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2.5 v8 oil pressure
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Thu Jul 04, 2013 5:40 pm    Post subject: 2.5 v8 oil pressure Reply with quote

So I've ended up with a late 2.5L V8 saloon. Fired up from cold the oil pressure gauge climbs over about 15 seconds to about 50psi. If left to tick over it'll slowly drop to about 30-35 psi at tick over as the motor gets hotter..it then seems to sit there quite happily until it's been running for about ten minutes or even longer then...next time you look at the gauge it's showing 0psi!!! I don't know exactly how quickly it drops off 'cos I've not watched it happed yet but I get the feeling it happens pretty damn quickly.

There is no bottom end rumble or knock to suggest the big ends are dry...my dad ( he;s 90 y'know Smile ) says he's convinced it sounds fine and he's been looking after his own motors since the old king died, and reckons he'd hear it if it was running no pressure. ....picking up off the throttle it doesnt rumble either. open it up to as little as 1800rpm or thereabouts and the gauge come up again.

I had the sump off at one point but was too stupid to check the pump. The strainer is clear. The filter is new. The car hasn't been on the road yet and I got it as a barn find...off the road for 10 years or more. I've run an engine flush through and changed the oil and filter again ( Oil is Comma classic 20/50 )

Now...some people have said the gauge is rubbish anyway..particularly at low revs and thus dynamo output voltages......I'm not keen on putting a wet gauge on it because..well.

..a) I don't have one. ..

.b) if I were to try to get one ...what thread would the sender be?

c) I've been told the housing the sender goes into it liable to crack if I try to get the thing out.!!!!!

It's also pretty difficult to get at.
Any thoughts or similar experiences with this engine?
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captain bobo



Joined: 02 Feb 2012
Posts: 43
Location: South West Cambs

PostPosted: Thu Jul 04, 2013 7:22 pm    Post subject: Reply with quote

The oil pressures sound a bit low all round for this engine. My V8 250 engine has run 2000 miles after rebuild. On start up I get close to 60 psi on tick over, this drops to 45 ish when warm and 35 ish when very hot on tick over. This seems to be the norm with these engines.

At 3000 rpm you should expect a minimum of 45 psi when running very hot(i.e. after 15 - 20 minutes of fairly fast driving). Before it gets that hot I typically experience close to 60 psi which gradually falls to 45 psi over time as the engine gets really hot.

Have you checked the oil pressure relief valve settings? There is a simple mod that you can do to the valve to raise the engine oil pressure all round, let me know if you're interested.

Mind you, my engine is the V8 250 version: with alternator: how stable is your tick over voltage?

Best wishes, Dave B
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1937 Daimler 15 Mulliner Sports Saloon & 1969 Daimler V8 250 Saloon
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Thu Jul 04, 2013 7:41 pm    Post subject: Reply with quote

oil pressure relief valve settings may be a way to go if it comes to it. Wish it didn't mean dropping the subframe to get the sump off mind.....
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Ashley



Joined: 02 Jan 2008
Posts: 1426
Location: Near Stroud, Glos

PostPosted: Thu Jul 04, 2013 8:29 pm    Post subject: Reply with quote

The oil pressure will drop at tickover and if the gauge reads low and it's electric, I'd replace the sender first.

I had a Silver Shadow that lost its oil pressure as it got hot and it overheated too, in both cases senders fixed the problem. Like yours, the engine was silent and obviously not hot.


Last edited by Ashley on Fri Jul 05, 2013 3:57 pm; edited 1 time in total
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Thu Jul 04, 2013 9:36 pm    Post subject: Reply with quote

I'd replace the sender at the drop of a hat..but I've been told that the casting it's in often cracks? Even if I did get it out without anything giving way it'd be sensible to check it with a wet gauge but is it a standard pipe thread?
If the feeling is that the sender is goosed do I just start using it? If it didn't have agauge I'd be none the wiser!!! Shocked
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Ashley



Joined: 02 Jan 2008
Posts: 1426
Location: Near Stroud, Glos

PostPosted: Fri Jul 05, 2013 3:58 pm    Post subject: Reply with quote

If you're sure it's not rattling on start up or when it's hot, I'd just drive it, I'm sure it'll be fine. I remember MK II Jags having the same issue.
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JC T ONE



Joined: 30 Oct 2008
Posts: 1139
Location: Denmark

PostPosted: Fri Jul 05, 2013 6:47 pm    Post subject: Reply with quote

Mine read around 65 to 70 psi when cold (mechanical gauge)

it fell to 35 ish, during the time it got to working temp.

This was with old & worn bearing shells.
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captain bobo



Joined: 02 Feb 2012
Posts: 43
Location: South West Cambs

PostPosted: Fri Aug 02, 2013 9:28 pm    Post subject: Reply with quote

I forgot to ask what oil you are using since this makes quite a difference with these engines.

Best wishes, Dave B
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1937 Daimler 15 Mulliner Sports Saloon & 1969 Daimler V8 250 Saloon
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gresham flyer



Joined: 06 Sep 2008
Posts: 1435

PostPosted: Mon Aug 12, 2013 9:12 pm    Post subject: Reply with quote

I use 20/50 Comma motor oil.and have done for the last 16 years since restoring my Daimler.
The running pressure on the internal gauge when hot is 40psi,and has been for the last 16 years.

I cannot remember the exact reading on an independent gauge but it was a little more the the indicated 40 psi on the internal one.

I have carried out about 40,000 miles in my car,even taking it round the Nurburgring,it did it no harm.

G F
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BigJohn



Joined: 01 Jan 2011
Posts: 954
Location: Wem, Shropshire

PostPosted: Mon Aug 12, 2013 9:57 pm    Post subject: Reply with quote

I had a similar experience with my Rover P6 V8, and the oil light didn't come on, so I knew I had a minimum of 8psi (ish). I changed the oil pressure sender and it cured the problem. I then cleaned the old sender and put paraffin (because it is thinner than oil) into it, pressurised with a syringe. I saw a thin black line appear on the plastic section of the sender, this was where I was losing my pressure, when the oil was hot and thin it forced its way out of the hairline crack, and registered zero pressure at the gauge.
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gresham flyer



Joined: 06 Sep 2008
Posts: 1435

PostPosted: Thu Oct 24, 2013 7:17 pm    Post subject: Reply with quote

Rover V8`s run at a lower pressure than the Daimler`s.

30 psi is normal for these unless the owner changes the relief valve .
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