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low oil pressure

Posted: Mon Mar 19, 2018 9:38 am
by jvasabra
Hello,
Sabra 4808 was fitted with another engine, had been "resting" for odd 40 years. Oil pressure was excellent, +/-50 psi , less on idle ( identical to my other Sabras). After some 600 kms oil pressure start getting low(er). Now 30 psi when running/revving and nearly at the 0 on the oil pressure meter when idling. At cold start takes some 5 seconds before the oil pressure builds up. Compression test shows all 4 cyl excellent and car runs fine. What has happened ( old deposits coming loose and blocking things? I run it now on 15/40 detergent oil, was probably SAE 30 in its former life) and HOW DO I GET GOOD OIL PRESSURE AGAIN? Thanks for your replies ( already got some on PM , but the wisdom of the group is aways nice to hear).
Jacques

low oil pressure

Posted: Mon Mar 19, 2018 10:20 am
by Coupe Racing
The compression test won’t have any relevance to oil pressure I’m afraid
Pressure is built by the oil pump and retained to some degree by the oil filter .
The space between the crank shaft bearings and the crankshaft ( also the camshaft) will have the biggest influence on oil pressure in general .
The first step is to use a good quality oil filter and the correct grade of oil
After this step you might have to inspect the oil pump for wear or faulty pressure control valve and also the bearings on the crankshaft and camshaft.

low oil pressure

Posted: Mon Mar 19, 2018 11:09 am
by scimjim
I’d drop the sump and check the oil pickup and pipe first - oil and filter replace at the same time. Check the oil for metallic particles (visual and with a magnet) as you drain it.

low oil pressure

Posted: Mon Mar 19, 2018 12:08 pm
by willholderogri
It should be running on 20/50 oil I tried using the 15/40 on one of my old motorbikes and it did the same. The pressure dropped (though not as low as yours seems to have dropped ) I went back to 20/50 and it sorted it out .The pressure went up to its normal which was 70 psi.

low oil pressure

Posted: Mon Mar 19, 2018 12:25 pm
by philhoward
Looking at the handbook, then it was either straight 20W grade or 10W30 - but that was based on oils around in the early 1960's. Personally, I'd go with a "classic" 20W50 but also dropping the sump is a very good idea as if you've now used a detergent oil it could have cleared some rubbish out (especially if it's been sat 40 years!) and blocked the pickup (and/or the filter).

low oil pressure

Posted: Wed Mar 28, 2018 9:25 am
by jvasabra
Hello all,
Problem solved. As you guys suggested it was a lot of sludge. Once the sump was off , about 1/2 cm ( 1/4") of thick sticky slugde was removed; the pick up mesh/pipe was cleaned and with new oil the oil pressure immediately went to 50 psi and when warm and driving it stayed at 40/45 psi. A bit lower at tickover as usual. I will keep an eye on it and maybe rechange oil and filter once more quicker than foreseen.

Thank you all for the interesting replies.
Jacques

low oil pressure

Posted: Wed Mar 28, 2018 10:04 am
by scimjim
excellent news.

low oil pressure

Posted: Wed Mar 28, 2018 11:57 am
by willholderogri
grand what oil did you decide to use

low oil pressure

Posted: Wed Mar 28, 2018 7:18 pm
by jvasabra
To answer your question about the oil I used.
I had put in 15/40 Total classic. Now was decided for a SAE 20/50 mineral ( according to the shop classic low or no detergent ) . I must say I thought all multigrade oils were detergent .... I will see and check regularly.
Kind regards,
Jacques
PS On my two other Sabra's I use 15/40 for years , no problem whatsoever.

low oil pressure

Posted: Thu Mar 29, 2018 2:08 pm
by Old and Slow
IMO you need to use an oil rich in zinc (ZDDP) between 1000 and 1600 parts per million (ppm) to minimise wear on the cam followers. Unfortunately most of the 'big' manufacturers don't list the zinc levels and also, some of the "Classic" oils don't contain enough (usually around 800 ppm) including Halfords Classic 20w/50, Comma Classic 20w/50 and Castrol XL 20w/50.
Some race engine lubricants contain more than 1600 ppm but this isn't good for older engines.
Penrite, Millers and Morris are all OK though.
The American Petroleum Index (API) has a code letter system for oils:
http://www.api.org/products-and-service ... gories#tab gasoline
If possible the oil should be labelled SG, SH, SJ or SL and anything labelled other than this is unsuitable for older engines as it will have the wrong additives.
NTDWM but Classic Oils of Bicester have suitable stuff at reasonable prices:
https://www.classic-oils.net/Classic-Oi ... tage-20W50