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V8 250 Significant Change in Oil Pressure

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captain bobo
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V8 250 Significant Change in Oil Pressure

Post by captain bobo » Thu Dec 13, 2018 8:44 pm

My V8 250 saloon has shown good oil pressure since the engine rebuild (indicated 65 psi cold, 50 psi running hot at 3000 revs). 4 weeks ago I changed the oil (used the same oil - Morris Golden Film Classic 20-50) and at the same time replaced the screw-in oil filter (with exactly the same product from the same supplier).

The oil level is full. Since the change, the oil pressure indicated is much lower than before the oil & filter change. Indicated 40 psi cold and indicated 30 psi running hot at 3000 revs.

I can't believe that the oil is the cause; it's the same oil. Is it possible that there's a coincidence with the sender being the culprit? How about the filter, is it possible for a replacement filter to have a fault that causes such a change? The filter is a Mann W719/15. Might there be a better filter that I could use?

I'd appreciate any insights anyone can offer - frankly I'm puzzled.
Best wishes, Dave B

Chris_R
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Re: V8 250 Significant Change in Oil Pressure

Post by Chris_R » Thu Dec 13, 2018 10:35 pm

Bear in mind the oil pressure reading is the resistance to flow in the engine. The more you try to pump through a given space the higher the resistance there will be.
The sensor will be located in the system after the oil filter. I think that a reduction in flow from the filter, in other words less oil getting through the filter could produce that result.

classiclife
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Re: V8 250 Significant Change in Oil Pressure

Post by classiclife » Thu Dec 13, 2018 10:56 pm

Hello Dave,

Mann filters are spot-on, German enginnering - need I say more.

My V8-250 runs with a Mann W916/1 which was supplied by Flexolite on converting the paper element to cannister. Your filter looks quite big so I presume it is an extra capacity type ??

It is very possible for a filter to cause an issue by altering the free flow due to a defect - rare but not unknown.

The other option could be the oil pressure relief valve not opertaing correctly, quite often it is a case of removing, cleaning and refitting. Sometimes they do need to be replaced due to wear - additionally the spring in the relief valve gets weak. These are all possible issues.

Your oil is average, there is far better out there. Morris only has a rating of 800ppm of zinc whereas oils such as Millers, Penrite and Classic Heritage have far higher - in excess of 1000ppm. It is a subject I have done a lot of research on and written a comprehensive detailed document for club magazines.

For the cost of a filter, I would replace it and try again.

Regards.

Richard.

Phillmore
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Re: V8 250 Significant Change in Oil Pressure

Post by Phillmore » Fri Dec 14, 2018 8:26 am

If you haven't binned the old filter put it back on and see what the pressure is.
Andy

1954 Conquest Mk1, 1956 Conquest Mk2, 1957 Conquest Century Mk2, 1955 Austin A90 Westminster

Christopher Storey
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Re: V8 250 Significant Change in Oil Pressure

Post by Christopher Storey » Fri Dec 14, 2018 11:20 am

Your earlier readings sound high ( possibly undesirably high ) to me . Your most recent readings are close to those which I get on my engine, now about 3,500 miles post rebuild . In any event , people get very hung up about oil pressure when flow rate is equally, if not more , important given that a major function of the lubricant is to carry heat away from the bearings, and pressure and flow rate are often inversely proportional to each other . It may be that your old filter had some kind of restriction that was impeding the flow and raising the pressure. Another factor to consider is that the Jaguar sender/gauge combination is notorious for its propensity to give inaccurate readings . Frankly, as long as the pressure rises reasonably promptly after either a cold or hot start, I wouldn't worry about it

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captain bobo
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Re: V8 250 Significant Change in Oil Pressure

Post by captain bobo » Fri Dec 14, 2018 7:38 pm

Thank you all for the comments.

I seem to recall reading somewhere that on SP 250 engines it's possible to have an airlock in the oilway that feeds the oil pressure unit which can skew the oil pressure reading. Might it be possible, I wonder, to have the same uncommon condition on a V8 250 engine?

Interesting comment about the Mann Fliter size & capacity. If any forum members have equivalent Flexolite adapters to their engines, which oil filters do you use? I'd be interested in finding out what alternatives I might be able to use.
Best wishes, Dave B

KV8
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Re: V8 250 Significant Change in Oil Pressure

Post by KV8 » Fri Dec 14, 2018 8:24 pm

Hi Dave

As you may remember my engine was rebuilt in 2015 by Russ Carpenter. I have changed oil and filter twice since then and since the rebuild still get 55 psi cold and 40 psi hot. I have the original oil filter type and have found it easy to fit. The filter I use is the appropriate Mann type which incidentally although a German brand are made in South America!.

Interestingly the oil he recommended when I collected the car was Texaco 15W40 and when queried he said that oils with high zddp were not necessary for the DV8 . I had difficulty sourcing the Texaco brand and thus used a Comma equivalent.

Regards

H

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Vortex O'Plinth
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Re: V8 250 Significant Change in Oil Pressure

Post by Vortex O'Plinth » Fri Dec 14, 2018 8:41 pm

My SP engine with the Flexolite conversion wears a WIX WL7074 filter. This is a compact canister. It can be bought on eBay or Amazonfor £4.70. The Flexolite is different for the saloon but the filter is probably interchangeable.
Nick

Pas d'elle yeux Rhône que nous.

Ian Hastings
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Re: V8 250 Significant Change in Oil Pressure

Post by Ian Hastings » Fri Dec 14, 2018 8:55 pm

I got this list of oil filters for the SP somewhere along the line - possibly from Wilf Stephens.

Recommended - AC20; FRAM CH813PL; COOPERS AZL012; PUROLATOR MF276A; GUD G562; TECALEMIT JACKSON FP3309; POWERTRAIN 420; CROSLAND 487; MOPAR 5039546.

DO NOT USE - TJ (TECALEMIT JACKSON) FP3317 or FP9503 or UNIPART GFE102

Other makes are available.

classiclife
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Re: V8 250 Significant Change in Oil Pressure

Post by classiclife » Fri Dec 14, 2018 10:23 pm

I've checked all my Mann filters (canister) and clearly say made in Germany; that said the company does have global production plants - wherever they are located their QA is strictly defined by Mann's HQ in Marklkofen Germany.

Comma oil is not a great oil, okay for 3k miles and then certainly needs changing it's the same as Halfords - it is low in zinc and has a poor shear factor rating.

Any engine running OHV requires decent zinc levels in the oil - the attached photos show what happens when you use an inadequate oil - poor quality oil on the left and decent oil on the right; both cam followers have received identical use.

The following is an extract from my article:
The majority of classic car owners will have tappet followers that are “flat-bottomed”, that is to say the bottom surface is flat to the naked eye. These followers have an extremely tough life; probably only second to cylinder head valves. As the camshaft turns, each lobe per revolution makes contact with the followers. The shape of the lobe is designed so that at its peak revolution it will push the follower up which then pushes the tappet rod up and opens the valve in the cylinder head, via the rocker. The valve is seated excessively tight by single or double springs to form a gas tight seal within the cylinder head combustion chamber.
So as you can see the force placed upon the bottom of the cam follower is significant to say the least. This “super-pressure” contact causes friction and as we know friction causes component wear. This is where ZDDP plays its part. Zinc is a polar molecule, so it is attracted to steel surfaces. Under high heat and extreme load (pressure), the Zinc reacts with the steel surface and creates a phosphate glass film that protects the steel surface by forming a sacrificial layer that covers the peaks and fills in any indents on the steel surface. Basically your flat bottomed follower, to the naked eye, really does become 99.9% flat and smooth. By forming this protective layer the cam lobes and flat bottomed followers are heavily protected against friction wear; remember friction wear can never be eliminated but much can be done to slow the process down.
WORN TAPPET FOLLOWER.jpg
Regards

Richard.
Last edited by classiclife on Fri Dec 14, 2018 10:39 pm, edited 1 time in total.

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