when I was on the track.
I have four gages, a boost/Vacuum gage, a water temperature gage, oil temperature gage and an oil pressure gauge. I if I could only have two gages, it would be water temperature and oil pressure. I have noticed that the water temperature and the oil temperature gages track pretty close on my MINI, so I could live without the oil temperature gage. Dave
I to have four gauges, a boost/Vacuum gauge, a water temperature gauge, oil temperature gauge and an oil pressure gauge. These are very helpful to me in assuring that all is well and when I have reached full operating temp.
Without hijacking the thread..... Where would be the best location for the oil temperature sender be located? Drill and weld a "bung" in the oil pan?
I used the Cravenspeed tapless oil pressure adapter for R-56, but I located the oil pressure sender remotely, using some 1/4" hydraulic hose. This left room to screw the oil temperature sender into the tapless adapter also. Just be sure to bleed the air out of the adapter or the temperature readings will act really weird. Dave
For the oil temp sensor, on my '03 JCW the temp sensor replaced the oil drain plug - a fairly slick solution.
I was thinking about that connection but since oil isn't flowing I was wondering if it would be an accurate indicator of actual oil temperature.....
There is enough ebb and flow of oil past the sensor, as the pressure rises and falls with rpm, to get a good reading. On the Series two MINIs, the drain plug solution puts the sender in a good place to get knocked off. Dave
I dropped and drilled my oil pan to install an electronic sender. I have two gauges in my R53, boost and oil temperature. The boost is a pretty good indication of how the accessories are going on the R53, and I use oil temp on the track to keep an eye on the engine. I hit 300*F somewhat easily without an oil cooler, so that tells me when to back off for a bit. A friend who club races his E30 M3 datalogs his oil pressure, among other things. He noticed a decline in average pressure over several track events and was able to rebuild his bottom end before catastrophic bearing failure.
With respect, while it doesn't fluctuate as much, it fluctuates a LARGE amount between "cold engine" and "up to temp", and between idle and redline. Cold it'll be 70+ PSI during normal driving, at idle maybe 20-30 (higher on cold mornings which, after yesterday's 101 in Pittsburgh, I'd welcome). Hot it'll hit 50+ nearer redline, at idle it's below the bottom line (&^% Mini for not labeling their gauges), and if REALLY hot it'll be >10. Agreed on lubricity from today's thin synthetics, but -0- oil pressure is bad no matter what, unless the engine is off. Oil temp and water temp track very closely over time, but on warmup there is a definite and important time lag where the water warms much much faster than the oil, at that point the OIL temp is the more accurate indicator of whether the engine is up to temp.
OE gauge on gauge pack - which is a typical OE gauge, inadequately marked, but at least shows actual values, as opposed to some OE gauges that simply put the needle in the middle if everything's OK, then peg it when it's not (like the "needle version" of an idiot light). I've seen same thing on an OBD2 reader on the MCS (how I know the factory gauge is actually a "gauge" was to doublecheck it), and on the VDO/ Autometer/ Aftermarket oil pressure gauges on each car I've owned. Thankfully, the one in the Mini was one I did NOT have to hook up myself! :-D If you've got an oil pressure gauge, with a warm engine the oil pressure should be relatively low at idle, climbing in rough proportion to the revs of the engine - which is good, since it tells you the oil pump (effectively geared to the crankshaft speed) is working. About the only time this isn't necessarily true is in a dry-sump engine with an external/electric oil pump, where you'd see higher pressure with colder oil and lower pressure once it warms and thins. Hope this helps...
Just asking cause I have never seen those kinds of differences in any of my other 4 cyl cars. I don't have a pressure gauge in my R53, just temp.