MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - Engine oil

Have had a quick ramble through the Archives but have drawn a blank.
When left for a few days, I could open an offshore company in Panama quicker than it takes the oil pressure to get fully up to speed (70psi cold). If it's started the following day then the needle leaps across the gauge.
I'm using Comma Classic 20/50 (looks like the old Duckhams) and a Mann filter. I've tried cranking before it fires but that makes little difference.
I'm considering a lighter oil (maybe 10/40), what's the consensus here?
Jeremy Tickle

Capillary oil pressure gauge?
My frog's capillary gauge takes several seconds (10 maybe) to reach maximum when starting from cold. The electric gauge in my elan takes about the same (damping I assume).
I would add that the supercharger oil feed is Tee'd off from the oil pressure capillary so that may contribute to the apparent lag.
Never considered using anything other than 20/50 in my A-series.
Simon
Simon Wood

Yes capillary. It's the difference between starting after a few days and the much quicker response when starting the following day, which is concernng. Not sure if it has something to do with a valve in the filter or not.
Jeremy Tickle

Jeremy, I don't see why a lighter oil (10W/40) would come up to pressure faster. Indeed if the problem is oil draining back out of the galleries when you leave it standing, then this will happen faster with the thin oil.

How long since you changed the oil and filter anyway? The 20/50 may have become diluted with petrol, making it thinner. With SU carbs never leave the car standing with the choke pulled out - it lowers the jet and can allow raw fuel to simply flow out and into the bores where it then washes down into the oil to dilute it.

It could just possibly be air in the capillary feed to the gauge. With the engine running, reach behind the dash and slacken, then re-tighten the capillary nut on the back of the gauge. This shouldn't really need doing, but if there is air trapped there it will let it out and may give you a more accurate gauge response and reading.
GuyW

Jeremy,
Does the gauge needle take a while to move from zero or is it that it immediately moves and then climbs slowly? I suppose that the former may be more of a concern than the latter.
I'm pretty sure that my gauge behaves in much the same manner as yours but mine starts to move immediately
Simon Wood

Good question Simon.
And also, whilst the needle is being slow to respond, what happens if you tap the gauge with your finger?
GuyW

I dont know that there is an actual issue... its sounds like this is a gauge problem and not an actual oil pressure conundrm

id try a temporry electric aftermarket oil pressure gauge in the system and see what that does

but i think lowering the oil density to 10/40 would be a bad mistake

or maybe run some paraphine (K1) thur the oil system to clean out the oil gallies for a few minutes might help the flow of oil
prop

Thanks for the replies.
My thinking was a lighter oil will be easier/thinner and therefore quicker, to pump round the sytem compared to a thicker oil - it seemed logical, well at least to me!
On my VW van I changed from 20/50 to 10/40 and the hydraulic lifters/tappets quieten down (after being filled with oil) much quicker with the thinner oil.
The gauge starts and moves very slowly but the following day it positively shoots around the gauge - hence the thinking about the filter valve. Tapping makes no difference unfortunately :( [love those old B&W films where tapping the gauge made all the difference to the steam pressure!]
Guy thanks for the prompt about the small oil feed pipe. It made me look under the bonnet and there seems to be a small leak from the capilary pipe where it disapears by the heater and through the bulkhead so I'll check the pipe and the tightness of the nut behind the gauge. If its leaking then maybe air is being drawn in?
Jeremy Tickle

Do you have an original midget engine, or Marina/Ital?
Dave O'Neill 2

Dave,
it's the original engine, rebored +60.
Jeremy Tickle

You shouldn't have any drain back from the filter, as it is suspended.

MGBs can suffer from it, if the wrong filter is fitted and so, presumably, can Marinas, as their filters are inverted.

Just re-reading the OP again...is it just that it takes a long time to get MAX oil pressure, not to get ANY oil pressure?
Dave O'Neill 2

If here is a "small leak in the oil capillary tube" this could explain it. It would simply make the gauge a bit slow to respond if its leaking out pressure.
GuyW

Dave,
yes but it climbs exceedingly slowy :( and I'm wondering why, especially after a few days not been started.
Thanks Guy, I'll check the capilary tube connections, hopefully that's the cause and nothing more sinister.
Jeremy Tickle

This thread was discussed on 07/04/2016

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.