Jocklandjohn Posted December 5, 2014 Share Posted December 5, 2014 I've got a pressure gauge on my oil line at the filter with an 1/8" NPTF sender onto a Durite meter. Yesterday the pressure whacked right over to the right hard against the far side of the gauge - so over 100psi. Easing off the throttle brought it back down again, blipping the throttle had it going back up and down wildly but so hard it was bouncing off the right hand side. The engine sounded and runs normal. I started it this morning and immediately the needle shot across to the right hard against the stop. Switched off the engine and it flew back but stopped about 20psi and gradually traveled the remaining distance to the left. Restarting several times produces the same behaviour, right over, back to 20, needle slowly easing down. My first thought is the sender unit under the engine may be knackered. Its currently being bathed in diesel as my fuel pump is leaking all over it (change over with refurb fuel pump imminent) but I wonder whether the diesel bath is responsible for the oil pressure sensor behaviour and is addling its brain......or ....there is something seriously wrong that is causing the over-pressure state. What could cause such an over-pressure situation that happens so dramatically? I have a new sender unit on order, be here Monday so I can check then. But if it is not that where should I be looking? Oil pump? Somewhere else? Quote Link to comment Share on other sites More sharing options...
Tanuki Posted December 5, 2014 Share Posted December 5, 2014 Is the gauge electrical or mechanical? If it's electrical I'd be looking at a short on the wire from sender to gauge. If it's mechanical - the only thing that I can think of would be a sticking pressure-relief valve. [One time I experienced this was on a Diesel Austin Maestro van we had as a general workshop-hack vehicle: one winter we managed to burst a couple of oil-filters due to the overpressure when starting a cold engine] Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 5, 2014 Author Share Posted December 5, 2014 Is the gauge electrical or mechanical? If it's electrical I'd be looking at a short on the wire from sender to gauge. If it's mechanical - the only thing that I can think of would be a sticking pressure-relief valve. [One time I experienced this was on a Diesel Austin Maestro van we had as a general workshop-hack vehicle: one winter we managed to burst a couple of oil-filters due to the overpressure when starting a cold engine] Thanks Tanuki - its an electrical one. The thought of a ruptured capillary one skooshing hot oil into the dashboard wasn't appealing! I guess I could run a wire from dash gauge to sender and bypass the existing wire if the new sender acts the same. Is a pressure relief valve going to do this if its defective irrespective of whether there's a gauge? (translated: I have no idea what the pressure relief valve actually does nor where it is!). Quote Link to comment Share on other sites More sharing options...
ejparrott Posted December 5, 2014 Share Posted December 5, 2014 use a jump lead to check the gauge function instead of the existing wiring first Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 5, 2014 Author Share Posted December 5, 2014 use a jump lead to check the gauge function instead of the existing wiring first Yes that's a good idea. Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 6, 2014 Author Share Posted December 6, 2014 Just to satisfy my ignorance - are my overpressure symptoms likely with a failed oil pump? What are the common symptoms of a failed oil pump? Quote Link to comment Share on other sites More sharing options...
Team Idris Posted December 6, 2014 Share Posted December 6, 2014 You are safe on the oil pump wear, as a worn one only gives you low pressure. The gaps from the wear let oil go back to the inlet. I've changed to mechanical for reliability. I have mechanical oil pressure and temperature (capillary). To save the fear of hot oil everywhere I used copper brake pipe and hydraulic rubber hose for pressure. The gauge is often 1/8" bsp thread on the back and by use of 'this and that' you can get to the brake pipe size. I'm not a fan of a bit of nylon pipe either Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 6, 2014 Author Share Posted December 6, 2014 Thanks Idris - so my symptoms are not an oil pump fail so at least I don't have to faff about with that then! Cheers. Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 7, 2014 Author Share Posted December 7, 2014 I've not yet swapped the pressure sender unit, nor bypassed the wiring to check if there's a short in the wire, I will do that today hopefully, snow permitting (it's dumping higher up but only a few flakes down here currently). Assuming a new sender and a wire check does not solve the problem and the gauge is still reading seriously high can someone give me some learned opinions re what else might be the cause of the oil overpressure. Is a failed oil thermostat likely to cause this problem? If not a thermostat fail then I assume that only leaves the main culprit as a stuck pressure relief valve in the sump?(Is a gummed up oil cooler a likely culprit?) And as a curiosity - I've had a fuel pump leak problem, could back-pressure from an overpressured oil system/engine cause the pump to leak as its working harder to shove fuel in, blowing back past the o-ring? I've got a slight oil weep from the rocker cover gasket which has been getting worse but which I thought was a failed o-ring on the separator or a pooped rocker cover gasket - the leak is coming from the area at the back of the separator. But maybe the overpressure is puffing the oil out the rocker cover? Now I'm wondering if rather than a gauge problem there is a real overpressure - which is causing all the various symptoms - and the gauge is in fact accurate with its display of initial high pressure from cold then back to 20-25psi at idle once warm but going very high when the throttle is blipped. I often warm the block with the Eberspacher in the winter before driving, so that would possibly have masked the major swing of the gauge needle that I noticed recently with a cold start-up, by heating the oil up so its warmer = less pressure - which is why I may not have noticed it until recently. Any thoughts? Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 7, 2014 Author Share Posted December 7, 2014 Ok - just in from lying underneath in the wet and snow (yuk) - I attached a separate wire to run inside and attach to the gauge, but before I even attached it I unscrewed the Mud console to access the back of the gauges and as soon as I moved it, it had the needle pinging over to the right way past 100psi - and this with the engine off. So I guess it is a power or earth glitch. I have three gauges in a line all powered (and presumably earthed) on a common circuit - none of the other gauges (water temp and oil temp) have been acting odd. What does that suggest to any electrical experts who may be reading? I'm leaning towards the signal feed wire as the problem- given that the other two gauges are ok. Would that be a fair assumption? Quote Link to comment Share on other sites More sharing options...
ejparrott Posted December 7, 2014 Share Posted December 7, 2014 sounds fair Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 7, 2014 Author Share Posted December 7, 2014 Ok I attached the new wire I've run from the sender to the gauge, removing the old wire. With a loose connection to the gauge it flicks hard across the scale to the rhs - exactly the same as with the old wire. Having checked the earths which seem ok judging by behaviour of the other gauges, both of which work fine, and several other items on that circuit, and thinking this through - I'm narrowing it down to the sender unit being knackered, as all the other stuff is ok and the high reading occurs with old and renewed wiring. I'll let you know tomorrow once I've swapped the sender units.............(I really really don't want to lie in an icy puddle with snow covering my feet taking the sump off to renew the relief valve.....) Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted December 7, 2014 Share Posted December 7, 2014 John, just run a new temporary earth to the battery negative terminal just to rule out the earth completely. It may be that your oil pressure gauge is more sensitive to influence of a poor earth path than the other gauges. Mo Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 7, 2014 Author Share Posted December 7, 2014 John, just run a new temporary earth to the battery negative terminal just to rule out the earth completely. It may be that your oil pressure gauge is more sensitive to influence of a poor earth path than the other gauges. Mo That's a good plan Mo. Will give it a try. (PS - with luck my fuel pump will be off and swapped before Christmas - will ping you about it when its done). Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 7, 2014 Author Share Posted December 7, 2014 Earth wire run direct to battery. Same symptoms. So next stop is sender replacement. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted December 8, 2014 Share Posted December 8, 2014 No worries John, when you're ready. Mo Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 9, 2014 Author Share Posted December 9, 2014 Ok new oil sender (transducer) fitted just now, gauge needle pings over to right off scale - with engine off and cold. Removed earth from gauge, needle goes back to rest, attached earth direct from battery to gauge (thus bypassing shared earth which connects several gauges) and needle goes ping off to the right again, completely off the scale (again engine off and cold) So I can deduce that A) the original sender was ok. B) it's not a bad earth that's the problem So if I run two wires direct to the pressure gauge from the battery + and - terminals, and a third wire direct from the new sender unit to the gauge and I still get the needle going off the scale, am I right that that proves that the gauge is defective? Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted December 9, 2014 Share Posted December 9, 2014 I think you've excluded all else. Mo Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 9, 2014 Author Share Posted December 9, 2014 Ok - just ran all separate leads, direct from battery + and - and from the sender, to gauge, and its showing off the right hand of the scale. I think I can conclude that the gauge may be defective. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted December 9, 2014 Share Posted December 9, 2014 Sounds like it to me Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 9, 2014 Author Share Posted December 9, 2014 Just ordered a new gauge. Of course, after buying the new (and unnecessary) sender this morning to see if it was at fault (and it's not), the 'kit' with a new gauge comes complete with.....a new sender. Ahhhh. Into the spares drawer. Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 9, 2014 Author Share Posted December 9, 2014 ....and to add.....at least the snow didn't happen and the torrential rain held off too whilst I rolled around on the ground fitting the new sender....however I now realize that the smell of sh*t I was getting outside the house is NOT coming from the farmer's field behind us, but from a pile of manure he dropped on the way to the field, and which I drove through and which has plastered the underside of the steering guard on the LR and is now all over the front of my old jacket which is totally minging.........and has been put outside to calm down. Ahh the joys of driveway mechanics....... I should rename this thread 'Strange blood pressure behaviour'.......... Quote Link to comment Share on other sites More sharing options...
Quagmire Posted December 10, 2014 Share Posted December 10, 2014 I must be in a particularly grumpy mood today, but its nice to see a thread where the OP went through the problem step by step instead of throwing loads of parts at the problem, which usually just ends up confusing things. Good job! Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 10, 2014 Author Share Posted December 10, 2014 Thank you quaggy. I may be an old fart but I appreciate the value of logic - a vastly underrated process. As an electrical novice I need to hold my own hand quite a lot and take a methodical approach. What I love about doing it like that is that it presents learning opportunities about all the various component bits in a way that makes sense. I've learned a fair bit about oil pumps, oil pressure, and capillary gauges in the last week! Quote Link to comment Share on other sites More sharing options...
Jocklandjohn Posted December 13, 2014 Author Share Posted December 13, 2014 Well bocklocks! New gauge arrived today, fitted and switched power on. And it went PING over to the right of the scale same as the one I just removed! So, so far I've replaced the sender/transducer unit, replaced the wiring (all of it, including new earth, power and sender wires) and now the gauge - and still have the problem!And thats with the engine off, stone cold, not run for a week, and the rocker cover has been off so no pressure build up of any kind. In fact the needle pinging happens even without the connection to the sender, so rules out anything there and points to a power/earth problem. So am I now looking at something odd in the power supply? Everything else is ok. So what else - a bad earth maybe? This is all running off an auxiliary battery if that makes any difference and when I tried the direct wire to the gauge I went directly from both + and - terminals on the battery to the gauge, and third wire direct from gauge to sender. Can any electrical genius point me in a direction I've not tried yet? Quote Link to comment Share on other sites More sharing options...
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