Discussion in 'Mech Tech' started by Pumpkin jack, Mar 24, 2019.
Mine is the same. 10psi per 1000rpm is an engineering ‘rule of thumb’.
On my badly worn engine the oil pressure would drop to 4psi at hot idle. If it got really hot over 120 degrees the electronic oil pressure sender would indicate negative. So I fitted a stock warning light switch on a T piece fitted in the oil pressure sender hole.
Tuning a high performance engine by smelling the exhaust is a bit random.
If you dont have an oil pressure sensor or temperature gauge you can cook your engine and carry on driving as the engine chews on its bearings.
It would be worth additionally fitting a lambda sensor amd acually measuring the exhaust O2 percentage and tuning with that.
Your engine sounds like it has been run lean, got hot and has scraped off bearings so the oil pressure has gone ..
Does the oil have a metallic sheen ?
44 IDF’s with default vents it’ll be washing the oil off the bores, it won’t be running weak.
It's worth changing just to eliminate, the one I've fitted is a Mahle oc28
I have a cylinder head temp sensor fitted. I haven't gone far enough for a consistent reading it doesn't go much over 100degrees, less when moving. In fact the one time I've seen it over 100degrees was when it ran with no problems.
Haven't noticed any metallic sheen to the oil
100* doesn’t sound very high for CHT.
I’d expect a running temperature between 135C and 150C under most conditions – cooler when idling.
For some reason the single relief cases seem to suffer oil drain back. This results in a slow pressure build up during engine re-starts and an oil filter with an anti-drain back valve should be used to reduce the problem. I’ve read conflicting reports of the Mahle OC28 filter; some say it has the valve others that it doesn’t.
As has been suggested, it could be oil filter related. For the sake of half an hour and about £10 you might as well change the oil filter. I was having pressure problems, tappets kept collapsing. Wish I'd changed the filter sooner, would have saved me hours of work.
This thread here briefly discusses oil filter drain back & shows some images of the anti drain valve
Back to oil filters. Do we have a definitive brand part number for one which definitely has the drain back valve.
Apparently this one...Mann w719/30
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I use Mann 920/17, cross references to VAG p/n 021 115 351 A used on Porsche and VW Type 4 engines. https://catalog.mann-filter.com/EU/eng/catalog/MANN-FILTER Katalog Europa/Oil Filter/W 920~17
Out of curiosity I’ve opened up a Mann 920/17 filter and it has neither an anti-drain back valve nor a by-pass valve.
I’ve edited my earlier post, obviously not all Mann spin on filters have an anti-drain back valve.
That's strange.. I found somewhere yesterday showing specs for them that said they did!...can't find it now..
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That’s what I thought too but I’ve just checked a couple of other 920/17 that I have in stock and neither of them have anti-drain back valves, however, three Mann 916/1 that I use in the V8 MGB do have the valve and it’s the same size filter.
I have ordered a Mann 719/30 this does have the anti-drain valve
https://catalog.mann-filter.com/EU/eng/catalog/MANN-FILTER Katalog Europa/Oil Filter/W 719~30
I'll fit it this weekend and see if it helps
The W 719/30 is 28mm longer than a standard filter and the length might be a problem if you have a sandwich plate for an external cooler. The W 920/14 has the same dimensions as standard and has an anti-drain valve. I might try one next time.
I hope it solves the pressure problem.
Fitted a gauge ( cheap one) changed the filter......30psi at start up dropped to 0 after 10 mins of driving. Oil light comes on at idle along with the knocking.
I'm sure the oil pump is engaged as it wouldn't bolt up otherwise and bolts don't interfere.
It's not looking good!!
That is not good . A guess would be that one of the oil pressure relief valves isn't working as it should, mebbe.
Unfortunately I have to agree it’s not sounding good and I fear the worst. Start-up oil pressure should be double what you have so there is a huge amount of oil being lost somewhere. It’s worth checking the diameter of the pressure relief valve and the length of the spring – as I said earlier I have two cases with different size valves and it would be possible to put the small valve in the big hole. And put another half-litre of oil in the engine even if it’s on maximum, it won’t do any harm and it might take the oil level above the pickup O-ring.
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