dmanaenk Posted April 16, 2007 Share Posted April 16, 2007 Installed electric oil pressure gauge (crappy ebay one). Now it reads 80-90+ psi at start up, goes down to around 40psi when warm and cruising around 2-3k rpms, around 60psi at 5k rpms which all seem ok. But it reads around 5psi at warm idle, and Subaru spec is like 14psi (?). Oil pump was resealed about 10k miles ago, no visible oil leaks from oil pressure sender/sensor units and line, oil (10w30 )was changed about 1.5 month ago and topped off a week ago (leaks a bit), so it is near max today. Milage is 120k. Engine runs as usual, no knocks or lifter noise etc... Should this worry me too much? I will probably rent mechanical oil pressure gauge, but will those be accurate around 0-20psi? Quote Link to comment Share on other sites More sharing options...
nipper Posted April 16, 2007 Share Posted April 16, 2007 First question is how many miles on the gauge. Next question, or statement is how gauges are calibrated. I used to do gauge calibration. Gauges come in degrees of accuratcy. These gauges are fairly innacurate at the extreem bottom and top. The bottom and top 20% of the gauge are considered innacurate (i said considered, as they may well be). The working pressure is in the remainng range. You dont use a 100 psig gauge to read 5 psig. The only gauge that is even all the way across are HEISE gauges, as they are used as calibration standards. What increments are the gauge in? Who made it? What is the first tic mark on the gauge? And with gauges you get what you pay for. As long as the oil pressure light isnt on i wouldnt worry about it too much. nipper Quote Link to comment Share on other sites More sharing options...
dmanaenk Posted April 16, 2007 Author Share Posted April 16, 2007 The sender is new, and the oil hole is very small, like a pin whole (no idea if its good or bad). No idea who made it Scale goes from zero to 110psi with 2psi tick marks and covers about 270 degrees. Oil pressure light comes on on 2.7psi, so its not too useful as a diagnostic tool. All I really want is to monitor oil pressure relative to its pressure few days ago, so that I do not miss when the oil level dips too low. I'm not that much worried, and my main question is whether a mechanical pressure gauge I can rent at, say, Autozone will be any better in terms of average accuracy around 0-20psi. Quote Link to comment Share on other sites More sharing options...
nipper Posted April 16, 2007 Share Posted April 16, 2007 The size of the hole doesnt matter as its a non compressable medium. As far as gauge accuratcy, unless your going to spend serious money, your not going to really get any. What i can suggest is look on ebay for a 0-30 psig gauge. Get the engine warm then swap gauges. DO NOT REV THE ENGINE WITH THIS GAUGE ON IT. You just want to see what the real pressure is. 2psi tics on a 0-110 psig gauge thats 2-3 inches in dia is impossible to be accurate at below 10, psi, and porobably below 20 psig. Thats an awful lot of tics in a very small space. nipper Quote Link to comment Share on other sites More sharing options...
dmanaenk Posted April 16, 2007 Author Share Posted April 16, 2007 The size of the hole doesnt matter as its a non compressable medium. As far as gauge accuratcy, unless your going to spend serious money, your not going to really get any. What i can suggest is look on ebay for a 0-30 psig gauge. Get the engine warm then swap gauges. DO NOT REV THE ENGINE WITH THIS GAUGE ON IT. You just want to see what the real pressure is. 2psi tics on a 0-110 psig gauge thats 2-3 inches in dia is impossible to be accurate at below 10, psi, and porobably below 20 psig. Thats an awful lot of tics in a very small space. nipper Thanks, I will look in autozone tomorrow if they have 0-30 gauges. Any idea how soon after engine has been stopped it is safe to open the oil line to swap the gauge? Quote Link to comment Share on other sites More sharing options...
nipper Posted April 16, 2007 Share Posted April 16, 2007 Thanks, I will look in autozone tomorrow if they have 0-30 gauges. Any idea how soon after engine has been stopped it is safe to open the oil line to swap the gauge? as soon as you shut off the engine the pressure goes to zero. Just dont burn yourself. If your going to autozone, just get a proper zero-100 psig gauge in 5psi incriments. I would have a little more faith in that then one thats generic in 2 psi tics. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted April 16, 2007 Share Posted April 16, 2007 sounds like you got the real issue covered. on a side note, i know a long time subaru service manager who is still working with them and worked all through the 80's with them as well. he said these oil pumps typically put out plenty of volume for the engine which is key, eventhough the pressure may seem low. he said the volume supplied to the cams and HLA's is critical and it is rare that the oil pump can't supply the necessary volume. Quote Link to comment Share on other sites More sharing options...
OB99W Posted April 16, 2007 Share Posted April 16, 2007 The sender is new, and the oil hole is very small, like a pin whole (no idea if its good or bad).[...] The restriction prevents rapid changes in pressure from impacting the transducer in the sender, thereby minimizing the gauge needle bouncing around; the pressure readings are smoothed/averaged/damped in the short term. Quote Link to comment Share on other sites More sharing options...
dmanaenk Posted April 21, 2007 Author Share Posted April 21, 2007 Cheap mechanical 0-100 gauge showed 10psi, cheap 0-30 showed 12psi. All at warm idle where electric one shows 4psi. Not great, but not that far from lower bound in FSM. And there are some weird electrical issues I don't get, I thought that electrical sender is just a variable resistance, and the gauge measures current. Resistance on electric gauge I measure is wildly different at the same rpms depending on whether sender is connected to the gauge or not. Maybe my multimeter needs a new battery or smth... Quote Link to comment Share on other sites More sharing options...
nipper Posted April 21, 2007 Share Posted April 21, 2007 Much better. Check the MM battery. It can also be one leg of the wheatstone bridge, not to sure. Electronics not my strongpoint. nipper Quote Link to comment Share on other sites More sharing options...
dmanaenk Posted April 21, 2007 Author Share Posted April 21, 2007 First, I'm gonna change the hose I used to mount sender in a convenient location. As of now it is a braided hose and seems like at times I have two ground connections, one going along braided hose (however gauge does not work while only grounded through the hose braiding), and a direct grounding. I thought that I might be screwing the resistance reading somehow. Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted April 21, 2007 Share Posted April 21, 2007 Resistance on electric gauge I measure is wildly different at the same rpms depending on whether sender is connected to the gauge or not.Yes you can't use a multimeter to measure resistance in an energized circuit because the meter applies its own voltage. With the sender connected to the gauge and energized, try measuring the voltage across the sender terminals. If it has only one terminal then measure that with respect to ground. I think cosworth makes a high volume oil pump for the Subaru's too. Quote Link to comment Share on other sites More sharing options...
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