Oil pressure drops to 15psi when rpm goes up to 2400rpm
Discussion
Hi,
Last week my 400 Chimaera developed an interesting oil pressure problem. The oil pressure drops right off at 2400rpm but comes back up as you back off to 2000rpm (this is when the engine is hot).
When the engine is cold, the oil pressure sits as normal on 55psi and doesn’t move much with revs, this drops off normally as the engine warms up. With the engine hot the oil pressure sits on 35ish at idle, rises to 40ish at 2000rpm then dives to 15psi at 2400rpm, it will recover to just over 30psi as the revs go up from 2800rpm. When the oil pressure drops backing off to 2000rpm also brings the pressure straight up to 35psi again.
The oil is at the max level on the dipstick, when the oil was lower (just over the min) the pressure drop at 2400rpm was down to under 10ish psi (the oil light didn’t come on though) Does anyone know why the oil pressure would drop so dramatically at this narrow rpm range?
Everything else seems fine.
For info the pressure sender has been replaced a year ago and the new one is apparently the correct on to suit the gauge not the TVR original part which I’m told under reads by about half. This checks out with the new reading never going over 55psi which is about the pressure relief valve setting. In other words since the sender was replaced the gauge reads double what it use to or what a standard TVR gauge reads, so the numbers above may be different from most TVR’s
Any insights as to what could cause this would be greatly received.
Last week my 400 Chimaera developed an interesting oil pressure problem. The oil pressure drops right off at 2400rpm but comes back up as you back off to 2000rpm (this is when the engine is hot).
When the engine is cold, the oil pressure sits as normal on 55psi and doesn’t move much with revs, this drops off normally as the engine warms up. With the engine hot the oil pressure sits on 35ish at idle, rises to 40ish at 2000rpm then dives to 15psi at 2400rpm, it will recover to just over 30psi as the revs go up from 2800rpm. When the oil pressure drops backing off to 2000rpm also brings the pressure straight up to 35psi again.
The oil is at the max level on the dipstick, when the oil was lower (just over the min) the pressure drop at 2400rpm was down to under 10ish psi (the oil light didn’t come on though) Does anyone know why the oil pressure would drop so dramatically at this narrow rpm range?
Everything else seems fine.
For info the pressure sender has been replaced a year ago and the new one is apparently the correct on to suit the gauge not the TVR original part which I’m told under reads by about half. This checks out with the new reading never going over 55psi which is about the pressure relief valve setting. In other words since the sender was replaced the gauge reads double what it use to or what a standard TVR gauge reads, so the numbers above may be different from most TVR’s
Any insights as to what could cause this would be greatly received.
You could well have a problem with the oil pressure relief valve or a weak pressure relief spring. My first thing would be to check this as its a cheap option, is the valve and spring accessable without stripping the engine, if so look at the valve seat and side walls of the valve, then the bore in which it sits for scoring or scratches also check its side movement also if you can get a new spring check the length of a new one against the one you have aready in the engine.
I had exactly the same problem on an Audi a few years ago and found that the spring had lost about 5mm in length (against a new one) due to compression, therefore was lifting way too soon....good luck.
I had exactly the same problem on an Audi a few years ago and found that the spring had lost about 5mm in length (against a new one) due to compression, therefore was lifting way too soon....good luck.
Agree with Phumy, early pressure relief while the oil pressure is building with revs, then the pressure builds further past the dip, increasing once again.
Pressure relief is supposed to work at the higher end of the rev range once the required pressure is reached and hold it there.
Interesting problem, well described, I think I have learned something new
Pressure relief is supposed to work at the higher end of the rev range once the required pressure is reached and hold it there.
Interesting problem, well described, I think I have learned something new
Interesting problem and well described with good clear detail. If the pressure dropped at a certain rpm and then got even worse I'd say blocked oil strainer but I can't see how pressure would then recover at even higher rpm. I confess to being stumped which is a fairly rare event for me with engine maladies and most annoying.
As the gauge and sender are electronic you could try monitoring your battery voltage over the same engine rev range. If the alternator is having issues then a change of volts to the gauge could produce this dip.
I'm with the others in not being able to fit a mechanical fault with those symptoms.
Steve
I'm with the others in not being able to fit a mechanical fault with those symptoms.
Steve
Possibly a wiring issue? A weak connection between senor and gauge that gets worse at certain vibration frequencies? Very peculiar one though. Might be worth checking with a mechanical old pressure gauge from the toolbox just to confirm what you are seeing is actually what you are getting. Stab in the dark this one 
Agree with the above, there is one more possibility, had this problem on a Caterham and it turned out to be a piece of gasket material being sucked up to the ol pickup and partially blocking it, as soon as the oil pump slowed down as revs dropped the debris dropped back and allowed oil to flow into the pickup unimpeded.
Dave
Dave
TVR instruments are notorious for incorrect reading and strange malfunctions mainly due to sender failure 
Quick Update...though no investigation started yet.
I got on the highway yesterday. My normal commute doesn't get above the 2000 RPM mark. So the highway is the only time I see the issue.
Jumped on the high way from cold, RPM on 2100 and cold pressure at 55PSI, engine gets up to temp after 10 mins. Pressure lowers to 40-45 PSI.
I tried to provoke the issue by increasing to 2600 RPM and back but no sign of pressure drop (tricky to maintain this speed as the coppers here are trigger happy, and yes i could just drop down a gear but there is something wrong with sitting in 4th on the highway)
After 45 mins (no change in engine temp since 10 min mark) the pressure drop comes back, regular as clock work, 2000 RPM pressure is 35 plus, increase to 2100 starts to drop, by 2400 RPM the pressure dropping past 15 PSI and I back off (not wanting to hear and seized engine sounds) at 2100 RPM pressure is straight back up to 30+ PSI.
On the way back (next day) the issue happened as soon as I hit 2400 RPM. I'm guessing because the engine was hotter sitting in traffic before I hit the highway.
As to the cause.
Don't think is voltage related, but I'll check as it's easy.
I'm due a oil change, possible broken filter mesh blocking the flow at higher suction? so will see if this changes anything.
Blocked oil way doesn't seem to fit the fault.
I agree with the reply's above, that the pump and pick are the likely causes. So will check this with the oil change.
Will check the pressure release valve too but it seems to work correctly when it's cold.
Does anyone know if I need a new sump gasket when I take the sump off?
Cheers.
I got on the highway yesterday. My normal commute doesn't get above the 2000 RPM mark. So the highway is the only time I see the issue.
Jumped on the high way from cold, RPM on 2100 and cold pressure at 55PSI, engine gets up to temp after 10 mins. Pressure lowers to 40-45 PSI.
I tried to provoke the issue by increasing to 2600 RPM and back but no sign of pressure drop (tricky to maintain this speed as the coppers here are trigger happy, and yes i could just drop down a gear but there is something wrong with sitting in 4th on the highway)
After 45 mins (no change in engine temp since 10 min mark) the pressure drop comes back, regular as clock work, 2000 RPM pressure is 35 plus, increase to 2100 starts to drop, by 2400 RPM the pressure dropping past 15 PSI and I back off (not wanting to hear and seized engine sounds) at 2100 RPM pressure is straight back up to 30+ PSI.
On the way back (next day) the issue happened as soon as I hit 2400 RPM. I'm guessing because the engine was hotter sitting in traffic before I hit the highway.
As to the cause.
Don't think is voltage related, but I'll check as it's easy.
I'm due a oil change, possible broken filter mesh blocking the flow at higher suction? so will see if this changes anything.
Blocked oil way doesn't seem to fit the fault.
I agree with the reply's above, that the pump and pick are the likely causes. So will check this with the oil change.
Will check the pressure release valve too but it seems to work correctly when it's cold.
Does anyone know if I need a new sump gasket when I take the sump off?
Cheers.
aussiedavo said:
........I agree with the reply's above, that the pump and pick are the likely causes. So will check this with the oil change.
Will check the pressure release valve too but it seems to work correctly when it's cold.
Does anyone know if I need a new sump gasket when I take the sump off?
Cheers.
So, you're going to strip down the bottom of the engine without proving there is actually a pressure drop.Will check the pressure release valve too but it seems to work correctly when it's cold.
Does anyone know if I need a new sump gasket when I take the sump off?
Cheers.
Just fit a mechanical gauge or a different electric gauge and sender.
Steve
Quickly fit a mechanical gauge first then as others keep saying - check the pressure relief valve - i.e. take the pump of an inspect it properly.
For a RV8 i'm impressed with your oil pressure, as they usally far lower than that - you may find the mechanical gauge reports a lower(truer) figure.
For a RV8 i'm impressed with your oil pressure, as they usally far lower than that - you may find the mechanical gauge reports a lower(truer) figure.
A quick update... I tried to get my hands on a pressure tester (was quoted $350 from a local store - yeah right, for a $30 gauge) so first off I did an oil service as this was due, changed filter and oil. Since then the oil pressure has been as good as gold.
I have done the same runs where I saw the original problem but no issues. I took the oil filter apart (thinking possible bypass valve failure) but that seemed all functional. And yes the old oil was topped up to the max line. So not sure what the issue was but it seems to have gone now (touch wood).
Thanks again for all the replies.
I have done the same runs where I saw the original problem but no issues. I took the oil filter apart (thinking possible bypass valve failure) but that seemed all functional. And yes the old oil was topped up to the max line. So not sure what the issue was but it seems to have gone now (touch wood).
Thanks again for all the replies.
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