oil draining back if left for a few days

[moggyman]

I have a 1968 MGB GT, and am having problems when I leave the car for a few days, when I try and start it, it take about 20seconds for the oil pressure to show on the oil gauge, I leave the choke in so it will not start to save doing any damage to the engine, once started it runs and drives great, with 65/70 lb when driving, and 35/40lb on tick over, there are no leaks from the engine, and a new engine was fitted about 10000 miles ago, also new oil cooler and braided oil pipes, I change the oil filer to a inverted spin on type, that I got from MGOC, that was just as bad, I phoned them about the problem, and they thought it was a faulty filter, so they sent me another FOC, but was no better, I then fitted a spin on filter that hung down, but still the same, I have a 1960 1.5 that has the same B series engine, and I have replaced the oil filter with the same one I have on my GT, and when I start it the oil pressure is there straight away, has anyone had this problem, or can anyone help ne sort it, many thanks.

[Paul Scott]

Hi Rolly,
welcome to the forum.

Graham Dix mentioned this in our Safety fast newsletter earlier this month. It might help https://www.mgb-register.org/safety-fast-may-2020/

Regards
Paul

[Ian F]

Hi Rolly,
I think your test with the other B series engine indicates that the problem is not with the oil filter set-up? If this is the case, then I would suggest checking the simple things first - check oil level and dipstick accuracy, that the gauge is not the source of the delay, and check the pressure relief valve is operating correctly.
If they check out OK then you may have to look inside the engine, eg at the oil pump and strainer assembly.
You did not say if this situation has arisen recently or whether it's always been like this since your rebuild 10,000 miles ago? That information may provide a clue to what the problem is.

Keep us informed and the forum may be able to provide some advice,

Ian F

[Vic Butler]

What is the other car with a 1.5 engine? Does it have an oil cooler? If not, the cooler is the only difference between the two and could that be the cause?

[Dave Wheatley]

When I changed my oil and filter last year, the oil pressure went down from 70 to 60, and took its time to register on the gauge. It might have been on here that someone suggested changing the filter again - bingo, pressure back up to 70 and no delay. Can't remember the make of the dud filter, but the replacement that worked OK was a Mann.
Could be the least expensive fix for the OP's problem.

[Paul Hollingworth]

I had an issue with oil pressure when my engine had been rebuilt. I had been using Mann filters with no problem but it was rebuilt with a Unipart. I switched back again and the problem went away. It turned out that the steel tube in side the filter was sticking up too much and fouling the relief valve inside the Unipart filter. It seems that this tube should stick up less that 40 mm above the aluminium housing (threaded bit). I gave it a tap with a hammer and it went down about 5 mm. I meant to Loctite it but never got around to it but I check it evert time I change the filter now.

[Peter Cresswell]

I had this problem with the oil pressure before I built the new engine. Like Graham Dix I changed from the renewable element type to a canister type - In my case both are the upside down filters - and now I get almost instant oil pressure. You have to be careful as not all canister filters have an in built non return valve, but at least the ones branded 'Heritage' and Mann do. I now use these as choice.
Incidentally, when I took the engine apart in order to build the new one, there was no sign of appreciable wear on any of the bearing. The problem was valve recession caused I think by constant engine speed for long periods on french autoroutes. This was despite using Castrol Valvemaster. The new head has unleaded seats fitted.