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MG Midget and Sprite Technical - Oil Pressure

Hi all,
On my drive up to and back from Peter Burgess's Sunday and yesterday, I noticed the oil pressure behaving very strangly. Cruising along at around 70 the pressure would sit at just above 60. Then it would drop to just under 60 for no reason that I could see. Then, if I was to feather the throttle a little, it would drop to around 50. Foot back on the throttle again and pressure back up to 60+. When stopping, no matter how slowly I came to a halt the pressure would drop to around 20 and then back up to around 40, unless I blipped the throttle when it would increase temporarily.
The sump is full to the max line but I do not know what oil it is in there (service is coming up over the bank holiday weekend Nigel ;)), so I don't think oil surge is causing that drop in pressure.
The only thing I can think of is the pressure relief valve is sticking open a little, or is a little slow closing. Has anyone any other ideas?
It is a 1275

Thanks
Dave
Dave Brown

Before everyone comes on and starts going on about all manner of complicated causes - the simplest thing to check is the condition of your oil pressure gauge!

They have a sticky tape sort of thing around the inside, and, over time, this gets unsticky and can break slightly - which affects the way that the needle moves and it can be totally erratic.

Start there and, if it's not that - then move on to other things - BUT, if it's reading ok, and survived a session on the rolling road - I wouldn't get too overly obsessed - keep a very close eye on the actual amount of oil and learn what it's "normal" is - as this is different on every single car (which makes for interesting worries if you drive several!!!!)
rachmacb

as rach's put

plus (perhaps but I'm not sure if this would cause it) check the pipe or gauge connections for weeps or leaks

and if you don't know what oil is in the engine (or how long it's been in there) then an oil and filter change with the correct oil might help

. . . as part of a full and proper service of course :)

. . . check the Driver's Handbook for what a full and proper service actually is :)

(or the Porter's manual)
Nigel Atkins

Hi Rach,
I am not that bothered about it, just curious really as I cannot work out why it is happening.
Nigel,
The service is due to be done over the weekend.

Dave
Dave Brown

Dave,
I noted from your first post you preparing for my ‘stock answers’ but I wouldn’t have put a service was required for this issue but you did put that you didn’t know what oil was in there so a cheap and easy remedy for that is an oil and filter change

Just for once I did fully read the post

Out of interest do you have an oil cooler?
Nigel Atkins

LOL - sometimes - the BBS never ceases to amaze me!
rachmacb

Hi Nigel,
The service is not for this issue but because I have not serviced the car since I bought it. Oh, I have left myself open for abuse from Nigel now!
I do not have an oil cooler fitted.

Dave
Dave Brown

sorry, both, I didn't mean an oil and filter change would remedy your gauge issue but it would remedy you not knowing what oil was in the engine and how old or used it is

I realised you'd hadn't serviced the car since buying it or you'd know what oil was in the car :)

I think the way I write perhaps makes me seem even more stupid than I actually am, I'm not as stupid as I seem - or perhaps I am but too stupid to realise

doing the full service work in itself would not have sorted your gauge but whilst doing the full service work you may well have come across the cause of this (if there is a cuase) and other issues and prevented them continuing or starting :p
Nigel Atkins

I'd be looking at the oil grade - without a cooler on a long journey the oil gets hot and loses viscosity leading to the drop off in pressure at lower revs... go with a decent 20/50 oil and if it continues to be a problem consider fitting an oil cooler and oil stat...

JB
James Bilsland

I didn't notice oil pressure drop with my 200 mile journey on Sunday - 0w-40 oil and no oil cooler, perhaps when it's a bit warmer I might

in my experience a road going 1275 doesn't need an oil cooler and certainly if you have an oil cooler you'd need a thermostat for it on a 1275
Nigel Atkins

Hi James,
I don't think oil temperature has anything to do with it as I watched the needle move down. It would go down within a second or two stay there for a few seconds (10 perhaps) and then go back up. In that time the oil temperature would be fairly static - I was only going 70 and the ambient temperature was not high (Sunday around 19.00 so perhaps 10 centigrade). Engine temperature was steady at just below the N.

Dave
Dave Brown

I think James was thinking more of the state or type of oil you've got in your car, which you don't know the type of :)

gauges are just gauges and as rach says readings vary from car to car perhaps even gauge to guage

having put that - does your temp gauge normally show just before N at 70 mph in temperate weather as both my previous and present guages show well before N in the same conditions, oil is the secondary engine coolant

did you see Christian's (C L Carter's) thread on his 1500 when he went away?
Nigel Atkins

Possibly the gauge is dodgy - first step is to try another gauge... I bet the oil pressure improves when you change the oil though... ;o)
James Bilsland

. . . well oil and filter change is part of a service

on a car that's not known to you I always suggest as soon as possible doing a full and proper service covering all but what can proved to have been carried out recently, this can be a staggered and staged service whilst you still enjoy driving the car regularly
Nigel Atkins

Dave. You said it happened both on the way to and from Peter Burgess'. Did you mention it to him? Did he comment at all?

Bernie.
b higginson

Hi Bernie,
Yes I did mention it to Pete. He was confused by it too.
I don't see that it is a big problem. New oil may make a difference. I will see at the weekend. If it does not make any difference I will change the pressure relief valve and spring. Swapping gauges is not easy when you don't have a spare.
Dave
Dave Brown

don't forget to buy a sump plug washer too just in case you can't reuse the old one - I'd be tempted to use this oil and filter change as a short flush type change using cheap oil for a couple of months or thousands of miles before changing oil and filter again with good quality oil if the short term oil looked good

if you lived nearer I let you have the oil and a spare new filter and sump plug washer so you didn't feel you were wasting your money, cost me all of £3/4 :)
Nigel Atkins

I have seen this on A series a couple of times. After fitting a checking gauge: Loose pipe fitting on the pickup pipe, which you can fix by dropping the sump. Cracked pickup pipe will do it too. Loose oil pump which is engine out.

FRM
FR Millmore

This thread was discussed on 01/05/2012

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