Morris Minor Owners Club

Hi all!

I recently bought Beryl, a 1971 Traveller. I drove her home 450 miles from Norfolk to Scotland, all B and A roads, which was a joyful experience! She runs happily, but for one thing. I noticed on day 2 (I split the drive into 2 days) that the pressure on the aftermarket oil gauge was dropping from 45-55, where it normally sits, down towards the 20s when I took my foot off the accelerator (even when doing around 50mph). Eventually it looked to be dropping further and faster when I slowed down, so I pulled over to a petrol station.

Pulling to a stop the pressure dropped to basically 0, pressure warning light on, all the bad signs. So I let the engine cool and settle for 10 mins, checked the level - sure enough, it was below the MIN line on the dipstick. Refilled with 10W40 (only thing in the shop) to mid-level on the dipstick, went on my way; pressure jumped to 60+ (which I believe is too high!) and then over the trip fell again. Zero black smoke, so I'm not burning any; no evidence of a catastrophic leak, but with the level once again seeming low, I topped off a little and made it home.

Overnight the "low" oil level on the stick returned to the MAX line, and running the car from cold shows v high pressure (65+). Which got me thinking; is the current oil in there simply too thin, and it's basically "disappearing" when the engine is hot? I've got some 20W40 I use for my Triumph, so I plan a full oil change this weekend (the oil is black anyway).

I'll update if this fixes things, but in the meantime if anyone has experienced this and found there was a different fix, I'd love to hear it. The head gasket line seems like it might be weeping a small amount of oil very evenly around, which again makes me suspect a thin modern oil.

Cheers,
Jack

Make sure that your pressure relief valve is not sticking when hot.
Remove the valve and examine for wear/damage. Replace if necessary.
Oil dispersed around the engine whilst running will drain down to the sump overnight.

Is the plastic dip stick tube all there,? we had similar symptoms on our and basically it was too low on oil because the top of the plastic tube was missing.

Also, I wouldn't use anything except a good quality 20/50 oil in a Minor engine. As you suggest yourself, a thinner oil is probably not ideal.

I will check the pressure release valve this weekend! Yes the dipstick tube is fully present, so it's not that, and I should note I meant 20W50 not 20W40 for the oil I'm using in the upcoming change The good ol' Castrol.

More as I know more...

Just a thought - if it were the pressure relief valve sticking, wouldn't the oil be returning to the sump? The dipstick readings suggest that wherever the oil is going when the engine is warm, it's not back in the sump... Or am I thinking about this all backwards?

If the oil pressure relief valve was sticking in the open position - some oil will be returned to the sump - but also you will experience low oil pressure especially at lower revs. The oil pressure relief valve is not set to be just in a on/off position. The valve piston moves in the block and regulates flow and pressure. The spring acting on the piston counteracts the oil pump flow and keeps the oil pressure and flow at acceptable limits. High oil pressure is just as bad as low oil pressure in that the oil pump is working extra hard and generates heat which is passed to the oil which can break down and cause engine wear and failure.

Anyone know the exact size of the oil pressure release valve cap? I'm working with limited tools at the moment and didn't have a socket big enough, don't really want to just buy sockets at random til I find one...

Beryl is now sitting on stands, drained of oil, and also awaiting an alternator (I have the alternator, but it was sent with a threaded hole for the slip adjuster attachment, and I have no bolts with the right thread). Frustrating to be paused, but hopefully I can find the right tools and bolt and move on soon enough!

I'm seeing 15/16 specified in another thread, I'm going to try a flex-head ratchet spanner in that size... Not much else that I can imagine getting into the gap!

The correct size of the oil pressure relief cover is 1" A/F.
For further info regarding the removal of the oil pressure relief valve cap see this thread from 2013 :-
viewtopic.php?t=53440
As the photos in the link above are now off line here is a couple of photos of the socket I made.

Thank you! I unfortunately don't have the setup to make custom sockets for now - might just remove the starter to get in more easily But that explanation definitely helps me see the issues at hand.