Oil pressure dropping
Discussion
Hello again!
Had the car checked over today. Good to run until the winter lay up. However, had the oil and filter changed just to be on the safe side. On the way home, whenever the revs dropped to little more than idle, the oil warning light started flickering and the pressure on the gauge fell a bit. Not to zero obviously as I would have stopped and out of the car quicker than the proverbial rat. Picked up again as soon as the revs rose. However, enough to induce a certain amount of consternation shall we say. Oil is Millers XFS 5W40.
I will contact the garage about it in the morning, but any ideas? Please no-one suggest big end bearings...
The car generally has a few electrical gremlims but, thus far, all the gauges work and seem to be pretty accurate. Thanks.
Had the car checked over today. Good to run until the winter lay up. However, had the oil and filter changed just to be on the safe side. On the way home, whenever the revs dropped to little more than idle, the oil warning light started flickering and the pressure on the gauge fell a bit. Not to zero obviously as I would have stopped and out of the car quicker than the proverbial rat. Picked up again as soon as the revs rose. However, enough to induce a certain amount of consternation shall we say. Oil is Millers XFS 5W40.
I will contact the garage about it in the morning, but any ideas? Please no-one suggest big end bearings...
The car generally has a few electrical gremlims but, thus far, all the gauges work and seem to be pretty accurate. Thanks.
There are a few clues in your post...
If the oil warning light has started to flicker and the gauge is reading lower than usual it looks like a real drop in pressure, since these are fed by two independent senders. Accuracy of the gauge in numerical terms is uncertain, but for what it's worth mine runs 25psi hot at idle. The fact that you've just had the oil changed may be related, especially as the grade of oil used is too light. The first number is fine, the lower the better, but the second number should be 50. With a 40 grade, your oil will be a little thinner than it should be when hot. However, it's surprising that such a small difference would drop your oil pressure into the warning light range. A distant memory tells me the warning light switches operate typically at around 7psi.
What was the gauge reading by the way?
Graham
If the oil warning light has started to flicker and the gauge is reading lower than usual it looks like a real drop in pressure, since these are fed by two independent senders. Accuracy of the gauge in numerical terms is uncertain, but for what it's worth mine runs 25psi hot at idle. The fact that you've just had the oil changed may be related, especially as the grade of oil used is too light. The first number is fine, the lower the better, but the second number should be 50. With a 40 grade, your oil will be a little thinner than it should be when hot. However, it's surprising that such a small difference would drop your oil pressure into the warning light range. A distant memory tells me the warning light switches operate typically at around 7psi.
What was the gauge reading by the way?
Graham
Combination of (relatively) expensive mistakes here I think.
It was on 15W50 the service before last. The guy who sold me the car said he had gone to fully synthetic, but looking back on what he purchased it was 10W50. I told the garage guys I thought it was 5W40 and that's what they've put in it. B*gger.
Right, so need to get that oil out of there pronto. Had thought I could do it myself, but had second thought about that now.
Thanks again. I don't know what I'd do without this forum (apart from probably break a perfectly good TVR).
It was on 15W50 the service before last. The guy who sold me the car said he had gone to fully synthetic, but looking back on what he purchased it was 10W50. I told the garage guys I thought it was 5W40 and that's what they've put in it. B*gger.
Right, so need to get that oil out of there pronto. Had thought I could do it myself, but had second thought about that now.
Thanks again. I don't know what I'd do without this forum (apart from probably break a perfectly good TVR).
Edited by Deadfast on Saturday 31st July 10:44
Update!
Had the pressure checked with the capillary gauge. The pressure seems fine on the face of it. It is only dipping a bit, but that is enough to bring the warning light on. Worringly, the difference between 5W40 and 5W50 is relatively small, which means that the pressure has probably been hovering a bit too near the borderline for some time.
Having spoken to Millers, we have chosen a 10W60 competition oil as a replacement.
The only other thing that has been mentioned is a voltage drop caused by an electrical fault somewhere. Given the reversing light problem I have (intermittently coming on when I'm driving) I'm beginning to wonder whether there is something in that.
Had the pressure checked with the capillary gauge. The pressure seems fine on the face of it. It is only dipping a bit, but that is enough to bring the warning light on. Worringly, the difference between 5W40 and 5W50 is relatively small, which means that the pressure has probably been hovering a bit too near the borderline for some time.
Having spoken to Millers, we have chosen a 10W60 competition oil as a replacement.
The only other thing that has been mentioned is a voltage drop caused by an electrical fault somewhere. Given the reversing light problem I have (intermittently coming on when I'm driving) I'm beginning to wonder whether there is something in that.
I didn't have an oil warning light in my old S3c so surprised that you have one - I suppose someone has fitted it as belt and braces as the sender units are not all that reliable, they can give all sorts of strange readings.
Re the oil I used Millers CFS 10/60 in the S and it was excellent; there wasn't an oil pressure problem but it really held up very well even when it was very hot the tick over stayed up there so recommended.
Jim
Re the oil I used Millers CFS 10/60 in the S and it was excellent; there wasn't an oil pressure problem but it really held up very well even when it was very hot the tick over stayed up there so recommended.
Jim
jimed said:
I didn't have an oil warning light in my old S3c so surprised that you have one - I suppose someone has fitted it as belt and braces as the sender units are not all that reliable, they can give all sorts of strange readings.
Re the oil I used Millers CFS 10/60 in the S and it was excellent; there wasn't an oil pressure problem but it really held up very well even when it was very hot the tick over stayed up there so recommended.
Jim
+1 for the oil warning light on an S3.Re the oil I used Millers CFS 10/60 in the S and it was excellent; there wasn't an oil pressure problem but it really held up very well even when it was very hot the tick over stayed up there so recommended.
Jim
I have used oil at 5W30 and now use a performance vehicle semi-synthetic 15W40. I think the OP above was wrong, but stand to be corrected as I am not totally sure with regards to the numbers. I believe the first figure is the viscosity when warm and the second higher number the viscosity cold, so 5W40 would be the same hot but thinner when cold than 5W50 and 15w50 would be higher viscosity cold and the same when hot.
I moved from 5W30 to 15W40 for three reasons (noting 15W50 is what the bible recommends), they were I couldn't get 15W50 very easily locally and wanted to do the change that day, the recommendation of a sierra enthusiast who has run a number of breathed on versions for many years and the 5W30 was so thin it was causing me minor weeps at sealing faces and the oil pressure did drop very low (although it was getting everywhere) when at idle. I have found that a good 15W40 is working very well to date.
Mark
The second number is the viscosity at 100 degrees C. (higher number = thicker)
The first, W number is the viscosity at much lower temperature
So a low W number is ideal (particularly in winter)so that oil is thin enough to flow well from cold and a higher second number will give a thicker oil when hot ( a thicker oil will produce higher pressures )
those were the days . . . . filling the sump of some old banger you were trying to sell with gearbox oil or several cans of STP to try and get the oil light to stay off !!!!
Personnally I use a 15W/40 all year round
I can't remember where I saw it but there is an oil pressure switch available for the V8 that puts the light on at a higher pressure level for performance applications.
A long shot but it might be worth a new switch they are only a couple of quid.
Light on at idle isn't ideal but not necessarily major cause for concern if the engine has a few miles on it.
Light on at anything above idle would be a worry.
Its a relatively easy job to swap out the oil pump gears which might help - you may find the oil pump base is quite worn though and a replacement is a couple of hundred quid, though you may be able to save it with abrasive paper on a bit of glass (to keep it flat).
There is also a pressure relief valve in the base that can stick.
You must reprime the pump with vaseline if you have it apart.
I am running 20/50 unipart oil while I'm running it in after rebuild and seeing about 25psi on the gauge at hot idle.
A long shot but it might be worth a new switch they are only a couple of quid.
Light on at idle isn't ideal but not necessarily major cause for concern if the engine has a few miles on it.
Light on at anything above idle would be a worry.
Its a relatively easy job to swap out the oil pump gears which might help - you may find the oil pump base is quite worn though and a replacement is a couple of hundred quid, though you may be able to save it with abrasive paper on a bit of glass (to keep it flat).
There is also a pressure relief valve in the base that can stick.
You must reprime the pump with vaseline if you have it apart.
I am running 20/50 unipart oil while I'm running it in after rebuild and seeing about 25psi on the gauge at hot idle.
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