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MG MGB Technical - Strange oil pressure after oil change

I've recently performed an oil change on my 1971 B. I've used the premium spin on oil filer from Moss and Penrite 20W-60 oil.

The oil pressure takes a while to build from zero(it was instant previously).

The oil pressure climbs to about 50 but will then fall to 30. After the engine has run for about 10 mins, the pressure has climbed up to about 50. Running for a longer period results in the pressure climbing to almost 60.

Previously the running pressure was between 60-65.

What could be giving me the low reading until the engine warms up?

I've had a filter problem before where the pressure would take a while to build from zero. I changed the filter and the problem was solved. I believe it was a problem with the anti-drainback valve in the filter. I've phoned Moss to ask about this but they say they've never heard of anti-drainback valves in filters.

Any help would be greatly appreciated.

James.
James Stewart

Hi James.

Do you really mean 20W-60 ?.

Sounds too heavy to me....

Don
Don

There should definitely be an anti-drainback valve in the filter, and I'm very surprised someone from moss wouldn't know about that. As was said above 20w60 is too thick for the car as well.
dave

Air bubble??
F Murch

I also believe 20w 60 is too thick, but, wouldn't the oil thicken after it warmed up. It should be as thin as 20w 50 when cold. Or do I have that backwards. Maybe someone with more knowledge of oil can shed some light. Perhaps a bad oil filter is causing the problem.
John

Have you used exactly the same oil, filter as before..? Also how old was the oil that you changed out..?

When oil is knackered it loses its lubrication ability - its polymers lose their surface tension and it becomes thin etc etc

New oil is nice and thick so you will see a difference in pressures of new oil. Generally for my car i see oil pressure at 60psi warm and 30psi warm idle - except when i change oil it usually takes about 500 or so miles for the warm idle to drop to 30psi, it normally hovers around 50psi. Within that 500-1000miles, the oil becgins to break down so reads a lower pressure thereafter.

I would not be unduly worried. Regularly change your oil at 3000miles if using a mineral. The correct mineral weight is 20W50.

IIRC 60 is thinner than 50...

~PHIL
Phil

I read somewhere in the TD?TF or MGA archive that bleeding the oil-gauge can cure erratic readings. Simply disconnect the oil line at the gauge-side, put a suitable cup/jar/container under line, start engine so that oil starts to run from line. Stop engine when stream is regular, reconnect oil-line.

I also think the filter should have a run-back valve but I'm not sure.

Penrite 20W60 can be used in an MGB without worries, although it might be on the thick side for a freshly reconditioned engine.

Explanation of oil codes:
20 = viscosity when cold (let's say 10 deg. C, I don't know the exact temperatures right now))
60 = viscosity when hot (let's say 100 deg. C)

The higher the number the thicker the oil, so COLD 20W50 is as thick as COLD 20W60. HOT 20W50 is thinner than HOT 20W60.

That said, you won't be able to read from the 20W60 code how thick the oil will be at 60 deg. C: it can be 50, but also 35.

Modern engines run much hotter (up to 130 deg. C) than our B-series engines, especially if an oil cooler is fitted, so the hot figure is less important than the low one? I use 15W50 in the B.
Willem van der Veer

Thank you to everybody who responded. I decided to replace the filter just to see if I could cure the drain-back problem.

I fitted a Fram filter and it has cured all of my problems! The oil pressure is now almost instant after starting the engine and climbs to 70 before falling to 65 (under load), 40 (idle).

It looks like it was a faulty filter that caused all of my problems.

On the subject of oil, Moss recommend using the Penrite HPR 30 which is a 20W/60 (on B's with a few miles on the clock) instead of the 20W/50.

This is the description from the manufacturers website:

Classic HPR30
An SAE 20W-60 oil which replaces SAE30 and 20W-50. A mineral oil formulated for most post-war classics, particularly high performance vehicles such as MG, Porsche, Jaguar and Triumph. Suitable for cars running six volt electric systems, where starter motor cranking speeds require an engine to turn over with minimal drag.

http://www.penrite.co.uk/

This oil costs £20 for 5L whereas I can buy Halfords 20W/50 for half the price and some other 20W/50 oils for much less still.
Does this oil justify the higher cost? Can anybody recommend an oil to use?
James Stewart

James,

All Engine Oil is too thick at start up, hence 0W synthetic oils.

Once at operating temp the last number is used as a guide. 60 being thicker at 100c than a 50, the assumption recommending 60 is that there is more bearing clearance on an older engine.

However oil at the bearing is at approx 150c. This is qouted as an HTHS number with higher giving the better protection. the information sheets for Castrol indicate that the high mileage version as a higher HTHS ie for older car.

The downside with thick oil is that it runs hotter wastes hp and thins anyway but to build a thick oil more viscosity improvers are used which quickly breakdown.

A 20W60 can be used as a race oil as fuel dilution can be an issue.

As most road cars may not even get the oil up to operating temp (say 20min run at least) IMO its better in these circumstances to use a oil closer to 0W say a 15W40 high mileage Castrol.

Research has shown most engine wear occurs during the 20min start up period.

Paul
Paul

I've had to wonder about oil filters and oil pressure at start up. I had to rebuild my MGBs head due to a broken exhaust valve. Prior to the problem when starting the car I noticed the oil pressure usually took a few seconds to rise. This was with a Fram oil filter and Castrol 20w 50 oil. After the rebuild I decided to change oil and filter in case there was any metal bits about. I splurged on a K&N oil filter and the same oil Castrol 20w 50. (About $8 for the K&N as opposed to about $4 for the Fram.) I noticed now on start up the oil pressure rises almost instantaniously. So fast in fact it actually surprised me. Now for the question- is it due to the rebuilt head (new valves, springs, gaskets, etc.) or the better oil filter that the oil pressure rises more quickly?
John

For UK people. I recently tried a Halfords budget filter. They are/were doing a 3 for 2 offer, meaning a cost of about £2.50 each for 3 filters. Fastest oil pressure build up I have ever had! Previously I had used Champion filters or the standard one the Moss UK supply (don't know the brand), but the Halfords chepo gets the thumbs up from me. I posted this on another forum I visit and another guy had a similar recent success with the Halfords filter.

There is a huge choice on the oil front. I use Duckhams Classic 20W/50, mainly because it is cost effective and carries all the right standards. But I do oil changes every 3k miles, and do 1k miles/month, so cost effective is important to me.

Iain
70 BGT
I D Cameron

Thanks for the tip Iain. I have been disappointed with the delay in reaching nornal pressure in my car. You wait a few seconds with a zero reading and then it shoots up to 50-60ish. I currently have a Champion filter fitted so I will try changing to Halfords own brand.

Thanks

David
David Witham

Maybe a stupid comment, but first i would start to clean the small cooper tube that goes to gauge.
alf
alfredo

Hi,

I am from American Samoa, small US Territory Island in the South Pacific. The temperature here is always in the high 80's and low 90's year round.

No gas station or parts store (NAPA) carry 20w50, what else can I use for a 1977 MGB.

I have been using 10w40 and I can never get oil pressure above 50psi and the needle fluctuates a lot.

The most common oil they see is 10w40, SAE 30w, I did see 15w40.

Please give me the best choice on this.

Ray 1977MGB
Ray 1977 MGB

James, John, yes it's the anti drainback valve in the filter which causes any delay in pressure. I know this first hand having recently swapped to the later inverted spin on assembly from the inverted element for this reason.

The old set up had no valving at all and would take many seconds for pressure to build up as it would empty back to the sump at stops. Pressure with the new one is there instantly on a day to day basis and in a count of 2 after standing a week. That's using a Mann W916/1 which is a specific fit, high quality filter.

B owners need the best we can get as most filters are fitted on their side or underslung, few are inverted, and modern cars are used daily so drain back is not as bad on them even if the valving isn't so good.

Another problem both at manufacturer and supplier level is cross referencing and range rationalisation. There are many similar filters which will "do the job" rather than being the exact one. The thread and gasket seal are the same but the bye-pass valve and anti drainback valves can be different specs or not exist at all in some cans which look otherwise identical. That's before you even get to the issue of actually filtering the oil and the quality and amount of paper etc.

Rich

Ray, Don't worry too much about the needle as once the oil's hot it will bounce around on tickover (even in the UK!) though it should be steady when driving.

Given those 3 are all the same quality I'd go for the 15W/40 or try the straight 30. You're in high temps so flow at start up isn't an issue. The unseen in this is that multigrade breaks down quite quickly and reverts to its base viscosity so a trial of different oil would be worthwhile. Straight 40 would be worth a go if you can get it.

Look for API SG or later SH, SJ, SL spec. The reality is the straight oil probably won't be high spec but the others may be. Perhaps try a synthetic if you can get similar grade, as they don't break down so quickly, otherwise mineral from a known maker changed at 3000 before it breaks down too much.

Rich

Ray

The relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related.

Agree with Rich that the viscosity of a 15W40 or straight 30 at your start up temps will be very similar.

Also from other discussions the following extract with regard to possible oil choices
When the Mini came out in 1959 a specially formulated oil was required Duckhams 20w-50. It was the first "heavy" multigrade - 10w-30s had been out for years. You could use the same oil viscosity today in the same engine without an issue of course. We used 10w-30 20w-20, 20w-30, 20w-50 and mono HD oils in BMC "A" "B" and "C" series engines around the world in various markets without problems - as you could today. We got very good engine life at that time.
The '74 MGB I sold a couple of years ago ran well on 15w-50 and 5w-40 synthetics - the 5w-40 wasn't in the Handbook but met the original viscosity "intent" of the Handbook
The engine felt better on the 5w-40 though


the "intent" with the B series engines was to run as I recall 20-20W (Castrolite) or 20w-30 Castrol XL. We also used HD30 oils such as Delo etc. Later this included 20w-50 as these oils became available. We used 10w-30 too and had exceptional engine life with all of these mineral oils if the car was serviced reasonably well. I know of one doing well over 300k miles without work (except for a water pump as I recall)

The availability of synthetic oils changed all this
Paul

Rich and Paul,

Thanks for the advice. We do have SAE 40w here also. Should I go with the SAE 40w?

I also have another question.

I just purchased a 5 speed Ford Sierra Conversion kit but it does not specify the lubrication.

Do you have any suggestions? I did find one site that stated 75w90 semi-synthetic oil, is this the correct type?

Thanks,

Ray

Going to pull the engine and install this weekend.

Ray 1977 MGB

Ray, Yes straight 40 was the recommended grade for "tropical and temperate down to 5°C (41°F)". Multi's were 20W/40, 40/50 or 20W/50 which I read as being a "heavy" multi. You don't need cold start help from a multi and mono will stay in-grade. Go for the best API rating and brand you can find. For that gearbox I'd use something semi-synthetic like Castrol Syntrax 75W/90 or Ford's own oil.

Rich

This thread was discussed between 14/06/2005 and 18/06/2005

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