shuttlefever Posted March 18, 2013 Share Posted March 18, 2013 First autocross with the z car today. Was a lot of fun! First time in over ten year racing a rear drive car. Here is my possible dilemma, during and immediately after a run i have no oil pressure. I realize the electric gauges are so-so at best, but its still alarming. I checked and cleaned the connections to the sender and it stabilized the gauge some. Could there be a problem with the pickup? The engine in my car is from a 83. The previous owner had a hack mechanic, so any number of issues could arise here. Under normal driving it has good pressure. Anyone have any thoughts as to where i should start? I am inclined to put in a redundant mechanical gauge to verify my electric gauge readings. D~ Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted March 18, 2013 Share Posted March 18, 2013 How old is the sending unit? Mine sucked, then I got a new one and its been so accurate its not even funny. I also use a turbo oil pump on my car since I figured more oil flow is better anyway. As for after laps, mine would dip for a min or two after along with my temp climbing a little. The readings would then stabilize after say 5 min, while waiting for the next lap. Quote Link to comment Share on other sites More sharing options...
djwarner Posted March 18, 2013 Share Posted March 18, 2013 The oil pressure sender has two modes of functioning depending on whether it feeds a gauge or a low pressure light. Below a certain pressure, it stops reading a resistance and simply shorts to ground. Shorting to ground is a signal to illuminate an idiot light. After a long hot run, oil viscosity may become so low that oil flow freely through the galleys with little or no pressure. Whamo, the sender shifts into idiot light mode. Our engines were designed in a different era when bearing lubrication was based on flow rather than pressure. If you look at the pressure specification, it is measured at 2500 rpm, not idle. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 18, 2013 Author Share Posted March 18, 2013 I understand viscosity, and the idiot light thing. My concern is that it is getting starved during the flogging that occurs during the fun that is autocross. However I understand that these engines are tough. Is the oil pump an easy change? And is there any possibility that the pickup is loose or at an incorrect angle? Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted March 18, 2013 Share Posted March 18, 2013 Doubt it, although if you are super worried you can pop the oil pan off and jack the engine up and check. Would be a good time to regasket also. It was a bitch to swap oil pans fyi but is possible. What kind of oil do you use? and you never answered my question about age of your sending unit/engine. When I first got my ZX the enign had about 180-190k on it. Oil pressure sending unit worked. Well right around 200k it just stopped working. So they do go bad. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted March 18, 2013 Share Posted March 18, 2013 I would get a new sender compatible with your gauge and try that before doing all that work. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 18, 2013 Author Share Posted March 18, 2013 BluD, i am not sure of the age of the sender or how beat the engine is. it was swapped in by the previous owner's hack mechanic. It has good compression and minimal cylinder leak down. And as a bonus it doesn't leak! I swapped it over to synthetic oil a while back. It's due for another filter to be spun on since synthetic tends to flush out the yuk. I will probably swap senders out and find a parking lot to thrash around in and see if that makes a difference. I might string in a temporary mechanical gauge too just for my own sanity. I am mainly just trying to make sure there is not any kind of issues that the L28s have with starvation under side loads. Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted March 18, 2013 Share Posted March 18, 2013 OK it could be the sender, I'd change that first just because. If the problem persists I would then run thicker oil. I run 20w-50 dino oil. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 18, 2013 Share Posted March 18, 2013 Hobbs switch at 5psi in the ignition circuit...loose oil pressure for real: kill engine NOW! On hard, extended turns it is possible to starve the engine and smoke it... Most people with money in their motors and who must run a stock unbaffled oil pan run a Canton Accu-Sump to give you the reserve necessary for high rpm oil pressure stability in turns. There is virtually no oil pressure at idle anyways. Use a big bore sensing line on your mechanical gauge, and you will get. Better readings. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 18, 2013 Author Share Posted March 18, 2013 So just for my own piece of mind, can i swap the oil pump without yanking the pan? Quote Link to comment Share on other sites More sharing options...
johnc Posted March 18, 2013 Share Posted March 18, 2013 Get the FSM for your car and yes you can swap the pump without touching the pan. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 18, 2013 Author Share Posted March 18, 2013 Ok so next goofy question. Is there a different drive shaft for the pump for the turbo pump? Or is it all the same stuff just the pump being the difference? Quote Link to comment Share on other sites More sharing options...
LanceVance Posted March 18, 2013 Share Posted March 18, 2013 Hmmm... I've been trying to find a way alleviate my worries about running my oil cooler boso' style. I'll have to look into this! Hobbs switch at 5psi in the ignition circuit...loose oil pressure for real: kill engine NOW! Quote Link to comment Share on other sites More sharing options...
BluDestiny Posted March 18, 2013 Share Posted March 18, 2013 There isn't a difference in the oil pump shafts, just the NA and turbo dizzy shafts Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 19, 2013 Author Share Posted March 19, 2013 There isn't a difference in the oil pump shafts, just the NA and turbo dizzy shafts Cool. Then that will be my next investment either way. More oil volume is good! thanks everyone for the info. If the mechanical gauge yields fowl results I plan to yank the engine and check the oil pickup, and at the same time build some baffles up in the pan. Quote Link to comment Share on other sites More sharing options...
shuttlefever Posted March 25, 2013 Author Share Posted March 25, 2013 Update!! Finally got a chance to hook up the mechanical gauge and test flog the car last weekend. Under hard acceleration at high revs the oil pressure goes away slowly. Even after letting the engine for back to idle, pressure still dropping. Once i stopped and shut the engine off then restart it, then pressure returns. My diagnosis is that the pressure relief is hanging open. So next paycheck I plan to change the pump. Hopefully this will end the oiling woes without having to pull the engine. Quote Link to comment Share on other sites More sharing options...
johnc Posted March 25, 2013 Share Posted March 25, 2013 IMHO... anything that shuts off the engine based on oil pressure, temps, etc. can be a very bad thing. Think driving at the limit in turn 9 at Willow Springs and havning the engine shut off and lock the rear wheels. You will be dealing with far more damage to your car and possibly yourself then just some spun bearings. A big yellow idiot light is a better idea. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 26, 2013 Share Posted March 26, 2013 "Canton Accusump" Sounds like you suck the pan of oil, and until it drains back, you suck aerated wind age slung off the crank. Competition pans are 7qts for just this reason. Quote Link to comment Share on other sites More sharing options...
djwarner Posted March 26, 2013 Share Posted March 26, 2013 Shuttlefever, What viscosity oil are you running? Oil pumps are known as a constant displacement pump. That is, for each revolution of the pump, it wants to push out the same number of cc's of oil. This type of pump will generate whatever pressure needed to push out the design volume. What limits the pressure is leakage around the seals and close clearances in the pump body. Pressure continues to build until the various paths for oil flow accept the requisite volume. This is why these pumps come with pressure relief valves. So what determines the pressure required? Size of the oil galleys, clearance of the bearings, viscosity of the oil, temperature that modifies the oil's viscosity, pressure relief valves, and leak paths. The pump is content to generate whatever pressure required to deliver its design volume, even 0 psi. Your last post expresses the concern that the pressure relief valve may be sticking open, however you describe exactly what would happen when the oil thins from rising temperatures. At normal loads oil temperature is near the coolant temperature of 180 degrees. SAE 30 weight oil at 180 degrees is 14 centipoise, SAE 40 measure about 21 centipoise. As you exercise your engine, cylinder blocks, heads, and oil temperatures rise and the oil thins. At 240 degrees, SAE 30 thins to 6 Centipoise and SAE 40 thins to about 8.5 Centipoise. As the Centipoise drops, the resistance to oil flow through the various passages drops and thus the required oil pressure drops. If you pull over and let the engine idle, it will take quite a while to dissipate the heat stored in the engine block, heads, oil, etc. As the engine cools, oil pressure slowly builds. I suggest you get a non contact thermometer from Harbor Freight and watch to see if oil pressure recovery matches the drop in the engine block temperature. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted March 26, 2013 Share Posted March 26, 2013 You know THIS is cheap and works really well: http://www.jegs.com/i/Auto-Meter/105/7921/10002/-1?parentProductId=#moreDetails Snake the copper tubing in thru the firewall and you're good to go. I never liked or trusted the OEM gauges. I'd ONLY use the mechanical Autometer stuff. their electric gauges are suspect. Beyond that, I'd get that roadrace oil pan Tony mentioned and the Turbo oil pump, AFTER you install that mechanical gauge and confirm you don't currently have an issue. Mike Quote Link to comment Share on other sites More sharing options...
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