Chimaera Mk3 4.5 - Oil Pressure Query
Discussion
Hello Folks,
I'm after some help and advice with respect to the oil pressure in my Mk3 4.5 Chimaera. My concerns stem from an oil pressure gauge that fluctuates and gives different readings for identical oil temp, rpm, speed indications.
Below are some readings from a recent drive.
IDLING FROM START
oil Cold @ Start / rpm 1000 / psi 20
oil 50C / rpm 900 / psi 30
oil 60C / rpm 900 / psi 30
oil 70C / rpm 900 / psi 30
BEGIN DRIVING
oil 80C / rpm 2000 / 35 psi with one drop to 20 psi then recovered to 35 psi - 30 mph
STOPPED FOR 5 MINS
oil 80C / rpm 900 / fluctuating between 20 psi and 30 psi
BEGIN DRIVING
oil 85C / rpm 2500 / psi 35 - 40mph
oil 85C / rpm 3000 / psi 35 - 70 mph (5th gear)
oil 85C / rpm 4000 / psi 35 - 70 mph (4th gear)
STOPPED
oil 90C / 800 rpm / psi 15
Notes
- At no point did the oil pressure go above 35psi on the gauge.
- When stopping at traffic lights and junctions, sometimes the oil pressure drops to zero and sits there for about 10 seconds before recovering to about 15 psi.
- There does not appear to be an oil leak (nothing under the car & oil quantity constant).
- I have Mobil-1 5W50 oil and the car is served in accordance with the correct schedule.
- There are no abnormal noises from the engine and the oil light on the dashboard does not come on (yes it works).
Thanks very much in advance.
I'm after some help and advice with respect to the oil pressure in my Mk3 4.5 Chimaera. My concerns stem from an oil pressure gauge that fluctuates and gives different readings for identical oil temp, rpm, speed indications.
Below are some readings from a recent drive.
IDLING FROM START
oil Cold @ Start / rpm 1000 / psi 20
oil 50C / rpm 900 / psi 30
oil 60C / rpm 900 / psi 30
oil 70C / rpm 900 / psi 30
BEGIN DRIVING
oil 80C / rpm 2000 / 35 psi with one drop to 20 psi then recovered to 35 psi - 30 mph
STOPPED FOR 5 MINS
oil 80C / rpm 900 / fluctuating between 20 psi and 30 psi
BEGIN DRIVING
oil 85C / rpm 2500 / psi 35 - 40mph
oil 85C / rpm 3000 / psi 35 - 70 mph (5th gear)
oil 85C / rpm 4000 / psi 35 - 70 mph (4th gear)
STOPPED
oil 90C / 800 rpm / psi 15
Notes
- At no point did the oil pressure go above 35psi on the gauge.
- When stopping at traffic lights and junctions, sometimes the oil pressure drops to zero and sits there for about 10 seconds before recovering to about 15 psi.
- There does not appear to be an oil leak (nothing under the car & oil quantity constant).
- I have Mobil-1 5W50 oil and the car is served in accordance with the correct schedule.
- There are no abnormal noises from the engine and the oil light on the dashboard does not come on (yes it works).
Thanks very much in advance.
Hi Citizen Smith,
When the ignition is off, the oil pressure needle sits on its stop at the left hand side of the gauge. This position is approx. 8mm distance left the ZERO mark on the gauge.
When the switched ignition on turned on the oil pressure needle makes a definite movement off its stop and moves to the zero mark. At the same time the fuel gauge need 'comes alive' and moves off its stop to the correct position.
When the ignition is off, the oil pressure needle sits on its stop at the left hand side of the gauge. This position is approx. 8mm distance left the ZERO mark on the gauge.
When the switched ignition on turned on the oil pressure needle makes a definite movement off its stop and moves to the zero mark. At the same time the fuel gauge need 'comes alive' and moves off its stop to the correct position.
MagicChimp said:
Hi Citizen Smith,
When the ignition is off, the oil pressure needle sits on its stop at the left hand side of the gauge. This position is approx. 8mm distance left the ZERO mark on the gauge.
When the switched ignition on turned on the oil pressure needle makes a definite movement off its stop and moves to the zero mark. At the same time the fuel gauge need 'comes alive' and moves off its stop to the correct position.
Sounds like the gauge is reading correctly. As already mentioned by a forum member, the sender is the next possible problem. Failing that it could be a problem with the pressure relief valve. When the ignition is off, the oil pressure needle sits on its stop at the left hand side of the gauge. This position is approx. 8mm distance left the ZERO mark on the gauge.
When the switched ignition on turned on the oil pressure needle makes a definite movement off its stop and moves to the zero mark. At the same time the fuel gauge need 'comes alive' and moves off its stop to the correct position.
My 450 would regularly showed as low as 10 psi, usually this means it’s about 15 psi.
If it drops off whilst moving check the connector on the sender as if it’s loose you’ll get low readings.
Depending what year your car is and the type of gauges fitted you’ll see different readings, later cars like yours and mine when everything is hot it used to read quite low so I used a mechanical pressure gauge and this confirmed 15 psi at tickover rising to 30psi 2000 revs then onto 45 from 3000 revs,,, my gauge never read higher than 30.
The gauge and sender don’t seem well matched and heat can effect the readings.
There’s some cheap oil pressure testers on eBay that do the job well enough for a home mechanic and well worth knowing for sure what the pressure actually is. I even drive around with it poking out the bonnet by the wipers and again the pressure was as above. Just make sure you cable tie the tester pipe or you might have a lot of oil to clean up
If it drops off whilst moving check the connector on the sender as if it’s loose you’ll get low readings.
Depending what year your car is and the type of gauges fitted you’ll see different readings, later cars like yours and mine when everything is hot it used to read quite low so I used a mechanical pressure gauge and this confirmed 15 psi at tickover rising to 30psi 2000 revs then onto 45 from 3000 revs,,, my gauge never read higher than 30.
The gauge and sender don’t seem well matched and heat can effect the readings.
There’s some cheap oil pressure testers on eBay that do the job well enough for a home mechanic and well worth knowing for sure what the pressure actually is. I even drive around with it poking out the bonnet by the wipers and again the pressure was as above. Just make sure you cable tie the tester pipe or you might have a lot of oil to clean up
Edited by Classic Chim on Saturday 9th June 20:00
Classic Chim touched on one possible reason - the single wire connected to the pressure sensor by a spade connector sometimes works loose.
First time mine did it, I was heading onto the A11 at the end of a hot track day at Snetterton and glanced down at the gauges, like you do, and saw I had zero oil pressure. After a brief flap and a panic (the wife's defibrillator - I assume that's what it was - sorted my heart attack) I pulled over and called my TVR guy, who was just leaving the circuit himself. He obligingly stopped in the same layby, checked the car over for obvious signs of a leak, calmed me down and told me that the wire was simply loose on the sender. He told me to ignore the gauge and drive home, all would be well. I did notice while driving that accelerating and decelerating could induce readings on the gauge, but this was simply small G forces pushing the spade connector into contact with the terminal, and off again. Worth a check - the sender is on the front of the engine, visible more readily from underneath.
First time mine did it, I was heading onto the A11 at the end of a hot track day at Snetterton and glanced down at the gauges, like you do, and saw I had zero oil pressure. After a brief flap and a panic (the wife's defibrillator - I assume that's what it was - sorted my heart attack) I pulled over and called my TVR guy, who was just leaving the circuit himself. He obligingly stopped in the same layby, checked the car over for obvious signs of a leak, calmed me down and told me that the wire was simply loose on the sender. He told me to ignore the gauge and drive home, all would be well. I did notice while driving that accelerating and decelerating could induce readings on the gauge, but this was simply small G forces pushing the spade connector into contact with the terminal, and off again. Worth a check - the sender is on the front of the engine, visible more readily from underneath.
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