Classic cars forum & vehicle restoration.

[Bitumen Boy]

Hi all, I changed the oil & filter on the Herald the other week, not quite due but as it looks like I won't be getting much use out of it for a while I thought I'd do it now and avoid leaving old oil in the sump. What I'm finding now though is that the oil pressure is noticeably lower than normal. It's not too bad when starting from cold, indeed so close to normal that I only noticed it when I was actively looking out for it, but it gradually falls away as the engine gets properly hot on a longish run until it can be 15psi or so below what I'd expect.

There are no other symptoms. No unusual leaks, oil up to the top mark on the dipstick, and no sign of coolant or fuel entering the sump. No overheating or rough running. No unusual noises or vibration. It's the 1147cc engine so it has the full-flow oil filter, so even if the new filter was duff (blocked/bypassing) I wouldn't expect the pressure to be affected in this way, likewise if the pressure relief valve was stuck or otherwise defective I'd expect to see poor pressure right from a cold start.

The oil is some I bought at a show several years ago (been in stock ever since) for what seemed like a bargain price. It purports to be Duckham's Q 20/50, sealed can and the right green colour, the can and labelling are identical to some that I bought a caseload of on another occasion (and which has proved good in service). However, at this stage I'm thinking it must be a can of dodgy oil that's thinning out too much at high temperature. The first time I noticed the problem was the first time I took it out after changing the oil, a good run out to Hereford on a warm afternoon where I ended up watching the gauge like a hawk! I kept a close eye on the gauge coming back home, but the return trip was in the cool of the night and it didn't drop quite as low as it had earlier in the day.

At the moment I'm thinking that the best course of action is to treat this lot effectively as flushing oil - get it nice and hot then drain and refill with fresh, which should solve the problem. I just can't think what else could be causing it, unless anyone else has any ideas?

[kevin2306]

If it was me and you have done no other engine related work, I would drop the oil and change the filter.
A fresh gallon of oil and a new filter is way cheaper than an engine rebuild.
Could be unrelated and pure co-incidence and something else is the cause though?

Kev

[goneps]

We had a 1964 Herald 1200 virtually from new. One day I made the huge mistake of buying at bargain price 4 gallons of Duckhams' green 20W/50 oil. After changing to the green stuff the oil pressure light would flash at tickover (Heralds were not originally equipped with a gauge), which it had never done before and never did again after the green garbage was replaced with proper oil.

'Nuff said.

Richard

[Bitumen Boy]

It hasn't been quite that low - I fitted the gauge myself, always have done with my oldies,but kept the oil pressure switch though it now works a loud buzzer. All the same, I think my next job is to drain the sump again and refill with fresh oil. It's not impossible that there's some odd, unrelated fault that's cropped up just now, but I think I'll start with the easy stuff first!

Incidentally I think some early Heralds did come with oil pressure (and water temperature) gauges as standard - the 948 twin carb models, if memory serves?

[V8 Nutter]

Many years ago I owned a 1954 Oldsmobile with hydraulic tappets. 20/50 was the only grade of oil readily available at the time. I changed the oil and the car developed a misfire when starting on cold mornings. I spoke to an American car expert, he said the problem was thick oil pumping up the tappets. He recommended using Duckhams because it was thinner than anything else. I did that and it solved the problem, but it could well be the basis of your problem

[Jim.Walker]

I could be wrong as much time has passed (and I have had a stroke which hinders re-call). But I am pretty sure that the 1147 engine had a BY-PASS FILTER , but the later FULL-FLOW filter of the 13??cc engines was/is visually identical and could be fitted in error.
Sorry if I am wrong, but check it out.
Jim.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

[Bitumen Boy]

I had to check it out Jim, you started a doubt in my mind of the "did I lock the back door" variety... but the bypass filter was only on the 948 engines, the 1147 has the full flow filter as per the larger 4 cylinder engines. Incidentally, if anyone has any of the early type bypass filters gathering dust, I believe they're quite rare now, and well worth listing on fleabay. Anyhoo, I got it hot yesterday and left the oil to drain overnight, then refilled with fresh this morning. Didn't do the filter - thought I had several in stock but actually had none - but removed it and let it drain overnight before replacing. Went for a run today, pressure holding up a little better but still not right, could have been down to the cooler weather as much as anything else. Next step will be the filter, not sure how it could cause this problem but it's a quick and cheap job when I can get hold of one (bloody bank holidays!) and a logical first step.

There's also a question mark over the running temperature of the engine, temp gauge has been registering rather less than its usual of late (before the oil pressure problem though) and, without getting round to actually doing anything about it, I assumed the thermostat was on its way out - but it could just as easily be the gauge or sender. Really, all I know for certain about the running temperature is that it's not boiling and the heater output seems OK. In an attempt to avoid wasting £££'s on unnecessary parts, I've invested in a suitable thermometer (£5) to carry out proper testing, long thought one would be handy but always assumed they would be more expensive than they are. Anyway, between the bank holiday and the inevitable post-privatisation slowdown of the Royal Mail it looks like I won't be doing much inside of a week from now

[Jim.Walker]

Sorry about that Bitumen Boy.
But at 75 my recall is not what it was! I am dreading the situation when I am 76!
Jim.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

[ajlelectronics]

I had a similar problem on an Essex. Replaced the oil filter again and all was well again. Branded filters too!
_________________
Evans Waterless Coolants
Find this and more at http://www.classicmicrocars.com
Sat TV / Aerial systems etc: http://www.ajlelectronics.co.uk

[baconsdozen]

I had a similar problem on an old land rover fitted with a oil pressure gauge. It was an air lock in the pipe to the gauge.
_________________
Thirty years selling imperial hand tools for old machinery(Now happily retired).

[ukdave2002]

[Bitumen Boy]

[Phil - Nottingham]

I had the flexi-pipe on the Mk2 Mini oil gauge frature and it sprayed loads of hot oil all over the engine and and exhaust - plenty of smoke and 3-4 pints of oil lost in seconds
_________________
Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2

[bob2]

Just had that happen to me last week in my blue mini, changed the oil pressure rubber hose during the weekend and all looks well now. Had to clean the engine bay, the one I had restored last summer, it was a mess and the smell of burnt oil inside the car was making me dizzy almost!!

[MikeEdwards]