djwarner Posted April 11, 2013 Share Posted April 11, 2013 (edited) I've been sitting here wondering the same thing. As I understand it, there is a pressure relief valve in the pump and a filter bypass valve for the filter. I was curious which one you were talking about in your prior post about cleaning one out. BTW took my '71 out on a cross country on a turnpike running the new AC, aluminum radiator and waterless coolant on a 94 degree day. Finally got the fan clutch to engage for the first time since buying the car last August. As I pulled off the turnpike, I noted the temperature up to 210 degrees and watched the oil pressure drift towards zero as I idled at 800 rpms at the stoplight. As the needle approached zero, the sender went open and the gauge dropped to the peg. I dropped the transmission into neutral and revved the engine up to 2000. The gauge promptly came off the peg and rose to 25-30 psi. The FSM check on oil pressure is 50+ psi at 2500 rpm warm. It does not give a minimum pressure reading or any other reading other than the pop off psi for the pressure relief valve. Edited April 11, 2013 by djwarner Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 11, 2013 Author Share Posted April 11, 2013 The factory gauge in most cars of the 70s and early 80s were sketchy at best. I swapped over to a mechanical. I am going to look for one that looks right in the dash after i iron out the oiling issue. Quote Link to comment Share on other sites More sharing options...
djwarner Posted April 11, 2013 Share Posted April 11, 2013 I agree about the accuracy of the factory gauges. After buying my car, one of my checklist items was to replace the oil pressure sender and to calibrate the coolant temperature and oil pressure gauges. Found the coolant gauge was reading 25 degrees high but the oil pressure was right on after I set the internal voltage correctly. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 13, 2013 Author Share Posted April 13, 2013 Ok I think I have It cured... I took off the oil filter and yanked that pesky little filter pressure relief valve. I don't intend to go more than 1500 to 2000 miles between oil/filter changes so it seemed like the next logical step in finding the whacky oil pressure issue. I was able to use the housing for the spring that slides into the block and made an insert that pushes very tightly into that sleeve. Then I pushed the whole plugged up sleeve into place. It is a good snug fit that I feel confident will stay in place. I spun on a nice new Bosch filter and started it up. Then topped oil off and took it for a test flog. It worked! It spins up to 6500 with no sign of the oil pressure going anywhere!! I feel better now... Autocross sunday!!! Most likely in the rain, but that can be a lot of fun too!! D~ Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 13, 2013 Share Posted April 13, 2013 Don't rev a cold engine now. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 13, 2013 Author Share Posted April 13, 2013 I don't usually anyway. And I am running synthetic. That seems to flow a little nicer. D~ Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 15, 2013 Author Share Posted April 15, 2013 Ok. Second autocross in the z car behind me. Had tons of fun! Managed to finish around the middle of the pack. But... Grrr... Still dropping pressure. Same situation. I am going to see if i can drop the oil pan reasonably easily without pulling the engine. It won't hurt my feelings if i have to yank it out since i won't be racing again til at least July and i can finally paint the engine bay. I will keep posting on this thread if it yields something obvious. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 15, 2013 Share Posted April 15, 2013 How about an oil cooler? Pulled this link off of a Google search because it has a good illustration - http://www.elephantracing.com/techtopic/oiltemperature.htm Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 15, 2013 Author Share Posted April 15, 2013 Well, its doing the same as before. Can shut the engine off and immediately re start it and pressure is normal. I am theorizing here, maybe the oil pickup is too close to the pan or has something blocking the screen or has gunk in the screen. Just not really sure what to think as of yet. My best friend is as big of a motor head as I am and we are both pretty perplexed. I really don't have a problem pulling the engine out. I am going to start stripping the nose back off this week. Since i just spent the last year and a half doing body work, i would like to protect it!! Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 15, 2013 Author Share Posted April 15, 2013 NewZed, it was really chilly yesterday, but I won't rule anything out yet!! Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 15, 2013 Share Posted April 15, 2013 Can shut the engine off and immediately re start it and pressure is normal. I missed that piece. Seems more like the relief valve in the pump then, but if you've tried two pumps that would be unlikely. You said that you have a mechanical gauge but are you sure it's reliable? You might have replaced a very bad gauge, the stock one, with a still bad gauge. The liquid-filled gauges are known to be susceptible to heat effects. Details on the gauge might offer a clue. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 15, 2013 Author Share Posted April 15, 2013 Its a mechanical autometer guage. As far as I know its fairly accurate. But to be honest i just wanted to see pressure, the amount wasn't as important as just the presence of it. D~ Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 16, 2013 Share Posted April 16, 2013 "something blocking the screen" That is a real possibility! Dropping the pan is a cinch in-car. My preferred method is to remove the motor mount bolts on the isolators (2 each side) the jack up the engine till it's touching the top of the tunnel or near it (watch your heater hoses), and put blocks of 2x4 under them to let it rest on... Drop it on the blocks, and take the pan off, remove to rear of car and down. Shouldn't have to rotate the crank to clear throws this way, but you might... It's not a big deal. I put studs into my block while it was off (four of them extended length to hold gasket and make pan line up easier) and replaced those damnable small heads with nice flanged-headed nuts, clamping a sandwich plate (like the back of the pans have from Nissan...) After doing that, leaks are not an issue, and that full-perimeter doubler makes for straight pan rais and nuts which don't come loose! I took mine off because the car slipped off the jack, and it dented the front portion of the pan enough that when I restarted it, you got that hollow "tok tok tok tok" and could feel the crank throw banging the damn thing! Drop it, undented it...then spent an hour making studs and then saying "that doubler would probably work..." So made it from strap I bought from Home Depot, then REmaking LONGER studs to accommodate the doubler... By 23:00 it was purring nicely and hasn't leaked a bit since! Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 16, 2013 Author Share Posted April 16, 2013 Would certainly be easier to leave the car together... Thanks for the advise Tony. I was thinking about taking my borescope home and trying to get a peek but i think if its not that hard to get the pan out i will just go that route. Besides i have an older scope so its fairly large. I doubt it would get anywhere close enough to the pickup to see the screen. Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 21, 2013 Share Posted April 21, 2013 Unless you have a hole below the separator/deaeration baffle, you won't snake a borescopedown the oil pickup tube AND turn it to see the screen! Quote Link to comment Share on other sites More sharing options...
TimZ Posted April 21, 2013 Share Posted April 21, 2013 Ok I think I have It cured... I took off the oil filter and yanked that pesky little filter pressure relief valve. I don't intend to go more than 1500 to 2000 miles between oil/filter changes so it seemed like the next logical step in finding the whacky oil pressure issue. I was able to use the housing for the spring that slides into the block and made an insert that pushes very tightly into that sleeve. Then I pushed the whole plugged up sleeve into place. It is a good snug fit that I feel confident will stay in place. I spun on a nice new Bosch filter and started it up. Then topped oil off and took it for a test flog. It worked! It spins up to 6500 with no sign of the oil pressure going anywhere!! I feel better now... Autocross sunday!!! Most likely in the rain, but that can be a lot of fun too!! D~ Sorry I'm a bit late to the party, but I'm not getting how we were expecting this to help. How was plugging the filter bypass valve supposed to increase oil pressure? Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 21, 2013 Share Posted April 21, 2013 If understand the flow paths and gauge port position correctly, blocking the filter bypass could actually increase the gauge reading (pressure before the filter) and reduce oil flow to the parts that need it. Giving a false warm fuzzy feeling. A pressure reading from the center supply line to the head would tell more about oil supply and pressure. Ideally, you'd have a guage in the head also, after the restrictor inthe top of the block. Quote Link to comment Share on other sites More sharing options...
TimZ Posted April 21, 2013 Share Posted April 21, 2013 If understand the flow paths and gauge port position correctly, blocking the filter bypass could actually increase the gauge reading (pressure before the filter) and reduce oil flow to the parts that need it. Giving a false warm fuzzy feeling. A pressure reading from the center supply line to the head would tell more about oil supply and pressure. Ideally, you'd have a guage in the head also, after the restrictor inthe top of the block. My N42 block has the gauge port on the main galley - _after_ the filter. Seems to me that blocking the filter bypass could _only_ make the main galley pressure the same or lower. Quote Link to comment Share on other sites More sharing options...
NewZed Posted April 21, 2013 Share Posted April 21, 2013 I guess I don't understand the flow path then (seriously, I don't). I looked at the illustration in the FSM and it seems to show the path after the filter in the center, down to the main bearings and up to the cylinder head, and the path from the pump in front of the filter, with the gauge port on it. Which seems to fit seeing an increase in pressure if the filter bypass was blocked, and it had been opening. If the gauge port is after the filter then blocking the filter bypass should drop the gauge reading since all oil will suffer the pressure drop of passing through the filter. From which your question follows. My mistake. I have a short block inthe garage but have never had one apart. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted April 22, 2013 Author Share Posted April 22, 2013 Ok so I dropped the pan yesterday. I am still pretty baffled about what's going on in there. I saw that the pickup is compressed around the tube. (maybe I should call it pressed against the round flat plate and the intake tube) It was not smashed or terribly disfigured. I was able to carefully use a pick and pull it back out to a nice dome shape. I also noticed that the paint on the inside of the pan is flaking and coming loose. The paint problem may possibly be part of the issue. I am not convinced of anything for certain. As far as eliminating the filter by-pass valve goes, as I understand it, that valve is merely for when a filter gets plugged up. Our filters on these cars do not have internal bypass in case of plugging. I have not cut the previous filter apart, but plan to soon. Something I am considering is that the schmutz flowing through the oiling system from the flaking paint in the pan may be causing things like the relief valve in the pump to stick open. I plan to try and clean things up as much as possible. I am going to pull the valve cover off just to see if there is paint sticking in the top of the engine. Any thoughts would be appreciated!! This one is quite a stumper. Quote Link to comment Share on other sites More sharing options...
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