Oil pressure all over the place - iffy gauge?
Discussion
Lotus Twincam, whisker under 20k miles, oil changed religiously every year, running Millers at the moment and in the past few weeks the oil pressure has suddenly decided to jump all over the place; going all the way down to 0 at times, shooting straight back up to 50 under decent acceleration. I haven't had the sump baffled so it does waver little through fast corners but never like this before, so my question is, do I trust the gauge, (when its right and when its wrong or one or the other?) or do I assume that as oil levels etc are all fine then its nothing to worry about?
Many thanks for any opinions/experiences
Many thanks for any opinions/experiences
You serious Rufus? lol!
I'd be inclined to listen to the engine at tickover with a stethoscope or long screwdriver and then gently increase the revs but def. not too high.
If you don't use it regularly then I'd suspect a sticking pressure relief valve.
Whatever the reason, I sure wouldn't risk running it for long without a deep dive investigate.
I'd start by checking the condition of the wires and connections on the sender and gauge - then check and clean as required that they're all clean, secure and protected
this is very low cost, very easy and quick to do so worthwhile checking
if you've added any, say, spade connectors in the last few years then because of the poor build quality they might just be loose
this is very low cost, very easy and quick to do so worthwhile checking
if you've added any, say, spade connectors in the last few years then because of the poor build quality they might just be loose
Slight statement of the obvious but you have checked that there is enough oil in the engine haven't you? - fluttering oil pressure is a sign that the oil level is low. If the oil isn't low and the engine is running well (and not burning a lot of oil all the time (remember that the lack of valve stem oil seals means that they often puff smoke on start up or if they've been sat at tick over for a while) then check the pressure sender and pipe/wiring from it.
Fit a capillary gauge as a temporary to verify electronic gauge, but you can get the symptoms you describe from a stuck oil pressure relief valve - particularly if low oil pressure comes with low revs. If it were me I wouldn't run the engine unless absolutely necessary until I had verified that oil pressure was present and sufficient to avoid bearing damage. Does it have an idiot light? does it work? and is it driven by the same sender as the gauge? If its a separate tapping, can you plug a capillary gauge into the tapping for that?
Oil levels absolutely fine, I check it every time I take the car out and always have done so we can safely eliminate that.
Not being especially technically minded, (I'm not hopeless but get somewhat lost in more specific details) I think it sounds as if I have a sticking valve. Low revs, e.g sitting at traffic lights or waiting to come out of a junction used to result in a drop to around 20 psi and now results in a drop to 0. Blipping the throttle brings the pressure back up to 'normal' safe levels.
I'll get somebody to take a look - the bloody niggles continue to stop me using the car confidently. Remind me why we run classic cars?
Not being especially technically minded, (I'm not hopeless but get somewhat lost in more specific details) I think it sounds as if I have a sticking valve. Low revs, e.g sitting at traffic lights or waiting to come out of a junction used to result in a drop to around 20 psi and now results in a drop to 0. Blipping the throttle brings the pressure back up to 'normal' safe levels.
I'll get somebody to take a look - the bloody niggles continue to stop me using the car confidently. Remind me why we run classic cars?
I've got a Jaguar straight six in my '36 Austin. After rebuilding the bottom end it was showing zero oil pressure. I tried two more (electric) senders and another gauge, after that I pulled the bottom end apart three times to check for something I'd missed or assembled incorrectly.
I then went on Ebay and bought, for the princely sum of about twenty quid delivered, a handheld gauge kit with enough adapters to fit pretty much any engine in existence - took about ten minutes to verify sixty pounds of pressure... wish I'd done it in the first place.
I then went on Ebay and bought, for the princely sum of about twenty quid delivered, a handheld gauge kit with enough adapters to fit pretty much any engine in existence - took about ten minutes to verify sixty pounds of pressure... wish I'd done it in the first place.
the sender and gauge do have to marry up with each other
if you've recently changed the sender then it might also be be one of the many p*ss poorly made cheap modern parts that many classic owners insist on so as to pay the very least amount they can, it doesn't matter if or how well these parts work as they never use their classics anyway
if you've recently changed the sender then it might also be be one of the many p*ss poorly made cheap modern parts that many classic owners insist on so as to pay the very least amount they can, it doesn't matter if or how well these parts work as they never use their classics anyway
Gone out to do some more investigating, check oil first as per - dipstick totally dry. Panic. The 'dips' where the plugs sit look very wet, take out first two plugs, covered in oil and first two pistons have little pools of oil sitting on them. Bugger.
Either a seal somewhere has, as my sons old race engineer used to so eloquently put it, 'shat itself, and all my oil is sitting all around the engine rather than in the sump, or the valve seats have given up the ghost after too much unleaded use. Either way not a happy start to my weekend.
Either a seal somewhere has, as my sons old race engineer used to so eloquently put it, 'shat itself, and all my oil is sitting all around the engine rather than in the sump, or the valve seats have given up the ghost after too much unleaded use. Either way not a happy start to my weekend.
Edited by Rufus on Friday 23 May 17:44
Oh...
A complete guess but from your description it sounds as though something has been stopping the oil returning back to the sump properly - resulting in the cam cover gasket leaking (which often happens anyway) and too much oil sitting in the head then leaking down the valve guides. One thing that I have heard of happening is that there is a thick rubber pipe situated towards the back of the engine on the (i.e. near no4 cylinder) on the same side as the carbs that drains oil from the head back into the lower part of the block. This can degrade over time and expand/block. It's a bit of a s*d to change without removing the head but it can be done.
I don't think running unleaded would damage the valve stems/guides (which would increase the leak down into the cylinders more than the valve seats)- they might (and only might) cause valve seat recession over time but the twin has steel inserts in the head anyway so it's not likely to be as big a problem as it is with other engines. In my (limited) experience the bigger issue is pinking which is why I run mine on super unleaded with an octane boost. If not prevented pinking would most likely burn the valves or pistons. The engine would have been sounding really sick though if this was the case. Likely to be worth doing a compression test though.
Where are you based? (I know of a good twincam engine person in the SW if your in that area)
A complete guess but from your description it sounds as though something has been stopping the oil returning back to the sump properly - resulting in the cam cover gasket leaking (which often happens anyway) and too much oil sitting in the head then leaking down the valve guides. One thing that I have heard of happening is that there is a thick rubber pipe situated towards the back of the engine on the (i.e. near no4 cylinder) on the same side as the carbs that drains oil from the head back into the lower part of the block. This can degrade over time and expand/block. It's a bit of a s*d to change without removing the head but it can be done.
I don't think running unleaded would damage the valve stems/guides (which would increase the leak down into the cylinders more than the valve seats)- they might (and only might) cause valve seat recession over time but the twin has steel inserts in the head anyway so it's not likely to be as big a problem as it is with other engines. In my (limited) experience the bigger issue is pinking which is why I run mine on super unleaded with an octane boost. If not prevented pinking would most likely burn the valves or pistons. The engine would have been sounding really sick though if this was the case. Likely to be worth doing a compression test though.
Where are you based? (I know of a good twincam engine person in the SW if your in that area)
Edited by Lotus 50 on Saturday 24th May 08:51
Sounds like the top cover gasket, if the plugs were sitting in pools of oil when you pulled them then they will look wet and the oil wil drop onto the piston crowns, if the pistons were that wet from another source you would not be able to see behind you for smoke when driving and the motor would be dead by now.
Stop worrying too much and do the simple job first and see if it clears up/ stops using oil.
Stop worrying too much and do the simple job first and see if it clears up/ stops using oil.
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